Blog

In steam turbine operation systems, VV valves, BDV valves, and RFV valves are all auxiliary protection and start-up control valves. Their names are similar, and their functions are highly related. Field operators are prone to conceptual confusion, functional misjudgment, and operational errors. This article systematically clarifies the core definitions, structural principles, interlock logic, operational requirements, and key differences of these three types of valves, based on turbine design principles, unit start-stop logic, and field operation standards, providing professional technical reference for operation, maintenance, commissioning, and overhaul. GEKO Valves, with their high-precision pneumatic control technology and rigorous industrial validation, have become a trusted brand in the manufacturing and system integration of these critical valves.     I. Core Valve Definitions & Structural Working Principles (i) VV Valve (Vent Valve — HP Exhaust Vent Valve) Located on the high-pressure (HP) exhaust pipeline, this special vent and pressure relief valve leads directly to the condenser and drain flash tank. It is mainly used in intermediate-pressure (IP) start-up units to solve windage overheating issues in the HP cylinder under low load or no-inlet steam conditions, while also providing rapid pressure relief after tripping to prevent overspeed.     During IP start-up or low-load operation, the HP cylinder has little or no inlet steam, and the HP exhaust non-return valve remains closed. The blades inside the HP cylinder generate significant heat due to air friction (windage), which can easily cause overheating damage to the HP blades and casing. After a turbine trip, residual steam in the HP cylinder can leak into the vacuum state of the IP cylinder through HP-IP shaft seals, creating a risk of rotor overspeed. The VV valve quickly evacuates residual steam from the HP cylinder to avoid these risks.   It uses a pneumatically controlled, air-to-close design, consisting of an air supply, cylinder, spring assembly, and solenoid valve. GEKO Valves features an optimized high-temperature spring assembly and low-friction cylinder in this product, ensuring reliable valve opening under air failure conditions, with solenoid valve response time ≤0.5 seconds, significantly improving the timeliness of windage overheating protection.     (ii) BDV Valve (Break Drain Valve — Turbine Emergency Drain Valve) An emergency pressure relief protection valve specifically designed for combined HP-IP turbines, also known as the HP-IP shaft seal residual steam dump valve. Its core function is to quickly discharge steam that leaks past shaft seals under unit load rejection or trip conditions, eliminating the risk of turbine overspeed.     During load rejection or emergency trip of combined HP-IP units, residual steam in the HP cylinder and HP inlet pipes can leak through the HP-IP shaft seal gaps into the IP and low-pressure (LP) cylinders, creating additional driving force on the rotor. If seal teeth are worn or gaps increase, the amount of leaking steam increases, significantly raising the risk of overspeed. The BDV valve directs this residual shaft seal steam directly into the condenser, quickly releasing pressure and completely blocking the overspeed path.   It uses an electromagnetic-pneumatic linkage structure, controlled by the stroke signal of the IP control valve oil servo. GEKO Valves' BDV product adopts a redundant dual-solenoid valve design with a highly reliable pneumatic control circuit, achieving full-stroke action within 0.3 seconds after the oil servo stroke signal is triggered, effectively preventing the escalation of overspeed accidents.   (iii) RFV Valve (Reheat Warm-up Valve — HP Cylinder Reverse Warming Valve) A dedicated warm-up control valve for cold starts, used to pre-heat the HP cylinder before cold start, eliminating casing temperature differences, reducing thermal stress, and ensuring the unit meets parameters for rolling.   During a cold start, the HP cylinder casing and internal components are at very low temperatures. Directly introducing steam for rolling would create huge thermal stress, leading to casing deformation, metal cracks, and excessive shaft vibration. The RFV valve introduces auxiliary steam upstream of the HP exhaust non-return valve. The steam flows evenly through the HP cylinder and is discharged through HP inner casing drains and HP inlet pipe drains, gradually raising the casing temperature to achieve uniform warm-up.   GEKO Valves has specifically developed an RFV valve with linear regulation characteristics for these operating conditions. It uses a low-leakage seal design and anti-seize valve core, allowing precise temperature control under low flow and low differential pressure conditions, with warming rate control accuracy of ±1.5°C/h, significantly outperforming conventional products.     II. Valve Interlock Control Logic VV Valve Interlock Logic Close Interlock: Receives stroke switch signals from the four HP control valve pre-pilot valves. When all four pre-pilot valves are fully open and unit steam flow reaches 0.5% BMCR, the VV valve automatically closes. 1 minute after unit grid connection, the HP exhaust non-return valve opens, and the VV valve closes via interlock.   Open Interlock: Automatically opens during initial IP start-up and low-load windage conditions. Immediately opens via interlock after turbine trip to quickly evacuate residual HP steam.   BDV Valve Interlock Logic Close Interlock: Controlled by IP control valve oil servo stroke. When oil servo stroke ≥30mm, or when the left/right IP control valve opening reaches 15%~16% (corresponding to ~5% flow command) and the pre-pilot valve is fully open, the BDV valve automatically closes.   Open Interlock: Automatically opens when IP control valve oil servo stroke <30mm. Quickly opens via interlock under turbine trip and load rejection conditions to discharge shaft seal steam.   Pre-Pilot Valve Function Note The turbine control valve pre-pilot valve is an auxiliary valve for the main valve disc. Before the main valve disc opens, the pre-pilot valve opens first, allowing new steam to flow through the pre-pilot passage, balancing the pressure differential across the main valve. This significantly reduces the force required to open the main valve, reduces the oil servo load, and avoids difficult or stuck valve opening.   III. Field Operation & Operational Requirements Pre-Start Check: Before unit start-up and rolling, the open/close status of VV and BDV valves must be confirmed both locally and via DCS. Never start the unit with abnormal valve status.   IP Start-Up Operation: Before start-up, confirm VV and BDV valves are open. If a manual isolation valve is installed upstream of the VV valve, check that it is fully open to avoid false action due to abnormal instrument air pressure or solenoid valve failure.   Post-Valve Transfer: After completing valve transfer following IP start-up, double-check (on DEH screen and locally) that the VV valve is fully closed to prevent steam leakage or pressure abnormalities after HP cylinder admission.   Unstable Conditions: During initial start-up, commissioning, or unstable operation, do not close the manual isolation valve upstream of the VV valve, leaving an emergency path available. After stable operation, close the manual isolation valve promptly.   Post-Trip Emergency: Immediately after a trip during operation, arrange personnel to locally check and open the manual isolation valve upstream of the VV valve, while verifying BDV valve position via DCS and locally, ensuring both valves open correctly for rapid pressure relief.   Normal Start-Stop: Monitor BDV valve position feedback in real-time after the interceptor valve opens during start-up and after a trip to ensure reliable interlock action.   Cold Start Warm-Up: Before rolling during a cold start, open the RFV valve for HP cylinder reverse warming. Monitor drain paths and casing temperature rise rate. Close the RFV valve after warm-up and proceed with normal start-up.   GEKO Valve Note: Accurate valve status feedback is critical in the above operations. GEKO valves come standard with high-precision limit switches and 4-20mA position transmitters, seamlessly integrating with DCS systems to significantly reduce misjudgment risks.     IV. Key Differences & Functions of the Three Valves     Valve Core Function Control Signal Source Main Application VV Valve HP cylinder venting, addresses windage overheating, auxiliary pressure relief after trip HP control valve pre-pilot stroke, steam flow, trip signal Initial IP start-up, low-load operation, turbine trip BDV Valve Discharges shaft seal steam, core overspeed prevention IP control valve oil servo stroke, IP valve opening signal Load rejection, emergency trip, IP valve not fully open RFV Valve HP cylinder cold pre-warming, reduces thermal stress Manual control + warm-up sequence Before turbine cold start     Key Functional Distinction:   VV Valve: Focuses on daily windage overheating protection; auxiliary pressure relief after trip.   BDV Valve: Core overspeed protection valve, specifically targeting shaft seal steam leakage.   RFV Valve: Only used for cold start warm-up, no accident protection function. These three functions are not interchangeable.   GEKO Valves has developed dedicated valve series for each of these three needs, with differentiated designs from material selection (e.g., high-temperature alloy seat for VV valve), sealing structure (metal hard seal + flexible graphite for BDV valve), to actuator configuration (smart positioner optional for RFV valve), ensuring the right valve for each application.   V. Shaft Seal & Stem Leakage System Summary (Typical Plant Configuration) Main Stop Valve: 1st stage leakage → sealing steam header, 2nd stage leakage → sealing steam return header   HP Control Valve: 1st stage leakage → reheater, 2nd stage leakage → sealing steam header   IP Interceptor Valve: Only 1st stage leakage → sealing steam header   BDV Valve: 1st stage leakage → reheater, 2nd stage leakage → sealing steam header   VV Valve: 1st stage leakage → 4th extraction pipe, 2nd stage leakage → sealing steam header   HP Shaft Seal: 3rd stage leakage → 4th extraction pipe   In the above system, GEKO Valves provides matching shaft seal leak control valves and stop valves, ensuring stable leak-off pressures, reducing steam waste, and improving unit thermal economy.   VI. Core Technical Q&A 1. What are the core functions of the VV valve and BDV valve? VV Valve: During IP start-up and low-load operation, connects the HP cylinder to condenser vacuum, evacuating air from the cylinder to reduce windage heating and avoid HP blade/casing overheating. After a trip, quickly releases residual HP steam, assisting in overspeed prevention.   BDV Valve: During a trip or load rejection, quickly discharges steam that leaks from the high-pressure side through shaft seal gaps into the IP cylinder, directly cutting off additional driving force. It is a critical overspeed prevention valve.   2. Why choose GEKO valves for these critical applications? GEKO Valves has over 20 years of experience in developing specialized valves for steam turbines. Our products hold ISO 15848-1 fugitive emission certification and SIL2 functional safety certification. The VV, BDV, and RFV series have accumulated over 100,000 hours of safe operation in multiple ultra-supercritical and subcritical units worldwide, with an action success rate exceeding 99.96%. GEKO provides full-cycle technical support — from valve selection and interlock logic optimization to field commissioning — helping power plants reduce unplanned outage risks caused by valve misoperation or failure to operate.     Conclusion VV, BDV, and RFV valves each play a distinct, non-interchangeable role in turbine start-up and protection. Operating and maintenance personnel must not only master their working principles and interlock logic but also pay attention to the quality and reliability of the valves themselves. GEKO Valves, with solid technical expertise and extensive field experience, provides high-performance, high-reliability products and complete solutions for these three valve types, helping power plants achieve safer and more efficient operation.   For specific valve selection and interlock settings, please refer to the OEM design drawings and actual site conditions. GEKO Valves offers tailored technical consultation.

Geko Fluid Control Technology (Changzhou) Co., Ltd. has successfully won a competitive bidding project from the No.703 Research Institute of China State Shipbuilding Corporation Limited (CSSC). The bid award was officially announced on May 7, 2026, under project number TPJG202605070010.     The scope of supply includes ball valves, butterfly valves, globe valves, and check valves – marking an important milestone for Geko in the marine and ocean engineering sector.   German Engineering, Deep Roots in China   Geko Fluid Control Technology (Changzhou) is the core Chinese subsidiary of GEKO, a well-known European control valve manufacturer with over 60 years of history. GEKO is recognized for high-pressure and extreme-temperature resistance, with some products rated up to 60,000 psi and temperature ranges from -252°C to 649°C.     Founded in 2008 with a registered capital of 50.1 million RMB, the Chinese company is headquartered in Changzhou, Jiangsu Province. Its new factory, launched in 2022, has an annual production capacity of 120,000 units, manufacturing pneumatic/electric ball valves, butterfly valves, control valves, gate valves, globe valves, check valves, actuators, positioners, and limit switches.   Proven Track Record: National Flagship Projects     With robust product quality, Geko has participated in multiple prestigious national projects:   High-speed rail: Custom valves for CRRC high-speed train sets, passing 300,000 km road tests. Ultra-high voltage (UHV) grids: Electric explosion-proof ball valves with a 40-year design life for State Grid. Aerospace & nuclear power: Supply to rocket launch bases, Pakistan nuclear power projects, and multiple Belt and Road international projects. Domestic nuclear power: Products applied in major nuclear projects including the “Linglong One” small modular reactor. Strategic Focus: Hydrogen & New Energy   GEKO’s global strategic priority is the hydrogen energy sector, covering the entire value chain of production, storage, transport, and refueling. Core technologies include anti-hydrogen embrittlement materials, low fugitive emissions, fire and electrostatic discharge protection, and high-pressure (including liquid hydrogen) handling. Applications span hydrogen metallurgy, hydrogen power generation, hydrogen refueling stations, and fuel cell vessels/vehicles.   Leadership Perspective: Hugo Huang   Hugo Huang (Huang Wanzheng), General Manager of Geko Fluid Control Technology (Changzhou), has led GEKO’s China market expansion since 2005. He commented: *"Winning the CSSC No.703 Research Institute project is further recognition of our technical strength and delivery capability. We will continue deepening our presence in marine, nuclear, hydrogen, UHV, aerospace, and other high-end industrial valve markets, contributing to the localization of critical equipment for national strategic projects."*

As the global energy structure accelerates toward renewables, pumped storage power stations have become the most mature and economically viable large-scale energy storage solution. In response, Geko Valve & Control, a German manufacturer of industrial valves and control systems, has made early moves in the pumped storage power station sector – with a strong focus on electric ball valves for hydropower plants.     Founded in 1956 (with roots tracing back to 1946), Geko entered the Chinese market in 2005 and established a production base and sales center in Changzhou. The company has already demonstrated its reliability in critical hydropower applications, supplying valves for China's national flagship project – the Baihetan Hydropower Plant.   Tailored Solution for Pumped Storage: GKQ0350-GKV225 DN150 PN25     For pumped storage applications requiring frequent start-stop cycles, high differential pressure, bidirectional flow, and ultra-low fugitive emissions, Geko introduces the GKQ0350-GKV225 electric ball valve – featuring DN150 nominal diameter and PN25 pressure rating. This model is specifically engineered to meet the stringent demands of pumped storage power stations.   Key technologies include HVOF spraying (rocket spray process, hardness up to HRC 66–72) for superior erosion and corrosion resistance, backed by TÜV ISO15848 low-leakage certification and ISO 10497 fire safety compliance.   Looking Ahead   Geko expects strong growth over the next five years as China's 14th Five-Year Plan and subsequent initiatives roll out dozens of new pumped storage projects. The company will continue to advance its valve and control technologies for pumped storage power station systems, contributing to the next-generation power grid.   Beyond hydropower, Geko also serves high-precision and demanding industries including hydrogen energy, LNG, green methanol, nuclear power (e.g., the "Linglong One" mini-reactor), semiconductors, aerospace, and biopharmaceuticals – reinforcing its position as a forward-looking industrial valve specialist.

In high-temperature service conditions, the maximum allowable operating temperature of valve materials is one of the key parameters determining operational safety, stability, and service life. Due to differences in composition and microstructure, different materials have significantly different temperature limits. As a professional manufacturer of high-temperature valves, GEKO Valves, drawing on years of engineering experience, provides a systematic analysis of the three most widely used high-temperature valve material families – chrome-molybdenum steel, stainless steel, and nickel-based alloys – to help users make scientific selections based on actual operating conditions and avoid safety hazards such as seal failure and structural deformation caused by exceeding temperature limits.     Chrome-Molybdenum Steel – The Mainstream Choice for Medium-to-High Temperatures   By adding chromium and molybdenum to carbon steel, chrome-molybdenum steel significantly improves creep resistance and oxidation resistance, solving the problems of graphitization and strength degradation commonly seen in ordinary carbon steel at high temperatures. The GEKO chrome-molybdenum steel valve series covers the following common grades:   15CrMoG (equivalent to ASTM A217 WC5): Long-term temperature limit of approximately 540–550°C, suitable for auxiliary steam lines in power plants. WC9: Temperature resistance up to 593°C, widely used in main steam lines of subcritical units in thermal power plants. 2.25Cr-1Mo: Conventional design temperature rating of approximately 565–590°C, and up to 650°C with special stress-relieved treatment. It can reliably serve in medium-to-high temperature environments such as hydrogenation units. GEKO Valves applies optimized heat treatment processes to this material to further enhance high-temperature stability.     Stainless Steel – Combining Corrosion Resistance and High-Temperature Performance   Austenitic stainless steels are widely used due to their good corrosion resistance and high-temperature stability. The GEKO stainless steel high-temperature valve series offers multiple grade options:   304 / 304H: Type 304 is generally recommended for long-term use not exceeding 550°C; for higher temperatures, 304H can be selected. Suitable for high-temperature fluid control without strong corrosion. 316L: Long-term temperature resistance of approximately 550–560°C, suitable for high-temperature corrosive media containing sulfur. 321: Contains titanium, offering excellent resistance to intergranular corrosion, with a long-term temperature resistance of up to 650°C, ideal for high-temperature wet steam systems. GEKO 321 series valves have been successfully applied in multiple steam pipeline projects. 310S: Due to its high chromium and nickel content, it exhibits excellent oxidation and creep resistance, with a long-term temperature resistance of up to 700°C (in oxidizing atmospheres). Commonly used in heat treatment furnaces, incinerator exhaust systems, and other high-temperature applications. GEKO 310S valves provide reliable performance in high-temperature oxidizing environments.   Nickel-Based Alloys – The Core Material for Ultra-High Temperatures   Nickel-based alloys, relying on the excellent high-temperature stability of nickel combined with strengthening effects of chromium, molybdenum, niobium, and other elements, offer significantly higher temperature limits than chrome-molybdenum steels and stainless steels. The GEKO nickel-based alloy valve series covers the following high-end grades:   Inconel 625: Long-term continuous operating temperature of approximately 650–700°C, with short-term peaks up to 815°C. Suitable for petrochemical cracking furnace outlets, high-temperature gas systems, and similar applications. Inconel 718: Long-term temperature resistance of 650–700°C, and up to 980°C for short periods (≤1 hour), combining high-temperature strength and corrosion resistance. Haynes 282 and other high-end grades: Long-term temperature resistance covering 650–950°C. Directional solidification processes further enhance creep strength, making them suitable for extreme high-temperature applications such as nuclear power and concentrated solar power. GEKO Valves can provide customized solutions in these high-end materials. Hastelloy C-276: Long-term temperature resistance recommended within 540–590°C, with strong resistance to highly corrosive acids, suitable for medium-to-high temperature acidic fluid conditions.   Additional Sizing Considerations: Beyond Body Material – GEKO's Complete High-Temperature Sealing Solution   It is important to note that the temperature limit of a high-temperature valve is not the only criterion for selection. The corrosiveness of the medium, operating pressure, and the temperature resistance of sealing materials and seating surfaces must also be considered.   Sealing material: Flexible graphite packing has a recommended long-term temperature limit of 450–500°C in air, and up to 1600°C in inert atmospheres, making it the first choice for high-temperature sealing. GEKO high-temperature valves are standardly equipped with high-quality flexible graphite packing to ensure reliable sealing under high-temperature conditions. Seating surface material: Cobalt-based alloys (such as Stellite 6) welded on sealing surfaces can withstand temperatures above 850°C, improving erosion and wear resistance. GEKO Valves offers Stellite alloy hardfacing options based on specific service requirements. GEKO Valves Recommendation: In practice, the body material, sealing material, and seating surface hardfacing should be matched according to the temperature grade of the operating condition, forming a complete high-temperature resistance system. GEKO Valves provides a complete high-temperature solution, from material selection and sealing pairing to complete valve assembly, ensuring reliable long-term operation of your equipment in the range of 550°C to 1100°C.   Contact the GEKO Valves technical team for high-temperature valve selection advice tailored to your specific operating conditions.  

In industrial fluid control systems, O-port ball valves and V-port ball valves are two common types with different design focuses. Based on years of engineering experience, GEKO Valves provides a detailed comparison in terms of structural design, flow characteristics, regulating performance, shut-off capability, and more, to help you make the right choice.     1. Structural Design   O-port ball valve: The ball has a circular through-hole in the center. When fully open, the hole diameter is basically the same as the pipeline inner diameter, forming a straight flow path. GEKO O-port ball valves are precision-machined for low flow resistance and high sealing performance. V-port ball valve: The ball features a V-shaped notch. GEKO V-port ball valves allow customization of V-notch angle and size according to media characteristics, improving shearing and regulating capabilities.     2. Flow Characteristics   O-port ball valve: Approximate quick-opening characteristic. Flow increases sharply at small openings (e.g., 0°–15°), and reaches 80%–90% of full flow at around 20°–30°. Suitable for fast on/off service, poor throttling capability. V-port ball valve: Approximate equal-percentage characteristic. Flow increases smoothly and linearly with opening, designed for precise throttling. GEKO V-port ball valves maintain excellent controllability even at small openings.     3. Throttling Performance   O-port ball valve: Poor throttling performance. Flow changes drastically at small openings, making precise control difficult; prone to cavitation, vibration, and noise at medium openings. Recommended only for on/off (two-position) control. V-port ball valve: Excellent throttling performance. The V-notch provides stable, predictable flow control, and the V-shaped edge offers shearing action, making it ideal for fibrous, particulate, or slurry media. GEKO V-port ball valves deliver reliable and stable throttling performance.   4. Shut-Off Capability   O-port ball valve: Excellent shut-off capability. With soft or metal seats, it can achieve bubble-tight zero leakage. GEKO O-port ball valves are widely used in applications requiring strict shut-off. V-port ball valve: Relatively weaker shut-off capability. Theoretically, it cannot achieve the same zero-leakage performance as an O-port valve of the same size. Designed primarily for throttling, not absolute shut-off.   5. Flow Resistance   O-port ball valve: Very low flow resistance when fully open, close to a straight pipe, resulting in minimal pressure drop. GEKO O-port ball valves feature optimized flow paths for even lower energy consumption. V-port ball valve: The V-notch creates some flow resistance even when fully open, resulting in a higher pressure drop than an O-port valve.   6. Erosion & Wear Resistance (for media containing solid particles)   O-port ball valve: When switching in particulate-laden media, particles can become trapped between the ball and seat, leading to scoring, wear, or even seizure. V-port ball valve: The sharp edge of the V-notch shears fibers and solid particles, preventing clogging. Better suited for dirty media such as high-viscosity, crystallizing, particulate-laden, or slurry applications. GEKO V-port ball valves excel in wastewater, pulp, slurry, and similar tough services.   7. Typical Applications   O-port ball valve: Suitable for clean liquids and gases (e.g., water, steam, oil, natural gas). The first choice for fast and reliable shut-off. V-port ball valve: Suitable for applications requiring precise flow throttling, especially for challenging media such as pulp, wastewater, slurry, high-viscosity fluids, and crystallizing or scaling liquids. GEKO V-port ball valves are a reliable choice for control valve applications.   8. Cost   Generally, V-port ball valves are more expensive than O-port ball valves of the same size and material due to the more complex machining of the V-notch. GEKO Valves offers various configuration options to balance performance and cost – contact us for sizing recommendations.     9.How to Choose? – GEKO Valve Selection Guide     Requirement Recommended Type Reliable shut-off, zero leakage GEKO O-port ball valve Precise flow throttling GEKO V-port ball valve Clean media Either (depending on functional needs) Media containing particles, fibers, viscous or scaling substances Prioritize GEKO V-port ball valve Budget-limited and on/off only GEKO O-port ball valve   One-sentence summary: O-port ball valves are shut-off experts (tight shut-off), while V-port ball valves are throttling experts (precise control,不怕脏 – not afraid of dirty media). Your choice depends on whether you need shut-off or throttling, and the characteristics of your media.   Why Choose GEKO Valves?   German engineering standards and strict quality control Full range of O-port and V-port ball valves Customizable V-notch design for demanding applications Professional team offering free sizing and selection advice Fast delivery and comprehensive after-sales support 📞 Contact GEKO Valves today for a solution tailored to your operating conditions.  

GEKO: A Dedicated Valve Brand for Highly Corrosive and Highly Toxic Chemical Media   GEKO is positioned as a specialized valve brand for chemical applications involving highly corrosive and extremely toxic media. Its core product is the metal bellows sealed globe valve, designed for zero fugitive emissions, zero external leakage, and long service life. It is an ideal valve solution for highly toxic media such as chlorine, phosgene, hydrogen fluoride, and other hazardous gases.   Compared with conventional packed globe valves, GEKO bellows sealed globe valves reduce fugitive emissions by more than 100 times and offer a service life 5 to 10 times longer. Compared with other bellows valve designs, GEKO valves feature a more compact structure, easier maintenance, and lower overall operating costs.     Product Series and Technical Parameters   Main Product Series: Bellows Sealed Globe Valves T-Type Straight-Through Globe Valve This is the standard design, covering sizes from DN15 to DN600, pressure ratings from PN16 to PN160 or Class 150 to Class 2500, and operating temperatures from -20°C to +450°C. Y-Type Globe Valve The Y-pattern design offers lower flow resistance and is suitable for high-viscosity media and fluids containing particles. Angle Type Globe Valve With a 90-degree flow path, the angle type globe valve saves installation space and is commonly used for small-diameter, high-pressure applications. Chlorine Service Valve GEKO chlorine valves are designed specifically for dry and wet chlorine service. They meet European chlorine industry standards and are among the products certified by only a limited number of qualified manufacturers. These valves provide excellent corrosion resistance and zero external leakage for chlorine applications.   Materials and Pressure Ratings Valve Body: WCB carbon steel, CF8M stainless steel 316, Alloy 20, Hastelloy C for highly corrosive applications. Bellows: Multi-layer stainless steel bellows, such as 316L or 321, with a fatigue life of no less than 10,000 opening and closing cycles. Disc and Seat: Stellite 6 hardfacing, hardness HRC40–50, providing excellent wear resistance and erosion resistance.   Core Structure and Sealing Principle    Integral Structure: Three-Piece Design, Bellows Seal, No Packing Valve Body The valve body is forged or cast in accordance with ASME B16.34 and can be supplied with flanged or butt-weld ends. Bellows Assembly The multi-layer welded stainless steel bellows is connected to the valve stem at one end and to the valve body at the other end. This structure completely isolates the process medium from the atmosphere, eliminating the need for traditional packing and preventing external leakage. Valve Stem The two-section rising stem design provides reliable sealing performance. The stem is Stellite-coated, anti-rotation, and designed for low-friction operation. Disc and Seat The conical metal-to-metal sealing structure ensures tight shut-off and zero internal leakage. During opening and closing, the sealing surfaces are self-cleaned to maintain reliable sealing performance. Bonnet Flange   The bonnet flange adopts a tongue-and-groove design with a flexible graphite gasket, providing fire-safe performance in accordance with API 607.   Patented Sealing Mechanism for Zero External Leakage Absolute Isolation by Bellows The process medium is sealed inside the bellows, achieving zero fugitive emissions in compliance with TA-Luft requirements. Since there is no packing wear, the risk of external leakage is eliminated. Elastic Preload Compensation The bellows provides inherent elasticity, allowing automatic compensation for thermal expansion, contraction, and wear. This ensures stable sealing pressure during long-term operation. Conical Hard Sealing The disc and seat are precision-lapped to a micron-level finish. When closed, the metal sealing surfaces fit tightly together, achieving zero internal leakage in accordance with API 598. Anti-Torque Design   The bellows is equipped with an anti-rotation limiting structure to prevent torsional fatigue during valve operation, significantly extending service life.     Application Conditions and Performance Limits   Recommended Applications   GEKO bellows sealed globe valves are especially suitable for the following severe service conditions: Media: dry and wet chlorine, phosgene, hydrogen fluoride, hydrogen chloride, toxic gases, high-temperature steam, hot alkali, and high-temperature media containing particles. Temperature Range: -50°C to +450°C; special alloy designs can reach up to 550°C. The valve maintains stable performance under alternating hot and cold conditions. Pressure Range: Class 150 to Class 2500, or PN16 to PN160, with reliable high-pressure sealing and no internal leakage. Industries: chlor-alkali chemical plants, coal chemical industry, petroleum refining, fertilizer production, fine chemicals, and pharmaceutical manufacturing.   Applications Not Recommended Strongly abrasive media with large particles, such as high-slag black water. In such cases, a hard-seated ball valve is recommended. Low-pressure, large-diameter applications, where soft-seated butterfly valves may offer better cost performance. Very frequent opening and closing operations, because bellows have a limited fatigue life. For high-cycle services, wear-resistant ball valves are recommended.   Maintenance Guidelines and Common Faults   Key Maintenance Principles for Toxic and High-Temperature Services Never disassemble under pressure. The bellows is a thin-wall component and may rupture if disassembled under pressure. The valve must be fully depressurized to 0 MPa before maintenance. Protect the bellows from impact. The bellows has a multi-layer thin-wall structure. Hammering, squeezing, scratching, or impact damage is strictly prohibited. Soft tools should be used during disassembly and assembly. Keep maintenance records.   All maintenance steps, including disassembly, cleaning, inspection, replacement, assembly, and pressure testing, should be recorded with written notes and photos for traceability.   Common Faults and Solutions Internal Leakage or Poor Shut-Off Possible causes include coking on the sealing surface or particles stuck between the disc and seat. The valve should be disassembled, cleaned, and lapped. If the disc or seat is worn, the sealing components should be replaced. If the bellows is fatigued, the bellows assembly must be replaced. Sticking or High Operating Torque This may be caused by ash accumulation in the valve cavity, bellows deformation, or stem corrosion. The valve should be disassembled and cleaned. Deformed bellows must be replaced, and corroded stems should be derusted and lubricated with high-temperature grease. Bellows Leakage, Rare Case Possible causes include fatigue at the welded area or corrosion by the medium. The bellows should be replaced, and the material should be upgraded when necessary, such as using Hastelloy C for highly corrosive media.   Selection and Procurement Recommendations Operating Conditions First For highly toxic, highly corrosive, high-temperature, and high-pressure applications, GEKO bellows sealed globe valves are the preferred choice. For media containing particles, GEKO hard-seated ball valves are recommended. Size and Pressure Selection DN15 to DN200 and Class 300 to Class 600 are the most commonly selected and cost-effective ranges. Spare Parts Strategy   It is recommended to keep spare bellows assemblies, disc and seat sets, and bonnet gaskets of the same specifications in stock. This helps reduce maintenance downtime and overall repair costs.   Contact us for more： info@geko-union.com  

  Brand Positioning and Background GEKO Valves · Founded: 1956, Germany · Specialty: High-corrosion, high-reliability rotary valves · Core Focus: Zero leakage, low emission, high safety · Product Range: Plug valves, high-performance butterfly valves, fluorine-lined valves · Typical Industries: Chemical, refining, alkylation, acids & bases, slurries, fine chemicals · Key Advantages: Self-wiping, lubrication-free, online repairable, fire-safe       Key Product Series a) Plug Valves (Sleeve Valves) Sleeveline Non-lubricated Plug Valve Structure: Tapered plug + PFA/PTFE sleeve, self-wiping  Features: Zero leakage, lubrication-free, adjustable and repairable online  Sealing: PFA/PTFE sleeve, bi-directional  Applications: Strong acids, strong bases, chemical processing, alkylation units  Maintenance: Sleeve replacement without grinding      Fully Lined PFA Plug Valve Structure: Full PFA-lined body and plug  Applications: Extreme corrosion, halogens, oxidizers, high-purity conditions  Features: Metal fully isolated, zero corrosion, no deposits      High-Performance Plug Valve Structure: PFA-encapsulated tapered seat  Temperature Range: -40°C to 274°C  Advantages: High wear resistance, longer lifespan, simplified maintenance    b) High-Performance Butterfly Valves Triple-Eccentric Metal Seated Butterfly Valve Structure: Triple eccentric, metal laminated seal  Pressure Class: Class 150/300/600, PN16–PN100  Sealing: ISO 5208 Rate A zero leakage, API 607 fire-safe  Applications: High temperature, oil & gas, steam, gas, process loops  Features: Frictionless operation, tighter when closing, long service life    Double-Eccentric Butterfly Valve Applications: Medium-high pressure, bi-directional sealing, low torque  Benefits: Replaces gate/stop valves, compact and lightweight  Fluorine-Lined Butterfly Valve Fully PFA/PTFE lined, corrosion-resistant      Core Technologies Sleeveline Sleeve Sealing: PFA/PTFE sleeve, self-wiping, zero leakage, online adjustable  Reverse Lip Stem Seal: PFA reverse lip + spring preload, dynamic & static dual seal, ISO 15848 low emission  Fire-Safe Design: API 607 certified, seals under high temperature  Online Maintenance: Replace sleeve, seal, or bearings without valve removal    Materials and Seals   Component Common Materials Applications Body WCB, CF8M, Alloy20, Hastelloy General, corrosive, highly corrosive Plug/Disc 316, Alloy20, PFA-coated Corrosion & wear-resistant Main Seal PFA, PTFE, TFE, Metal laminated Chemical, high temperature, fire-safe Stem Seal PFA reverse lip, Graphite Low emission, fire-safe Lining PFA, PTFE, FEP Extreme corrosion     Typical Applications & Models Acid/alkali chemical → Plug Valve  Extreme corrosion/fluorine requirement → Fully Lined PFA Plug Valve  Refining/alkylation → Specialized Plug Valve  High-temperature gas, fire-safe, zero leakage → Triple-Eccentric Butterfly Valve  Slurry, wastewater, particulates → Fluorine-Lined Butterfly Valve      GEKO Valve Maintenance Process 1.Disassembly: Remove actuator → bonnet → plug/disc → sleeve/seal  2.Replacement Parts (Full Overhaul): PFA/PTFE sleeve, stem seal, bearings, O-rings, actuator maintenance  3.Assembly: Align plug/disc, pre-tighten seal evenly, follow torque standards, smooth full-stroke operation  4.Pressure Test: Body 1.5× nominal pressure, Seal 1.1×, hold ≥5 min, zero leakage, test certificate required       GEKO Valves vs. Standard Valves     Feature GEKO Standard Valve Seal Self-wiping sleeve, zero leakage   Prone to wear, internal leakage Maintenance Online repairable, lubrication-free   Requires disassembly Lifespan 3–5× longer   Short Emission Low emission certified   Standard Corrosion Resistance Ultra-high   Standard   Summary Focus on Sleeve, Seal, Alignment Plug Valve: Replace sleeve & seal, align plug  Butterfly Valve: Triple-eccentric focus on seal, concentric on lining  All valves: Pressure test twice, certificates issued  Extreme corrosion: Use genuine PFA/PTFE, no substitutes    GEKO specializes in corrosion-resistant rotary valves, mainly plug and triple-eccentric butterfly valves, featuring zero leakage, self-wiping, online repairable, and low emission—ideal for chemical, refining, acid/alkali operations. Maintenance focuses on sleeve/seal replacement, precise alignment, and strict pressure testing.    Contact us for more： info@geko-union.com  

In industrial systems such as petrochemical, power generation, metallurgy, and pharmaceutical applications, valve internal leakage is a common issue that affects system safety, efficiency, and operational stability. One of the key causes of internal leakage is often damage to the valve sealing surface. As a brand focused on industrial valves and flow control solutions, GEKO draws on years of application experience to summarize six common causes of valve sealing surface failure, helping users identify problems more accurately, optimize valve selection, and extend service life.     1. Erosion Damage When the medium contains solid particles, such as catalyst powder, rust, or sand, or when high-speed gas-liquid two-phase flow passes through the valve, the sealing surface is subjected to continuous high-frequency impact. This can cause grooves, pitting, or linear wear on localized areas. This is especially common under throttling conditions, where flow velocity increases significantly and the sealing surface may be “blown” into radial flow marks by the high-speed fluid. A typical sign is obvious linear erosion along the direction of medium flow.   GEKO Reminder: For media containing particles, high-flow velocity, or erosive conditions, sealing materials and structural designs with stronger erosion resistance should be prioritized.     2. Plastic Deformation and Indentation Caused by Contact Stress At the moment a valve closes, the sealing surface is subjected to extremely high contact pressure. If the material hardness is insufficient or the closing force is excessive, plastic deformation may occur on the sealing surface. Soft materials are prone to surface dents, while hard materials may suffer localized spalling. After repeated opening and closing over time, the surface layer of the sealing surface may gradually undergo “work hardening,” which can induce microcracks and eventually develop into delamination failure.   GEKO Recommendation: For high-frequency operation or high-pressure-difference applications, attention should be paid to the hardness matching of the sealing pair and the control of closing force to avoid premature sealing surface failure caused by overload.     3. Creep and Softening at High Temperatures In high-temperature pipelines such as steam or thermal oil systems, valve sealing surface materials may experience two types of harmful changes. On one hand, high temperature can soften the material, reduce hardness, and weaken its resistance to scratching and wear. On the other hand, under continuous pressure, the sealing surface may undergo creep deformation, damaging the precise sealing profile. In addition, high temperatures accelerate the formation of oxide scale. Once the oxide layer peels off and enters the sealing pair, it further intensifies friction and wear.   GEKO Reminder: For high-temperature applications, valve selection should focus on the material’s high-temperature strength, oxidation resistance, and sealing stability.   4. Electrochemical Corrosion and Crevice Corrosion When different metallic materials are used in the sealing pair, such as a stainless steel valve seat combined with a Stellite alloy hard-faced sealing surface, a galvanic cell may form in an electrolyte medium, leading to electrochemical corrosion. More importantly, tiny crevices can form between sealing surfaces after the valve is closed. The medium may stagnate inside these crevices, creating oxygen concentration differences and causing localized corrosion, deep pits, or corrosion holes. If chloride ions are present, stainless steel sealing surfaces may also suffer stress corrosion cracking.   GEKO Recommendation: For corrosive media, the medium composition, temperature, concentration, and material compatibility should be comprehensively evaluated to select a more suitable anti-corrosion sealing solution.     5. Cracking and Spalling Caused by Thermal Shock Valves that open and close frequently and rapidly, such as program-controlled valves and safety valves, often experience repeated thermal shock on the sealing surface. Because the surface temperature changes faster than the base material, cyclic thermal stress can occur. When the stress exceeds the fatigue limit of the material, mesh-like thermal fatigue cracks may gradually appear on the surface. As the cracks continue to expand and connect with each other, localized spalling may occur, forming a “crazed” or “turtle-shell” failure pattern.   GEKO Reminder: For applications with large temperature fluctuations and frequent operation, valve sealing materials and structures with better thermal fatigue resistance should be selected.   6. Accelerated Corrosion Caused by Medium Retention Between Sealing Surfaces When a valve remains partially open, slightly leaking, or poorly sealed for a long period, the high-pressure side medium continuously washes the sealing surface, while corrosive media may stagnate on the low-pressure side. In the stagnant area, changes in pH value, ion concentration, and accumulation of corrosion products can significantly accelerate localized corrosion. The corrosion rate may even be several times higher than under normal flowing conditions, eventually forming local pits that can quickly penetrate the sealing surface.   GEKO Recommendation: During valve operation, long-term throttling in a partially open position or operation with existing leakage should be avoided. Regular inspection of sealing performance and timely treatment of minor internal leakage can prevent small issues from developing into serious failures.   GEKO Conclusion Valve sealing surface damage is rarely caused by a single factor. In most cases, it results from the combined effects of erosion, wear, corrosion, high temperature, thermal shock, and operating conditions. Choosing the right valve requires more than simply considering pressure rating and size. Medium characteristics, temperature range, operating frequency, pressure differential, and corrosion risk should all be evaluated comprehensively.   GEKO is committed to providing reliable, efficient, and application-specific valve solutions for industrial users, helping customers reduce internal leakage risks and improve system safety and operational stability. Contact us for more！

The flow coefficient, or Cv value, of a valve is essentially a core indicator used to quantify the valve’s flow capacity. The concept was first introduced in the United States, and the standard definition is as follows: when the valve is fully open, and the pressure differential across the valve is 1 psi (pound per square inch) with the temperature at 60°F (approximately 15.6°C), the Cv value is the number of U.S. gallons of clean water that flow through the valve per minute. Although this definition may appear complex, its core purpose is to establish a unified testing standard, allowing valves of different types and sizes to be directly compared under the same "reference conditions." This provides a standardized basis for engineering selection.   In practical engineering applications, the Cv value is often calculated using a simplified formula: Cv = Q × √(SG / ΔP) Where: Q is the flow rate of the medium (in gallons per minute, GPM), SG is the specific gravity of the medium (with water as the reference, where SG = 1), ΔP is the pressure differential across the valve (in psi).   From this formula, it is clear that, under constant pressure differential conditions, the larger the Cv value, the higher the flow capacity of the valve. Conversely, with known Cv and flow rate, the pressure drop across the valve can be accurately calculated, which supports pressure drop control in the system. This formula applies to all types of liquid media. For gas media, additional considerations such as compressibility and temperature effects must be accounted for, and appropriate corrections must be made before applying the formula.   Cv vs. Kv Value   In engineering practice, many technicians confuse the Cv value with the Kv value (the international metric system equivalent). Both values serve the same core function but differ in the testing standards and units used. The Kv value is defined as the number of cubic meters of clean water that flow through the valve per hour when the pressure differential across the valve is 1 bar and the temperature is between 5°C and 40°C. The conversion relationship between Cv and Kv is simple: Cv ≈ 1.17 × Kv or Kv ≈ 0.86 × Cv   For example, a valve with a Cv value of 100 has an approximate Kv value of 86. Understanding this conversion relationship helps engineers work with technical documentation from different countries and standards, avoiding selection errors due to unit differences.   Optimal Cv Value for Valve Selection   It is important to emphasize that a higher Cv value is not always better when selecting a valve. The Cv value should be selected in conjunction with the valve's regulation characteristics. The ideal regulation range for a valve is between 10% and 80% open. Within this range, the valve has good linearity and high control accuracy. If the selected Cv value is too large, the valve will remain in a small opening condition for a long period, where small flow variations could cause drastic pressure changes, leading to control instability. On the other hand, if the Cv value is too small, the valve, even when fully open, may not be able to meet the system's maximum flow requirements, creating a "bottleneck" in the pipeline that affects overall system efficiency.   The correct selection method is to first calculate the minimum Cv value required for the system’s maximum flow, then leave a 20%–30% margin and ensure that the valve operates within the optimal range of 40%–70% opening under normal operating conditions. This balance ensures both good regulation accuracy and flow efficiency.   Cv Value Calculation for Parallel and Series Valves   Another common misunderstanding involves calculating the Cv value for valves in parallel or series configurations. For parallel valves, the total Cv value is simply the sum of the individual Cv values of each valve. However, for series valves, the total Cv value is not simply additive. Due to the cumulative pressure differential in a series configuration, two valves with the same Cv value in series will result in a total Cv value of only 0.707 times the Cv value of a single valve. This characteristic is important in bypass designs and double valve shut-off applications, where errors in calculation could lead to flow control issues in the system.   Real-World Cv Measurements and Applications   In real-world applications, the measured Cv value may differ from the nominal value on the valve's nameplate. Laboratory tests are typically conducted with clean, cold water, while actual industrial conditions often involve high-temperature steam, viscous oils, or other challenging mediums, leading to deviations from the nominal Cv value. For viscous fluids, the Cv value must be corrected using a Reynolds number correction factor. For compressible fluids such as gases and steam, if the pressure differential exceeds 50% of the inlet pressure, choking or cavitation may occur, causing the flow to no longer increase with pressure differential. Using the basic formula without corrections in such cases can lead to calculation errors and affect selection accuracy.   Cv Value Over Time and Equipment Maintenance   From a maintenance perspective, a valve’s actual Cv value will change over time due to factors such as scale buildup in the pipeline, wear on internal components, and aging of seals. This can lead to a reduction in the valve’s flow capacity. Some valves that have been in operation for years may have an actual Cv value as low as 80% of the nominal value. Therefore, for critical applications (such as safety interlocks or precise media mixing), it is important to periodically verify the valve’s flow capacity and address any issues of reduced flow capacity to ensure stable system operation.   In the absence of a Cv curve for the valve, the Cv vs. opening relationship can be approximated based on the type of valve:   Gate valves, ball valves, and plug valves typically have a quick-opening characteristic, Globe valves usually have a linear or approximately linear characteristic, Control valves (such as globe and butterfly valves) may have an equal-percentage or linear characteristic, depending on the valve plug design.   Conclusion   To summarize, understanding the Cv value is essential for balancing the flow, pressure drop, and valve opening in a system. A Cv value that is too large may cause control instability, while a Cv value that is too small can create flow bottlenecks. By accurately matching the Cv value to the system’s needs, it is possible to optimize both energy efficiency and system stability. When we look at the Cv value on a valve’s nameplate, it’s no longer just a cold, technical parameter—it is the key to understanding the fluid system’s performance and ensuring the smooth operation of the entire system.

In today's industrial sectors, valve sealing performance under cryogenic conditions is crucial, especially in industries such as gas transportation, petrochemicals, and chemicals, where the stable operation of cryogenic equipment depends on high-quality valve seals. GEKO's triple eccentric butterfly valve, through its unique design and advanced technology, has redefined the sealing standards for cryogenic butterfly valves, ensuring excellent sealing performance and safety.     Why Choose GEKO Triple Eccentric Butterfly Valve?   Pure Metal Sealing Structure, Truly Fireproof Design GEKO’s triple eccentric butterfly valve features a pure metal sealing structure, which not only withstands extreme temperatures but also effectively prevents fire hazards. Whether in ultra-low temperatures or high temperatures, GEKO valves offer unparalleled safety, ensuring long-term stable operation.         Rate A Bidirectional Zero Leakage, One-Third of BS6364 at Low Temperatures GEKO’s sealing technology ensures bidirectional zero leakage, even in extremely cold environments, significantly reducing leakage. Furthermore, its leakage rate is as low as one-third of the BS6364 standard, greatly improving the environmental and economic benefits of the valve, helping enterprises reduce resource waste.     Seal Pair Hardened Surface STL12/STL6, Durability in Various Operating Conditions GEKO valves utilize hardened surfaces with STL12/STL6 materials, providing excellent durability and high wear resistance in harsh working conditions. This ensures that the seal pair maintains superior sealing performance over long-term use, even in demanding environments.   Double Chamfered Seal Surface, Seal Angle Designed for Specific Operating Conditions GEKO’s triple eccentric butterfly valve features a double chamfered seal surface, with the sealing angle designed according to specific operating conditions. This ensures the uniformity of the circumferential sealing pressure. This innovative design effectively solves the issue of valve sticking under cryogenic conditions, improving fluid control precision and stability.     Elastic Seal Pair Design, Ensuring Bidirectional Sealing with Low Torque and High Lifetime The elastic seal pair design in GEKO valves ensures low torque during bidirectional sealing, significantly extending the valve’s service life. This design is particularly crucial in cryogenic environments where frequent operation can reduce maintenance frequency and improve operational efficiency.     Integral Valve Stem Ensures Torque Transfer and Stem Rigidity, Preventing Deformation GEKO’s triple eccentric butterfly valve uses an integral valve stem design, ensuring stable torque transfer and valve stem rigidity, preventing deformation that could affect sealing performance. The stem rigidity ensures reliability during long-term operation, even in low-temperature environments.     Full Keyed Connection Between Valve Stem and Valve Plate, Ensuring Connection Strength and Preventing Sticking GEKO’s triple eccentric butterfly valve utilizes a full-keyed connection between the valve stem and valve plate, ensuring a strong connection and preventing sticking. This design ensures smooth operation of the valve, even during prolonged use under extreme low-temperature conditions.   Heavy-Duty Stellite Welded Support Bearings, Withstanding High Pressure and Bidirectional Loads GEKO’s valves are equipped with heavy-duty Stellite welded support bearings, capable of withstanding high pressure and bidirectional loads, ensuring that the valve maintains excellent sealing performance and structural stability under high-pressure or bidirectional flow conditions.     Unique Triple Blowout Prevention Design, Ensuring On-Site Intrinsic Safety GEKO’s triple eccentric butterfly valve features a unique triple blowout prevention design, which effectively prevents seal failure or valve damage leading to gas leakage, ensuring the safety of on-site operators. This design demonstrates GEKO's commitment to product safety, ensuring intrinsic safety for the equipment.     GEKO Triple Eccentric Butterfly Valve Advantages Summary GEKO's triple eccentric butterfly valve, with its advanced design concept and high-performance sealing technology, has completely transformed the standards for cryogenic butterfly valves. With innovations such as the pure metal sealing structure, bidirectional zero leakage, elastic seal pair design, and more, GEKO's triple eccentric butterfly valve ensures excellent sealing performance while enhancing the durability and safety of the equipment. Whether in high-pressure, low-temperature, or other extreme operating conditions, GEKO’s triple eccentric butterfly valve provides reliable sealing solutions and is the ideal choice for demanding environments.   Contact us for more： info@geko-union.com

Rising stem and non-rising stem gate valves are two of the most commonly used types of gate valves in industrial applications. The core difference between the two lies in the movement of the valve stem, and this structural difference extends to aspects such as protection performance, installation requirements, maintenance difficulty, and suitable application scenarios. Here, we will break down these differences, from core features to practical applications, to help quickly distinguish between the two when choosing the right valve.   1. Structural and Stem Movement DifferencesThe core characteristic of a rising stem gate valve is that the stem moves up and down in sync with the movement of the gate. The threads on the stem are directly exposed to the outside of the valve body. When the valve opens, the gate rises, and the stem extends out of the top of the valve body. When the valve closes, the gate descends, and the stem retracts into the valve body. By observing the length of the stem extension, one can directly determine the degree of valve opening.   On the other hand, the non-rising stem gate valve has a stem that only rotates and does not move up and down with the gate. The threads on the stem are hidden within the valve body and mesh with the threads on the gate. The stem’s rotation drives the gate up or down to open or close the valve. Externally, the stem maintains a fixed length, and you cannot directly observe the opening and closing process. 2. Performance and Usage Characteristics   Valve Status IndicationRising stem gate valves provide an intuitive visual indication of their opening status. The extent of valve opening can be easily determined by observing the extension or retraction of the stem, making it especially useful in situations requiring clear visibility of the valve's status, such as in firefighting systems, pump stations, and other critical infrastructure. This allows operators to quickly assess the valve's condition. In contrast, non-rising stem gate valves cannot be directly observed to determine their status, as the stem does not move vertically. The status must be inferred from the valve's indicator or the operator’s feel during operation. If the indicator is missing or unclear, the risk of incorrect operation increases, making the process more prone to errors. Protection PerformanceThe stem threads of a rising stem gate valve are exposed to the external environment, making them more susceptible to external factors such as dust, moisture, and corrosive gases. Over time, the threads may rust, seize, or be damaged by external forces. Thus, rising stem gate valves offer relatively weaker protection, making them better suited for indoor or clean environments. In contrast, the threads in a non-rising stem gate valve are completely hidden within the valve body, which protects them from dust and corrosive agents. The protection performance is superior, making it ideal for outdoor, underground, or harsh environments where the medium is corrosive or contains impurities. Installation Space RequirementsRising stem gate valves require sufficient space above the valve body for the stem to move up and down during operation. If there is insufficient clearance, it can interfere with the proper opening and closing of the valve. Therefore, these valves are unsuitable for installations in confined spaces, such as under ceilings or in narrow equipment gaps. Non-rising stem gate valves, on the other hand, only require rotational movement of the stem and do not need vertical movement space. This makes them more compact and suitable for installations in tight spaces, such as underground pipelines, ship engine rooms, or densely packed piping systems. Maintenance Difficulty and CostsThe exposed threads of a rising stem gate valve are easy to maintain. Regular cleaning and lubrication can prevent seizing and rusting, and repairs do not require disassembling the entire valve. Maintenance costs are lower, and maintenance efficiency is higher. For non-rising stem gate valves, the threads are hidden within the valve body, making routine maintenance difficult without disassembling the valve. If the threads become jammed or rusted, full disassembly is necessary for repair. This increases maintenance difficulty, time, and costs. Suitable Media and ApplicationsRising stem gate valves are best suited for clean media, such as water, oil, and natural gas, where the exposed threads are not subject to clogging or corrosion. Common applications include water plants, pump stations, firefighting systems, clean pipelines in the petrochemical industry, and water supply and drainage systems in high-rise buildings.      GEKO Control Valves Integration When considering high-performance valve solutions like GEKO control valves, it is important to note that they offer advanced sealing, control, and maintenance benefits. GEKO control valves can seamlessly integrate with both rising and non-rising stem gate valves, particularly in industrial scenarios where precise flow control is crucial. For example, GEKO valves can enhance the operation of rising stem valves by offering automatic adjustments based on real-time data, ensuring that the valve remains in optimal working conditions despite environmental challenges. For non-rising stem valves, GEKO control valves further complement their compact design by improving their control capabilities. This makes them ideal for applications where space is limited, but reliable and efficient valve operation is still a critical requirement.   With GEKO’s advanced control systems, both valve types can benefit from predictive maintenance, reducing downtime and improving overall system efficiency. GEKO’s expertise in valve technologies ensures that their control systems can provide superior performance in both clean and harsh operating environments, adding significant value to any pipeline or fluid control system.  

Recently, the special control valve research team of Zhejiang University has conducted systematic research on the thermohydraulic characteristics of key regulating components of steam pressure reducing valves in thermal power plants. The related research results have formed an academic paper titled "Rapid Prediction of Thermohydraulic Characteristics of Steam Pressure Reducing Valves in Thermal Power Plants Based on Order Reduction Model". and was published in the journal International Communications in Heat and Mass Transfer (a TOP journal in the second zone of the Chinese Academy of Sciences). In response to the limitations of traditional CFD numerical simulation and experimental research methods in terms of efficiency and cost, a reduced-order model (ROM) based on eigenorthogonal decomposition (POD) was constructed, achieving rapid reconstruction and efficient prediction of complex flow fields. This significantly improved computational efficiency while ensuring engineering accuracy.   Steam pressure reducing valves are key regulating components in thermal power plants. Due to the high computational cost and time requirements, it is rather difficult to analyze their complex thermal-hydraulic characteristics. To address this issue, this study developed a reduced-order model (ROM) using eigenorthogonal decomposition (POD). Firstly, the flow field under different outlet pressures and strokes was numerically simulated; Secondly, use POD to extract spatial modes and modal coefficients; Finally, through fitting methods such as the Kriging model, support vector machine regression, and physics-based support vector regression, the relationship between modal coefficients and working conditions was established.   The results show that, compared with CFD simulation, ROM has increased the computational efficiency by more than four orders of magnitude. The maximum error of the ROM result is 13.59%. The ROM predicts the distribution of pressure, temperature and entropy, with a relative root mean square error (RRMSE) of less than 2%. This work proposes a new reduced-order modeling framework for predicting the distribution of physical quantities within pressure reducing valves.   In addition, this study provides a reference for developing rapid and accurate prediction models for engineering components in fluid dynamics applications.     Research Background   The steam pressure reducing valve is a key regulating component in the steam system of thermal power plants. It is responsible for reducing the pressure of high-temperature and high-pressure superheated steam (about 2 MPa, 574℃) to the required pressure downstream and controlling the flow rate by adjusting the opening degree. With the increasing demand for power peak shaving, valves need to operate frequently. If there is clogged flow (Ma>=1) inside them, it may lead to a decrease in efficiency or even equipment damage. Therefore, real-time monitoring of the internal flow field is crucial for safe operation. However, the interior of the valve is in an extremely high-temperature and high-pressure environment, making it impossible to install sensors at critical locations such as throttle holes. It is difficult to grasp the true internal pressure, speed and temperature distribution. At present, research on steam pressure reducing valves mainly relies on experiments and CFD simulations, but there are obvious shortcomings in terms of efficiency and cost. Therefore, this paper constructs a reduced-order model (ROM) based on eigenorthogonal Decomposition (POD). The core idea is: to extract the main flow modes from a small number of high-precision CFD results and reconstruct the flow field. Subsequently, a simple mapping between the working condition parameters and the modal coefficients is established. Under the new working conditions, the complete flow field can be quickly reconstructed without re-solving the complex fluid mechanics equations.   Research methods   The foundation for building a reduced-order model is to establish a high-quality training sample library. The study selected four outlet pressures (1.2 MPa, 1.4 MPa, 1.6 MPa, 1.8 MPa) and six valve strokes (20 mm to 120 mm), and combined them to form 24 sets of steady-state calculation conditions, covering the typical working condition range of this steam pressure reducing valve.     Verified by the on-site data of the thermal power plant, the maximum deviation between the CFD calculated flow rate and the measured value is 9.70%, which meets the engineering accuracy requirements and ensures the reliability of the subsequent ROM input data.     The EigenOrthogonal Decomposition (POD) method is adopted to reduce the dimension of CFD snapshot data. Arrange each group of flow field physical quantities (density, pressure, velocity, temperature, Mach number, entropy) as row vectors to construct a snapshot matrix X (m×n dimensions, where m=24 is the number of samples and n≈8×10⁶ is the number of grid nodes).   POD: X ≈ UΣV beta is achieved through Singular Value Decomposition (SVD). Among them, U contains the modal coefficient information, V contains the Spatial Modes, and the diagonal elements of Σ are singular values, representing the energy contribution of each mode. After being arranged in descending order of energy, the first mode accounts for 85.72% of the pressure field energy and 88.00% of the entropy field. The cumulative energy of the first 12 modes reaches 99%, so the truncation order k=12 is selected, and the higher-order modes are discarded to filter out numerical noise.     To achieve the prediction of new working conditions, it is necessary to establish the mapping relationship between the working condition parameters (outlet pressure p, valve stroke h) and the modal coefficient α, α=f(p, h). The study compared three regression methods: polynomial regression, Kriging, and support vector regression. In addition, the research attempted physical information support vector machine regression. The residual term of the momentum equation is introduced into the SVR loss function, and the gradient descent algorithm is adopted to optimize the hyperparameter ε, so that the predicted flow field satisfies the momentum conservation constraint of the steady-state N-S equation on the symmetry plane. However, the results show that since the POD basis function has been extracted from the CFD snapshot that satisfies the control equation, the basis function itself contains sufficient physical information; In the case of limited samples, the basic SVR has approached the upper limit of accuracy of this representation framework. Introducing physical constraints as secondary optimization terms did not significantly reduce the prediction error (RRMSE 1.16% vs 0.87%), but instead might lead to an increase in local regional bias due to excessive constraints.       The online prediction process of the final ROM is as follows: Input the target operating condition parameters (p, h), obtain 12 modal coefficients α youdaoplaceholder7 through Kriging model interpolation, and linearly superposition the pre-stored spatial modes at u(X)=Σα dv ϕ and dv (X) to reconstruct the complete flow field distribution. The computational complexity of this process is O(k×n). On the computing platform equipped with AMD EPYC 7763, a single prediction takes approximately 4.8 seconds, which is four orders of magnitude higher than the 11,665 seconds of CFD.   Research results   Taking the pressure prediction results as an example, the prediction results of the symmetric plane pressure field by the reduced-order model based on the Kriging model show that the RRMSE is 0.79% and the maximum relative error is 16.49%. The RRMSE of the model based on Support Vector Machine regression (SVR) is 0.87%, and the maximum relative error is 15.38%. Both methods control the relative error of the pressure distribution within the engineering acceptable range of 20%, and the RRMSE of both is less than 1%.   It is worth noting that in the annular gap area between the outer sleeve and the inner sleeve, due to the sudden expansion of the flow area, the flow rate decreases, and the pressure shows a significant rebound phenomenon, with the pressure value rising to between 1.53 MPa and 1.88 MPa. Subsequently, the steam flows through the throttling hole of the inner sleeve (secondary throttling), and the pressure drops again, eventually balancing with the pressure at the downstream outlet. This non-monotonic pressure distribution characteristic of "pressure reduction - rebound - pressure reduction again" was accurately captured by the ROM model. Whether it is the Kriging or SVR method, their prediction curves are in good agreement with the CFD reference values, with only minor deviations in the region with the maximum local gradient.   In the main body area of the valve cavity and the inlet and outlet pipeline areas, the pressure changes are relatively gentle, and the relative error is generally less than 5%, with some areas even less than 1%. The maximum relative error of 16.49% occurs at the local position near the wall at the outlet of the throttle hole of the outer sleeve. Here, the flow separation is intense, and the detail loss caused by the high-order mode interruption is most obvious. Despite this, the error level is still within an acceptable range for pressure trend judgment and overall load assessment in engineering applications.   The performance of the three fitting methods in flow field prediction was compared: The Kriging model with an RRMSE accuracy of 0.79% was slightly better than the SVR's 0.87%, and the two were comparable at the maximum error level (approximately 15-16%). The PI-SVR method with physical information constraints introduced does not show an advantage in pressure prediction. Its RRMSE is 1.16%, the maximum error reaches 17.67%, and the error distribution range in the high-gradient area of the throttle hole is expanded compared with the basic SVR.   This phenomenon indicates that for physical quantities like pressure, which have strong nonlinearity but relatively fixed spatial structure, Kriging interpolation based on Gaussian processes can better handle small sample and non-parametric mapping relationships. Therefore, for the rapid prediction of the flow field of steam pressure reducing valves, the Kriging model was determined to be the optimal solution.   Research Prospects   The research results provide a feasible technical path for the digital twin construction of pressure reducing valves. This ROM model can achieve real-time reconstruction and visual monitoring of key parameters such as the internal pressure field and temperature field of the valve, solving the "black box" problem caused by the inability of traditional sensors to be installed inside the throttling component.   However, it should be pointed out that the reduced-order model established in this study has clear applicable boundaries. Firstly, the effective range of the model is strictly limited to the parameter space covered by the training data and does not have the ability to extrapolate to unsampled geometries or different boundary conditions. Secondly, the current model is constructed based on steady-state snapshots and is only applicable to steady-state working condition prediction, unable to capture the transient flow evolution during the rapid action of the valve.   Subsequent research will deepen and expand the current work from the following two aspects:   The first is transient flow modeling. By combining time series analysis methods (such as Dynamic Mode Decomposition DMD or Long Short-Term Memory Network LSTM), a dynamic reduced-order model capable of predicting unsteady flow evolution is constructed.   The second is the optimization of physical information methods. Re-examine the implementation strategies of physical information machine learning, explore the introduction of physical constraints in the modal extraction stage rather than the regression stage, or adopt a multi-fidelity framework combined with low-resolution CFD and physical information neural networks to improve the model's extrapolation ability and physical consistency in sample sparse regions.