In-depth Analysis Of The Sealing Principle Of Wedge Gate Valve

 

I. Core Definition and Sealing Principle

The wedge gate is sealed by a mechanical wedge between the wedge disc and the valve seat seal. It is a typical unilateral forced seal structure. The core design principle is to utilize the geometric characteristics of wedge disc (such as wedge angle, taper, etc.) to increase the auxiliary sealing load, so as to achieve reliable sealing under high and low pressure conditions. Compared with the parallel double disc structure, wedge gate can be sealed by a single-sided wedging force, with compact structure and controllable operating torque.

 

Wedge Seat Installation Mechanism

1.Mechanical Wedging Principle

The core design principle of wedge gate lies the geometry of the wedge angle (typically 5°-15°). When gate disc is closed, the wedge angle produces a vertical downward force component, forcing gate disc into close contact with valve seat seal. The smaller the wedge angle, the stronger the wedging force, but this must be balanced with operating torque. For example, a 5° wedge angle provides a higher sealing pressure ratio but requires greater closing torque; a 15° wedge angle is easier to operate but has a relatively lower sealing pressure ratio. According to technical documents from Tianjin Kaiweis Valve Manufacturing Co., Ltd., the wedge angle design range of the company's products is strictly controlled between 8 and-12° to balance sealing performance and operating efficiency.

2.Material Matching

·Hard Seal (metal-to-metal): tungsten chromium cobalt overlay with a precision grinding surface roughness ≤ Ra0.4 micron. Case study of Olam Valve Technology Co., Ltd. shows that the Stellite HRC ≥ 45 hardness, 300% abrasion resistance, and suitable for high temperature and pressure conditions (≤550°C).

·Soft Seal (metalto non-metal): PTFE/graphite composite gaskets are filled with micropores by elastic deformation. PTFE braided packing has a compression rate of 15%-25%, rebound rate ≥ ≥85%, applicable temperature range ≤ 200 ℃. Graphite gaskets have a a thermal conductivity of 80 W/ (m·K), a strong thermal expansion compensation capability, and are suitable for low temperature or cycling conditions.

3.Structure of the guide

To ensure precise precise wedging direction, the disc guide rail limits horizontal deflection of the gate disc, and the anti-twist stem prevents stem rotation from causing the the sealing surface to misalign. For example, a certain type of wedge gate valve has a dual guide groove design that keeps horizontal deflection of the gate disc to ± 0.05mm, greatly reducing the risk of leakage.

 

Effect of media pressure on Sealing Performance

1. Positive Sealing Mechanism

The dielectric pressure acts on the upper surface of the gate, and the gate is transformed into a a vertical sealing force through a wedge structure. Experimental data indicate that a medium pressure of 10 MPa can produce an additional sealing pressure of approximately 3-5 MPa, resulting in a a "self-reinforcing" sealing effect. Through the technical discussion, a pressure conversion model is established, which demonstrates that under positive sealing conditions, the sealing pressure is linearly and positively related to the medium pressure

2.Reverse Seal Limitations

The pressure ratio of the inlet seal depends on wedge force, and when the dielectric pressure is inverted, it is easy to cause leakage. Fujian Detsen Valve Co., Ltd. test data show that the metal seal wedge gate leakage rate can reach 0.1 mm3/s in inverted condition, significantly higher than the 0.01 mm3/s in inverted condition.

3. Pressure-Balanced Design

• Dual seal end structure: leakage rate reduced to less than 0.01 mm3/s through self-balancing of media pressure. For example, a certain type of double-sealed face wedge gate valve has a 90% reduction in reverse leakage at 10 MPa compared to a single-sealed end structure.

Disc spring auxiliary seal: Disc spring assembly provides a constant preload (typically 5-10 N/mm2) to compensate for pressure fluctuations. Some spring-assisted seal valve maintain a stable leakage rate of ≤0.005 mm3/s at ± 2 MPa.

 

INTRODUCTION Differences in Sealing Surfaces Principle of Different Materials

1. Metal Hard Seal

The Stellite cobalt coating is sealed by mechanical deformation and interlocking with micro-convex surfaces. Its applicable temperature range is ≤550°C. Abrasion resistance is ≥ 45 hardness, corrosion resistance, suitable for steam, high temperature oil and other media.

2. Non-metallic soft seal

· PTFE braided packing: Compression ratio 15%-25%, rebound rate ≥85%, suitable for neutral media such as water and air (≤200 ℃).

· Graphite gasket: Thermal conductivity 80 W/(m. K), high thermal expansion compensation, suitable for cryogenic liquid nitrogen (-196°C) or hot oil pipelines.

3. Composite sealing structure

Adopt 304L + PTFE double-layer gasket: metal layer provides support, non-metal layer ensures seal. Suitable for a combination of corrosive media and high temperature conditions. Graphite-stainless steel spiral wound gasket: Leakage rate ≤ 1×10−4Pa·m3/s (helium test) for more demanding applications such as ultra-high pressure hydrogen pipelines. The case study of Changzhou Karls Fluid Control Equipment Co., Ltd. shows that its composite gasket maintains zero leakage at a pressure of 15 MPa.

 

Application Scenarios and Selection Recommendations

1. High-pressure applications

Tungsten chromium and cobalt alloys are preferred to cover hard seals with a design pressure of up to 16 MPa. For example, a nuclear power plant's main feedwater pipeline, which uses a 16 MPa-rated wedge gate valve, has been leak-free for 10 years.

2. CryoApplications

PTFE soft seals is suitable for liquid nitrogen pipelines operating at -196 ℃. Its linear expansion coefficient (approximately 10−4/°C) compensates for sealing gaps. A cryogenic storage tank project uses PTFE sealing valves to maintain sealing reliability during circulation from -196°C to room temperature. Corrosive Media

The 316L stainless steel valve body and Hastelloy C-276 sealing surface resistant to chlorine ion corrosion (concentration ≤ 200 ppm). According to the Model Selection Manual for Thermal Power Plant Equipment, this combination has a useful life of more than 10 years in seawater desalination systems.

 

Conclusion:

The sealing principle of wedge gate is achieved by mechanical wedging material matching and pressure balancing design. Performance differences come from material performance and structural optimization. When selecting wedge gate valve, work pressure, temperature and dielectric characteristics should be taken into account to maximize sealing reliability and service life.