1. Comparison of structural characteristics
- Gate shape
Wedge gate valve: The gate is wedge-shaped (single gate or double gate), and forms a forced seal with the valve seat through the wedge angle. The sealing surface is a full-contact metal hard seal.
Knife gate valve: The bottom of the gate is blade-shaped, usually a thin flat structure, which cuts off fibers or particles in the medium through shearing. The sealing surface mostly uses soft seals (such as polyurethane) or floating metal seals.
- Flow channel design
Wedge gate valve: Circular flow channel, suitable for clean fluids, with small flow resistance but sensitive to impurities;
Knife gate valve: Square or rectangular flow channel, which is conducive to the passage of high-viscosity and solid particle-containing media, and has outstanding anti-blocking performance.
2. Differences in sealing and working principles
- Sealing mechanism
Wedge gate valve: The wedge gate disc is embedded in the valve seat by the valve stem thrust to form a self-enhanced sealing force. The sealing pressure increases with the increase of medium pressure, which is suitable for high-pressure working conditions;
Knife gate valve: After the impurities are cut off by the blade, the gate disc and the valve seat are fitted to achieve sealing. Some models are pressed tightly by the medium pressure to prevent blocking and anti-blocking.
- Opening and closing characteristics
Wedge gate valve: The opening and closing stroke is long, and precision processing is required to ensure the wedge angle matching. It is easy to cause blocking due to thermal expansion at high temperature;
Knife gate valve: Compact structure, fast opening and closing speed, low installation space requirements, suitable for frequent operation scenarios.
3. Differentiation of applicable scenarios
Wedge gate valve:
Clean high-pressure medium: such as steam and natural gas pipelines (Class 150 and above);
High-temperature stable working conditions: main steam system of thermal power generation, oil refining unit (need to resist thermal deformation). Knife Gate Valve:
Complex Media Handling: Sewage, pulp, powder transportation (including fiber, particles);
Space-constrained scenarios: The short wafer-type valve body design is suitable for compact pipeline layout.
4. Performance bottlenecks and maintenance differences
Wedge Gate Valve:
Disadvantages: Sensitive to impurities, easy to cause seal failure due to particle blocking; frequent maintenance of the sealing surface at high temperature;
Maintenance: Professional grinding and repair of the sealing surface is required, which is costly.
Knife Gate Valve:
Disadvantages: Low pressure resistance level (mostly below Class 150), and soft seals are prone to aging at high temperatures;
Maintenance: The gate is easy to replace and supports online maintenance (such as PZ673H pneumatic model).
- Selection recommendations
Prefer wedge gate valves: Working conditions that require high-pressure sealing and clean media (such as natural gas transmission pipelines);
Prefer knife gate valves: Handling industrial scenarios with impurities, high-viscosity media or limited space (such as sewage treatment plants).