Classification by the position of sealing components
Dynamic seal
Packing seal: Fill flexible materials (such as graphite, PTFE) around the valve stem, rely on the pressure of the gland to achieve sealing, and require regular maintenance and adjustment.
Bellows seal: Use metal bellows to weld and isolate the valve stem from the medium to achieve zero leakage, suitable for high-risk media.
O-ring seal: Seal the valve stem by compressing and deforming the elastic rubber ring, low cost but limited pressure resistance.
Static seal
Gasket seal: Place non-metallic/metallic gaskets between the valve cover and the valve body flange, and seal by bolt preload.
Thread seal: Apply sealant or wrap raw tape at the threaded connection to fill the tiny gap.
Classification by sealing surface geometry
Plane seal
The sealing surface is flat and relies on vertical pressure (such as gate valves). The flow resistance is small but the high-pressure sealing is weak.
Conical seal
The conical valve disc is pressed against the inclined surface of the valve seat (such as a stop valve). The sealing pressure is high, high pressure resistance but large flow resistance.
Spherical seal
The sphere contacts the curved surface of the annular valve seat (such as a ball valve), with extremely small flow resistance and rapid opening and closing, which can achieve bidirectional sealing.
Classification by sealing material characteristics
| Type | Material Examples | Feature |
|---|---|---|
| Soft seal | Rubber, PTFE, nylon | Good elasticity and zero leakage, but poor temperature and pressure resistance (≤200℃). |
| Hard seal | Stainless steel, carbide | Resistant to high temperature and high pressure (≥425℃), erosion resistance, but there may be slight leakage. |
Special sealing mechanism
Media pressure sealing
Use the fluid's own pressure to push the sealing element (such as the valve disc) to press the sealing surface tightly, enhancing the sealing effect.
Forced sealing
Force the sealing surface tightly by external mechanical force (such as bolt pre-tightening), and the pre-tightening force needs to be precisely controlled.
Application scenario comparison
High-risk media (such as poisonous gas, highly corrosive liquid): bellows seal or metal hard seal is preferred.
High-temperature and high-pressure steam: cone hard seal or spherical hard seal is applicable.
Space-limited/precision instruments: O-ring soft seal or precision small ball valve is more suitable.
