A straight-through single-seat control valve has only one valve core and one valve seat. When DN≥25, the valve core is double-guided (modern miniature single-seat control valves have been converted to single-guided); when DN≤25, the valve core is single-guided. This valve originated abroad in the 1940s and was jointly designed domestically in the 1960s. Its characteristics are as follows:
Because there is only one valve core, it is easy to ensure sealing and low leakage, but it cannot completely shut off the valve. Its standard leakage is 0.01%Kv, therefore it is suitable for applications requiring low leakage. With further design, it can be used as a shut-off valve.
Because there is only one valve core, the pressure difference generates a large unbalanced thrust on the valve core. Let the upstream pressure be P1, the downstream pressure be P2, the valve stem diameter be ds, and the valve seat diameter be dg.