The ZMAN pneumatic double seat control valve applies with the double-guided structure, and equipped with the multi-spring diaphragm actuator. It has many advantages such as compact structure, light weight, quick action, "~" shape flow channel, less losses of the pressure reduction, accurate flow characteristic, convenient installation and so on. This series valves can be widely used in controlling the medium like gas, liquid, steam and so on, and keep the working value like the pressure, flow rate, temperature, liquid level at the specific value, especially suit for the working condition of relatively big allowable leakage and big differential pressure.
The difference between the normal type double seat control valves and cage type double seat control valves are as bellow:
There are two units’ seat, plugs and sealing surface in the normal type double seat control valves, while as for the cage type, it also has two units sealing surface, but it only has one plug. Because of the two flow channel, so the flow capacity (CV) of the double seat control valves are bigger than the single seat type, but the leakage grade is lower than the single seat type, it is usually grade Ⅱ, at most grade Ⅲ.
Same with the cage type control valve, the double seat type also apply with the balanced structure, and the principle is different, the cage type applies with the balanced valve plug structure, while the double seat type applies the balanced structure with the double plug. Compare with cage type, the double seat type are more suitable for the medium with slight impurity or dust. Because of the complex flow channel of double seat control valve, its unbalance force direction will changed with the fluctuation of the differential pressure, so it will vibrate when in the position of small opening, even the serious vibration and noise sometimes.