Solenoid valve involves the pilot-operated solenoid valve and the direct-acting solenoid valve as per its working mechanism. The pilot-operated solenoid valves are also as widely used in various pipelines as direct-actings.

How does it work?

After being installed on the pipeline and setting up to work, the fluid comes into the inlet side. Then the lower chamber below the diaphragm is filled with the fluid, meanwhile the fluid passes through the orifice on the diaphragm into the upper chamber above the diaphragm. At this point, the pressure between the upper chamber and the lower chamber reaches an equilibrium.

Once the coil of the solenoid valve is energized, the armature lifts and then the pilot hole opens. Promptly thereafter, the fluid in the upper chamber flows out through the pilot hole.

As a consequence, there is a differential pressure between the upper chamber and the lower chamber. The pressure in the lower chamber will exceed the friction between the diaphragm and the valve body plus the elastic force of the spring above the diaphragm, so that the diaphragm lifts and leaves its original position. Then the fluid passes through the valve body and leaves from the outlet side.

What is the difference between pilot-operated and direct-acting?

As stated above, a pressure of not less than 0.05 MPa is required before the pilot-operated solenoid valve is activated. While for the direct-acting solenoid valve, the armature will directly lift when the coil is energized, and then the fluid passes through the valve body. Accordingly, no pressure is required in the action process of a direct-acting solenoid valve.

Correctly because of this, the pilot-operated solenoid valves can be used in the pipelines with intermediate and high pressure, while direct-acting solenoid valves are primarily suitable for pipelines with inferior pressure.