Solenoid Valve

Two-way solenoid valves are shut-off valves with one inlet port and one outlet port. In the de-energized state, the core spring, assisted by the fluid pressure, holds the valve seal down on the valve seat to shut off the flow. When energized, the core and seal are pulled into the solenoid coil and the valve opens. The electromagnetic force is greater than the combined spring force and the static and dynamic pressure forces of the medium.

Three-way solenoid valves have three port connections and two valve seats. One valve seal always remains open and the other closed in the de-energized mode. When the coil is energized, the mode reverses. Various valve operations are available, according to how the fluid medium is connected to the working ports. The fluid pressure builds up under the valve seat. With the coil is de-energized, a conical spring holds the lower core seal tightly against the valve seat and shuts off the fluid flow. Port A is exhausted through R. When the coil is energized, the core is pulled in, and the spring-loaded upper core seal seals off the valve seat at Port R. The fluid medium now flows from P to A.

Unlike the versions with plunger-type cores, pivoted-armature solenoid valves have all port connections inside the valve body. An isolating diaphragm ensures that the fluid medium does not come into contact with the coil chamber. Pivoted-armature valves can be used to obtain any three-way solenoid valve operation. Pivoted armature valves are provided with manual override as a standard feature.

Internally piloted solenoid valves are fitted with either a two-way or a three-way pilot solenoid valve. A diaphragm or a piston provides the seal for the main valve seat. When the pilot valve is closed, the fluid pressure builds up on both sides of the diaphragm via a bleed orifice. As long as there is a pressure differential between the inlet and outlet ports, a shut-off force is available by virtue of the larger effective area on the top of the diaphragm. When the pilot valve is opened, the pressure is relieved from the upper side of the diaphragm. The greater effective net pressure force from below now raises the diaphragm and opens the valve. In general, internally piloted valves require a minimum pressure differential to ensure satisfactory opening and closing.

Internally piloted four-way solenoid valves are used mainly in hydraulic and pneumatic applications to actuate double-acting cylinders. These valves have four port connections; a pressure inlet P, two-cylinder port connections A and B, and one exhaust port connection R. When de-energized, the pilot valve opens at the connection from the pressure inlet to the pilot channel. Both poppets in the main valve are now pressurized and switched over. Now port connection P is connected to A, and B can exhaust via a second restrictor through R.

With these types, an independent pilot medium is used to actuate the valve. In the unpressurized condition, the valve seat is closed. A three-way solenoid valve, which can be mounted on the actuator, controls the independent pilot medium. When the solenoid valve is energized, the piston is raised against the action of the spring and the valve opens. A normally open valve version can be obtained if the spring is placed on the opposite side of the actuator piston. In these cases, the independent pilot medium is connected to the top of the actuator. Double-acting versions controlled by four/two-way valves do not contain any spring.