Among the most common control elements in fluidics, solenoid valves are used to regulate the flow of liquids and gaseous media. They offer high reliability and low control power. They can be operated directly, indirectly, or by remote controls. They are also suitable for use with liquid, gaseous and mixed media.

Solenoid valves are divided into two basic types: the normally closed and the normally open valve. Each type is designed for a particular application. The main difference between the two is the difference in pressure that must be supplied to activate the valve.

The normally closed type requires zero line pressure, while the normally open type does not. This means that the solenoid can be used for both high and low-pressure applications. The higher the pressure, the greater the force required for the actuating valve. The optimum pressure range for a solenoid depends on the process fluid and the environment.

The core of a normally closed solenoid is made of soft magnetic metal. When a magnetic field is generated, it attracts the core. This in turn pushes the plunger down. The retaining clip holds the coil on the core tube. The orifice is also encapsulated in the core tube. The orifice opens when the pressure on either side of the membrane is lower than the pressure in the core.

Solenoid valves are available in various types such as two-way, three-way, and four-way. In a two-way valve, the diaphragm and the orifice are separated by a diaphragm. In a three-way valve, the diaphragm is separated by a third chamber. The orifice is a pilot orifice. A single-port valve has one inlet and an outlet. The two-way valve has two inlets, with a passage to connect the upper chamber to the upstream through a pilot hole.

The differential pressure required to operate the valve is also determined by the application. It can be a direct measurement, or it can be based on the inlet pressure and the outlet pressure. Usually, a pressure of 90 PSI is considered equivalent to a pressure of 10 PSI. In a direct operation, the fluid's pressure is directly proportional to the size of the solenoid.