Pneumatic Solenoid Valve Tutorial

Feb 1, 2016

Pneumatic solenoid valves are on-off valves widely used in manufacturing, industry and power production to provide an interface between electrical and electronic control systems and the pneumatic or air-driven process equipment they regulate. These can be air cylinders, actuators, machines, switches, motors and other valves. Pneumatic solenoid valves provide users great flexibility, along with economy, for precisely controlling large complex processes.

Valve Operation
The input to pneumatic solenoid valves is an electrical signal such as 24 volts DC or 120 Volts AC, which energizes an electrical solenoid. Solenoids are a wound coil of insulated copper wire, and energizing them causes a strong magnetic field that pulls in a magnetic plunger. This motion opens or closes the valve, either allowing or blocking air flow. Most valves have a return spring to return the valve to its nonenergized position.

If the valve allows flow when in its nonenergized state, it is called a normally open valve. If the valve blocks flow when nonenergized, it is called a normally closed valve. If a valve has two connection ports, an input and an output, it is called a two-way valve. Way in this case refers to the number of ports or connections. If it has three ports, it is a three-way valve.

Position refers to the maximum number of positions the valve element can assume within the valve body--a two-position on-off valve has two positions. One position is on, and the other is off.

Other Valve Action Types
Besides on-off applications, pneumatic solenoid valves can also act as selectors. They can select one of two inputs to output, or direct an input to one of two destinations. Another configuration simultaneously crosses over two inputs to two outputs. If inputs A and B are sent to outputs C and D respectively in the nonenergized state, they will be crossed when energized, and inputs A and B will be sent to outputs D and C, respectively. This is a two-position, four-way valve.

A supply-exhaust valve is a variation of a three-way selector valve. In this case, the third port is just a hole that allows the output to bleed back out through the valve when it is not energized. Exhaust valves may include a small muffler to quiet the exhausting air pressure, which could be quite high.

Materials and Physical Configurations
Pneumatic solenoid valves are available in a wide variety of materials--not so much for the air flowing through them but because the external industrial environment in which they are implemented may be quite corrosive (such as in some chemical plants) or sanitary (such as in food production plants). Here stainless steel or even more exotic materials are available to allow the valve to work in the long term. Solenoids are normally housed in small watertight enclosures on top of the valve, with explosion-proof options available.

Off-the-Shelf Configurable
Many manufacturers provide easily configurable options where an AC or DC solenoid can be matched to any configuration of valve body. Others have plug-in and stacked systems, which allow many pneumatic solenoid valve functions to be performed on one easily installed package.

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