Air-piloted valves are operated by an external air source such as a solenoid-operated valve in a remote location. The valve can also be internally air-piloted, enabling use of a smaller integrated electric solenoid to provide an air pilot signal to control the larger valve spool.
Pneumatic valves, also called directional control valves, are activated in a variety of ways including manual, solenoid-operated, and air-piloted (Figure 1). In their simplest form, 2-way and 3-way valves can be normally open (NO) or normally closed (NC) — terms that refer to their normal states without power applied. Another very common valve is a 4-way valve, which switches supply and exhaust between two outlet ports.
Solenoid valves are control units which, when electrically energized or de-energized, either shut off or allow fluid flow. The actuator takes the form of an electromagnet. When energized, a magnetic field builds up which pulls a plunger or pivoted armature against the action of a spring.