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A pneumatic solenoid valve is a type of standard electro-mechanical solenoid that, when activated by electrical power, opens a valve under positive or negative air pressure. In standard industrial applications, they have been used for many years as a type of on/off switch for pneumatically powered systems such as with air-powered drills. They have also been commonly employed in fluid control systems such as for releasing hot and cold water into a washing tub in an automatic washing machine, or for outdoor lawn sprinkler systems.
A solenoid valve in general works by utilizing the process of electrical induction. It consists of a wire winding around a movable shaft that is similar to the design of an electrical motor assembly. When electrical power is passed through the winding, it creates a magnetic field that pushes on the shaft, which acts as a form of actuator arm to trigger a switch, valve, or other mechanical unit. The pneumatic solenoid valve differs from the traditional solenoid in that the actuator controls a valve that is under some level of pressure. It can either function to release pressure and allow gas or liquid to flow when electrical current is applied, or the pressure itself can activate the valve in reverse and create an electrical signal that is channeled to a monitoring station.
Some pneumatic valve assemblies are also small control units that act as triggers for larger solenoids, and together these types of pneumatic solenoid valve designs are often referred to as a pilot valve or as a compressed air pilot valve. Pilot valves can be stackable, meaning that they can be arrayed in series on a pipeline or other fluid or gas flow assembly so that pressure and flow can be channeled at key points in an industrial process. A single pneumatic solenoid valve that is installed as a pilot valve also often has a manual level of actuator control. This means that the solenoid function of the unit, where the actuator opens and closes the valve, can be controlled manually by pushing a button or moving a mechanical arm. In more sophisticated industrial systems, however, the pilot valve unit is electrically controlled through a series of programmable settings for running power to the solenoid when needed to open or close the valve.
In automated industrial systems where large amounts of inaccessible pipeline exist that must be controlled remotely, pneumatic solenoid valve systems are often chosen, as they can be operated by ambient pressure that builds up in the system itself and they don't require external power. This allows them to act as a type of safety valve to release pressure when needed, and, in the process, the mechanical motion of the pressure release can activate the electro-mechanical feature of the solenoid so that a brief electrical signal is transmitted to a control station to indicate that the valve state has changed. They also serve a reverse function where they can be opened or closed from the control station if an operator determines that a system is not performing properly.
Solenoid valve parts can range from very small units for rapid, micro-control systems, where they have a 0.4-inch (10-millimeter) diameter and can be run on low-level direct current (DC) voltages of 12 volts. High-power industrial level valves at the opposite end of the spectrum are made of strengthened steel alloys. They can handle pressures of up to 4,500 pounds per square inch (316 kilograms per centimeter squared) and temperatures as high as 1,200° Fahrenheit (649° Celsius).
The types of solenoids used in electro-mechanical systems vary greatly depending on the needs of the system. A pneumatic solenoid valve can control multiple inlet and outlet ports, with complexities ranging up to a 5/3 air valve system. A 5/3 pneumatic solenoid valve has 2 exhaust ports through which gas or fluid are regulated as they flow out, 2 power ports that serve as actuators for the system, and 1 supply port for inlet gas or fluid pressure. Most pneumatic solenoids are built on a 2/2 design, however, with an inlet port, outlet port, and pilot port that serves as a shifting mechanism to fully open or close the system. Depending on the needs of the machinery, the pneumatic solenoid valve is designed with a normally open (NO) or normally closed (NC) latent state that it maintains against pressure when no power is being applied to it.