Solenoid valves are units which can be used to control the flow of a liquid or gas through a pipeline. These valves are built to respond to electrical current, allowing engineers to control the flow automatically or from a distance. Used in nearly every industry, from air conditioning systems to oil refineries, solenoid valves allow for more control without the need to manually operate a valve.
How does a solenoid valve work?
Solenoid valves work by converting electrical energy into mechanical force. Aside from the usual components of a valve, they contain a piece of armature which sits in the middle of an insulated copper coil. Inside of the armature is a plunger which, at rest, is pressed either inside or outside of the valve to control flow. Depending on the direction an electric current is passed through the valve coil, the resulting magnetic field will either pull the armature upwards against the spring or force it down into the pipe, sealing it off. When no current is present, the spring has enough force to hold the plunger in its normal position.
Types of Solenoid Valves
Solenoid valves can be categorized in several ways, however the broadest means to separate them is by the condition of the valve when at a normal position. In a “normally open” solenoid valve, a spring keeps the plunger out of the valve tube, leaving gas or liquid to flow freely. When a current is sent through a normally open solenoid valve, the plunger will force down against the spring and seal the pipe. In a “normally closed” solenoid valve, the spring pushes the plunger downward, closing the valve until influenced by an electric current. A bistable valve can work in both ways.
Solenoid valves typically come in three varieties of design: poppet, diaphragm, and piston valves. A diaphragm valve can be closed by tightening the pipe to restrict flow whereas in a poppet valve, a rounded stopper can be triggered to plug the tube. While both diaphragm and poppet valves can be adjusted to restrict flow, piston valves can only be used to fully open or close a valve, sealing the pipe with a blockage.
Another way to categorize solenoid valves is by the number of pipe connections. There are valves which are one-way, having only one opening. These are typically used to rapidly release steam or liquid at too high a pressure. Double-acting valves are the most popular and have an opening at two ends, allowing for the entrance and exit of a flow. Triple-acting valves have three openings and are an important element in heating systems allowing you to easily redirect the flow of water or gas from one circuit to another.
Solenoid valves may also be classified based on working principles. In order to prevent the buildup of too much pressure in a device, direct-acting solenoid valves are used. In a direct-acting solenoid valve, an electrical current is all that is needed to operate the valve, causing it to either open or close when a signal is sent. Indirect solenoid valves are available with connection sizes from 1/4” to 3” and are used to cope with pressure changes created by larger diameters.
Finally, solenoid valves can be categorized by type of seal and diaphragm. The solenoid valve diaphragm is in the housing to shut off flow. A sealant layer is also usually laid between the coil and nozzles. Both of these components are typically made of polymer materials. They can be made from either EPDM (an inexpensive polymer resistant to salts, acids, and alkalis), FPM (resistant to oils and gasoline, with the widest range of operating temperatures). Or NBR (an oil-tolerant polymer).
The ease of control inherent to solenoid valves makes them useful in a range of areas from private households to industrial systems. Understanding the different types can give you a helpful background for approaching maintenance or choosing the right tool in the future. Aerospace Services is a leading authority in aircraft maintenance repair with a background of expertise which our customers rely on. If you are an aircraft owner or operator that is seeking a reliable source for parts, we have you covered. Browse our extensive online inventory and request a free quote today!
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