A Guide to Solenoid Valves
Solenoid valves are used to convert electrical energy to mechanical energy and cause a magnetic response. The solenoid activates when an electrical current travels through the wire coil. Once activated, solenoids in hydraulic and pneumatic valves control the flow of fluid when a fluid power system is in motion. There are many different types of solenoid valves, though direct-acting and pilot-operated are the two main categories. In this blog, we will discuss the many types and configurations of solenoid valves.
As stated, the two main categories of solenoid valves are direct-acting and pilot-operated. In direct-acting valves, solenoids open the valve magnetically through direct action. The coil pushes and pulls a shaft, causing the seat of the valve to shift. When there is no electrical current, the spring coil returns to its default position. To operate the valve, direct-acting valves need full power. Whether the valve’s position is normally-open or normally-closed depends on the application.
In an energized normally-closed valve, the inlet pressure is released when the solenoid coil retracts, therefore allowing the fluid to pass through the outlet. The solenoid coil is typically larger in a direct-acting valve than in a pilot-operated valve. Pilot-operated valves use the pressure of the fluid in the line to open the valve. The benefits of these valves include lower cost and the ability to use a smaller coil. While pilot-operated valves use less electrical power, they require enough available pressure to operate the valve.
Solenoid valves are available as two-way, three-way, and four-way, depending on the type of application. A two-way valve is used in on/off applications that require high flow rates and quick responses. They can be used to replace a lever to automate a process. In venting applications, the valve is actuated to release excess pressure on the fluid. Three-way valves have three ports, allowing it to be used in one of two states or circuits. Three-way valves can open, close, convey, distribute, or combine media. In a four-way valve, all ports are in the off position by default. They create two states and have two exhaust ports. The speed of each action can be controlled by attaching a flow control valve to the exhaust ports.
Another way to categorize valves is as normally-open, normally-closed, or universal. In a normally-open valve, the valve remains in the open position when de-energized. These are commonly used in safety applications where the process is exhausted following a loss of power. In normally-closed valves, the valve remains closed when de-energized. In general, normally-closed valves are used in on/off or venting applications where the process is meant to stop when there is a loss of power. After a power loss, the valve closes and fluid will not exhaust. Finally, universal valves can be either normally-open or normally-closed depending on the way the valve is piped up. Universal valves are typically found in three- or four-way valves where you are able to put pressure on any port in the valve. For instance, a three-way valve would feature a supply port, exhaust port, and delivery port. This offers flexibility in application and allows users to tailor it to their specific needs.
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