Solenoid valves are used in myriad pneumatic and hydraulic applications in which there is a need to control the flow of fluids and gases. They operate via an electrical current. The current travels through a solenoid (a helix-shaped coil) to open and close an orifice. When the orifice opens, the target medium is allowed to pass; when it closes, the medium's passage is blocked.

Solenoid valves come in a variety of configurations. It's important to select the design that is best-suited for the valve's intended application. Failure to do so sets the stage for poorly optimized flows and other problems.

This article will describe the components that make up a solenoid valve, and explain how they work together to control fluid and gas flows. It will also provide a few guidelines for proper valve selection.


Components Found In A Solenoid Valve

The simplest and most common configuration used is a direct-acting valve. This is a design in which a core - sometimes referred to as a "plunger" - opens and closes the valve's orifice. (We'll discuss the device's operation in more detail in the following section.)

In addition to the solenoid, the core, and the core's sleeve, a typical solenoid valve has an inlet port, one or more outlet ports, and a spring. These parts are contained in the valve's housing. As indicated earlier, the core is the part that controls the flow of the medium through the device's orifice.

The solenoid is tightly wrapped around the core's sleeve. It produces a magnetic field that causes the core to move, an action that is essential to the valve's operation.


Basics Of How Solenoid Valves Work

For the purpose of this explanation, we'll suppose that a solenoid valve has been installed to control the flow of a fluid. The fluid enters the valve through the assembly's inlet port. In order to pass into the outlet port, it must first pass through the device's orifice.

The orifice is blocked by the core. The core is pressed against it by a spring, creating a seal along its perimeter. The only way for the fluid to pass through the opening is if the seal is broken.

When a switch is turned on, an electrical current is sent through the solenoid. The current generates an electromagnetic field, which causes the core to move. As the core moves, its seal with the orifice breaks and the fluid is allowed to rush past. The fluid moves into the assembly's outlet port, and onward to its intended destination.

Turning the switch off interrupts the electrical current, which causes the electromagnetic field to dissipate. As the field does so, the spring pushes the valve's core back upon the orifice, once again creating a seal.


3 Factors To Consider When Selecting A Solenoid Valve

A number of items should be taken into account when choosing a solenoid valve. The breadth of options available makes selecting the right configuration particularly important. Below, we'll offer a few guidelines to use when making your selection.


#1 - Number Of Required Ports

A simple solenoid valve comes with two ports: an inlet port and an outlet port. These are known as two-way valves, and can be controlled with an on-off switch. Designs with one inlet port and two outlet ports are known as three-way valves. Here a switch can be used to change the flow path of the medium from one outlet port to the other. Some solenoid valves are designed with four ports.


#2 - Required Flow Rate

Different applications require different flow rates for the target medium. The key here is to select an assembly that offers the proper size of orifice. An orifice that is too large for the application is likely to produce waste and result in suboptimal performance. Conversely, an orifice that is too small may provide insufficient capacity to achieve the desired flow rate.


#3 - Voltage Requirements

The size of the electrical current needed to move the solenoid valve's core off the orifice changes with the size of the orifice. Essentially, the larger the opening, the more power (or voltage) that is needed to engage the core. It's important to choose a design that accommodates the available power supply. Insufficient voltage is likely to prevent the valve from opening properly, which in turn would adversely affect the medium's flow rate.

Selecting a solenoid valve requires a careful review of the objectives set for the intended application. Improper selection is common and sets the stage for waste. Choosing and implementing the right design leads to optimal flow rates, greater efficiency, and lower costs.