Solenoid Valves

What is a Solenoid Valve?

A solenoid valve is characterized by the presence of a solenoid, which is an electromagnetically inductive coil of wire wound around a sliding ferromagnetic core known as a plunger. The solenoid converts electrical energy to mechanical energy, allowing the valve to be mechanically opened or closed to control the flow of liquid. Featuring two or more ports, solenoid valves can be designed to perform a number of fluid-control functions, from blocking or permitting fluid movement to dosing, distributing, or mixing media. While solenoid valves are available in several types, most can be categorized as either direct-acting or pilot-operated valves.

How Does a Solenoid Valve Work?

Solenoid valves maintain either a closed or open position in their resting or de-energized state. When an electric current enters the solenoid’s coil, the coil becomes energized and generates a magnetic field. In normally closed valves, the energized coil forces the plunger to rise and allow fluid to pass through the valve. In normally open valves, the energized coil signals the plunger to close, which blocks the valve’s orifice and prevents fluid from passing through it. When the solenoid’s coil returns to its de-energized state, the magnetic field dissipates, and the valve’s spring action forces the plunger back to its open or closed resting position.

Solenoid Valve Types

Solenoid valves can be categorized into various types depending on their configurations and operating mechanisms. Some of the most common designs include:

• 2-way solenoid valves. A 2-way solenoid valve features an inlet port, an outlet port, and two switching positions. Depending on the specific configuration, these valves may either permit or prevent the flow of media through a system. 2-way solenoid valves are available in normally closed, normally open, and bi-stable configurations.
• 3-way solenoid valves. 3-way solenoid valves are designed with three ports and two switching positions. This allows them to perform several functions, such as stopping or starting fluid flow, mixing, or distributing media. 3-way solenoid valves are available in normally closed, normally open, and bi-stable configurations. 
• Proportional valves. Proportional solenoid valves use a solenoid to vary the position of the valve plunger, enabling precise regulation of the fluid’s flow rate. The plunger’s position is manipulated by varying the amount of power delivered to the solenoid’s coil. Flow rate regulation is typically used to control system parameters such as pressure and temperature.
• Pneumatic solenoid valves. Pneumatic solenoid valves direct or block the flow of compressed air to a device. These valves are available in various designs, which are classified by their number of switching positions and ports. For example, a 3/2-way pneumatic solenoid valve has three switching positions and two ports.

Solenoid Valve Applications

With a variety of designs available, solenoid valves can support a range of fluid handling applications with varying pressure, flow rate, and fluid compatibility requirements. Examples include:

• Directing or stopping the flow of compressed air in pneumatic systems
• Controlling the flow of high-pressure oils in hydraulic equipment
• Regulating the flow of water in agricultural irrigation devices
• Dosing, mixing, or restricting the flow of liquids in manufacturing systems
• Regulating the flow of oil, brake fluid, fuel, and other automotive fluids in motor vehicle systems
• Distributing heated water among various home fixtures and appliances (showers, kitchen faucets, washing machines, etc.)

Selection Criteria

When choosing a solenoid valve for an application, it is important to make sure the selected design is compatible with the conditions of the operation and provides the required functionality. Key factors to keep in mind during the selection process include:

• Valve type. The selected solenoid valve must have the required ports, positions, switching functions, and actuation method to perform your application’s specific fluid handling tasks.
• Fluid compatibility. The body and seal materials used in the valve must be compatible with the types of fluids used in your application. For example, fluid handling systems involving corrosive or harsh chemicals generally require stainless steel valves with corrosion-resistant seals.
• Pressure. Each type of solenoid valve is designed to function within specific pressure ranges. The selected valve should be rated to handle the operating pressures that will be encountered in your application.
• Valve diameter. Since the valve’s orifice diameter will influence the rate at which fluids can pass, it is important to choose a valve with the appropriate diameter and flow capacity to support your application.
• IP rating. The Ingress Protection (IP) rating indicates a device’s level of resistance against the ingress of water, dust, and other foreign particles. This is an essential safety factor to keep in mind when choosing a valve, especially for operations involving excessively damp or dusty conditions.