Learning Center: Different Types of Solenoid Valves

Equipment and devices are there to make work easier – and that’s what solenoid valves are designed to do! Engineers and different end-users rely on solenoid valves for their automatic operation. You don’t have to be there to operate a valve manually…all you need is to install an automatic solenoid to control and monitor fluid or gas flow.

What Is a Solenoid Valve?

It is an electromechanically operated device that controls the gas or fluid flow rate in a mechanical system. In other words, you can also refer to it as an electric coil with a movable ferromagnetic core (a plunger) at the center. When solenoids at pneumatic valves and hydraulic valves are activated, they control the fluid flow when the unit in question is powered.

How Do Solenoid Valves Work?

Solenoid valves are simply fluid control devices that either enable or restrict flow. Usually, the valve is directly connected to the plunger, and the plunger is located in a hollow tube known as the solenoid ‘core’.

When the device is energized, the wire coil on the outside creates a magnetic field in the core. In turn, the magnetic field causes the plunger to move in a specific direction to either close or open the flow system. That’s basically how a solenoid valve works when activated: opening or closing a gas or fluid flow.

Different Solenoid Valve Types

Solenoid valves can be customized for different and specific uses and used to carry out simple and complex tasks efficiently. Here are the top types of solenoid valves.

1.    Direct-Acting Solenoid Valves

These types of solenoid valves employ the simplest technique to operate. As the name suggests, the coil opens the valve in direct action – it lifts the seat and shifts the valve’s shaft without depending on some outside pressure.

When there’s no power, the spring coil will return to its default position. That means that a direct-acting valve has to have a constant supply of electrical current to work correctly. Direct-acting solenoids can either be Normally Closed (NC) or Normally Open (NO), depending on the application. A NO valve closes when an electric current is applied, while an NC valve opens when the coil windings are energized.

Direct-acting solenoid valves are fast-acting and can operate under different pressures.

Pros

• Accurate
• Fast-acting
• Can work with different pressures

Con

• They require a lot of current to work (especially in large-scale systems)

2.    Pilot-Operated Valves

The pilot-operated (or indirect-operated) valves use pressure difference between the valve ports to open or close. They utilize the pressure of the fluid or gas in the line to open the valve. These types of valves require less energy to operate compared to the direct-acting ones.

That doesn’t mean that they don’t require power to run. No. Pilot-operated valves still need to maintain full power to remain open since they work slower than the direct-acting valves.

The pilot-operated valves can either be externally or internally piloted. The internally piloted valves are ideal in high-pressure systems such as pipelines. On the other hand, the externally piloted ones require a third-party component to pull or push the valve.

Pilot-operated solenoid valves are ideal for systems with sufficient pressure differences, such as car wash equipment and irrigation systems.

Pros

• Use a smaller coil
• A smaller coil means lower cost
• Use lesser power compared to the direct-acting valves

Cons

• They are only one-way
• Compared to the direct-acting solenoid, they are slow
• They require a minimum operating pressure

3.    Two-Way Valves

These types of valves are common in on/off applications that require higher flow and quick response. They are at times referred to as shut-off solenoids. A two-way valve can be the perfect replacement for a lever to automate a given process.

This type of valve uses its two ports to alternately close and permit flow. A two-way valve can either act as a normally open (NO) or a normally closed (NC) valve in its operation. As a NO, the valve will remain open till some current is applied to close it. The opposite is also true for NC; it remains closed until the supply of current opens it.

4.    Three-Way Valves

These types of solenoids have three output/input ports and two valve seals. One seal is always closed, and the other one is open in normal mode. When electricity is supplied, the open/closed conditions of the ports are reversed.

Three-way valves are ideal in situations that require alternate and exhaustive pressure, such as with a dishwasher or a coffee machine.

5.    Four-Way Valves

The four-way solenoid valves have four ports. By default, all these ports are usually in the off position. When in action, they create two inlets and two exhaust ports. They are mainly used with a double-acting cylinder or actuator. In this setup, two ports supply pressure and the other two act as the exhaust pressure openings.

There are different types of solenoid valves, each with different construction and working mechanisms…every valve suits a specific particular application. The best thing is to select a suitable solenoid according to your needs and preferences.