Solenoid valves allow you to control the flow of gas and liquid remotely and autonomously. They regulate air in pneumatic tools, adjust the flow rate of sprinkler systems, and modulate brake fluid in your car. Homeowners rely on them as well. They control the flow of liquids in your shower, dishwasher, and washing machine, not to mention the gas in your furnace and refrigerant in your air conditioner. Understanding how solenoid valves work helps homeowners diagnose problems, troubleshoot minor issues, and determine when professional help is needed to restore their systems.
How Solenoid Valves Work
The way solenoid valves work is surprisingly simple. They are divided into two parts, the solenoid and the solenoid valve. Solenoids sit atop the valve and control the plunger or armature, which seals the valve opening. The plunger is controlled by a spring, which is surrounded by a coil of wire known as the solenoid coil. Passing an electric current through the wire generates a magnetic field that pulls the plunger up, against the force of the spring, allowing material to pass through. When electricity is cut, the magnet de-energizes and the spring pushes the plunger back into place.
Types of Solenoid Valves
There are several types of solenoid valves. You’ll find some of them scattered in numerous devices around your home, especially your HVAC system.
- Normally Closed Solenoid Valve. The spring holds the plunger down until the magnet pulls it up, so the valve is closed unless activated. These valves are commonly found in applications where it’s important to stop the flow during a power failure. They’re a common feature in gas furnaces and air conditioners, where they control the flow of refrigerant through the compressor.
- Normally Open Solenoid Valve. The spring holds the plunger up until the magnet pushes it down, so the valve is open unless activated. These valves are normally found in applications where it’s important to maintain a steady flow of liquid or gas at all times. Examples include fire suppressors, water treatment plants, and irrigation systems. In a boiler, they allow water and steam to circulate during a power outage, ensuring the unit cools down safely.
Most valves are two-way, with an inlet port connected to the fuel or gas supply and an outlet port connected to the device or actuator. However, some valves have an additional exhaust port that vents excess fluid or gas. It’s a standard feature on pneumatic devices.
Direct vs. Indirect Valves
Most solenoid valves are direct-acting, meaning the plunger is the only mechanism used to seal or open the valve. Indirect solenoid valves, on the other hand, use a small solenoid to operate a larger valve. An indirect valve is comprised of:
- Solenoid coil, mounted to the main valve
- Diaphragm, a flexible rubber membrane separating the inlet and outlet ports
- Spring, located above the diaphragm, responsible for holding it in place
- Valve body, houses the diaphragm and valve seat
- Pilot chamber, sealed by the plunger connected to the solenoid coil
- Pilot valve, releases material from the pilot chamber
The valve’s working principle is simple. Gas or fluid enters the inlet port and presses against the diaphragm. However, while the solenoid is inactive, the pressure from the pilot chamber acts as a counterforce, holding it in place. Energizing the solenoid empties the pilot chamber, which creates a pressure differential, allowing the fluid or gas to push the diaphragm open. When the solenoid is de-energized, the plunger reseals the pilot chamber, which pushes the diaphragm back into place.
While direct-acting solenoid valves have a lot of residential applications, indirect valves are used almost exclusively in industrial operations. Because they rely primarily on pressure rather than magnetic force, installing them significantly reduces power consumption.
Save Money on HVAC Repairs with Agway EnergyGuard™
Solenoid valves play a critical role in your furnace and air conditioning. Unfortunately, their constant, internal motion creates a lot of mechanical strain. Home insurance doesn’t cover this type of damage, but Agway does. Our EnergyGuard™ program protects your heating, cooling, and electrical systems from problems caused by everyday use.
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