At Mokon, we’ve been engineering excellence for over 70 years. We love to talk technical, especially about any of our water, oil, chiller, and full range temperature control systems. Solenoid valves are one part of these systems that we’re always excited to shed some light on.
Solenoid valves are one of many temperature control system components. These valves, although small, play a big part in how these systems operate. That’s why we wanted to answer what we think are some frequently asked questions about solenoid valves. Read on to expand your knowledge (or review what you already know).
Q: What is a solenoid valve?
A: It’s an electromechanically controlled valve that regulates the flow of gas or liquid through a system. The valve uses a solenoid, which is a helical coil of wire that serves as a magnet when electric current flows through it. This creates a strong magnetic field that moves a plunger that’s within the valve and physically causes it to open or close, allowing the passage or blockage of liquid or gas. Solenoid valves are frequently found in domestic devices like dishwashers and washing machines to more technical and manufacturing sectors via temperature control systems.
Q: What’s the difference between direct-acting and pilot-operated solenoid valves?
A: Direct-acting means the valve closes or opens because of the plunger. An energized coil generates a magnetic force that lifts the plunger and opens a channel to allow fluid or gas to flow. A de-energized coil closes this channel, thus stopping the flow. The plunger does not open or close with fluid pressure, but with the magnetic force. The solenoid directly moves the valve in a direct-acting manner.
Pilot-operated solenoid valves rely on system fluid pressure through a small pilot hole or passage to lift a piston that opens or closes the valve. These valves need a minimum operating fluid pressure to work and do not rely only on the magnetic force generated by an energized coil. Although the solenoid controls the pilot hole, the fluid pressure handles the main work.
Q: What are the differences between normally open (NO) and normally closed (NC) valves?
A: The big differentiator between NO and NC solenoid valves is based on electrical power. In an unpowered state (meaning no electrical power being applied), NO solenoid valves stay open. They close when the solenoid coil becomes energized, causing the plunger to close the valve. This means that if a machine or system loses power, the NO valve stays open and allows its flow to continue. NO valves are ideal for situations when uninterrupted flow is needed, such as cooling or venting systems.
NC valves are closed in an unpowered state. They only open when the solenoid is energized; so, in the event of a power failure, the valves will shut, and nothing will flow out. This is why NC valves are chosen in situations where flow stoppage is necessary when power is stopped; consider gas and fuel systems, due to the safety risks and volatility associated with those settings if control is not exercised as needed.
Q: Explain the role that solenoid valves play in temperature regulation.
A: Solenoid valves are crucial in the role of temperature regulation. These valves maintain the flow of fluid, such as hot water, refrigerants, coolant, oil, or other fluids, through signals the valves receive from controllers or thermostats. A fluctuation in temperature causes the controllers or thermostats to send electric signals to the solenoid valve; the plunger is then moved to allow or stop fluid from flowing.
Using coolant as an example, if the thermostat receives a signal indicating the temperature is too hot, then the valve will open and let the fluid go through; if the signal says the temperature is cold or cool, then the valve will shut, resulting in no more fluid flowing.
Solenoid valves allow accurate temperature control by changing the fluid flow as needed. They also adjust to changes in temperature quickly to ensure systems run as efficiently as possible.
Q: What’s the relationship between fluid viscosity and solenoid valve effectiveness?
A: High fluid viscosity increases the flow resistance and the required force to move the valve’s internal parts. A rise in viscosity causes valves to open and close more slowly, lower rates of flow, and actuation failure; this is especially true in direct-acting solenoid valves, where it competes with springs and the magnetic force of the solenoid. Pilot-operated valves are also at risk of struggling because the viscous fluid slows pilot flow and reduces the pressure the valve needs to work. Cold environments accentuate the negatives since fluid viscosity increases at lower temperatures.
Q: How can I extend the lifespan of the solenoid valves?
A: Extension can occur with preventative maintenance and frequent monitoring. Keeping valves clean is extremely important, as blockages from fluid line contaminants can slow down or reduce the effectiveness of the valve, or entirely stop the valve from working. Check fluid lines frequently for contaminant deposits or rust.
Monitoring pressure is another aspect. If you operate outside of the minimum and maximum pressure range of the valve, it can cause detrimental, long-term effects that will ruin the valve, resulting in leaks or total failure. Pressure regulators can be used to keep proper system pressure.
Also, keep an eye out for potential coil overheating. Solenoid valves can become very hot with use, which can damage the coil or cause it to fail. Make sure the coil isn’t damaged and that the valve is receiving the correct voltage from its power source, as both can cause excessively high temperatures. Solenoid valves can overheat due to the ambient temperature in the room they’re in; if the valve cannot withstand higher temperatures, make sure the area where the valve is being used is well-ventilated.
Frequently Asked Questions About Solenoid Valves
March 3, 2026