They’re in washing machines, dishwashers, and automatic irrigation systems, also known as sprinklers. You’ll even find them in the paintball industry. Solenoid valves are simple devices that work to shut off, release, dose, distribute, and mix fluids. They are important components in most pneumatic systems. While these valves are simple and inexpensive, it may be confusing to choose the one best suited for your needs.
A Simple Solenoid
To fully understand how these solenoid valves work it’s best to start by understanding what a solenoid is. A solenoid is a coil that is tightly wound into a helix. This coil is wrapped around a metallic core which when energized, creates an electromagnet. The greater the current of electricity, the more powerful the electromagnet becomes. The beauty of an electromagnet, and what makes it different from a regular magnet, is that it can switch on and off. Therefore, solenoids work in systems that latch, lock, or trigger another mechanism.
So, when a solenoid is part of a valve it triggers the opening and closing of the valve. The force generated by the electromagnet pushes and pulls a piston up and down which consequently stops and releases the flow of air, gasses, or liquids.
Some of the pros of using solenoid valves include:
- Fast and safe switching
- High reliability
- Long service life
- Good medium compatibility of the materials used
- Low control power
- Compact design
Direct Acting v. Pilot Operated Solenoid Valves
Of course, solenoid valves come in many different types to suit different flow rates, types of fluid, and tasks.
The two main types of solenoid valves are direct acting and pilot operated valves. Direct acting valves “directly” use the power supply from the electromagnet to open and close the valve. On the other hand, pilot operated valves use the electromagnetic power combined with the pressure of the flowing air/liquid/gas to open and close the valve.
Choosing which one to use mainly depends on the flow rate of the fluid used.
Since direct acting valves rely solely on the electromagnetic power of the solenoid, these types of valves work best for smaller flow rates. One of the benefits to using these is that they only need to use full power when opening the valve. Once the valve is open, these valves can hold the open position even when operating on low power.
If something that can withstand a higher flow rate is needed, then pilot operated valves will do the trick. These valves use the combined force of the electromagnet and the fluid itself to open and close the valve. You may be wondering how this is even possible. Tim Hunkin from the classic show, The Secret life of Machines, explains it best.
Pilot operated valves require less energy to operate but they do need to retain full power in order to remain in an open state. Consequently, they perform at a slower rate than direct acting valves. This, however, doesn’t stop them from being the most widely used type of solenoid valves.
Solenoid Valve Variations
From the two main types of solenoid valves stems a couple more variations. They include 2-way valves, 3-way valves, and 4-way valves.
These simply indicate how many ports the solenoid valve has. In a basic 2-way solenoid valve, two ports are used alternatively to permit flow and close it. In a 3-way valve, two ports are used to permit flow and close it, while the third port is used to exhaust pressure. A 4-way valve uses half of the ports to provide pressure and the remaining ports to exhaust pressure. 4-way valves are typically used with a dual-acting cylinder or actuator.
Another option is whether to have the valve perform in a “normally closed” state or a “normally open” state. A “normally closed” valve is the most common as it remains closed until a power source causes it to open. A “normally open” valve remains open until some type of current is applied to close the valve.
One more thing to consider while deciding on a solenoid valve is the material the valve is made of. Some of the most common valve materials include brass, stainless steel, aluminum, and plastic. Consideration should be given to what type of fluid will be used in operation and what type of material should be selected for the seals. This ensures that the valve will function properly.
Lastly, make sure you know the thread type you need to install the valve. This little detail often gets overlooked until you’re sitting at checkout wondering if you need PT or NPT threads. Head over to our Thread Type Identification Guide to learn more.
Innovations and Improvements
In the manufacturing industry, we’re always looking for ways to make improvements and increase efficiency. Even with devices as simple as solenoid valves, the goal is for them to withstand even higher flow rates and simultaneously make them more environmentally friendly. In 1910 ASCO Numatics was the first company to develop and manufacture the solenoid valve. In the 1990s the German chemical industry developed the NAMUR standard, which standardized the actuator interface to the solenoid valve. This helped to increase the flow rate threshold. Recently, there have been efforts to decrease the amount of power used by solenoid valves. However, lower power presents several challenges to the designers of these valves. Issues such as orifice size, clogging potential, pressure rating and other characteristics of the valve must be taken into consideration. Nevertheless, several manufacturers of low-power solenoid valves have decreased power usage from 1.5 watts to .5 watts.
So whether you’re in the automobile industry or you’re simply trying to fix your washing machine, solenoid valves can come in quite handy. The seemingly endless variations can be overwhelming
at first, but that just means there’s bound to be one that’s a perfect fit. Additionally, with innovations and improvements to solenoid valve technology be on the lookout for new efficient and energy-saving solutions.
Here at Trimantec we proudly offer solenoid air valves and solenoid fluid control valves. Choose from either direct acting or pilot operated with multiple ports and positioning options. If you have further questions, let us know in the comments below or feel free to contact us via phone or email.