A solenoid valve controls the flow of fluid in a tube or duct. Different mechanisms are employed to control the media, which means a wide range of these valves to cater to the variations.
In addition to the designs, these valves come with different operating mechanisms. Here, we take a look at the 5 types of solenoid valves and their working principles.
1. Direct Acting Solenoid Valve
These valve types employ the simplest operation to work. A direct acting solenoid valve consists of a plunger that closes a small orifice directly, without relying on an outside force.
These types of solenoid valves are fast acting. They can also operate under different pressures, from the lowest to the maximum allowable levels.
A direct acting solenoid valve can be a NO (normally open) or NC (normally closed) valve. When a NO valve, the orifice closes on the application of an electric current.
In a NC, direct acting valve, the orifice remains closed and opens when the solenoid coil windings are energized.
A variant of the direct acting valve is the 3 way 2 position solenoid valve. It operates identically to the 2/2 valve, with only differences in the way it exhausts fluid. It can do so using a seal at the plunger top or bottom.
The use of direct acting solenoid valves comes with advantages and disadvantages. These valves are fast acting and accurate. Another advantage is that these valve types can work with different line pressures, from low to high.
The downsides of direct acting solenoid valves are mostly in their strength and size. Because the valves depend on the closing force provided by the solenoid coil, they usually need a lot of current to operate.
This often means large solenoid construction, especially if the systems are large-scale.
2. Pilot-Operated Solenoid Valve
Also called an indirect-operated, a pilot solenoid valve utilizes the pressure difference across the valve ports to close or open the orifice. The working of these types of valves is somewhat more complex than that of direct acting valves and with a few more parts.
Here is how the pilot solenoid valve works.
A diaphragm separates the inlet and outlet ports of these types of solenoid valves. On the diaphragm is a small hole tha allows the medium to flow into the upper chamber. A small duct connects this chamber to the low-pressure port.
The system’s pressure and a small spring keeps the valve closed. When the solenoid is energized, the pilot orifice opens, causing the pressure in the upper chamber to drop.
This results in the diaphragm lifting and the medium to now flow freely from the inlet to the outlet port.
The pressure chamber in a pilot-operated solenoid valve serves to amplify the closing and opening forces. This enables small solenoids to operate a high-flow line.
Because of this amplification of pressures, this type of solenoid valve mostly doesn’t require large amounts of current to operate.
Despite their powerful operation, pilot solenoid valves have several limitations. They are a one-way solenoid valve, capable of regulating a medium that only flows in one direction.
Pilot solenoid valves are also slower than the direct acting types, plus they need a minimum operating pressure level, unlike direct solenoid valves that can work with 0-bar circuits.
Pilot solenoid valves are suitable for systems with sufficient pressure differences, such as irrigation systems and car wash equipment.
They’re most commonly used in applications where flow rates or capacities are high. These include systems that control the flow of water such as faucets.
3. Two Way Solenoid Valves
These valve types use two ports to close or open the flow of fluid. A 2-way solenoid valve is classified as normally open if the orifice allows media to flow when the coil is de-energized and normally closed if energizing the coil allows fluid to flow through either port. The NC or normally closed solenoid valve is more common than the NO type.
Two-way solenoid control valve systems where only release and restriction of media is needed. These include air compression machines and similar equipment.
4. Three Way Solenoid Valve
A 3-way solenoid valve usually comes equipped with three ports and two different orifices. The two orifices open alternatively, according to the state of the solenoid coil.
Typically, these valve types have two inlet ports with a single outlet. When used in this design, a three way solenoid valve mostly mixes two different fluids.
Some three way solenoid valves utilize two outlets and a single inlet port. This kind of design allows the valve to control the flow of a medium in one of the outlet ports by directing it into the other. 3-way solenoid valves can be found in common home appliances such as the household dishwasher.
5. Four Way Solenoid Valve
This type of valve utilizes four ports; two pressure inlets and two exhaust outlets. 4-way valves are commonly used to work double acting solenoid valve actuators.
The inlet ports provide incoming pressures to the actuator or cylinder, and the outlet pipes are exhaustive pressure openings.
Conclusion
Solenoid valves come in different types, with different working mechanisms and constructions.
The type to use depends on many factors. Mainly, the required action dictates the design and working principle.
Direct acting and 2-way solenoid valves suit systems where only shut off is needed. Complex systems that mix or direct fluids require more than the simple action.
In those circuits, additional ports are required.
Overall, each type of solenoid valve suits specific applications.
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