A solenoid is a type of electromagnet that generates a controlled magnetic field. It has the capacity to create a magnetic field from electric current and in turn, uses the magnetic field to create linear motion.
It can be used to power a switch, like a starter valve in a sprinkler system or the starter of an automobile. It has an important component known as the solenoid valve, which is also an electromagnetic device through which the solenoid uses an electric current to generate a magnetic field thereby operating the mechanism that regulates and opening of fluid flow through a valve.
A solenoid valve is always used whenever fluid flow is to be controlled automatically, as they can shut off, release, mix, dose, or distribute fluids.
It is used in washing machines, gas boilers, air hammers, hydraulic pumps and so on. They can be customized to meet specific needs and have been used in controlling different mediums like electricity, steam, gas, air and oil.
There are various types of solenoid valves based on the difference in the electric current used, the mechanism used to regulate the fluid, the characteristics of the fluids controlled and the strength of the magnetic field generated.
But I will focus the types to be discussed here based on their modes of operation.
1. Direct Acting Solenoid Valves:
In this type of solenoid valve, there is a coil that always opens the valve magnetically in a direct action, thereby lifting up the shaft and the valve seat without depending on an external pressure. They only need full power when opening the valve, as they have the power to hold their open position even while operating on low power.
2. Pilot-Operated Solenoid Valves:
They require less electrical energy for their operations but must maintain full power to remain in an open state. The pilot opening is opened by the plunger and in that process, the valve opens and closes through the built-up pressure. And they perform at a slower rate when compared with direct acting solenoids valves.
3. Two-Way Solenoid Valves:
These have two ports in which each is alternately used to allow or close flow. And based on their operation, the two-way solenoid valves could be the “normally open" or the “normally closed” type. For the normally open, the valve remains open till some current is applied to it before it can close and when the current stops, it opens up again to its normal state. But for the normally closed, it works in the opposite manner, that is, it remains closed until electricity is applied for it to open. And they are the most common types.
4. Three-Way Solenoid Valves:
They normally come with three ports and are commonly used when there is a need for both alternate and exhaustive pressure in an operation such as in dishwasher or in coffee machine.
5. Four-Way Solenoid Valves:
Though four is the normal ports for these type of solenoid valves, they could have more port connections. They could be normally closed, normally open or universal in their operations. And they are usually used with an actuator or with a dual-acting cylinder. The main thing here is that half of the port connections supply pressure while the remaining connections provide exhaust pressure.
In general terms, solenoid valves are used to control the flow and the direction of liquid or air in fluid power systems which have been extensively used in both hydraulic and pneumatic power systems.