The Working Principle of Solenoid valve

A solenoid valve consists of  two main parts: the valve and the solenoid. A direct acting valve has only a small flow circuit, shown within section E of this diagram (this section is mentioned below as a pilot valve). The solenoid converts electrical energy into mechanical energy which, in turn, opens or closes the valve mechanically. The diaphragm piloted valve multiplies this small flow by using it to control the flow through a much larger orifice.textile cylinder

Solenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control. A spring may be used to hold the valve opened or closed while the valve is not activated. pneumatic control valve

A- Input side

B- Diaphragm

C- Pressure chamber

D- Pressure relief conduit

E- Solenoid

F- Output side

The diagram to the right shows the design of a basic valve. At the top figure is the valve in its closed state. The water under pressure enters at A. B is an elastic diaphragm and above it is a weak spring pushing it down. The function of this spring is irrelevant for now as the valve would stay closed even without it. The diaphragm has a pinhole through its center which allows a very small amount of water to flow through it. This water fills the cavity C on the other side of the diaphragm so that pressure is equal on both sides of the diaphragm. While the pressure is the same on both sides of the diaphragm, the force is greater on the upper side which forces the valve shut against the incoming pressure. In the figure, the surface being acted upon is greater on the upper side which results in greater force. On the upper side the pressure is acting on the entire surface of the diaphragm while on the lower side it is only acting on the incoming pipe. This results in the valve being securely shut to any flow and, the greater the input pressure, the greater the shutting force will be.

In the previous configuration the small conduit D was blocked by a pin which is the armature of the solenoid E and which is pushed down by a spring. If the solenoid is activated by drawing the pin upwards via magnetic force from the solenoid current, the water in chamber C will flow through this conduit D to the output side of the valve. The pressure in chamber C will drop and the incoming pressure will lift the diaphragm thus opening the main valve. Water now flows directly from A to F.

When the solenoid is again deactivated and the conduit D is closed again, the spring needs very little force to push the diaphragm down again and the main valve closes. In practice there is often no separate spring, the elastomer diaphragm is moulded so that it functions as its own spring, preferring to be in the closed shape.

From this explanation it can be seen that this type of valve relies on a differential of pressure between input and output as the pressure at the input must always be greater than the pressure at the output for it to work. Should the pressure at the output, for any reason, rise above that of the input then the valve would open regardless of the state of the solenoid and pilot valve.

In some valves acts directly on the main valve. Others use a little known valve, solenoid valves, as a driver to operate a larger valve.

While the second type is actually a magnet in combination with a pneumatic valve, sold and delivered as a unit called the coil. controlled valves need to control much less energy, but much slower. Magnets are usually full power to open and remain open at all times, where a solenoid valve direct acting high enough for a short time to open it, and little power to support it.