Solenoid valves:
A solenoid valve is an electro mechanical device used to obtain mechanical movement in machinery by utilizing fluid or air pressure. The fluid or air pressure is applied to the cylinder piston through a valve operated by a cylindrical electrical coil. The electrical coil along with its frame and plunger is known as the solenoid and the assembly of solenoid and mechanical valve is known as solenoid valve.
In fig (a) is shown a single solenoid spring return valve in its de-energized condition. In this condition the plunger and valve spool position are as shown, port P is connected to port A and port B is connected to tank or exhaust, if air is used. The spring(S) pressure keeps the spool in this condition as long as the coil is de-energized. Fluid pressure from port P through port A is applied to the left side of the cylinder piston. Thus the cylinder piston moves in the right direction.
In fig (b) is shown a single solenoid spring return valve in its energized condition. When solenoid coil is energized, plunger is attracted and it pushes the spool against spring pressure. In this position of spool, port A gets connected to tank and port P gets connected to port B . Fluid pressure from port P through port B is applied to the right side of the cylinder piston.
Thus the cylinder piston moves in the left direction. At the same time fluid in the other side is drained out to the tank. When the solenoid coil is again de-energized, spring (s) will move the spool to its
original position.
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