Applications of the Solenoid Valves
The solenoid valve are used extensively in large number of devises that are used in various industries like refrigeration, air conditioning, automobiles, hydraulics, pneumatics, and many more. Only a few of the applications of the solenoid valves have been described here:
1) In refrigeration: One of the most popular applications of the solenoid valve is in the refrigeration systems. They are used in air conditioners to change the direction of the flow of the refrigerant so that they can be used for the cooling purpose in the summers and for heating purpose in the winters. In summers the cooling coil of the air conditioner is located inside the room and the condenser outside the room while their functions are reversed in the winters as the machine acts as the heat pump. The roles of the condensers and the evaporators are reversed due to reversal in the flow of the refrigerant which is brought by the solenoid valve. You can see the detailed working cycle of this machine here.
In the large refrigeration plants the compressors are of multi-cylinder type. Each cylinder or the groups of the cylinders are connected to the unloaders, which are nothing but the solenoid valves. These solenoid valves are operated by the discharge pressure of the compressor. In the normal working cycle this solenoid valve allows the refrigerant to flow from the compressor to the condenser and then to the other parts of the refrigeration cycle. But when there is no cooling load (cooling is not required) the solenoid valve closes and directs the refrigerant to the suction valve instead of to the condenser. Thus the refrigerant keeps on moving from suction side to the discharge side and back to suction without producing any cooling effect.
2) In hydraulics and pneumatics: The pneumatic valves are operated by the pressure of the compressed air. They comprise of the piston and cylinder arrangement or some rotating parts called as the actuator. The solenoid valve controls the pressure of air flowing to the actuator and thus controls the action brought about by the actuator. The arrangement of the hydraulic systems is similar to the pneumatic systems. In hydraulic systems the fluid used is liquid, which is called as the hydraulic fluid. The solenoid valve controls the direction of the flow of the hydraulic fluid inside the cylinder, which controls the motion of the piston or the ram.
3) In automobiles: The solenoid valve is an active part of the starting system of the automobiles like cars and trucks. When the operator turns on the ignition switch of the automobile, the current is passed from the battery of the vehicle to the solenoid valve. This forces the solenoid valve to close the heavy pair of contacts that enables the flow of the current to the starter motor of the vehicle. The starter motor brings about the initial motion of the piston inside the cylinder before the piston achieves self actuating motion due to burning of the fuel inside the cylinder. Once the engine starts the operator stops the further motion of the ignition switch, due to which the flow of the current to the solenoid valve and hence the starter motor is stopped. If the flow of the current to the solenoid is not sufficient the contacts are not closed and the vehicle fails to start. This usually happens when the battery is low or damaged or problems in the cables.
In automobiles the solenoid valves are also used in automatic gearbox drive selectors, locking of the petrol cap, air conditioning controls, security systems etc.
4) For locking: The solenoid valves are being used for the locking of doors in hotels, offices, secure areas and others. In these systems the solenoid valve is connected to the locking mechanism of the door. When the door is locked no power is drawn by the solenoid valve and they are usually operated by power from the battery. The solenoid operated locking systems are also used in the vending machines, car parks, access barriers, remote access systems etc.