The working of a solenoid valve is similar to hand operated stop valve. However, this valve can be conveniently operated in remote locations by any suitable electric control device. Solenoid valve is a two-position (open and close position) shut-off valve used in fluid lines, such as in refrigeration equipments, water lines, airlines etc. It is operated using an electromagnet consisting of a coil of wire placed on an iron spool, which is fixed over the valve body.
Construction of Solenoid Valve
Solenoid valve consists of an insulated copper wire coil, which is commonly known as a solenoid coil. An iron core or armature core or plunger, is placed inside the coil. By attaching a valve stem and pin to the coil armature, a valve port can be opened and closed as the coil is energized and de-energized respectively.
Fig. 1: Solenoid valve
Working of Solenoid Valve
When electric current is passed through the solenoid coil, it gets energized. Further, the iron spool is magnetized and the magnet c field attracts an armature or plunger up into the core of the coil. This pulls up the plunger along with the valve stem, thus opening the valve. When supply of electric current is stopped, the solenoid coil gets de-energized and magnetic field gets destroyed. Therefore, the plunger along with the valve stem falls down or drops down due to its own weight and gravity, which closes the valve. Thus, the operation of this valve can be cycled automatically through a control. For example: When a solenoid valve is installed on the liquid line of a refrigeration plant, the solenoid can be control ed by a room thermostat, to close the valve and cut off the liquid feed to the evaporator, when the room temperature attains the set point of the thermostat. Solenoid valves are unidirectional valve (i .e. flow occurs in only one direction) and direction of flow to be kept is always marked on the outer surface of body by an arrow head. They are always fitted in vertical direction. They are used to maintain desired temperature, pressure, level of any liquid etc.
Applications of Solenoid Valve
- A solenoid valve is installed in the liquid line just ahead of the expansion valve to prevent flow of liquid refrigerant from evaporator, when the compressor is not working.
- To provide individual temperature control in each refrigerated space of a multiple system.
- Solenoid valves are frequently used to control the flow of condensing water. A solenoid valve reduces the water cost by stopping the flow of water as soon as the compressor stops. It will open the supply, only when, the compressor starts again.
- Water lines, airlines etc.