Solenoid valves are used in many heating and cooling systems. They are electrically operated. Solenoid valve, if it is connected as shown on Fig. 14-10, remains open when the current is supplied. It closes when the current is switched off. In General, solenoid valves are used to control for liquid refrigerant flow to the expansion valve or gas refrigerant flow to the evaporator when he or device control reaches the desired temperature. The most common use of the solenoid valve on the liquid line, and it works with thermostat (see Fig. 14-11).
Electromagnetic shown in Fig. 14-12 controls the supply of natural gas in hot-air furnace. Note how the coil is wound on a piston. The piston is the core of the solenoid. She has a tendency to be involved in the coil when the current feed on the current flowing through it. Electromagnetic effect causes the piston to be brought up to the spool area. When the piston moves upward pull of the electromagnet, soft disk (в„–10) is lifted up, allowing the movement of gas through the valve. This is a basic technique used for the control of water, petrol, oil, or any other liquid or gas.