1. Evaporator coils
4. Expansion Valve
Types of Expansion Valves
There are basically four types of valves that are in use. These valves are also referred to as metering devices.
Automatic Expansion Valve: It regulates the flow of refrigerant from the liquid line to the evaporator by using a pressure-actuated diaphragm. It maintains a constant pressure in the evaporator.
The setback is that it is not efficient if the load fluctuates hence this type is not suitable for use in air conditioning as the load fluctuates a lot during its operation.
Thermostatic Expansion Valve : It uses a valve mechanism to control the flow of liquid refrigerant into the evaporator coil. The flow is controlled by the pressure in the evaporator.
This type of metering device is able to operate well when the load fluctuates and hence is suitable for use in air conditioning systems. When the evaporator warms, the valve provides a higher flow rate and when it cools, it reduces the flow rate.
It is also commonly referred to as the TXV, TEV or TX valve. There is a sensing bulb which detects the temperature of the coil and is usually located at a higher temperature within the evaporator.
The bulb must be clamped firmly to the coil to ensure proper sensing. When the temperature of the evaporator increases due to the demand for cooling, the pressure in the bulb will also increase hence pushing the spring to open the valve.
Similarly, when the temperature of the evaporator reduces due to a lack of demand for cooling, the pressure in the bulb will drop hence causing the spring to close the valve.
Capillary Tube: It is a tube with small internal diameter and could be coiled for part of its length. It is installed to the suction line. A filter-drier is sometimes fitted before the tube to remove dirt or moisture from the refrigerant.
Float valve: It is actuated by a float that is immersed in the liquid refrigerant. Both low-side float and high side-float are used to control the flow of liquid refrigerant.
The low-side float helps to maintain a constant level of liquid refrigerant in the evaporator. It opens when there is no liquid in the evaporator and closes when there is liquid in the evaporator.