Duty of Expansion Valve in Cooling System
Expansion valve,is a control element which controls and regulates the liquid fluid transmits to the evaporator and delivers it to the evaporator by accurately measuring the amount of liquid refrigerant evaporated in the evaporator.
In other words; These are the expansion elements that precisely regulate and control the amount of refrigerant input to the evaporator depending on the evaporator load changes. It supplies the required amount of fluid to the evaporator depending on the superhead value.
Expansion Valve Types
Expansion Valve (TXV)
Expansion Valve (EEV)
Thermostatic External Balanced Expansion Valve (TXV) Working Principle
Electronic Expansion Valve (EEV)
In cooling systems, electronic expansion valves operate more efficiently than thermostatic expansion valves. The control at EEV is based on the superheat value of the refrigerant at the evaporator outlet.
Electronic Expansion Valve (EEV) Types
In cooling systems, we can classify electronic expansion valves into four groups as heat-motor controlled, electromagnetic modulation, pulse modulation (on-off) and stepper motor control.
In general, pulse modulation (on-off) up to 10 kW is used in cooling systems and stepping motor controlled electronic expansion valve is used for more than 10 kW.
Working Principle of Electronic Expansion Valve (EEV)
In EEVs, which are commonly used in practice, the motor shaft is moved up or down with the signal value from the control unit in order to keep the Superhead in the set value. If the motor shaft moves downward, the amount of refrigerant passing through the valve is reduced (the heat increases), while the upward movement increases the amount of refrigerant passing through the valve (the heat decreases). In sum; depending on the measured superheat value, the stepper motor is signaled to make the corresponding movement. The controller sends an on or off signal to the stepper motor depending on the difference between the actual superheated value at the evaporator output and the expected value. As it is known, as the superheat increases, the expansion valve should open and deliver more refrigerant, and in case the superheat decreases, the expansion element should close.