Overview of Expansion Valves

1.Condensing Temperature (CT)
The highest temperature of the liquid condition of refrigerant in the refrigerant cycle. (Temperature of saturated refrigerant liquid at the expansion valve inlet)
2.Evaporating Temperature (ET)
The temperature at mixture condition of refrigerant gas and liquid to cool water or air load etc.(Temperature of saturated refrigerant vapor at the expansion valve outlet)
3.Subcooling (SC)
The degree of temperature reduction, without changes of pressure, against the pressure equivalent to the refrigerant liquid temperature. (Difference between the temperature at the expansion valve inlet and temperature equivalent to the refrigerant pressure)
4. Superheat (SH)
The degree of temperature increase, without changes of pressure, against the pressure equivalent to the refrigerant gas temperature. (Difference between the temperature at the sensing element of the expansion valve and the temperature equivalent to the pressure at the equalizing section)
5.Condensing Pressure
The pressure equivalent to CT.
6.Evaporating Pressure
The pressure equivalent to ET.
7.Cooling Capacity
The amount of cooling heat in kW.
1 U.S. Refrigeration ton (U.S.R.T.) = 3.52 kW
8.Pressure Drop
The major cause of pressure drop is frictional resistance in piping. Pressure drop in the high-pressure side causes a reduction in the degree of subcooling or the generation of flush gas, while pressure drop in the low-pressure side causes temperature variance in the evaporator and a reduction in capacity. Pressure drop in the internal pressure equalized expansion valve leads to an increase of operating superheat.
9.Maximum Operating Pressure
The maximum pressure (designed pressure) at which the expansion valve functions without problems under normal conditions of use.

It is necessary to select the most appropriate charging type in accordance with the type of refrigerant, evaporating temperature, thermal effect by defrost, ambient temperature of the mounting part, etc.

Special Charging Types (S) (SA) (SL)
Composed a mixture of different gases, minimize the operating superheat compared with charging type (G) and control the maximum operating pressure (M.O.P.).
・Symbols are changed in accordance with the difference in the applied range of evaporating temperature and M.O.P.
・Mainly for cooling units (protected horticulture), heat pump equipment, and low temperature equipment

Gas Charging Type (G)
The same refrigerant used for the equipment is charged, and there is a point at which charged liquid becomes superheated gas at the certain temperature rise. This point is called the maximum operating pressure (M.O.P.).
・Mainly for cooling units
Controlling M.O.P. enables to prevent liquid return at startup and to prevent overload of the compressor motor.

Special Charging Types (C) and (CL)
Adsorbent and special gas are charged. Using changes in pressure by high-temperature desorption and low-temperature adsorption, these types can minimize the operating superheat at low temperature condition. These types can be controlled correctly regardless of temperature difference between sensing bulb temperature and ambient temperature around the body. There is no control of M.O.P.; however, overload prevention effect can be expected.
・Symbols are changed in accordance with the difference in the applied range of evaporating temperature.
・Mainly for low and extremely low temperature equipment

Charging types shown in ( ) are special charging types.

〇 means “applicable,” and △ means “may not be applicable.”
＊１ : Applicable AEX only.
＊２ : Depending on the M.O.P. setup.

Please select external pressure equalization types for equipment with large pressure drop and fluctuation of evaporator, and internal pressure equalization types for equipment with smaller pressure drop in the evaporator.
For example, when there is pressure drop of 0.102 MPa on the low-pressure side, the internal pressure equalization type will increase operating superheat approximately 5℃.
Setting :
Refrigerant R404A
Point A 0.702 MPa abs (5℃)
Point B 0.6 MPa abs (0℃)
Spring Pressure P₃ 0.102 MPa

Pressure in Sensing Bulb (P₁)
　= 0.6＋0.102
　= 0.702 MPa Saturation Temperature
Operating superheat is 5℃－ 0℃ = 5℃.

Pressure in Sensing Bulb (P₁)
　= 0.702＋0.102
　= 0.804 MPa Saturation Temperature
Operating superheat is 10℃－ 0℃ = 10℃.

Equivalent to pressure drop appears as an increase in operating superheat, which leads to pressure drop in suction piping and reduction of cooling capacity. Therefore, it is necessary to pay attention to excessive increases in operating superheat.
A pressure difference equivalent to 1℃ temperature difference is a guideline for the selecting pressure equalization type.
When there is a pressure difference higher than the values shown in the table bellow, is the external pressure equalization types are effective.

The degree of temperature increase, without a change of pressure, against the saturated vapor temperature of the refrigerant. Expansion valve superheat has static superheat (SSH) and superheat change (SHC), and the sum of SSH and SHC is the operating superheat (OSH), which is equivalent to the degree of superheat generated at the evaporator outlet.

Static Superheat (SSH) : Superheat from valve closing position to valve opening
Superheat Change (SHC) : Superheat from valve opening to required flow rate
Operating Superheat (OSH) : Static Superheat + Superheat Change

Adjustment of superheat means the adjustment of static superheat.
Please set the static superheat for the safety of equipment unless there is a specific reason.