Superheat depends on the type of metering device you are using in the equipment as well as the current state of the load. With a fixed orifice, the superheat will be high, about 20 to 30 degrees when the box is warm, down around 10-15 when the box is cold. With a txv, the superheat should be constant, normally between 10-15 degrees. It is best to check the superheat at the outlet of the evaporator. this will ensure that the compressor does not slug with liquid refrigerant.
Temperature is not a pressure or force acting on a TXV (Thermostatic Expansion Valve) diaphragm. The TXV diaphragm is primarily influenced by refrigerant pressure and spring force to regulate the flow of refrigerant into the evaporator coil. Temperature affects the superheat setting of a TXV but is not a direct force acting on the diaphragm.
The purpose of the External equalizer on the TXV is to compensate for the pressure drop in the evaporator coil , This is done since the superheat calculation is based on the difference in the Saturation temperature corresponding to the Suction pressure (Measured after the coil) and the actual suction line temperature. Now, in a TXV measurement of actual line temperature is accomplished by using the Sensing Bulb and the Measurement of the Suction pressure by the External Equalizer of the TXV. The opening/Closing of the Expansion valve is controlled by the setting of the superheat which is governed by the setting of the Spring.
None, a TXV operates by it's sensing bulb sensing superheat of the suction line as it exits the evaporator coil.
take your gages and put them on the beginning of the evaporator (afte metering device or txv) and look at saturation temp then get your temp at the suction line (before the compressor)
Three factors that determine the capacity of a TXV are superheat setting, pressure drop across the valve, and the flow rate of refrigerant passing through the valve. These factors work together to ensure that the TXV maintains proper refrigerant flow to achieve efficient system operation.
Liquid cross charge in a thermostatic expansion valve (TXV) occurs when the refrigerant flowing through the valve is at a temperature below the designed setpoint. This can affect the valve's ability to maintain proper superheat and refrigerant flow, impacting the system's performance and efficiency. Adjusting the valve setpoint or system charge may be necessary to correct the issue.
Superheat is measured by calculating the temperature of the refrigerant vapor above its saturation temperature at a given pressure. This is done using a pressure-temperature chart for the specific refrigerant being used. The difference between the actual vapor temperature and the saturation temperature at that pressure is the superheat.
Difference between txv and exv.
Metering device The metering device controls the flow of liquid refrigerant through the system. The liquid enters at a high-pressure, high-temperature, sub-cooled state and leaves as a low-pressure, low temperature, expanded liquid state. Accurator Piston and Thermostatic Expansion Valves are the most widely used metering devices. Accurator Pistons are widely used because of their low cost and flexibility. The piston can easily be changed to match the capacity of the condensing unit. The Thermostatic Expansion Valve (TXV) is the most efficient type of metering device. The TXV automatically adjusts the flow of the liquid refrigerant based on the superheat of the refrigerant leaving the evaporator coil. As the load on the evaporator increases, the TXV increases the flow of refrigerant. This maintains the proper superheat. The TXV is efficient throughout a variety of system operating conditions, while the accurator is efficient only under designed conditions.
Superheat was created on 2000-01-25.
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