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Thermostatic expansion valve adjustment process


Thermostatic expansion valve adjustment process

 1.1 Before thermostatic expansion valve adjustment inspection

      Before adjusting thermostatic expansion valve, must confirm that the equipment refrigeration abnormal is caused by the thermostatic expansion valve deviation from the optimal operating point, but not because of less freon, dry filter plug, filter, fan and other reasons caused by. At the same time, the accuracy of the sampling signal must be guaranteed, the temperature sensor must be installed horizontally in the lower 45 degrees of the return pipe position, must not be installed directly below the pipe, in order to prevent oil accumulation at the bottom of the tube and other factors affect the correct temperature sensing package. Can not be installed on the riser. Check the condenser fan control mode, as far as possible to use speed control, to ensure constant condensation pressure. 

1.2 Matters needing attention during the adjustment of the thermal expansion valve

     The adjustment of the thermal expansion valve shall be carried out under the normal operation of the refrigerating device. Because the surface of the evaporator can not be placed thermometer, can use the compressor suction pressure as the saturated pressure in the evaporator, table to get approximate evaporation temperature. The temperature of the return air pipe is measured with a thermometer and checked against the evaporation temperature. In the adjustment, if the overheat is too small, you can turn the adjusting screw according to the clockwise direction (that is, increase the spring force, reduce the opening degree of the thermal expansion valve) , so as to reduce the flow; That is, the lack of liquid supply, you can adjust the screw in the opposite direction (counterclockwise) rotation, so that the flow increase. Because of the thermal inertia of the temperature sensing system of the thermal expansion valve in the actual work, the signal transmission lags behind, and the next adjustment can be made after the operation is basically stable. Therefore, the whole adjustment process must be patient and careful, and the number of turns of the adjusting screw should not be too many too fast at one time (the adjusting screw of the straight-rod thermostatic expansion valve turns one turn, and the change of the superheat temperature approximately changes 1 ~ 2 ° C) .

1.3. Method for measuring superheat of thermal expansion valves. 

The steps are as follows: 

1) shutdown. Insert the probe of the digital thermometer into the insulating layer at the air return port of the evaporator (corresponding to the position of the induction temperature package) . Connect the pressure gauge to the three-way of the compressor low pressure valve. 

2) start, let the compressor run more than 15 minutes, into a stable running state, so that the pressure indication and temperature display to a stable value. 

3) reading out the temperature T 1 of the digital thermometer and the temperature T 2 of the pressure measured by the pressure gauge, the superheat degree is the difference of two readings T 1-t 2. Note that both readings must be read at the same time. Thermal expansion valve overheat should be between 5 ~ 8 ° C, if not, then the appropriate adjustment. It can be seen that after the adjustment of the compressor shell temperature than before the adjustment will have a significant change.

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