The chiller has the most important accessories: expansion valve, thermal expansion valve can perform automatic adjustment within a certain working condition range, but it needs to be adjusted when the refrigeration system is debugged. When the expansion valve enters normal operation, it It can be adjusted automatically correctly.

Whether it is an air-cooled chiller or a water-cooled chiller, the adjustment of the thermal expansion valve is to adjust the pressure of the spring by adjusting the adjusting rod, that is, to adjust the static assembly superheat of the expansion valve. The adjusting rod is rotated inward to compress the spring; The adjusting rod is rotated out to relax the spring. Clockwise rotation of the adjusting lever is to rotate in, counterclockwise rotation adjustment is to rotate out.

When the operation of the refrigeration system is adjusted, the adjustment direction and range of the expansion valve can be judged from the level of the evaporation pressure value. The evaporation pressure is higher than the set value, that is, when the flow rate of the expansion valve is too large, it should be appropriately adjusted (rotate the adjustment lever clockwise); when the evaporation pressure is lower than the set value, that is, when the flow rate of the expansion valve is low, it should be appropriately adjusted Large (rotate the adjustment lever counterclockwise).

In the adjustment process of the expansion valve, we should pay attention to the different physical phenomena of the compressor under different operating conditions and ambient temperature. For example, under the conditions of (high temperature -10 ℃- 10 ℃), (medium temperature -10 ℃ -20 ℃) and (low temperature -20 ℃ -45 ℃), the evaporation pressure gauge of the compressor has different frosting conditions on the suction pipe. In the process of debugging the expansion valve, the opening degree (I .e. the flow rate) of the expansion valve should be adjusted according to the load. This process requires the accumulation of experience. When adjusting the expansion valve, a low pressure gauge can be installed on the suction pipe of the compressor to observe the change of suction pressure (equivalent to evaporation pressure).

Adjustment of the setting range of the expansion valve can generally be carried out in two steps, with coarse adjustment at the beginning of operation. Each time the rotatable adjustment rod is adjusted, about one turn (360 ℃). When the working temperature of the refrigeration system is close to the given value but cannot reach the given value, fine adjustment should be carried out, and each time the rotatable adjustment rod is adjusted, 1/2-1/4 turn (180-90).

The following three pictures show the three different superheat states generated by the refrigerant at the suction end of the evaporator and the compressor when the expansion valve is opened and adjusted differently.

Basic concept: superheat = return gas temperature-evaporation temperature: superheat = 10 ℃-4 ℃ = 6 ℃: superheat is temperature difference, not temperature. * * * timing of reading superheat; Stable high load, stable low load, before equipment shutdown due to temperature or pressure, before defrosting, when there is liquid return, especially to observe.

Due to the transmission delay (thermal inertia effect) of the temperature sensing bag, after each adjustment, the system should be operated for minutes or even more than ten minutes, depending on the capacity of the refrigeration system). And observe the change of suction pressure to determine the next adjustment direction. In short, the adjustment of the expansion valve is a more meticulous work, which requires patient observation and analysis. In order to do a good job in the adjustment of the expansion valve.