Dry shell and tube evaporator is a kind of liquid refrigerant which enters the tube side from the end cover of one end of the evaporator after throttling. There is a diaphragm cast on the end cover. The refrigerant evaporates through two or more processes and absorbs the heat of the refrigerant, then comes out from the same end cover and enters the compressor. If the end cover diaphragm gasket leaks, the refrigerant will be short circuited, resulting in the decrease of liquid return and refrigeration capacity. Dry shell and tube evaporators are generally made of copper tubes, either plain tubes or inner finned tubes with longitudinal fins.