 In internally equalized valves, the evaporator pressure against the diaphragm is the pressure at the "inlet" of the evaporator, whereas in externally equalized valves, the evaporator pressure against the diaphragm is the pressure at the "outlet" of the evaporator.Externally equalized thermostatic expansion valves compensate for any pressure drop through the evaporator.Internally equalized valves can be used on single circuit evaporator coils having low-pressure drop.