Valve for refrigeration plant

A refrigeration system comprising, a compressor and an evaporator, a valve unit having an inlet and an outlet with an opening therebetween, said valve unit inlet being connected to the output side of said evaporator and said valve unit outlet being connected to the suction side of said compressor, chamber means for said valve unit, valving means comprising a movable wall for said chamber and closure means for said opening, a filling medium for said chamber having a vapor phase exerting a temperature responsive reference pressure P.sub.f biasing said wall of said valving means in a valve closing direction, passage means for allowing the vapor pressure P.sub.o or refrigerant in said inlet to bias said wall in a valve opening direction to provide a valve opening for said closure means corresponding to the difference between said P.sub.o and P.sub.f pressures, control means for controlling the temperature of said filling medium including heat transfer means and first feedback temperature sensing means in said chamber, said control means further including second feedback temperature sensing means in the air flow stream of said evaporator on the downstream side thereof, said filling medium having characteristics so that its temperature which brings about equilibrium between said biasing of said closure means in opening and closing directions is greater than either said refrigerant in said inlet or the surrounding air or both.