Balanced thermostatic expansion valve for refrigeration systems

Claim 1

In a refrigeration system having a compressor, condenser and evaporator operatively interconnected, a thermostatic expansion valve, comprising: (a) a valve body, an inlet chamber, an outlet chamber and means for separating the inlet chamber from the outlet chamber, an inlet connecting the inlet chamber with a refrigerant line connected to the refrigeration system high pressure side, an outlet connecting the outlet chamber to a refrigerant line connected to the evaporator, (b) means for controlling the flow of the refrigerant through the expansion valve separating means, (c) means in the separating means for further defining a valve port which operatively receives the flow controlling means, the valve port providing communication between the inlet chamber and the outlet chamber for the flow of the refrigerant, (d) a biasing member for biasing the flow controlling means towards a closed position tending to close the valve port thereby reducing the flow of the refrigerant through the valve port, (e) a flexible motor element carried by the valve body and operatively connected to the flow controlling means for moving the flow controlling means between an open position and a closed position thereby increasing and decreasing the flow of the refrigerant through the valve port, (f) means for sensing a temperature at an evaporator outlet and subjecting one side of the flexible motor element to a pressure that is a function of the evaporator outlet temperature, (g) first communicating means for subjecting another opposing side of the flexible motor element to an inlet chamber pressure so as to tend to resist the movement of the flexible motor element in response to the temperature sensing means and counterbalance the force of the refrigerant flow tending to open the valve port, whereby the first communicating means sensing the inlet chamber pressure does not substantially restrict or obstruct refrigerant flow through the inlet chamber, the first communicating means including a piston having one free end located in the inlet chamber for sensing inlet chamber pressure without substantially restricting or obstructing refrigerant flow, and an opposing end operatively connected to the flexible motor element so as to communicate inlet chamber pressure to the other opposing side of the flexible motor element, (h) a second communicating means intermediate the flexible motor element and the biasing member for communicating a pressure difference to the biasing member, the pressure difference corresponding to a difference between the inlet chamber pressure and the pressure that is a function of the evaporator superheat, the second communicating means including a push rod intermediate the flexible motor element and the biased flow controlling means.