A common accessory added to multiple evaporator systems operating at different evaporating temperatures is the evaporator pressure regulator (EPR). It is a refrigerant flow control device that prevents the refrigerant pressure in an evaporator from operating below a minimum value. It is typically installed on those evaporators designed to

Joe Marchese
Joe Marchese

operate at a pressure higher than the evaporator with the lowest design operating pressure. The EPR will prevent these evaporators from operating at the lower operating pressure. It is normally installed in the suction line just after the outlet of these evaporators and upstream of any other suction line controls or accessories.

An EPR is an open on rise of inlet pressure regulator. There are two forces which regulate its port opening: an internal spring pressure and the evaporator’s pressure. The outlet pressure of the regulator is not a factor in the opening or closing of this regulator. The internal spring pressure is the closing force and the inlet evaporating pressure is the opening force.

As the inlet pressure drops, the internal spring pressure will start to close down the port preventing the inlet (evaporator pressure) from dropping below its setting. As the inlet pressure increases, the port will open until it reaches its maximum port size. Once its maximum port size has been reached the evaporator pressure can continue to rise. The EPR does not control or regulate the maximum operating evaporator pressure of a system; it only prevents this pressure from dropping below a minimum setting.


The selection of an EPR is based on three basic system conditions:

1. Refrigerant used in the system;

2. Evaporator design capacity; and

3. Available pressure drop across the valve at its design load.

Once these conditions are known, a valve can be chosen from the manufacturer’s selection table. These valves should not be selected based on the line size of suction line since a manufacturer may use the same line size for many different capacities.

When installing an EPR with solder connections, the internal parts must be protected by wrapping the valve with a wet cloth to keep the body temperature below 250?F. The tip of the torch should be large enough to avoid prolonged heating of the connections.

To adjust the control point of an EPR, first attach a pressure gauge on the inlet side of the regulator. Normally you turn its adjustment screw clockwise to increase the valve’s control point, and counter-clockwise to decrease its control point. However, always refer to the valve manufacturer’s instructions for the company’s preferred adjustment procedure.

It may take up to 30 minutes for the new balance to take place after an adjustment is made. If the valve is being adjusted to a lower setting, an immediate response to an adjustment should be noticed. It is best to make adjustments to an EPR when the evaporator is under a minimum load condition.

When adjusting both an evaporator pressure regulator and a thermostatic expansion valve, first adjust the EPR with the thermostatic expansion valve (TXV) at the manufacturer’s predetermined set point, and evaporator under the actual minimum load condition. Then, if necessary, the TXV can be adjusted to the desired superheat setting while under the design conditions.

Publication date: 2/3/2014 

Want more HVAC industry news and information? Join The NEWS on Facebook, Twitter, and LinkedIn today!