EPR valves 101


I don't do much in the way of “rack” refrigeration. However, I recently had a conversation with experienced rack refrigeration tech Jeremy Smith, and he got me thinking about EPR valves.

I've heard EPR (evaporator pressure regulator) valves called suction regulators or hold back valves. In essence, they hold back against the suction line to maintain a set temperature for evaporation or boiling in the evaporator.

In refrigeration rack systems, EPR valves play a vital role in ensuring that the product is cooled consistently and nearly constantly.

In an A/C system, we have a TXV that maintains a constant superheat at the evaporator outlet. The evaporator temperature itself will fluctuate up and down depending on the load.

In a refrigeration case, you must first ensure you have a full line of liquid using a sight glass or by checking the subcooling. Then, you make sure the case has proper airflow, etc. After that, you set the EPR to maintain the proper coil evaporation temperature (by holding back pressure as needed), and then you check and/or set the TXV to the proper superheat. This procedure ensures BOTH proper coil feeding as well as proper coil temperature.

Pretty cool, right? (Pun intended.)

—Bryan

4 responses to “EPR valves 101”

  1. You do not need to have a “rack” system to need an E.P.R.. Any time you have two refrigeration applications on one condensing unit. I.E. One med. temp. Cooler and one low temp.(freezer). The E.P.R. would be installed on the med. temp. cooler.

  2. Also in multipule circuits you can use it to maintain temperatures more steady per circuit, but like it was commentes you have to have a soild liquid line (full sight glass) and condenser gotta be in good shape and clean… there’s a crankcase pressure valve (cpr) that works similar but mantains a constant suction at entry of compressor its used the majority of times on low temp apps also can be used on medium temp is capacity is to close… it’s good to have a little more btu for when system is at max demand example (loading merchandise or leacing door open for long time… good article keep up the good work!!

  3. hi from Lebanon. i have built a display case with 3 evaporators on a single condensing unit each with its own txv. the thing is the system goes down in temp so rapidly and then makes a halt @ 45 F on any of the evaporators. the back pressure is quite high (around 60 psig r404a)(the pressure goes way down if i turn on only one evap.(8psig) or two (30psig) . i am not able to make the sight glass full or the compressor will flood. i was wondering if an EPR can solve this issue

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