Adjust an EPR w/o a pressure tap?

[3800tom]

I am new to refrigeration and have nobody i work with to ask questions....

that being said i am working on a piece of equiptment and it has a TXV,EPR,a liquid injection valve, and hot gas bypass. i have replaced the txv, and liquid inj valve, and i am now trying to get the thing tuned in, but am having troubles... one of my questions is what do i set my EPR to and how do i set it without a pressure tap on it? thanks guys, you help would be very much appriciated

[jpsmith1cm]

Cut one in.

ONLY way to do it accurately.


You are describing a low temp system. Are you SURE it is an EPR? It could be a CPR which CAN be accurately set without gauges.

[3800tom]

pretty sure its an EPR. it is located downstream of the evap coil, but before joinin the liquid injection on the suction line.

[3800tom]

it is not a low temp system, this is a stability chamber that must run between 0*c- 100*c

[3800tom]

my mistake, i looked up the part number and it is listed as a CPR.
so i adjust this so the compressor will not draw more then RLA on startup?
anyone know the order in which the components txv,liquid injection and cpr should be adjusted?

[EZE2489]

Yes I do. A CPR valve is in place to do nothing more than ensure the compressor doesn't overload on a hot start after defrost. An EPR valve is there to maintain a certain evaporator pressure so the coil won't drop it's saturation temp too low and freeze. It does this by flowing high temp gas into the evaporator coil, again, to maintain evaporator pressure. And finally you're hard shut off TXV or MOV valve as you call it does nothing more then to prevent the system from equalizing completely during an off cycle. It really is only there to ensure as soon as the system does start back up there is a solid column of liquid already at the inlet of the TXV so we don't have and starved compressor starts.

[jpsmith1cm]

Yes I do. A CPR valve is in place to do nothing more than ensure the compressor doesn't overload on a hot start after defrost. An EPR valve is there to maintain a certain evaporator pressure so the coil won't drop it's saturation temp too low and freeze. It does this by flowing high temp gas into the evaporator coil, again, to maintain evaporator pressure. And finally you're hard shut off TXV or MOV valve as you call it does nothing more then to prevent the system from equalizing completely during an off cycle. It really is only there to ensure as soon as the system does start back up there is a solid column of liquid already at the inlet of the TXV so we don't have and starved compressor starts.

An EPR valve does not do this.

[thermojohn]

An EPR valve does not use hot gas to regulate evaporator pressure. That is a hot gas bypass valve that does that. It introduces hot gas into the low side usually at the distributor nozzle to maintain velocity through the evap coil for proper oil return.

An EPR just maintains a pre-determined pressure in the evaporator coil at the outlet of the coil. They are usually used when there are evaporators tied in the same circuit with differing saturation temperatures.

A CPR works similarly, but opposite to an EPR.

Remember, an EPR regulates pressure before the valve, and a CPR regulates pressure after the valve.

[git-r-dun]

Yes, as mentioned above, think of an EPR as an inlet pressure regulator and a CPR as an outlet pressure regulator.

[MicahWes]

I used to work in a few supermarket motor rooms that had hot gas operated EPR valves on the suction branches. They didn't inject any hot gas for controlling evaporator pressures, but they did use hot gas to actually operate the valves. There were hot gas headers running down right next to the suction headers.

[jpsmith1cm]

I used to work in a few supermarket motor rooms that had hot gas operated EPR valves on the suction branches. They didn't inject any hot gas for controlling evaporator pressures, but they did use hot gas to actually operate the valves. There were hot gas headers running down right next to the suction headers.

Yes.

Sporlan SORIT valves and Alco BEPRS valves both use high pressure gas for closing force.

The pressure actually bleeds out downstream of the valve, though.