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marc5180
14-03-2009, 03:26 PM
Hi all, i have a few questions that i can't find the answers to and i'm stuck, if any of you could help me out i'd appreciate it.

What is the purpose of the pilot valve on an EPR?

In pumped liquid recirculation system what is the purpose of a low pressure receiver? ( i know what the purpose of a normal receiver is but i got this question wrong)

NH3LVR
14-03-2009, 09:13 PM
If I understand the first question correctly, you are referring to a pilot valve that can shut off the flow during a hot gas defrost. If I am incorrect, let us know the valve model and we will go from there.

The LPR in a Pumped System provides separation of liquid and vapor. Remember that these are liquid overfeed systems and the returns are wet. The vapor volume of the receiver allows the liquid to fall out of the returning gas. Without the LPR you would have to cut down the liquid until the suction line was superheated to prevent slugging.
Another reason is to provide sufficient Net Positive Suction Head (NPSH) for the pumps to function without cavitation. Without enough NPSH the pressure loss in the pump suction will cause cavitation.

marc5180
14-03-2009, 09:20 PM
Thanks for that NH3LVR, they were questions that i had on a test and i wasn't sure of the answers.
With regards to number 1 that seems correct as the answer you gave was one of the options.

Number 2, so 100% liquid is flooded into the evap and 100% liquid leaves the evap. It then goes into the LPR where the compressor takes the refrigerant vapor from the top of the receiver?

NH3LVR
14-03-2009, 11:37 PM
Number 2, so 100% liquid is flooded into the evap and 100% liquid leaves the evap. It then goes into the LPR where the compressor takes the refrigerant vapor from the top of the receiver?

Close, but not quite right.
The evap is overfed by several times the amount of liquid that is required. An overfeed ratio of four to one, for instance. (Four pounds of NH3 Liquid for every pound of liquid evaporated)
In other words the suction will return four pound of liquid for every pound of vapor.
This creates a wet return which is separated in the LPR.

There is a another method which is similar, but I have worked on only one of them.
In this case R22 was used as a brine and pumped through horizontal plate freezers. It was cooled by a heat exchanger running a two stage R502 system. Little if any phase change occurred in this system. I have not seen another one since.
This one took me a little head scratching to figure out. It worked very well after I got it up and running.
It was assembled in Japan and many of the components were close to American parts, but not identical.

RANGER1
15-03-2009, 01:37 AM
Have also seen this method on fishing boat from Japan , but it was using R11 as brine .
A pilot on any valve is used on bigger valves eg EPR so any size required main valve can be used to suit requirements / capacities . It also saves manufacturers to have so many varients of each type of big valve .
The pilot is a small valve which can be swapped or built on to do other functions on the main valve .

marc5180
23-03-2009, 04:24 PM
Cheers Guys