Supermarket rack question

[reftec021702]

Dear fellows:

I just got in charge of a parallel compressor low temp R-22 supermarket refrigeration rack. I have noticed that all of the compressors have factory supplied cartridge type suction filters. Do I need to change them periodically or just remove them after the initial installation? Also, each system is connected to the main suction manifold by an evaporator pressure regulating valve. I have de-assembled one of them which was not working properly, and seem to be mechanically complex. How do these valves lubricate, if most of the oil goes back to the compressors through an oil return system ?
Thank you!!

 

[tbedford]

Good morning reftec,

These filters protect the compressors. It is common trade practise to leave CLEAN cores (or for less $$$... felt cores) in the system after any work completed and before system start-up. And an even better idea to leave a comlete core change in the machine room for emergency ( depending on distance to nearest supplier and unfortunately $$$) In addition to providing filtration for any crap coming back to the compressors, it provides a baseline for yearly, visual, maintenance checks. Check filter pressure drop. The system oil in each compressor and the oil separator should be checked regularly. There should be a similar filtration system in the liquid line header after the receiver to protect the expansion valves.

Oil is found throughout the system as a mist and provides adequate lubrication for all remote accessories.

I don't know which system and accessories you work on but sporlan has a great website at

http://www.sporlan.com/literature.

Good luck, packs are fun.

Tom

 

[absrbrtek]

Low temp R22 runs pretty high discharge temperatures and cooks the oil. To keep your system clean, change the oil a minimum of once a year or twice if possible. If you don't change the oil you'll be pulling strainers and valves to clean them. Leave the suction driers/felts in to help protect the compressors. A little bit of PM will save you multiple failures in the long run. JMHO

 

[tbedford]

absrbrtek thanks,

R-22 is not in common use as a LT system and utilizes liquid injection to keep oil temperature down. Another maintenace project for you.
In addition to this fact, remember that the phaseout date for R-22 is fast approaching. The manufacturer of the rack will likley have appropriate recommendations for a replacement refrigerant.

Tom

 

[deppler]

More than likely if your EPR's are not working correctly you could have moisture in the system making the pistons freeze up. Check the pressure drop across the LL drier, should not see more than 1# of pressure drop' anymore than that I would change out the LL driers. Also I would go ahead and pull out all the suction filters If the rack has been in operation for more than a year, they should have caught all the materials in the system by now.

 

[tbedford]

Hello deppler,

There is not supposed to be any moisture in the system. Moisture in the system is likely to cause problems other than piston or sleeve damage. Moisture would likley raise head pressure, become ice plugs in the cases, affect oil quality, etc.etc.

Tom

 

[sterl]

Re: Suction lines: piped properly UPSTREAM of the regulators, -20 deg R-22 vap will carry a lot more oil than the lower end of the regulators will need; but failure of any TXV or Regulator to a low flow condition will cause low velocity in same piping thus oil will not transport with refrigerant, or may accumulate short term and subsequently burp over on one circuit. Worst combinations, that same burp of oil will film the suction filters and cause a big delta-P on running compressors for at least an interval of time; on recips that reduces crankcase press to well below suction header pressure and suddenly crankcase injection can't cool fast enough.

Does system have a Suction Accumulator? Does it have an Aspirating Arrangement?

If compressors are crankcase injected, does it have a high suction or alternate pump down arrangement when a machine cycles off due to (lack of) load?

Does it have a desuperheater arrangement? Upstream of the oil separator? Is there a common oil separator/sump/return arrangement or does each compressor have individual?

If these are Sporlan low pressure drop regulators on elevated set points they are also receiving oil via the little hot gas pilot, unless the machines can't make suction pressure which means they are not receiving any pilot gas. Are there intervals where every compressor is running but the suction main pressure is still high?
Same thing can happen on a given valve simply by setting it lower than the rack pressure set point; or as a result of it being undersized to the load.

Most of the other forms of pilot operated regulators utilize the upstream gas to move the valve toward open; thus the pilot stream is the same as the upstream and both the lower end and the upper end receive lubricant from the same source.

Fill in a few blanks on the nature of the equipment and pieces please. There is a good chance of some contamination as well as some lazy oil in the circuits but these systems have quite a few intricacies; and are not simple to convert to an alternate refrigerant partially because of the difficulties getting all the "old" oil out. There are also a multitude or pressure conditions to consider; most of the replacements will operate at a higher discharge pressure and may require the renewal of high side vessels and even condenser(s).

 

[deppler]

Hello tbedford

Small amounts of moisture will freeze up an EPR AT -22f evap temp; been there done that; break out the torch, free it up then do a complete oil and drier change.