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  1. #1

    Internal inspection of Discus compressors

    Ive been hired to perform an internal inspection of several Discus compressors belonging to a refrigeration rack. They are both medium temperature and low temperature units, with the bigger compressors being 30 HP units. The owner wants to know if any of them shows any sign of internal parts wear that might justify its replacement. Im suppose to start pulling out compressors next week, and Im already imagining myself trying to turn upside down those 30 HP beasts on a flat table in order to remove the bottom plates and/or heads. Kinda dangerous job for hands and fingers, isnt it? Does anyone have tried automotive engine stands or another alternate method to manipulate those compressors while doing these inspection jobs?

  2. #2
    Join Date
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    How in the world could you find a job like that?You must have some credentials..
    Sorry I have no answer to the question though.

  3. #3
    Join Date
    Jan 2006
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    Quote Originally Posted by coldkeeper1 View Post
    Ive been hired to perform an internal inspection of several Discus compressors belonging to a refrigeration rack. They are both medium temperature and low temperature units, with the bigger compressors being 30 HP units. The owner wants to know if any of them shows any sign of internal parts wear that might justify its replacement. Im suppose to start pulling out compressors next week, and Im already imagining myself trying to turn upside down those 30 HP beasts on a flat table in order to remove the bottom plates and/or heads. Kinda dangerous job for hands and fingers, isnt it? Does anyone have tried automotive engine stands or another alternate method to manipulate those compressors while doing these inspection jobs?
    Look inside the crankcase - if there are no metal chunks laying in the bottom and the valve plates are in tact why in the world would you want to yank these bodies out to see if they show signs of wear?

    If there is a concern about premature wear/failure, I'd be focusing more on system set-up than if the pumps are wearing or not.

  4. #4
    At first, I was surprised too when the owner of the supermarket asked me about such a job. But he said that in Spain, his country of origin, and in other Latin America countries where he also has businesses this type of job is routinely made every so many hours (1,000s). He even said that most compressors which are found with defects are then locally rebuilt by the technician at the spot, something Im really against too, unless it involves simple repairs like gaskets or valve plate replacement. It seems that across the Atlantic, compressors manufacturers are having some hard times meanwhile compressor spare part dealers are happily cashing in.

  5. #5
    My cousin is a Tecnico in Mexico. They do have an overhaul schedule for open drive, belt drive compressors. With the smaller size semi-hermetics he deals with though, it's just 'if it ain't broke, don't fix it.'

  6. #6
    Join Date
    Mar 2008
    Posts
    257
    We do routine inspection on around 300 racks in my company. Removing a working compressor does not make alot of sense, how about an amperage check under load to start. Net oil pressure? Pump down each pump closeing the suction valve slowly to around 1 psig, close suction valve and see if it holds, best test yet to check valves. Next check, just shut the pump off wait 15 minutes, does the suction end bell get hot? Some older mechanics now test high pressure safety at 350 psig with the pump runnig and slowly closeing the discharge valve, not always something I like to try,. Pull the drain plug and drain the oil, all of the drain plugs on copland are magnetic and usually I see some metal fileings, a small amount is normal and on a rack they may not be comeing from the pump your inspecting as the oil is common to all the pumps. At this point I check and clean the oil inlet screen, and the sentronic screen and replace the oil. If the pump passes all these checks its back in service.
    Change all suction filters, liquid driers, and the oil filter. Check defrost differential pressure.
    Two mechanics should be able to check 2 racks in 8 - 10 hours depending on the number of pumps.

    If you did go as far as removing and checking crank bearings and rod bearings, how are you going to tell me how much wear is actually there unless there really pooched? I would be able most of the time to tell a bad bearing or rod pin while its running

    Seems to me your store owner has more money than brains, sell him a new rack, I can ship it to you in 6-8 weeks.
    Last edited by frigeguy; 07-24-2008 at 07:21 AM. Reason: oh 1 more thing

  7. #7
    Join Date
    Mar 2007
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    7,183
    An inspection camera might help and they are relatively cheap now.
    If You Can Dodge A Wrench You Can Dodge A Ball

  8. #8
    Join Date
    Jun 2008
    Location
    toronto, canada
    Posts
    8

    Thumbs up checking for broken internal components.

    You can check reciprocrating compressor internal wear by checking its oil strainer which is located in the front on the crankcase housing. With a small spatula or a siphon you can collect the oil settled at the bottom and determine if it has foreign particles.

    Remember to isolate and recover refrigerant from the compressor.

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