View Full Version : Oil pressure fault on Bock Compressor

13-03-2015, 07:52 AM
Hi all,

Just hoping someone could shed some more light on the situation im facing. We did a compressor change about 6 months ago to a (HGX6/1080-4) Bock compressor all has been fine since it is 1 off 3 in a low temp rack. Got a call out the other morning as the oil safety had tripped. Checked oil level all was fine checked the oil pressure that was fine everything seemed to be working fine i reset it and it all got up and worked fine no problems at all.

The next morning woke up to the alarm going again. Went in to find same compressor out on an oil fault. Oil level threw sight glass was fine but no oil pressure. I thought the strainer had some how got some **** in it so check it and it was clean as a whistle same with the oil. Vacced out system and filled with oil and then started up compressor again. Still no oil pressure

The suction is sitting around 85kpa and the oil pressure is sitting around 100 kpa.

2 other compressors are running fine and are managing to keep up with the demand which is good.

Is there something i haven't checked that could be causing this fault? There is next to no flood back. Years ago when we took over the store the comps had huge flood back issues and have never had this problem so i dont see how it could be that.

The trax oil is working fine and the compressor has heaps of oil.

Im going out of my mind here as everyone i have asked has said that the oil pumps never fail just wondering if anyone has any help they could shoot me.

Thank you so much for your time

Rob White
13-03-2015, 08:50 AM

The oil pressure is kept up as the oil is pushed through all
the small holes, channels, trunnion ways and bearings.

To stop the oil pressure getting too high there is a small
pressure relief valve in the pump that leaks oil back to the
compressor sump.

If the pump is OK then the oil pressure is low because either
the compressor has developed a fault in one of its components
or the oil pump pressure relief valve is releasing early.

You will need to prove the pump is fine and then check for
failure in the compressor.



Glenn Moore
13-03-2015, 03:28 PM
Hi frazzel.
As Rob says it could well be the oil relief valve relieving or jamming open, it may have a damaged spring inside which is now failing to hold a constant pressure.
It could also be the oil pump is worn. If this compressor has suffered liquid flood back at any time in its life, this entrained liquid in the compressors oil will at sometime been compressed and vaporized inside the compressor oil pump due to friction. As the liquid "Flashes" it can wear the tips of the oil pump, to a point that as the oil becomes hot and the viscosity goes down oil can leak back over the pump tips thereby failing to pressurize the oil gallery. If you strip the oil pump and find the pump tips have shiny scratches across the tips this is indicative of liquid wear, one of the problems that can occur during liquid flood back situations. I have seen this type of problem on York "J" compressors HAll V92 with worn pumps, and Bitzers and Dunham Bush where the oil had been changed from Mineral to POE but the wrong Grade.

13-03-2015, 05:41 PM
H Frazzel.
I'm not really familiar with Bock comps, and was wondering if it would be possible to swap over an oil pump from one of the other 2 compressors, if they are of the same type. The results would then point you in the right direction.


13-03-2015, 06:06 PM
You did not mention defrost, check the behavior of the gas return at defrost, when liquid is entering the sump, it flushes the oil out, check this point out before you start replacing parts, it very common problem with hot gas defrost.

15-03-2015, 07:51 AM
Thank you so much for all the replies. Sounds like it might be a relief valve jamming open will check that tomorrow. Being the compressor is only 6 months old seems very strange but stranger things have happened.

Chemi-cool the defrost is just electric elements not hot gas.

thanks for all the help hopefully be able to get it back on ASAP.