View Full Version : Dorin excessive crankcase pressure

26-04-2016, 08:40 PM
We have a problem, with a Dorin k15000CC Compressor
The unit is installed on a testing chamber
The unit has a oil separator.
The pressures are 10-11 bar discharge (water cooled condenser), and 3 bar suction.
The problem is that on the oil return pipe to the compressor, the pressure is very big, and can't understand why.
The pressure on the crankcase return pipe is around 9 bar, and because the pressure difference is
not big enough not enough oil comes back to the compressor, and the oil remains stuck in the oil separator.
I can't find documentation on the compressor, so i can understand the internal parts and find out why there is such a big difference between suction pressure and crankcase pressure
But maybe you guys can help

27-04-2016, 07:12 AM
My best guess is that the compressor, piston rings are worn down, so pressure is escaping to the crankcase at a speed that is grater than it can equalize with the low side .

27-04-2016, 08:08 AM
Pressure in crankcase should be same as suction pressure.
Could be several possibilities, one in previous post, also Brocken suction & or discharge valves.
Normally oil return from oil separator normally would have a float valve so only oil returns, not high pressure gas.
If there is something wrong with it, it can pressurise sump & blow oil out.
Check if oil return line hot.
Check valves for leak back

27-04-2016, 08:09 AM
3 bar suction, 9 bar oil return to crankcase. Float is stuck open in oil separator.
Can't have 9 bar in the oil return line AND oil logging in the separator.:eek:

27-04-2016, 01:22 PM
For a better understanding
the pressure of oil in oil separator (on the exit) is 10 bar same like the discharge
The oil separator is having a oil lever regulator installed upside down and the scope of this is when oil is coming from oil separator to open, and when gas is coming to close we checked them and they are working.
after this we have 10 bar oil pressure, the pipe is coming to a electric valve, that we replaced and is working ok , after the valve if it is open we have 10 bar, if closed 9 bar, and then the pipe is gowning directly to the compressor no other device, so ..... it's clear, we have 9 bar crankcase pressure and the pressure is not coming from the oil separator. The sight glass of the oil pipe is full of oil, and the compressor sight glass is low on oil
I know that the crankcase pressure should be the same as suction, but because i don't have a schematics of the inside of the compressor i have to guess that the crankcase is separated from the suction and only a pipe is connecting the crankcase to the suction and so much refrigerant is escaping to the crankcase that is to much for that pipe

install monkey
27-04-2016, 10:10 PM
check if the compressor will pump down- manually shut the suction valve on the compressor and de energise the solonoid on your oil return line to see if you can pull 15 inch vac (within the compressor sump/crankcase)within say 90 second- if so stop the compressor to see if it holds- if neither are achieved then check your reeds/valve plates

28-04-2016, 06:54 AM
We did that , and it dose not pull down the pressure on the oil line.
We came to agreement with the client, to take out the compressor and investigate, but this is pretty difficult because it is a 16 piston compressor and very heavy in a difficult position.
I will keep u posted about the findings

12-05-2016, 06:53 PM
So .... the update:
the main damage is that one of the valve fixing bolt broke and fell in the cylinder and the piston pressed it all around until it broke the piston.
parts of the piston and valve fell true the piston down in the crankcase and some got in to the oil pump witch is deteriorated, still working but needs to be replaced.
there are a lot of parts to be replaced not to expensive (compared to the compressor), but Dorin take's its time to respond about the parts, time that the client dose not have.
other parts are like 16 piston rings, 16 piston rods, 8 valve plates and some other small stuff.
Because of Dorin slow response time i would like to replace the compressor entirely (time is a critical problem) but we can't, because of the compressor being so big, and in a small enclosure.

monkey spanners
12-05-2016, 08:33 PM
If cost is not an issue, could you get a new compressor and swap the part into the exiting one?

13-05-2016, 06:59 AM
We could , but we should have a new compressor that is having common parts, and because this compressor isn't produced for a lot of years, it is likely that we won't find one .
The response from Dorin was that they have to search in the old stock, so i should think that the parts have changed this was about the piston rods, that only come with the piston, and this is the parts that need to be replace the most.
I can put pictures if someone is interested.

13-05-2016, 09:30 AM
Depends, I might be off the mark, but Hanbell semi-hermetic screws or similar can be a good option.
Compact, built in oil separator, put them anywhere on a flat surface & where electricals can reach.


13-05-2016, 11:07 AM
It would a good idea to post some photos related to damaged parts.

13-05-2016, 03:05 PM
And here are some pics 1412514126141271412814129

13-05-2016, 03:06 PM

13-05-2016, 04:21 PM
it seems that this bolt caused all that trouble to you.

14-05-2016, 07:50 AM
Depends, I might be off the mark, but Hanbell semi-hermetic screws or similar can be a good option.
Compact, built in oil separator, put them anywhere on a flat surface & where electricals can reach.


It would had been a good idea if we would had build the unit, so we could change stuff in the electrical part but it is controlled by a touch screen and a PC so adding additional safety components that the screw needs would be harder, so it is easy-er if we could replace with the same compressor type, not that screw compressors aren't better

14-05-2016, 07:52 AM
it seems that this bolt caused all that trouble to you.

Yes, probably if the bolt wouldn't had made the damage, probably other parts would had not been a problem so big to take the compressor apart.

14-05-2016, 11:14 PM

Maybe these people or similar suppliers can help you with spares etc