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View Full Version : Cornell Liquid pumps using way to much oil!?!?!?!







MillerRefrig
10-09-2013, 09:37 PM
We have a customer with a pump package that we as a contractor put together 3+ years ago. The everything worked great for 2+ years. Starting last October the Cornell pumps started consuming oil at a rate greater then normal. If we rebuild the reservoir it will go for about two weeks and then start slowly ramping up the amount it consumes. We have had some black stuff stuff show up when rebuilding it. We have tried external nitrogen pressure to the back side of the plunger as well as a Hansen strainer on that line as well. We have data logged the vessel suction pressure, pump discharge, vessel level, and Hansen HMMR position and everything is very very stable. Very little cavitation. There are pump guardians on the pumps that never trip the pumps off. We tried a larger minimum flow bypass line thinking that wasnt big enough for low production days but that made no difference. The customer is getting pretty fed up with buying as much Cornell oil as they have had to and are really looking to resolve the issue.

The last thing we are going to try is take an ammonia sample and see how contaminated it is. Possibly their charge is very dirty and causing contaminants to get into the seal?
The shaft seals have not been a problem what so ever throughout the whole ordeal.
Thanks
Jesse

passandscore
11-09-2013, 02:21 AM
I have had similar issues with Cornell pumps in the past and I have found that the main problem is the operator. I have watched the operators add oil to the reservoir when needed and they do it incorrectly. They do not leave the vent screw at the top of the reservoir cracked open when pumping in oil and it leads to reservoir over-pressurization and the o-ring being moved from it seat. Worse case is it leads to a ruptured shaft seal. Perhaps this is your problem.

If oil is being added properly then perhaps the o-rings are not standing up to the ammonia and ones made of something else should be considered. You could always try a different oil.

http://cornellpump.com/lit/pdf/ReservoirOil.pdf

Taking an ammonia sample is a good call.

RANGER1
11-09-2013, 08:49 AM
MillerRefrig,
You mention the reservoir uses oil so where does it go?
I would have thought it only go into shaft seal area & if seal leaks oil goes into system.

Common problems can be using wrong viscosity oil for especially low temp application.
Oil heater in seal chamber not working, must work all the time.
Damaged shaft seal.
Also as Passandscore has mentioned filling procedure.

MillerRefrig
11-09-2013, 01:27 PM
Thanks for the replies.
Little more info. 30psi suction only Cornell oil ran in it.
We have been discussing this problem for the last hour with our 4 techs.
The oil has to be going thru the inner shaft seal on the impeller side as its not coming out the motor side.
We see black crap in the spring side of the reservoir but don't seem to see any on the oil side.
The best we are figuring at this point is the system is contaminated enough that when the pump is running it is getting a piece of contaminants between the seal mating surfaces causing it to start loosing the oil?
Like I said before we have rebuild the reservoir and it will go almost exactly two weeks and then begins using oil. The operator has to add oil daily once it starts. WE have pressure tested the shaft seals and they always test good but that's just a stationary test, possibly when running the inner seal is getting enough contaminants in it to allow the oil to leave?
We have just been grasping at straws with this. We have a ammonia sample kit coming to see what we find with that. Not sure how the customer is going to feel about the high price of some kind of filter system for the ammonia if the test comes up with a lot of contaminants.
Thanks

Josip
11-09-2013, 07:38 PM
Hi, MillerRefrig :)

as I understood this (have no experience with Cornell pumps, but lot of experience with some other refrigerant pumps) only problem is with inner shaft seal on oil/refrigerant side ...no need to look after contaminated refrigerant (I assume some other pumps on the same system working OK) ... just change damaged inner shaft seal and avoid headache both to you and to your client

... it will be good to install some good strainer on suction pipe (should be installed in the beginning ;) to avoid all what you have now ...)

... it is true, sometimes pump shaft seal can run for a quite long time without any problem but sometimes not ... shaft seal is wearing part and must be changed after some time ...

Regarding lubrication oil for pump ... it must be possible to use the same oil used for compressors working on the same system ... request for special oils is a manufacturer trick ... oil used for screw compressor must be good for low speed pump ... I can accept request for lower oil viscosity because refrigerant pumps are working cold, but nothing special ... just oil for refrigeration compressors ...

Best regards, Josip :)

iBigChill
06-10-2013, 06:07 AM
I have a a lot of experience with Cornell 2CB pumps.

First off, Josip is incorrect on the oil. ISO 68 Capella is a high temperature lubricant and not suitable for most liquid pump applications due to it turning to sludge at low temps. I always use Camco 4600B, which is recommended by Cornell. Looks like water its so thing at room temp.

You have leaking shaft seals. It's a double mechanical seal. One seal is inbetween atmosphere and the oil "pocket" and then there is another seal inbetween the oil "pocket" and volute. If you have never changed one of these before, I can't stress to you how important it is to be thorough and clean. Cornell has a video they give away for free on seal changes, just follow it. Use STP and compressor oil.

Josip
06-10-2013, 09:24 PM
Hi, iBigChill :)

welcome to RE forums ....


I have a a lot of experience with Cornell 2CB pumps.

First off, Josip is incorrect on the oil. ISO 68 Capella is a high temperature lubricant and not suitable for most liquid pump applications due to it turning to sludge at low temps. I always use Camco 4600B, which is recommended by Cornell. Looks like water its so thing at room temp.

You have leaking shaft seals. It's a double mechanical seal. One seal is inbetween atmosphere and the oil "pocket" and then there is another seal inbetween the oil "pocket" and volute. If you have never changed one of these before, I can't stress to you how important it is to be thorough and clean. Cornell has a video they give away for free on seal changes, just follow it. Use STP and compressor oil.

are you sure :confused: ... I check my post, but I cannot see that I mentioned ISO 68 Capella oil ... generally I can agree with you, but as per my experience there are some other refrigerant oils of different viscosity used for screws .... with viscosity 46 or 32 ....

also there were times with mineral refrigerant oils only ... with many healthy running refrigerant pumps ...

Best regards, Josip :)

Grizzly
06-10-2013, 10:23 PM
First off, Josip is incorrect on the oil. ISO 68 Capella is a high temperature lubricant and not suitable for most liquid pump applications due to it turning to sludge at low temps

Don't worry Josip.
Not only is Ibig chill accusing you of saying something you have not!
He has his facts all wrong.
Because if you check Chevron's website who manufacture Capella 68.
They describe it as a Low temp compressor oil.
Ibig chill, if you want to take part try and get your facts correct.

It is a mineral sae68 oil and you are recommending adding a PAO oil, which is not a good combination.

It would appear that I have my facts wrong because if you read the link supplied by passandscore ISO68 is not recommended.

For that iBigchill I appologise.
Grizzly

I can post the MSDS sheet if you wish?
Grizzly

Josip
07-10-2013, 09:14 PM
Hi, Grizzly :)

I'm not worrying ...

just matter of discussion ... different people exchange different experience i.e. knowledge ...

Best regards, Josip :)

NH3LVR
08-10-2013, 11:28 PM
I have been in many plants that use 68 in their Cornell pumps without problems.
I have been to the Cornell factory many times.
I discussed it with an Engineer there one day. He definitely recommends the thinner oil.

That being said I have been in many NH3 plants that use 68 in their Cornell pumps without problems, low and high temp both. It has never been a issue. Several years ago I rebuilt two pumps that had the reservoirs filled with 68. They were run with one on standby. The operating pump seal began to lose oil after four years constant duty.

I made up two caps that would fit on the Weatherhead fittings on the seal itself so I could pressurize the seal chamber with N2. A good new seal will hold most of the gas pressure overnight. It also give you the ability to increase the pressure on the seal to seat it if need be.
The one thing I was always concerned about is that if the seal heater failed the seal pump might be damaged or the seal might lose adhesion to the shaft (or other bad things) on startup with the thicker oil.

RANGER1
09-10-2013, 10:35 AM
I think seal faces will tear or be damaged on start up with low viscosity oil.
Heater is important on low temp.
Also correct seal has to be installed, bronze on ni-resist steel face.