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scuba
20-03-2010, 02:29 PM
Is it possible to change the rear motor bearing in a cornell 2CB nh3 refrigerant pump without disturbing the shaft seal

simplygold
20-03-2010, 03:47 PM
On the pump side no. If it is the actual motor bearing you are talking about then I'm not so sure, as we send our motors out for rebuild. And in doing so the shaft seal is disturbed and must be replaced.

NH3LVR
20-03-2010, 05:38 PM
I have never tried that. If you are careful it probably could be done. I would certainly not do it without isolating the pump and bleeding the NH3 off. If I was going to try it I most likely would heat the bearing before putting it on the shaft in order to lessen the impact during installation. Be careful!

St.John@SSIRT
20-03-2010, 06:06 PM
The Cornell 2CB nh3 refrigerant pump uses a standard C-face type motor. These motors use ball bearings at each end if you remove the rear end bell to replace the bearing odds are the play produced in the shaft will couse the seal to leak. If you need the CD on seal replacement contact me. DavidSt.John@SSIRT-edu.com

mrfreezeit
21-03-2010, 12:38 AM
I do not believe so since the seal rides on the shaft of the motor. The movement and pulling could and probably would cause the seal to skid. I would go ahead and do a complete motor replacement or rebuild instead. If a motor bearing is about to go, other parts are not far behind. Replace the motor and seal, after you will have a like new pump. Of course, I am assuming you mean a direct drive style pump like 2cb, 2.5cbh, 1.5 cbh, 3cb. You can also contact the factory, tech support has probably faced the question or give you more insight. (503) 653-0330.

RANGER1
21-03-2010, 06:01 AM
Surely the pump impellar and front bearing of motor give seal enough support .
Can't you change a motor if it burns out or something without disassembly of whole pump ?
Of course isolate and empty contents of pump for safety .

mrfreezeit is still probably right though as front bearing etc will be next .

scuba
21-03-2010, 10:07 PM
Thanks for all the replies. I believe the front bearing will support the rotor if you remove the rear end bell because it has a backing plate screwed right into the front bell which will remain bolted to the pump,but I do not know for sure.We are in the process of submitting a C.E. for a project to replace our pumps with hermetically sealed pumps so I am just trying to keep these pumps running for now.

NH3LVR
21-03-2010, 10:27 PM
If I may ask, why do you want to get away from the current pumps and go to the hermetic style?

scuba
22-03-2010, 12:18 AM
NH3LVR personally I like the cornell pumps and feel they are a very reliable pump, but the company is under new ownership and they have diffrerent views

McFranklin
26-03-2010, 06:24 AM
School of Hard Knocks moment!
Check the NPSH before you change the pumps.
Some of the hermatic pumps need significantly more to work properly.

RANGER1
26-03-2010, 08:57 AM
NH3LVR ,
Do you have a soft spot for Cornell pumps ?
We have one plant with them and no real problems , but they were only selected because of large size required .
I would have a hemetic pump any day of the week as no leaks from seals ever .
If plant is designed correctly you also have no problem with hermetic style .

ref717
02-04-2010, 06:05 PM
I prefer to use the cornell pump than the hermetically selaed pump due to reliability factors. Cornell open pumps can adjust to system varying loads still maintain its prime. But it is not advisable to remove only the rear motor bearing w/out removing the whole pump itself because for sure the mech'l. seal will be disturbed.

redz
09-04-2010, 12:12 PM
Scuba,

I've rebuilt the 2CB style Cornell many times and have never just replaced one bearing. I always replace both bearings and a complete seal kit.

That said: observing all safety practices, sure you can can just change the rear bearing.:eek:

However my knowledge of rebuilding these pumps comes from the fact that, I was not operating them correctly from the get go. After many calls to Cornell and the system designers and lots of research and totally ignoring the system design engineer (which was the cause of the failures) I finally got it figured out.

I to was considering switching to canned pumps, however after I figured out my problem, the Cornells are running just fine and I no longer have an issue with them. If you are having seal failure issues or bearing issues it may not be the pumps but a design placement issue.

Also if you do go with the canned pumps like McFranklin says the NPSH is usually greater and a bypass line is required to maintain refrigerant flow to keep the motor from overheating, Cornells use a vent line and depending on your piping it may be possible to use that for the bypass, but it can not be ran parallel with another pump.

NH3LVR
11-04-2010, 09:31 PM
However my knowledge of rebuilding these pumps comes from the fact that, I was not operating them correctly from the get go. After many calls to Cornell and the system designers and lots of research and totally ignoring the system design engineer (which was the cause of the failures) I finally got it figured out.

I to was considering switching to canned pumps, however after I figured out my problem, the Cornells are running just fine and I no longer have an issue with them. If you are having seal failure issues or bearing issues it may not be the pumps but a design placement issue.

Redz;
Welcome to the forum!
For educational purposes could you describe the problem you had with the seals, and the design issue? I had a problem with two pumps some years ago and have never worked it out to my satisfaction.
The story is a long one and I cannot go into at the moment, but we had a caavitation issue develop and seal problems.

redz
12-04-2010, 12:44 PM
NH3LVR,

Thanks for the welcome.

I had the same problem, cavitation as well as design issues. I just would not accept it. I was changing seals every 3 to 6 mo. My refrigerant level was topped off and my NPSH was 6' with an 8" drop leg feeding two 4" suction lines discharging to 2". The design is to run one liquid pump to overfeed the evaps and keep the second as a standby. Here are the problems I had and the corrections I used.

(1) Low refrigerant level (Oil in Economizer sight glass, gave me a false reading)
Drained to oil pot and charged system.

(2) Wrong oil in the oil reservoir.
I was told by the manufacturer of the package (JBT) to run standard refrigeration oil (ISO 60 their formula of course $4000 a drum) in the oil reservoirs, do not do this run Camco 15 (It's pricey but not that bad compared to others) which is what Cornell recommends or another suitable replacement Turmaco 15, Zerice 22 or WF32. When I switched to Camco my outboard seal failure went down about 50% but still unacceptable, Cornell was telling me they have pumps in service for 10 or 12 yrs. without a failure?

(3) Vent line open on both pumps, recirced back to off-line pump with a lower feed rate.
Vent the pump at start up then close the valve per Cornells instructions. Keep the off-line pump vent closed until needed. Adjusted bypass line according to cornell recommended procedure.

(4) The piping design is slightly complicated(technically it follows recommended industry standards and manufacturing guidelines I just think it could have been done better everything is the minimum required no more no less), both pumps are parallel to each other and are valved to be isolated with check valves prior to the isolating valve and a bypass line set between those valves, each pump also has a vent valve. All of the bypass and vent lines are tied to a common line running back to the recirc tank above the liquid level. This design allows excess flow from either pump to reroute to the back up pump if the appropriate valves are not closed, the discharge lines are so close together and 90 immediately after the isolating valve, IMHO they are far too close together. This entire set up is piped in a space about 3' x 3' x 5'.
My fix for this, is to close all the valves on the off-line pump with the exception of the bypass valve which is a metering style valve ahead of a 100# bypass. I have no idea why this works (unless my check valves are bad), but I have not had a seal failure, oil reservoir or volute o-ring go out in well over a year.

(5) One other issue was hard starting the system and pulling it down too fast, I was actually boiling off the ammonia so fast that I could not maintain my NPSH and cavitated the pumps.
This required telling the Plant Manager that regardless of what time production was scheduled to start I would require at least 2 hours to bring the system down period. This did not go over very well, but it also eliminated most slugging and will extend the compressor life.

Most of my problems were due to a lack of PM and lack of training. I've been doing this for 7yrs. and had complete control of the Refrigeration systems for a little over two years now, and I'm finally getting caught up on the mechanical side, next stop efficiency. Hope this helps. :confused:

redz
12-04-2010, 12:53 PM
Sorry, I did'nt specify the actual problem with the seals.

The outboard seal kept blowing, I would lose all my oil from the oil reservoir into the volute. I never had an inboard seal leak. Also lost the o-rings on the oil reservoirs regularly usually the one on the plunger and ocassionally on the volute.

redz
12-04-2010, 12:57 PM
Sorry, I did'nt specify the actual problem with the seals.

The outboard seal kept blowing, I would lose all my oil from the oil reservoir into the volute. I never had an inboard seal leak. Also lost the o-rings on the oil reservoirs regularly usually the one on the plunger and ocassionally on the volute.

I'll get this right someday, the INBOARD seal was the culprit. :o