Frick shaft seal-NH3 leak

[modvalve]

Has anyone come across a shaft seal that sucks in air while running at -20kpa but seals perfectly under pressure when you go to leak check it. The plant has been suffering high discharge pressures due to non condensables but when we switch plant off for leak checking we cant find a leak. The plant is running 2 Frick scews as booster machines and is about 5 years old. Any help on this subject would be much appreciated.

[Grizzly]

Yes it is not unknown for a seal to leak whilst under negative pressure.
And to be gas tight when under positive pressure.
Or vice versa!
If you think about it when positive pressure is applied the seal internal seals.
Are being forced > out wards along the
drive shaft and therefore being pushed together.
Whereas when under a vacuum the seal faces are being forced apart < along the drive shaft. Pulling the seal faces apart.
So you have a 5yr old shaft seal?
Which has worn faces and a weakened spring. (Which pushes the faces together.)
Change the Shaft Seal.

Grizzly

[josef]

Yes, as written Grizzly, change Shaft Seal, 5 years and a lot of carbon ring with robs

[Grizzly]

Yes, as written Grizzly, change Shaft Seal, 5 years and a lot of carbon ring with robs


Slight miss-spelling josef.
I assume you meant Ribs or Rings?
But still good advise whatever the spelling.
Cheers Grizzly;)

[modvalve]

Ok thanks for that. Now we just have to work out which compressor has the faulty shaft seal. Unfortunately we cant have the plant off too long as it is a meat processing plant. But I forgot to add that one of the frick machines was rebuilt about 18 months ago.

[Grizzly]

Modvalve.
Is there any way you can isolate either comp and rig up a vacuum pump to it.
Then attempt to pull a vacuum through a set of gauges and observe whether the pressure is stable.
Or fluctuates up and down as the air is drawn in!
What you observe will then tell you
which one has the leaking s/seal.
Both could be leaking mind!
Please use an older vacuum pump if possible. Because over a period of time I have had the plastic handles become brittle and fracture.
The Ammonia must affect the plastic somehow.
Well it does on the Robinet ones we tend to use!
Cheers Grizzly
PS which Frick comps are we talking about?

[modvalve]

Hi Grizzly
The model is a RWF 11-191 or 193 cant quite remember
The idea of pulling a vacuum is a good one but the client wont let us have the plant off for very long but its getting to the point that he might have to.
My pump is a JB which is all steel but it gets a oil change every time it gets contaminated with ammonia
thanks modvalve

[Magoo]

Try getting a laser alignment done, hot alignment checks can really tell you whats going on . Suspect the recent re-build machine may be the culprit, if set up cold. Can be done with minimal delays / shut down time. After that check each shaft seal for carbon gunge.
thinking out load. Magoo

[modvalve]

Hi Magoo
I suspect it is the machine which has been rebuilt.
The new Frick machines are self aligning as there is a bell housing joining the motor to the compressor. The alignment guys hate them as it does them out of work.

[nh3wizard]

Depending on how bad it is leaking; I dont know if I would worry about unless it happens to get worse as long as your purger is working correctly, Im sure thats not the only place where air is being sucked in.

[Segei]

Has anyone come across a shaft seal that sucks in air while running at -20kpa but seals perfectly under pressure when you go to leak check it. The plant has been suffering high discharge pressures due to non condensables but when we switch plant off for leak checking we cant find a leak. The plant is running 2 Frick scews as booster machines and is about 5 years old. Any help on this subject would be much appreciated.
Are you sure that seal is leaking? Usually, pressurized oil supplied to the seal. I doubt that you suck air through the seal. Check solenoids for loading and unloading. When solenoid plunger is worn out, air can be sucked through this solenoid during unloading or loading.
Don't vacuum your compressor. Very often good seal starts leaking after vacuuming.

[josef]

Grizzly Yes, you are right, I teach English. My idea I have attached ;)

[J.D]

Hi Guys

Within the last couple of years, I've seen this on several Frick machines, however it is usually on the smaller RXF packages with the XJF 120 compressor . On the RXF machines, which have a different style seal than the RWF, I had to install an oil orifice in the gearbox to keep the seal under pressure at all times, then Frick changed the seal design and incorporated a lip seal into the assembly and problem was solved. The seal on the RXF 101 with the XJF 151 compressor has the same style seal as the RWF with TDSH compressors. The new style seal uses a lip seal that presses into a modified seal spacer. I'm not sure if Frick makes a new style seal for the TDSH compressors. I just overhauled a 193 and I didn't here of any option to opt for a new style seal so I assume they aren't making one yet.

One other thing is check the axial movement of the shaft, it shouldn't be more than .005"

J.D.

[modvalve]

Hi Segei
We dont know where the leak is suspect shaft seal but we have found little leaks on some of the danfoss PM valves for the freezers. Problem is all the valves are blocks of ice. The purger seems to keep up but the plant engineers/fitters like to fiddle with things. One day you will arrive at site and they have turned the Hanson auto purger off. The solenoids on the rebuilt machine leak oil from base due to faulty o rings. I would have thought that even though the loading block is leaking it is always under oil pressure so it cant suck in air through there
cheers modvalve

[Magoo]

Modvalve
it is not uncommon for a valve stem to leak under vacuum and not at positive pressure. as a standard I leave grease on all valve stems, particually the stems that wind in and out, OK I am an old person.
With regard to shaft seals, now we know they are flange coupled. Do not disregard that fact that the motor bearings can possibly be out of spec and thrusting, chips on carbon face can indicate this and scoring can indicate mis-alignment. What ever which way, if shaft seal is leaking you get lots of oil coming out of seal., as it is at positive pressure.

magoo

[Segei]

Hi Segei
We dont know where the leak is suspect shaft seal but we have found little leaks on some of the danfoss PM valves for the freezers. Problem is all the valves are blocks of ice. The purger seems to keep up but the plant engineers/fitters like to fiddle with things. One day you will arrive at site and they have turned the Hanson auto purger off. The solenoids on the rebuilt machine leak oil from base due to faulty o rings. I would have thought that even though the loading block is leaking it is always under oil pressure so it cant suck in air through there
cheers modvalve
During loading or unloading, one side of slide valve piston is connected(through solenoid) to the suction. It means that part of the solenoid is under vacuum. To test this solenoid, increase suction pressure above atmospheric and run this booster. Manually load and unload slide valve. Check solenoid for the leaks(coil area).

[Grizzly]

During loading or unloading, one side of slide valve piston is connected(through solenoid) to the suction. It means that part of the solenoid is under vacuum. To test this solenoid, increase suction pressure above atmospheric and run this booster. Manually load and unload slide valve. Check solenoid for the leaks(coil area).


Nice one Sergei.
Good sound and knowledgeable advise.
Modvalve.
If a valve is a block of Ice it ain't leaking.
For example if you have a slightly leaking valve stem. (This is applicable to Ammonia only Guys!)
You can slowly trickle water across the valve and the Ice that builds up will seal the leak.
Only as a temporary measure mind!

Grizzly
"If your initial thoughts are the S/Seal. Then it's likely to be the cause!"