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Thread: Bellows seal
04-16-2008, 07:38 PM #1
any techniques on lapping the stationary seal seat and the seal seat retainer
04-16-2008, 08:35 PM #2Professional Member
- Join Date
- Aug 2000
Send it out to the seal manufacturer to get relapped. A new bellows seal on a York machine is flattened to 2 to 3 helium lightbands. We do not have the proper tooling or measuring devices to relap the seals properly. JMHO
Helium Lightband info:
A monochromatic or single wave length light source (mono means one, and chromatic means color). Any color (wave length) could be used, but most companies use a pink color that comes off a helium gas light source. This color has a wave length of just about 0,6 microns (0.000023 inches).
You will also need a precision ground and polished clear glass of optical quality (like the type you would find in a good pair of eye glasses or binoculars) that has been lapped flat on one at least one side.
The optical flat is placed on the piece to be measured. The monochromatic light is aimed at the piece and this light reflects off of the piece back through the optical flat causing interference light bands. If the distance between the optical flat and the piece we are measuring is one half the wave length of helium, or an even multiple of the number, the band will show black. This is referred to as a helium light band and because it is one half the wave length of helium it measures 0,3 microns or 0.0000116 inches.
To understand this measurement I might mention that the smallest object that can be seen with the human eye is forty (40) microns. Another way to understand this measurement is to know that the average coffee filter is in the range of ten to fifteen (10 to 15) microns. Sophisticated seal people know that this means that solids cannot penetrate between the seal faces unless they open.
There are some things that you should know about flatness readings :
Hard seal faces should read less than three light bands for seal faces with a mean diameter up to four inches (100 millimeters). There should be no visible leakage. Leakage is always subject to definition, but three light bands of flatness will allow a mechanical seal to seal vacuum down to a measurement of one Torr (one millimeter of mercury).
Carbon graphite faces relax after lapping. Although lapped to less than one light band by the seal manufacturer, you will see readings as high as three light bands if you check the faces. These faces should return to flat once they are placed against a hard face that is flat.
Most large seal manufacturers use finite element analysis techniques to design these faces. Some repair and smaller seal facilities supply, replace or repair these faces with no provision for keeping them flat during temperature and pressure transients.
Carbon/ graphite seal faces should not be relapped because the relapping procedure will drive the trapped solids further into these faces. It goes without saying that lapping powder or paste should not be used to lap carbon / graphite faces. They should be lapped dry on ceramic stones of varying grit or finish.
Seals that are going to be used in cryogenic (cold ) service should be lapped at the cryogenic temperature.
Some seal companies use a concave taper to prevent the ingress of solids at start up. This is one of the reasons for the three light band allowable tolerance.
Normal lapping produces a slight convex taper because the outer diameter of the seal face is larger than the inner diameter causing more wear as the piece rotates. Some seal companies use a convex lapping surface to compensate for this.
If the seal faces stay flat within three helium light bands, and the lapped seal faces stay in contact, a single stationary type mechanical seal can easily pass fugitive emission specifications of less than one hundred parts per million.
Carbon faces that have been pressed into a metal holder have special flatness problems. The metal "modulus of elasticity" is almost ten times that of the carbon face, so the assembly must be stress relieved to keep the carbon flat.
Carbon pressed into a metal holder shears at its outside diameter and stays flatter than a design where the carbon is inserted into a metal holder that has been expanded with an induction coil.Your poor planning does not constitute an emergency on my part!!!!
04-16-2008, 11:23 PM #3
Seal cavity pressure?
Even the bellows seal has to be wet with oil but not over pressurized.God Bless the USA
04-17-2008, 07:38 AM #4Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002
04-17-2008, 04:44 PM #5
sorry,I should have been a little more specific this is on a old old carrier 17P bellows type seal in which you have to lap all the seals to fit.(the seals are not carbon) i was just curious if any one had a technique for doing the stationary seal seat. i have never done one before
04-17-2008, 08:58 PM #6
i know i have some old manuals somewhere in the catacombs. i'll try to find & get back
04-18-2008, 07:05 PM #7
found the binder. fitter retired, left me a wealth of info.got factory procedure, and a bunch of inside info, some dated to the early 50's.contact if your interested
04-18-2008, 08:08 PM #8
scuse me, I was thinking York.God Bless the USA
04-19-2008, 09:13 PM #9
I have never heard it explained in such detail as your thread, I've worked on a lot of Yorks (now Johnson Controls) and knew of the lightband measurement. Here in Houston we have several specialty machine shops that have this capability. The last few seals I purchased from York were on the money, carbon and hardface. Thanks for the education.
05-28-2008, 08:14 PM #10
how did the job go?
06-09-2008, 06:39 PM #11
Heavymetaldad, Jobs went well if you meant me, ga1279, even found several of the "D" rings out of alignment in downtown Houston. These machines were taken apart to get them downstairs in basements. Theren is a lot of slop between the motor, D ring and compressor.
06-09-2008, 08:21 PM #12Professional Member
- Join Date
- Sep 2004
I've done several on the 17S Carrier centrifugals with the contact seal & carbon rings, I think I have the literature for the bellows seals also. Send me an email if interested. email on profile