[AT] Lapping Valves for Air Compressor

[Pete Celano]

I was an air compressor mechanic in a previous life.  It's been a LONG 
time, but...

When you are doing the lapping, use a figure-8 pattern to achieve a 
cross hatch, and rotate the valve often.  Otherwise you won't get it 
flat.  The valve seats need to be handled the same way, being very 
careful to randomly rotate as you do the lapping.

If you don't see any spots, you are flat and shouldn't have any problem. 
  You don't need a mirror finish or anything.

Are you replacing the valve springs?

Sheppard, Charles E wrote:
> Has anyone experience in lapping air compressor valves?  I'm trying to
> recondition an old Westinghouse Air Brake compressor that has ring-type
> valves.  They look like a washer, spring-loaded, that faces against a
> seat that has two raised ridges contacting the inside and the outside of
> the washer.  What I have done is lap (sand) the pieces on a piece of
> plate glass with 320 grit, then 600 grit W/D paper, then spot them on a
> surface plate with Prussian blue.  Well, I have done that but I don't
> see any spots.  I tried to rub a fairly thin coating of blue on the
> washer-like piece.  Either it is flat within 1/10 or I'm spotting it
> wrong (too much movement, too much pressure) but it comes off the plate
> clean.  I've never done this before so I don't really know what to look
> for!  Should the low points be bright blue?  Appreciate any comments?
> 
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