[AT] Lapping Air Compressor Valves

[Sheppard, Charles E]

Thanks, Pete.  I wasn't sure I had the right approach.  The springs seem
OK to me.  I called the WABCO folks and they say parts are no longer
available for this compressor.  Any thoughts on how I might actually
pressure test the valves?  It's a Y pattern, two-stage machine.

 

Chuck

 

 

Message: 5

Date: Fri, 15 Jul 2005 12:00:10 -0400

From: Pete Celano <petecelano at sbcglobal.net>

Subject: Re: [AT] Lapping Valves for Air Compressor

To: Antique tractor email discussion group

      <at at lists.antique-tractor.com>

Message-ID: <42D7DD8A.7090709 at sbcglobal.net>

Content-Type: text/plain; charset=ISO-8859-1; format=flowed

 

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?

>