[AT] Lapping Air Compressor Valves

[Pete Celano]

If they're flat, they'll seal.  I don't really know how to tell you more 
than that.  It was something you just listened for and learned, and as I 
said... it's been a very long time.

When you take it over by hand, the valves will all give a nice, throaty 
burping sound.  Cover the exhaust port with your hand and gently turn 
the flywheel until you have some pressure, and you should hear no leaks 
from the intake valves.  You can do this on the intake side too and 
listen to the exhaust for sucking - but be careful not to suck the blood 
out of the pores in your hand... which will be easy if everything is right.

Also remember that there is a breakin period once valves have been 
lapped.  Tiny leaks are no big deal - they will disappear.  Basically, 
if it sucks and makes pressure, you will be fine.



Sheppard, Charles E wrote:
> 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?
> 
> 
> 
>  
> 
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