Success in recharging Audi Bomb

[Joel Skousen <jskousen@enol.com>]

Good news Audi fans--the audi bomb can be turned into a rechargeable
unit--for only $15 in parts and nitrogen charging fee (mine ran
$20--mostly because of the time it took him to set up all the
adapters--yours could be even cheaper).  

Here's how to do it.  

1.  Drill a 1/8" pilot hole in the top of the bomb, about half way
between the edge of the top stub fitting and the rounded shoulder of the
bomb.  This is a very critical maneuver since you don't want to puncture
the bladder inside--which is usually fully inflated due to no gas
pressure in the bomb to resist it.  The casing is about 1/4" thick so
ease up on the dril and go very slow at the end.  The bladder is pretty
thick so it will take a little damage, but don't press your luck.  

2.  Take the dull end of another slightly smaller drill and push it into
the hole to apply pressure to the bladder--this will start to push out
the Pentosin inside the bladder.  Keep pushing inward until all of the
fluid is out and the bladder no longer comes back up (it will tend to
collapse and partially invert itself.  Now you are ready to drill a
larger hole so that you can install a high pressure schraeder valve.  

3.  I used a standard sized schraeder valve (same size as an automobile
tire valve).  You can buy them with various threadings on the insertion
end of the valve.  Mine was a 3/8" #3 SAE thread.  So I drilled a 5/16th
inch hole through my pilot hole, then inserted a small cylindrical
magnet to pull out the metal filings.

4.  Thread the hole with a 3/8" #3 SAE tap, and then remove any
additional filings.

5.  Most of these high pressure valves are meant to be used with an O
ring seal--but that takes a special O ring groove around the threaded
opening, which I could not accurately do.  So I simply removed the O
ring seal and used epoxy (JB Weld is the strongest) as a thread sealer. 
I first cleaned up the cutting oil residue so that the epoxy would make
a good seal.  Then I roughed up the metal surface around the hole and on
the wrench faces of the valve so that the excess epoxy would have plenty
of grip.

6.  After letting the epoxy set for 24 hours, I took my accumulator to
my nearest heavy equipment dealer.  Heavy equipment companies usually
have nitrogen charging equipment for charging the larger hydraulic
accumulators that are used in big equipment.  I had him charge it to
1150 psi (Bentley says between 1120 and 1180 psi.  The rule of thumb for
accumulators is 1/2 the working hydraulic pressure. 

7.  I got my schraeder valve at a hydraulic controls supply house in
Salt Lake City.  I wasn't easy finding one--I had to really search
around until I found someone who carried them. 

So, go out a get those bombs fixed and save yourself a lot of $$$.

Hope that helps,  Joel
-----------------------------------------------------------
Joel M. Skousen         <mailto:jskousen@enol.com> 
Joel Skousen Designs    WebSite: <http://xsw.com/securehome>
290 W. 580 S.           Telephone:  (801) 224-4746        
Orem, Ut 84058