Good question. The Bentley manual (shop manual reprint) makes no mention
of the thing.
My guesstimation: The non-return valve does two things:
1) keeps a carb/intake manifold backfire from pushing hot gasses into the servo
2) if the engine quits, retains a little vacuum to assist one last stop
Also, the valve probably keeps the servo from acting like a vacuum leak when
you stomp on the accelerator.
I used to think the valve prevented brake fluid that may have leaked into
the vacuum canister from getting into the intake manifold, but if you think
about it the valve should allow the manifold to "suck" from the canister
and any fluid in the canister would happily follow the suckiness into the
manifold (sorry, it's hot and I'm tired ;)
At any rate, BMC wouldn't have put one on the servo unless it was
absolutely required, since they probably cost about $.09 new.
My BJ8 came with a plastic, aftermarket one inserted into the vacuum
hose and mounted on the passenger (right) side foot box. I would think
any vacuum valve that will fit the hoses will do ... the original ones for
the Girling servos are all but unobtainable (I got a used one from the Nocks
a few years ago).
bs
********************************************
Bob Spidell San Jose, CA bspidell@pacbell.net
'67 Austin-Healey 3000 '56 Austin-Healey 100M
********************************************
----- Original Message -----
From: "andy65" <andy65@snet.net>
To: "Healey healeylist" <healeys@autox.team.net>
Sent: Tuesday, June 15, 2004 9:30 AM
Subject: brake servo non-return valve-necessary?
> A non-return valve comes for the vacuum line with the Lockheed brake servo
> units.
> I have the original Girling servo just rebuilt. Is a vacuum non-return
> valve recommended or even needed for the original Girling servos? I doesn't
> appear to have had one. Are their any specs on these i.e. are they
> available at Pep Boys or do we have to get the $39 one from Victoria British
> or the like?
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