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This is also re: Don gordon's query about what to do about the exhorbitant
prices for the Airborne (?) fittings.
The threads in the pump are standard pipe threads like the ones on a
mating AN fitting. The popular mythology (promulgated, no doubt< by
the pump/fitting makers) is that there's too much "restriction loss"
in a standard AN 90 degree pipe to hose fitting. Nonsense! Maybe, just
maybe, if you needed every bit of the flow from the pump to drive a lot
of stuff in addition to what you're probably driving, i.e., an artificial
horizon and heading indicator, you might need to go with ultra-low-
restriction fittings.
Your vacuum regulator is probably going to bleed off half the flow
anyway, so why ream your wallet if you don't have to?
If I remember, the AN fitting to use is a pipe to hose, 90 degree (to
fit under the cowl). If you turn your pump so the fittings are on the
side, you may be able to use the 45 degree pipe-to-hose which will
present a somewhat lower "flow restriction".
I think the fittings I used were 3/8" pipe to 1/2" ID hose (-8D I think)
but it may have been one size larger. Depends on the pipe threads in
your vac pump. In any case, the AN fittings (I used aluminum since they're
not carrying flammables) price was around $7.50 or so each.
As the man says, "You pays your money and you takes your choice". Mine
have been working for almost 500 hours, no prob. I also went to the local
auto parts store and bought the appropriate sized high temperature
water heater hose (the red stuff) for the vacuum lines - also no
problem so far. Just be sure to clean the ID carefully after cutting to
the desired length. the pump will surely choke on even the smallest piece
of debris. Wash it out and then drag a clean piece of cloth through it
and let it dry thouroughly.
Then go have a Chevis or six with the money you saved (just don't go
flying real soon after).
Cheers,
Dan Schaefer
N235SP
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