From: CHRISTOPHER_ZAVATSON@udlp.com
Date: Mon, 11 Jan 1999 08:15:43 -0600
Message-ID: <001DD8F4.C21254@udlp.com>
Subject: vacuum pump fittings
To: Lancair.list@olsusa.com
Mime-Version: 1.0

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>>
     
     
     
     
     >>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?
     
     I agree that a lot of flow is bled off at the regulator.  A different 
     argument that could be made for low loss fittings is pump cooling.  
     The pump will move more air as the restriction on the inlet and outlet 
     ports is reduced.  This will cause the regulator to start dumping 
     sooner as the normal operating vacuum will be reached at a lower 
     engine rpm.  Just a thought.
     
     Chris Zavatson
     N91CZ