As you know, there is no such thing
as “suction” – it’s just if one volume has less
pressure than another connecting volume then the one with the high pressure
pushes toward the one with the lower pressure. This might give the
impression that the one is “sucking”, but its really the other (higher
pressure one ) pushing.
So with your venture tube (Bernoulli effect)
is creating an area of lower pressure in the venture tube. Since the
pressure there is less than in your hose, the air flows from you cabin through
your vacuum gyros and vacuum gauge to the venture tube. Any restriction
between your cabin and the venture tube will reduce the air flow into the hose
thereby reducing the amount of air in the hose and therefore the associated
pressure.
You didn’t state where in the system
you put the restriction, but if you put between you cabin inlet and before your
vacuum gauge, then in effect you are restricting the flow of air from your
cabin (higher pressure) into the vacuum system. Therefore there is less
air in that hose volume that there was before and therefore less pressure and your
gauge reads lower pressure (more suction {:>).
Well, at least that’s the way it
looks to me – but then I’m an electron guy.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Jeff Whaley
Sent: Wednesday, November 25, 2009
4:11 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Vacuum System
Regulation Basics
Can
anyone explain the following:
I
have a 9” venturi on side of fuselage – connected with a 3/8”
hose, the suction gauge reads 9”. This is too much for gyros, so I
put a restrictor in the line expecting to get less vacuum – instead it
goes to >10”. This would imply that if hose was larger, vacuum
would be less.
If
I was to install a regulator should it go between venturi and gauges? or after
gauges between them and filter?
I’m
getting the feeling that a regulator is actually a “controlled
leak” – adjusted by a needle-valve? True or False?
If
True, it would make sense to put a controlled leak between venturi and gauges,
as any dust would get sucked out of cabin without passing through gauges.
Jeff
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