Yes Ed, I put the restriction
between the inlet and the suction gauge … thinking this would reduce the
venturi’s ability to “suck” … I knew from the results that the restriction was
wrong, but now with your explanation I understand why. Thanks.
Jeff
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Wednesday, November 25, 2009 5:03 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Vacuum System Regulation Basics
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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