If I recall correctly most gyro instruments have a port for connecting the suction gauge so that you can read the vacuum right at the instrument. That is where I connected mine.
The restrictor goes between the vacuum source (pump or venturi) and the gyro instrument that you are trying to reduce the FLOW to. It is a flow restrictor not a vacuum restrictor. The gyro instrument spin speed is governed by volume or flow of air not just the difference in pressure.
Jim
--- On Thu, 11/26/09, Jeff Whaley <jwhaley@datacast.com> wrote:
From: Jeff Whaley <jwhaley@datacast.com>
Subject: [FlyRotary] Re: Vacuum System Regulation Basics
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Date: Thursday, November 26, 2009, 8:41 AM
That’s what I thought too … but spoke with a flight engineer AME last night and he says a 9” venture is minimum to run my 2 gauges AH and DG.
He says the high reading is due to the location of the suction gauge in relationship to the venturi and instruments … closest to venturi will give highest reading.
I need to take a good look at the plumbing to check/move location of the suction gauge.
Jeff
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Monroe
Sent: Wednesday, November 25, 2009 4:40 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Vacuum System Regulation Basics
Sounds like you really just need a smaller venturi. How many vacuum powered gauges are you running?
Regulators usually go between the vacuum source and the rest of the system but I can’t recall ever seeing one used in a venturi system, usually only on vacuum pump equipped installations.
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Jeff Whaley
Sent: Wednesday, November 25, 2009 1:11 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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