Mailing List flyrotary@lancaironline.net Message #49242
From: James Maher <delta11xd@att.net>
Subject: Re: [FlyRotary] Re: Vacuum System Regulation Basics
Date: Fri, 27 Nov 2009 07:29:11 -0800 (PST)
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Jeff,
I believe that it was on the AI that I connected the vacuum gage to, as shown in the attached schematic. The port (if you have one) will have a plug in it. This simplified schematic (from the Aircraft Spruce catalog) only shows one side of the vacuum system. The missing half is the connections to the filter but this gives a good example of how to plumb the system.
Jim

--- On Fri, 11/27/09, 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: Friday, November 27, 2009, 9:51 AM

Thanks Jim, but I don’t recall seeing a separate “suction” port on my instruments … it was 5-6 years ago, I’ll take another look.

Jeff

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of James Maher
Sent: Thursday, November 26, 2009 9:26 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Vacuum System Regulation Basics

 

Jeff,

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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