Vacuum system question

[bradp]

Hi all-

We're about to do a G5 HSI install, keeping an existing Attitude Indicator and the vacuum system that drives a century autopilot.

I was looking at the vacuum setup and noticed that the vacuum suction gauge comes off a second AN port on the DG.  The attitude indicator lacks a similar additional port.   

I'm gathering accouterments for this part of the installation.  I'm thinking the most simple acceptable way to do this is to measure the suction from the line on the vacuum regulator by using a barb reducer hose adapter from 3/8 ID to 1/4 ID and then capping the second orifice on the instrument air filter. 

Before I have a discussion with my IA - this sound about right?  Picture below to illustrate what I'm talking about.  My SN seems to not be well illustrated in the parts catalog - otherwise I'd use that instead of a hand-drawn picture.  But... whatever works.  

Thanks for the advice -Brad

Edit: Brain fart removal.

 

[takair]

Seems like a reasonable way to do it.  Ultimately, the gauge is just measuring the overall health and integrity of the pump and lines.  A serious leak or failure of the pump would be noted in your proposed solution.

[RobertGary1]

I’m surprised there isn’t a vacuum manifold off the regulator. Usually there are 5-6 ports off the manifold.  

-Robert

[Hank]

There's just a T connector on a vacuum line near my firewall, with a piece of 1/8" tubing going to the gauge.

It doesn't have to be complicated. 

[Awful_Charlie]

I do hope it is not your ASI connected to the vacuum system!

If it is the AH though, I think your proposal will be ok

[carusoam]

In line with awful chuck above...

Label Check!

Throw a label on the vac gauge on the new drawing.

Is that the AI, The HSI, or ASI?

Less confusion for anyone looking at it the wrong way.  (Me). 

Inline with RG above, some people have added a small device to allow multiple connections to the vacuum system. The old systems saved a pound or two and had standard routings using the daisy chain method as depicted in the first drawing...  today we have multiple legal options that can be added such as a JPI and other things in the future... Aircraft Spruce has a couple of multi-port manifolds...

PP thoughts only, not a mechanic or instrument guy....

Best regards,

-a-

[EricJ]

I think what you really want is to know whether the AI (or AH, but not the ASI) is getting vacuum.   In your proposed diagram the gauge will be measuring whether the pump is making suction, but not whether the AI is getting any.   In other word, if the line between the vac pump and the AI broke, or some other leak on that side of the system occured, your gauge would still show things were fine when they're not.

I'd tee the gauge off the line from the AI as close to the AI as possible, or off the regulator if there is one.

 

[bradp]

I'm sorry - that's the Attitude indicator that I mis-labeled.  Teach me to try to multi task (it doesn't work). 

I'll look into the multi-port manifold as well as the T connector -  those are decent ideas.  

-Brad