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Vacuum line cap off

Hello Everyone,

I am currently in the middle of installing dual G5s in my -4 and have been going at it with a phased approach. I currently have a single G5 installed with magnetometer and OAT. In order to install the second G5 I will need to remove the DG, but I'd like to remove the AI while I'm at it. I'm not quite ready to pull the whole vacuum system yet so I was wondering if simply capping off the vacuum lines was acceptable. My initial thought is "no" since the vacuum pump is pulling air from the cabin and needs that constant airflow to function smoothly, but on the other hand you'd think there would be a pressure relief valve built in somewhere in the case of a clogged indicator or something. I'm unable to really find any information on the internet about how this system actually works.

Any input would be much appreciated!
Thanks
 
If your system is somewhat “standard”, the vacuum reg is a relief valve. The pump is a positive displacement device; provides a set amount of volumetric flow at xx rpm. The reg draws the required air into the system to maintain the desired vacuum. Rangeability may be an issue for the reg. Cap the intended line off and watch the pressure. If it stays in range your vac pump will be fine.
 
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Vacuum Stuff

Removing a couple of vacuum instruments will not likely change the vacuum pressure much, but in case you need to fiddle to keep it in the majickal 4.6 - 5.4” range… The vacuum regulator on most light singles is diabolically mounted on the aft side of the firewall, at the top, where the hose goes thru the firewall from the pump. There’s a foam filter on it (the so-called garter filter) that is normally changed at each yearly condition inspection. It was a yearly nightmare changing that thing and the main vacuum filter on our RV-6 until I removed the vacuum system in favor of a G5. Anyway, there’s a little T-handle on the regulator that adjusts bleed air into the regulator to set vacuum pressure. It’s secured with small, soft metal tabs to keep it from drifting. You can bend the tabs out of the way with your fingers to tweak the T-handle. Twist right (in) to raise the vacuum pressure, left to decrease. It shouldn’t take much, usually a quarter turn or so is all you need. Don’t forget to bend a couple of tabs up once you have it all set.
 
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