The International Cessna^® 170 Association

Hi Bruce,

To continue both this thread and a conversation we had last Saturday morning while waiting for the weather to clear in Wilmington...

I figured out why we don't have any problems with our newer type of DG even though we only have one venturi. It turns out we also have a vacuum pump. I knew I was forgetting one of the power sources when we were talking! (I'm not a mechanic and this is all still a bit new to me.)

Anyway, the venturi system is tied into the vacuum pump system with a flip valve so that whichever one of them is pulling the most vacuum, is the one that is powering the instruments that use vacuum power.

Thought you might be interested. Please say hello to your wife for me. It was really nice meeting you both!

Your pump would be the way to go all the time till it fails then switch to the back up venturi. Before the pump falls and your counting on the venturi I'd switch and fly it. You will probably find that your one venturi will not provide enough vacuum to run both instruments reliably. Something you might want to know before you count on the venturi in a cloud.

Hi Bruce,

Thanks. I'll keep that in mind when I practice emergency procedures. If all goes well, I'm starting back with flying lessons in the 170 in mid-August.