The Cessna 120-140 Association Forum

I have an acquaintance who is performing an annual inspection on a 140. The owner recently passed away, and the 140 is to be given to grandson. The grandson is not a pilot - is now taking lessons.
The IA is not familiar with 120/140s and I offered to assist in any way I could.
It appears the three instruments being driven by vacuum system are not functional. He indicates instruments connected in series, he is thinking should be parallel. Is this correct?
He also asking if there is a vacuum regulator for a 140?
He is thinking vacuum line is blocked, will be checking on this.
The 140 is located at Peru IN airport
Any comments will be greatly appreciated.

L. Benson

Hello,

Just a few ideas as a starter:

How is vacuum produced ?
Venturi (s) ?
Pump ?

In most small Cessnas of series 100, the AI and the DG are vacuum driven, and the Turn&Bank is electric.
In that way, if you loose one source of energy you have at least one gyro turning. Or two, if you loose electricity.
My C140 has a Cessna Precision AI venturi driven, no regulator valve, and a Rapco filter.
Plus an electric T&B. No DG.
Very happy with this simple setup, both instruments work nice.

I have never seen series connections, but from a point of view of physics is not impossible.
I attach documents that may help (or not) if they are applicable.

Have a nice day,

It is a venturi providing vacuum.

Originally there was no vacuum system offered. The only additional flight instruments are an electric T&B and a VSI.

I have seen systems plumbed both ways. None of them worked worth a darn with a single venturi. Technically, a 9" venturi should be able to run a DG, AH and T&B. The T&B requires a device to reduce the vacuum. I've never been able to get a 9" venturi to reliably power a DG and AH, never mind the T&B. I've tried series and parallel. The vacuum regulator was just lipstick on a bulldog.

I'm sure this is a lot of help...

If you're hell-bent on making it work, I'd use two venturis and a regulator. Or, one of these modern electronic gizmos. Or. learn to fly needle, ball and airspeed... (Maybe that should be at the top of the list!)

Which 3 instruments are vacuum? What year 140? My 140 has a vacuum T&B venturi driven. Nothing more than Airspeed, alt, vvi, mag compass. What else do you need? Adroid phone with free Avare GPS.

A T&B requires very little vacuum to drive. The old AN style DG and AH require quite a bit more, and the newer ones more still. I've gotten 2 modern gyros to work off a 9" venturi at 120 mph but that's about as good as it gets.

Thanks all for your input.
I have shared these with the IA working on the 140.....is now up to him and new owner as to how to proceed.

I forgot the conclusion...

I'd use two 8 or 9 inch venturis and a vacuum regulator if you want gyros you can depend on.

Thanks, I will pass this along.

I removed the entire vacuum system on my 140.
It is a VFR airplane and I see no need to haul around instruments that I have no intention of ever using.
It still has an electic T&B if I do something silly and have to get out of a jam.
By removing the very old Artificial horizon, DG, vacuum guage, two venturis and all accociated plumbing I got rid of 10 pounds of dead weight.

Rick