The International Cessna 170 Association

Does this appear to be an original regulator? The ports are marked with "P" and "H". Also a third hole that is plugged. The other side says Pesco 200.

I am looking to hook up a vacuum DG in my panel and was wondering if I could use this regulator.

Looks like the one I took out of my plane, but I don't know if it's an original part or a replacement.

I believe that would have been a regulator of the time and commonly seen in a 170 installation. However a Pesco No. 3V-195 is what is listed in the B model IPC item 76-19. Remember many Venturi installations where not done at the factory as they where an option. Who knows what was used in the field.

Bruce Fenstermacher wrote:,,, Remember many Venturi installations where not done at the factory as they where an option. Who knows what was used in the field.

The factory options included an "Instrument Flying Equipment" installation which would have followed the IPC and would have included dual venturiis and a regulator plumbed as depicted. However, as Bruce points out, who knows what many folks may have done in the field...? ... the installations I've personally viewed rarely follow the IPC, ... (and are often judged unsatisfactory by their owners who seem more eager to re-invent the wheel instead of following factory designs, yours truly included.)
I hope that sorry-looking regulator can be salvaged and rebuilt. They are simple devices but if they fail to force development of sufficient vacuum you are better off without one at all.

Here's Fig 76 from the B-model IPC which illustrates the factory method as well as that regulator:

Basically what you have is a flap or ball held against it's opening by a spring. The pressure on the spring is adjusted by the screw. They really can't fail so long as the spring doesn't break, unlikely, or the flap or ball doesn't get stuck closed by a substance such are rust.

Adjustment is made with the screw to relieve pressure on the spring until that point that the max vacuum you want in the system will pull the flap or ball open allowing normal air pressure into the system. Basically a controlled leak.

I think most people do not understand fluid (air) flow. They do not realize the friction of bends in their system and the reason for expensive bend fittings that reduce friction to a minimum. I'm certainly not an expert but I have studied it a little cause I'm one of those who's systems have not operated as expected.

Vacuum systems, those powered by venturi's anyway, are a black art. Vacuum pumps provide plenty of vacuum and it seems one can be more sloppy with their installation. Not so with venturi's, most of which are 4" venturis. 4" has nothing to do with the size of any part of the ventrui but how much mercury in inches the vacuum (or pressure) can raise. Today's modern gyros are designed for 4.5" to 6" of vacuum that a 4" venturi just cannot produce.

Thanks guys. I took it apart and cleaned it really good. I have the larger Venturi, 9" I believe. I removed the big AN gyro and am replacing it with a modern style DG. It will be the only Vacuum instrument I have. I was really close to just getting rid of the vacuum system altogether but I already had the Venturi and need to fill the hole in the panel.

AN type gyros require 3.5" Hg vacuum while "modern" pictorial types require 4.5".
This info is from my instrument overhaul manual by G.E. Irvins.
http://cessna170.org/forums/viewtopic.p ... uum#p77192

This is the one I removed when I switched to a pump. It is gathering dust.

When these airplanes were built the common AN style hardware fittings were the most used in vacuum systems. Subsequently, better, more modern materials are used which reduce the "friction" or resistance within the fittings to which Bruce alludes. Polyethelene line systems have much fewer fittings because the lines are flexible and can be routed without as many fittings. Additionally, the poly lines are "slicker" inside when fewer fittings are utilized. As early as the '62 model years, Cessna had begun to use poly vacuum lines.

The materials may be bought from Aircraft Spruce and others. It's what I used when I installed my 2nd Horizon project.
http://cessna170.org/forums/viewtopic.p ... +venturiis

nippaero wrote:Thanks guys. I took it apart and cleaned it really good. I have the larger Venturi, 9" I believe. I removed the big AN gyro and am replacing it with a modern style DG. It will be the only Vacuum instrument I have. I was really close to just getting rid of the vacuum system altogether but I already had the Venturi and need to fill the hole in the panel.

A very long time ago, when I lived in DallasTX in the '90", I experienced the same problem you have. My plane has a 9" Venturi with modern DG and AH. The instrument shop that reparied my vacuum system removed the old regulator and told me I didn't need it. With out the regulator, in cruise flight, I was pulling the correct vacuum to operate all the instruments. And, the system continues to operate to spec still today. Give it a try.

I finally got my new overhauled DG back in the plane. I tried running without the regulator but I was pulling up over 6" on the vacuum gauge. So I reinstalled the regulator and after a couple flight to adjust the vacuum, it is working great!

nippaero wrote:I finally got my new overhauled DG back in the plane. I tried running without the regulator but I was pulling up over 6" on the vacuum gauge. So I reinstalled the regulator and after a couple flight to adjust the vacuum, it is working great!

Good Job! (Where is that pat-on-the-back-emoji...??)