The International Cessna^® 170 Association

I've searched and read various topics about installing a dual venturi / vacuum regulator in my plane, but I'm a little unclear about the best way to connect the venturis to the vacuum regulator.

I plan to use the 9" Venturis from Aircraft Spruce that have 1/4" NPT outlets (http://www.aircraftspruce.com/catalog/i ... nturi3.php) and a Rapco RA-2H3-12 that has 5/8" hose fitting for it's input (http://www.chiefaircraft.com/ra-2h3-12.html).

Any suggestions on the best way to plumb this would be greatly appreciated.

The regular goes between the gyro and the venturi.

If you have two ventures both go to the regulator then to the gyros.

Thank you. I was asking more about the actual fittings/hose to go from 1/4 NPT threads on the venturis to the 5/8" hose fitting on the regulator.

A AN912-5D bushing goes from 1/4 to 1/2 pipe. A AN910-4D is a 1/2 pipe coupling. A AN840-10D is a 5/8 hose nipple with 1/2 pipe threads. Screw the AN912 into one side of the AN910 and the AN840 into the other side. This would be the simplest method and other parts could be substituted. You could probably find all these fittings in Weatherhead brass at your hardware store.

The regulators available today aren't designed to be used with 1/4 plumbing of the venturi so you have to adapt it up or find a older style used regulator with 1/4 fittings.

AS I recall, the illustrated parts catalog (IPC) shows detailed parts and arrangement of the dual venturi vacuum systerm.

Miles, speaking of dual venturi's, your plane had one on each side as does mine. As I recall you did some testing some time back to determine which venturi (left or right) drew more vacuum. If I remember you felt the one on the right side produced the most vacuum. With the rebuild of your plane do you plan to put both venturi's on the same side or are you going to leave them as they have been?

cessna170bdriver wrote:AS I recall, the illustrated parts catalog (IPC) shows detailed parts and arrangement of the dual venturi vacuum systerm.

But the IPC shows a regulator which connects with 3/8 pipe thread, not 5/8" hose. So the parts in the IPC won't help

The Accessory Kit documentation is found here but I don't think it will help you much as the size of the fittings in/on your hardware is different. If you were to follow it you could use Bruce's advice and then in place of the AN825-6D in the top venturi use an AN917-2D tee with two AN911-2D nipples (in the top and side of the tee) and an AN816-6D nipple (on the bottom of the tee) to connect to an AN822-6D elbow in the bottom venturi.

Alternatively, if you've got money to burn, you might consider something like George has done here. Use four RA1K1-4-6 elbows between the venturis and the manifold p/n 04-00116. Then use p/n RA 1K10-6-10 to the inlet of the manifold. This will give you the 5/8" tube to connect to your regulator. Nylo-Seal fittings like George used would be cheaper but the sharp 90 degree bends would not be as efficient as the Rapco fittings. (I have no idea how much difference in vacuum the two different styles would make. Note that the original Cessna installation used sharp 90 degree bends with AN fittings.)

As Gary has demonstrated (with George's help), there is a myriad of whys and parts that can achieve the same end result and none of them are necessarily better than the other.

One thing you have to consider is what gauges exactly your driving. The old large AN gyros run on 4" while modern pictorial gyros need 5.25" or so to run properly. I have a mixed panel, one AN and one modern gyro. I only installed one super venturi and for the most part 3000 agl and less it is enough for both but higher than that I found the gyros did not perform as expected. I plan to add a second super venturi to double the volume of vacuum and you are planning. In consideration the one gyro needs more vacuum than the other but I would only have one adjustment, I plumbed the AN gyro the least direct. In other words when faced with a T in the line the route to the modern gyro took the straight through path rather than the 90. I don't know if this makes a difference but it makes me feel good.

Thanks for all the help/suggestions.

I stopped by Air Salvage Of Dallas to see what Vacuum Instrument Fittings they had and found a 5/8" x 3/8" x 3/8" Tee that I believe will work for connection of the two venturies to the 5/8" hose fitting on the regulator.

Do you think this will work instead of fittings into a manifold?

TechnoMayor wrote:Do you think this will work instead of fittings into a manifold?

It IS a manifold. Should work fine with one exception. The sharp 90° will restrict that line. But then so would any other 90°unless you bought the expensive specially designed reduced drag 90° fittings like the RA1K1-4-6 Gary showed in his post.