Recently when I shut off the engine, I hear an air leak coming form the front. When I opened the door leading to the generator in the front, here is what I saw.

http://smg.photobucket.com/albums/v438/raymag/Vacuum/

Look at the first picture.

From the black ball ( about the size of a grapefruit), come out 2 tubes. They are normally attached to some kind of a valve. The valve is not visible in this picture because my mechanic has removed it and is trying to locate a source for it. That valve, in addition to having these 2 tubes attached to it also has a piece of tubing about 4 inches long that floats around because it's not attached anywhere ( some kind of overflow he tells me). That is from that small tube that the air is coming out.

I'm able to drive without that valve being present. It doesn't seem to affect anything important ( like brakes or air-rides). What does that black ball do ??

From the bottom of that ball, the right most tube is labelled VAC. The other goes to a Tee connection. From the Tee comes out the second vacuum line and also a smaller tube.

Look at the second picture for details.

That wire or tube goes to a connector fixed to the wall about 6 inches above the black ball. I have not followed the circuit past that point.


Look at the third picture for details.

Can somebody shed some light on the purpose of all this and why it is now leaking air? And why It doesn't seem to affect my drive?



Thank you

It's hard to tell for sure - and my Breakaway has a GM drivetrain, but I suspect the ball is the vacuum accumulator and the valve is the dump valve for the cruise control (activated when you hit the brakes or turn it off). That small piece of tubing is probably the tube for vacuum dump.

With the valve removed, you likely have no vacuum.

So, what you may have is a situation where the cruise control won't work because there's no vacuum at the actuator. The HVAC system is also vacuum actuated, so the flappers for inside/outside air, vent/floor registers, etc. may not work because the valve is removed and the vacuum system is sucking air.

Those are the only two things the vacuum system operates on my Breakaway.

I also had a vacuum leak on mine, and the culprit was a plastic vacuum line to the HVAC plenum where the flapper valves are. The main line (blue) was completely deteriorated. That line went to the selector valve on the dash A/C controls. All the oher actuator lines are internal to the coach, and are in excellent shape.

Rusty is right, that black ball is the vacuum accumulator for the vacuum that works all the heating controls up front, You need to get that "valve" back that the mechanic took out, it is the vacuum generator, it is what is known as a venturi vaccum generator. It make vacuum by allowing air to escape thru an orifice. That is the 4 inch tube that is attached and goes nowhere.

It will normally cycle with air on and off as the venturi trys to maintain a certain vacuum in the black ball. You probably have two of them, one in front for the heating controls and if you have a vacuum operated cruise control there will be one there also.

On my Breakaway, they will continue to cycle on and off with the engine off until the air pressure in the tank gets to about 50 PSI and then they will stop. I find it annoying because I have to listen to that beeper for a long time when first starting in the morning. I am going to replace with an electric vacuum pump eventually.

If you hear air escaping all the time rather then a cycling, then there is something leaking in the vacuum system or a defective vacuum venturi. I believe it is a Ford part that they used on their diesel pickups.

HTH

My GM-powered 28' has an electric vacuum pump mounted in a compartment in the right rear. I suspect it's a quieter arrangement than the venturi.

I have a Ford disel van (6.9L NA) with an engine-driven vacuum pump, so there's no venturi.

Ok I think I understand now. Is the black ball just a tank and the missing piece is a venturi that actually create the pressure in that tank?

So right now what I am missing is a way to control my heating flaps in the dash?
You mentionned that the venturi is a standard part in some Ford pick-ups.
Are they diesel? What year or models?

Thanks guys! You're great!

You probably don't have air to the flappers in the A/C airhandler, and may not have cruise control.

Also, based on Ed's knowledge, the air leak could have been either on the pressure side to the venturi or the vacuum side; either would make a hissing sound. In fact, again from what Ed knows, that hissing sound may be normal...

I think both Ed and I are in accord that it's a vacuum accumulator; one way to produce a vacuum (as odd as it sounds) is to force pressurized air through a venturi, and pick up a vacuum (actually, lower pressure than atmospheric) in the venturi throat, based on Bernoulli's Principle. A venturi designed to do this is called an "ejector", as it ejects air from the vacuum system, creating a vacuum.

Apparently the valve Ed referred to regulates the amount of vacuum and shuts off airflow when not needed.

Well said Rusty!

Yes the hissing sound (air escaping) is normal but again it cycles, it should be a steady and continual sound. If it is, then there is something wrong with either the venturi or there is a vacuum leak. The venturi device has a built in regulator that will shut it off when the vacuum reaches a preset level. These can can dirt inside and stop working but it is fairly goof proof!

There are two devices like these one in front of the coach to provide vacuum that is stored in the black ball for running the heater flaps and vents. The other is in the back usually down lower on the right side frame rail and it also has a black ball to store vacuum for the cruise control servo. (if you have the automotive type, I think made by Dana).

When you shut off the coach, you will hear an occasional hiss from either front or rear of the coach as it trys to maintain vacuum. Mine was quite rapid in the back and found a vacuum hose has a very slight leak, replaced and now the hiss is not so often.

If you notice, your air pressure will drop over night, normal if you have these vacuum venturis working. It should not drop below 50 PSI over night, if it does then you have either a air system leak or one or both of the vacuum venturis are defective.

These devices were on diesel ford trucks but I do not have a part number or year of manufacture, would assume it would be around the time of the Barth manufacture thou. so early 90s would be my guess.

HTH

quote:

Originally posted by MWrench:
It should not drop below 50 PSI over night, if it does then you have either a air system leak or one or both of the vacuum venturis are defective.

On an air system you’re bound to have air leaks. I good mechanic can find most of these. Time/age will cause some valves to weep. There are many fittings and valves on any airbrake system. If you have the time and money you'll be able to find and repair these. I use Joy or some other type of soapy water to track down air leaks. It mostly takes patience and perseverance.

If you're loosing vacuum and the venturi is trying to make it then replacing the venturi will still not help you. Make sure you can make and hold a vacuum. Just because one thing is leaking don't assume that's your problem.

If your coach drops below 55 overnight don't assume it's your vacuum venturi. The venturi should have a low psi cutoff device mounted to the air tank. This shutoff will cut off air psi to the venturi at around 65 lbs and the venturi shouldn't leak any more air below this. It might even be tied into your airbag supply. The airbag supply should also have a low psi cutoff too.

If you want to get creative you can plumb in a normally closed fan stat controller and tie it into your venturi air supply and the ign side of the key switch. This way when your key is off all air psi will get cut off to the venturi.

Doug Vanse posted about similar troubles back on 03 APR 06 in the Barth Journey forum titled "Back in Michigan". post about vacuum generator

He posted a picture of the device



Part number that he got off the device is:

D7HT-19C747-AB

HTH

Yes that is exactly the device that I was talking about. I just read the post. Thanks a lot.

The black ball is the vacuum accumulator for the HVAC system. It has a check valve on the supply port to keep the vacuum from bleeding off as manifold vacumm drops as you accelerate with a gasoline engine. We don't have that problem on a diesel. As stated earlier, the hissing is from the venturi that creates the vacuum for the HVAC by using a small amount of coach air but will shut itself off at 70 psi. Under 70 psi, AC air comes out of the defrost vents due to the absense of vacuum I removed the venturi from our 94 Sovereign and replaced it with a small 12 volt vacuum pump from the 7.3L Powerstroke powered ford HVAC system because I was trying to preserve the air. I had a box of these pumps that I replaced with larger units to power the BD Exhaust brakes we were installing. I think I threw them away