Air Filter Vacuum Valve

[mondshine]

I am having trouble understanding PN 113 129 828A; the vacuum valve mounted on the air filter.

It seems to me that the manifold should be connected to the plastic nipple (that's the side with the threaded orifice/check valve) and the flap diaphragm should be connected to the brass nipple.

I haven't owned a Thing with a stock intake for over 30 years, and I can't remember how this gizmo is supposed to work. The flap on my air filter "closes" on startup as expected (drawing warm air through the preheat hose), but it seems like it stays closed too long.

Does anybody know at what temperature the flap should open to admit cold air? I'm curious.

Thanks, Mondshine

[Semper_Dad]

I'm sure you've checked the threads but here's one that could explain a little.
https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0
Damn complicated and expensive little bugger.
_________________
Walküre Restoration Thread: https://www.thesamba.com/vw/forum/viewtopic.php?t=737492

[mondshine]

Thanks for that Dad, I hadn't noticed that thread.

I cleaned the check valve under the threaded orifice (looks a little like a main jet), but I never thought about unscrewing the brass nipple.

I will look at that tomorrow.

[Gene Kisner]

Gary,
I don't know the thermostat temperature setting.
The thermostat is actually a three-way valve with the common port connecting to the vacuum-operated damper actuator. When the temperature is below the setpoint temperature the common port is connected to the vacuum source, thereby pulling the damper up, letting the warm air into the oil bath air filter. When the thermostat set point is reached, the common port switches to the atmosphere bleed port, letting the actuator bleed off while blocking the vacuum line and closing the damper, thereby blocking off the warm air source.
As for which hose connects to where, go to the Domeck Brothers gallery site and pull up picture #11 of 25 on Lee Caplins 1974 Thing. It provides a great photo of an original engine.

[mondshine]

Thanks Gene-
After some more testing, I have concluded that my vacuum valve is as dead as Julius Caesar.
After an hour of driving, the flap is still fully diverting hot air from the preheat hose.

Ordinarily, those valves are a little expensive, but I found one (new) for 20 bucks.
The bad news is that it comes from Riga, Latvia!
I have previously purchased several OEVW parts from this guy, so I will just have to be patient until it arrives. Until then, I think I will just pull the hose off of the actuator, plug the hose, and run on cold air.

Other than that, everything's good; looking forward to warmer weather.

[Vanapplebomb]

Are you sure it’s dead? It doesn’t matter how long it has been running, it is temperature AND vacuum actuated.

At idle, you have very high manifold vacuum, so it will hold closed even when ambient air temp is well above the bleeder valve opening temp. This is because even with the air bleed valve fully open, the small orifice will still be a substantial restriction to full manifold vacuum, which can be as high as 18-20 InHG on a healthy engine with a stock (or near stock) camshaft. Unless you are in an area with very high ambient temps, expect the flap to be closed at idle.

If you have a camera you can rig it up, and record the flaps motion while you drive. Accelerate pedal to the metal, and the flap should open to ambient (cooler) air as manifold vacuum is broken by the opening throttle plate.

Basically the temp sensing nature of the bleeder and the bleeder orifice size determines at what manifold vacuum the flap opens at what temp. Low ambient temps will require manifold vacuum to drop significantly (full throttle acceleration) before the flap allows cool air in. With higher ambient temps, the flap will allow cooler air in at higher manifold vacuum (cursing).

The more aggressive your camshaft, the less load your engine will need to be under to allow cool air to enter. Likewise, for a given engine load, a more aggressive camshaft will allow cool air to enter the engine at a lower temperature.

It isn’t a simple on/off device. Make sense?
_________________
1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021

[mondshine]

Yes Vanapplebomb,
Your description makes perfect sense.

Unfortunately, I don't own a go-pro or similar gizmo to record the flap action.

I can try some more experimentation with my hand-held vacuum pump.
At idle, I typically see ~18" HG (which I can simulate with the pump).

In any event, thanks for your help!

[Gene Kisner]

Less than $20 will get you an endoscope from Amazon with a 15 ft. long lead that attaches to your phone. Tape or wire tie it to view the area you want to see. Live, real-time, photos, or videos. No need for a Go Pro.

[mondshine]

[Wildthings]

The valve has multiple stages.

Cold the valve acts as a check valve so once the flap closes it will stay closed until the valve heats enough to open.

In the medium position the dashpot for the flapper get manifold vacuum, so the flapper will be open at full throttle but closed when the manifold vacuum is high.

In the hot position the valve bleeds off vacuum so the flapper is open all the time. The underhood temperatures need to be pretty warm for the flapper to be open at all time maybe 80+°F or so.

With the gasoline and motor oil that was available in the early 1970 when these "Things" were new, the valves would gum up in short order, but I haven't needed to clean the ones on my daily drivers in many years at this point in time. When cleaning the valve it is important to make sure the air bleeds are clear.

[mondshine]

Got a package in the mail today from Riga, Latvia.

YIPPEE!