PCV valve: Missing somethng?

[wayneh]

Attached is my PCV valve after I took it apart and cleaned it. Air flows freely in both directions, which leads me to believe that the valve part (third thing from the left) might be missing a rubber washer or something to seal and restrict the air flow. Has anyone ever seen one like this?

Thanks

Wayne

[Gordon Maney]

It should function as a check valve.

[wayneh]

Gordon: Yes, I know it is supposed to function as a check valve, but this one looks like it is missing a round rubber gasket like part to make the seal. Air blows equally as well in both directions.

thanks

Wayne

[Gordon Maney]

I don't know that you will be able to source parts for that. You may have to improvise and adapt a contemporary PCV valve.

[Cheyenne Dave]

I don't believe there is any rubber involved. This PCV valve is mounted vertically, according to the arrow stamped on the body of the valve, and relied on a precision fit of the internal parts.

If you test it in a vertical orientation, you may find that it works properly.

CD

[wayneh]

Dave: Thanks. Yea, rubber does not make sense, it gets to hot that close to the manifold. But I think there must be a ball or some sort to restrict the airflow in one direction. Right now I can blow quite nicely through either end. There is an arrow on this, along with an AC part number, but I have not been able to find anything on line with that part number. This one was mounted vertically on the intake manifold right below the base of the carb.

Wayne

[Frank Irons]

VPW has the valves and I believe Midwest Military does too. Dave is right, there is supposed to be a steel ball inside. Donaldson also was a manufacturer of these valves.

Frank

[Charles Talbert]

Never saw one of these that was not manufactured by AC I don't think. A Donaldson brand on this part is definitely not a familiar one for me. I have never seen one that had a ball inside either, nor do I recall seeing internals like the one Wayne has pictured here. The familiar ones to me do not have a spring, but a weighted device with a cone shaped end that makes the directional flow seal. Pretty obvious that several different types from differing manufacturer's were used I guess.

[wayneh]

Well, I have improvised, at least for now. I took the "valve" part, the one with the wire in it, and JB welded a flat round metal thing I made up to where it is supposed to seat under the spring load. At least now it functions like the PCV valves I'm familiar with, letting air go past in one direction. Since it only takes five minutes to put it in, I put it in yesterday to try out. It certainly fixed the "lean under acceleration with load" that I been working on, although now the Maryland emission police will get on my case...

In the mean time, VPW is sending me a "recycled" one so at least I know what it is supposed to look like. I'll be sure to take it apart and post it in case anyone is interested, since these seem to be getting harder to find.

Wayne

[Clint Dixon]

Here is a NOS Donaldson brand metering valve, part number 928411, that I just opened from package that was sealed in 1952. No springs or check balls inside - just a weighted needle valve. This is the correct part number according to my 1953 parts list. I did not look in any other parts lists, but the six digit number tells me this part had been in use for at least a few years anyway.

I don't doubt Charles, but I personally have had the opposite experience in that the only metering valves I have ever found on any of my early trucks have all been made by Donaldson. In fact, for years I had only heard them referred to as "donaldson valves" in a generic sense kind of like "kleenex". I only later learned that Donaldson was the manufacturer and that the proper term was metering valve.

I imagine each manufacturer had their own patented design. The one pictured works by manifold vacuum pulling the weighted needle valve upward against gravity. The manifold vacuum does this because there is a slight restriction to air flow around the needle in that direction. Once the needle is pulled all the way up to the top end of the metering valves cylindrical housing, flow of air from the crankcase to the manifold is cut off substantially. As vacuum decreases, the needle starts to drop back down towards the bottom of the cylinder and flow of air and vapors from the crankcase increases due to less restriction.

I think the idea is that the flow is regulated to a determined volume regardless of the amount of vacuum the engine is producing, thus preventing an overly rich or overly lean condition since the port in the manifold is located below where the air is regulated and the fuel is atomized by the carburetor. Back flow from the manifold back to the crankcase is never restricted in this valve. Even when the weighted needle falls to the bottom of the cylinder, the design is such that there is no restriction to air movement in either direction.

The other metering valves from other manufactures may be designed to function differently.

[Charles Talbert]

The one Clint has pictured is the exact type we are used to seeing here. I do recall the AC trademark, but I imagine like many accessory components on vehicles, they were produced by any number of manufacturers over time.

[wayneh]

Clint: Thank you. That picture and explanation is exactly what I was looking for. Sure as heck, my "metering valve" is probably an aftermarket.

So the funny part about all of this is that I noticed the engine running slightly lean under acceleration after I had the manifold off and cleared the metering valve passageway from carbon. That led to me learning and figuring out all about the "metering valve".

Thanks again taking the time do dig that up and explain it.

Wayne