Posted by Clint Dixon on Wednesday, September 07, 2005 at 7:40PM :
In a tread below titled “Vacuum Leak”, by Robert N., I posted an explanation of the role that a donaldson valve plays in ventilating the crankcase of the POWER-WAGON. In the parts books, this valve is referred to as: “Valve, Crankcase Ventilator Metering, Assembly.” It is shown as part number 928 411. This valve is one component in the POWER-WAGON’S crankcase ventilating system that Dodge referred to as the “Positive Sealed Type.”
I erred in reporting that the design of the valve was to allow air to flow in one direction only. Bruce B. was kind enough to contact me and bring this to my attention. He had a valve apart and indicated that its construction would not stop air from flowing in either direction but would provide a metering, or automatic restriction, in one direction. I took my spare valve apart thinking that mine must have a malfunction. Bruce is correct. The design of the valve will not prevent the mixture of manifold air and gasoline from flowing back into the crankcase if conditions caused it to do so. It also appears that it would provide very little restriction for a backfire.
It appears that the valve provides a metering of the flow of gasses from the crankcase to the manifold to match the continuous fluctuation of manifold vacuum during normal engine operation. During times when manifold vacuum is at its highest, the metering valve is in its most closed condition, causing it to partially restrict the flow to the manifold, and to prevent the mixture of gasoline and air entering the combustion chambers from being too lean. When manifold vacuum is at it lowest, the metering valve is in its most open condition and restricts the flow very little.
Thanks Bruce for pointing out my mistake. I continue to learn new things all of the time because of the great minds that frequent this Forum. (Notice that I didn’t ask for him to continue pointing out my spelling errors.) ;^)
Junior
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