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Posted by Sherman in Idaho [72.47.153.24] on Friday, July 27, 2012 at 21:49:49 :
I was cleaning an M37 PCV valve and got to thinking about how it works. I couldn't quite puzzle it out, so thought I'd ask. Obviously the weight of the plunger keeps it open unless there's high enough manifold vacuum to suck it up and close it. I'm thinking that's to keep it from causing a rough idle. When it's open, the plunger rests on a spring that keeps the pointy end from going down into the lower bore. What could possibly compress the spring? You'd need more pressure in the manifold than in the crankcase, and that's something that would never happen. Also, what's with the holes in the end of the plunger? If for some reason, the plunger gets pushed down all the way, the holes in it would still let a certain amount of air flow through it. It sure seems like it's designed to carefully control the amount of fuel/air mixture being sucked into the crankcase from the intake manifold, but that makes no sense at all.
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