Originally Posted By: ragtoplvr
The PCV valve closes in case of backfire, so the pressure pulse is not sent to the crankcase. Also, the vapor is combustible, you do not want to light it and blow off the pan. The orifice used in jeeps is to me a BAD idea.
Rod
That's ONE of its functions. The other is to regulate the PCV air flow volume and keep it more or less constant. When manifold vacuum is very high (like idle or deceleration) the PCV valve restricts the flow by moving to the "thick" section of a little metering rod inside it. When you're accelerating, manifold vacuum drops and flow would go down, but the spring in the PCV valve opens it to a low restriction setting (thin point of the metering rod in the orifice) so keep the flow moving. And then if there's a backfire (as stated above) it slams shut.
The PCV valve closes in case of backfire, so the pressure pulse is not sent to the crankcase. Also, the vapor is combustible, you do not want to light it and blow off the pan. The orifice used in jeeps is to me a BAD idea.
Rod
That's ONE of its functions. The other is to regulate the PCV air flow volume and keep it more or less constant. When manifold vacuum is very high (like idle or deceleration) the PCV valve restricts the flow by moving to the "thick" section of a little metering rod inside it. When you're accelerating, manifold vacuum drops and flow would go down, but the spring in the PCV valve opens it to a low restriction setting (thin point of the metering rod in the orifice) so keep the flow moving. And then if there's a backfire (as stated above) it slams shut.