PCV Valve

[tetlow]

I am at last putting the V8 back into the B now the box has been checked over.

I want to fit a PCV valve.

Am I correct in the way the valve works?

With the engine off (no vacuum) a spring holds the valve open.

When idling the max vacuum closes off most of the valve. As revs increase the vacuum drops and the PCV valve opens more to allow the blow-by in the heads to be re-circulated through the carb.

i.e. to fit the valve if I hold the hose end that would be attached to the PCV port on the carb, and suck, the more suck the more flow will be restricted.

Thanks folks

Dave

[JP.]

With the engine off (no vacuum) a spring holds the valve open.

No it closes it

When idling the max vacuum closes off most of the valve. As revs increase the vacuum drops and the PCV valve opens more to allow the blow-by in the heads to be re-circulated through the carb.

The more vacuum the more it opens. Incase of a backfire there's no vacuum but boost so it closes inmidiatly the valve to protect the engine.

It doesn't need that much vacuum to operate. Suck it your self


and find out...........

[tetlow]

Thanks JP.

[tetlow]

I am getting confused now!!

I have just found this!!

"How does a PCV valve work? You would think that the PCV valve would flow more at high vacuum situations like at idle and less at lower vacuum situations like pulling a hill. It does the complete opposite. At idle or cruising when the vacuum is high the plunger is pulled farther into the body. The taper reduces the opening and the amount of air flow through the valve is reduced. Under acceleration or heavy load, such as pulling a hill, the vacuum drops. There is more blow by under a heavy load producing more vapors. In this case when the vacuum drops the spring pushes the plunger to the left opening the port up for more air flow when it’s needed the most to remove the extra gasses."

What you recon!!!

[mgbv8]

My PCV valve should be wide open at max engine vac Dave.

[tetlow]

Hi Pel. Merry Christmas

It seems that some PCV valves vary slightly, but from what I have found out from the net is, that at idle when the vacuum is high, blow by/crankpressure is low and the valve is almost closed. At WOT/full power, blow by is at a max, vacuum low or zero and the valve is fully open.
It also seems that the valve is closed at each extreme, almost shut when high vacuum(idle-cruise) and will shut completely at high +ve pressure(backfire).

I will just check how to fit it when I buy the valve.

Thanks for the help chaps.

Dave