I’ve been pondering how the PCV ‘hockey puck’ valve operates (pn 06A 129 101 A)… i.e the one that the crankcase/cam cover Y hose feeds into?

There seems to be no resistance when I blow through either hole

I wondered if it had a thermostat type operation where it opens up or closes when it gets hot but placing it in hot water had no effect on it.

Any ideas what it’s supposed to do or how it works?

I think it's supposed to let pressure from the crankcase through to the intake, but not the other way.

Basically, a one way valve.

Yours sounds shot.

I think it's supposed to let pressure from the crankcase through to the intake, but not the other way.

Basically, a one way valve.

Yours sounds shot.

Ah I see. I did wonder what was stopping the boost released through the DV to the intake pipe from rushing down the PCV hoses.

Thanks for that, it all makes sense now.

You can blow gently through them in both directions, and that's normal. I've replaced mine before and fiddled with the new one!

They seem to have a very light spring in them. I think the valve is more to do with the atomisation of the oily vapours. But it requires a sufficient pressure differential across it to function. Which is normally provided by the vacuum in the compressor inlet hose, and the positive pressure from the crankcase. Try sucking through it really hard and you'll see what I mean. Don't suck hard through it if it's a used valve though, because you might get a mouth full of oily crap when it works!

It's not a one-way valve, as it must let clean air back into the crankcase when the engine cools.

You can blow gently through them in both directions, and that's normal. I've replaced mine before and fiddled with the new one!

They seem to have a very light spring in them. I think the valve is more to do with the atomisation of the oily vapours. But it requires a sufficient pressure differential across it to function. Which is normally provided by the vacuum in the compressor inlet hose, and the positive pressure from the crankcase. Try sucking through it really hard and you'll see what I mean. Don't suck hard through it if it's a used valve though, because you might get a mouth full of oily crap when it works!

It's not a one-way valve, as it must let clean air back into the crankcase when the engine cools.

I noticed the spring but couldn’t see a diaphragm or plunger type mechanism that might activate under vacuum conditions.

I don’t fancy sucking it, blowing was bad enough… left a nasty taste.

Best I can do I suppose is to pressure test it to rule out any potential for a vacuum leak.

Hmm,

I thought it was just a one way valve. Learn something new every day.

What are the symptoms of them failing?