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crankcase breather non return valve

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Anyone have experience fitting a non return valve to the crankcase breather hose, the hose that goes back to the oil tank for dry sump engines?

What could be the benefit, is it dangerous or good for the engine, apparently preventing leaks ...?

Thanks a lot


Could you give more detail of what you mean with the hoses, what you seem to be suggesting isn't like anything I'm familiar with?

Naturally aspirated engines generally respond well to running the crankcase sealed. Generally measurable power increase from the better ring seal and less windage effects. If you have a lot of scavenge pump you may need a vacuum regulator in some cases - but this is usually only needed with the higher-end engines with big roots scavenge stages and often a secondary vacuum pump. For high power boosted engines there is typically too much blowby to achieve a crankcase vacuum so most boosted engines are run with open breathers.

Adam, the part that I don't understand is that he is apparently running the engine breather directly to the oil reservoir.

He really needs to post a detailed diagram, or a good explanation, of what he's doing so we understand the plumbing being used/planned.

It seemed pretty clear to me, but maybe im reading it wrong. It is common to put a check valve where I have placed the red circle below. This crank case "breather" doesnt necessarily need to go back to the tank, but often does if tank is close to the engine. Where the tank is more remote then it is more common to have a seperate "catch tank" close to the engine that this hose would be connected to instead of going back to the tank.

Hello, Konstantin does Adam's explanation answer your question?

Thanks, Adam, that's what I thought he meant. I guess I was thinking of a rear mounted tank which would be more problematical.

Personally, I'd be wary of doing that because it'd lead to oil contamination from some of the water and fuel vapours condensing out which would offset any oil recovery that may occur. If the engine has a poorly designed internal breather and/or has a lot of blowby to carry oil out, there may be justification with frequent, regular oil changes?

Konstantin, if you're looking at a vacuum valve to run a partial crankcase vacuum, I'd use one sized for the total scavenge pump volume and a bit of reserve, and use a check valve in the line to the tank to prevent scavenging from there but allow excess crankcase pressure to be bled off. I'd prefer to divert directly to the catch tank, but that's me.

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