THP155 engine breather one way valve

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gwest
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Joined: 27 Apr 2020, 08:07

THP155 engine breather one way valve

Post by gwest »

On my Jan 2013 DS5 turbo petrol THP155 I recently replaced the hose from the air cleaner outlet to the turbo housing inlet - the rubber end near the turbo had cracked. The replacement part I ordered from China (1440Q6 1440.Q6 9811909980 Air Intake Turbo Hose) included the engine cover breather hose as well, and it had a removable one-way valve in it, that I think is meant to fit into the housing close to the turbo end. In this position it would open when there was suction from the turbo but close if there was suction coming from the valve cover. My original setup did not have this valve, or it had been lost before I bought the car in 2018. I have an oil breather catch can on this circuit, and it intercepts a very minor amount of fluid compared to the can I connected to the breather line going to the intake manifold on the RHS of the motor (LHS=2ml, RHS=21ml, over 2900km). I might have considered fitting a one-way valve on the inlet manifold line on the RHS of the engine to keep turbo boost out of that catch can, but I could not find a suitable one. The catch can I bought can handle boost as well as vacuum, and assume that the valve inside the engine cover would stop the boost pressure getting in to the motor. I also assumed that any vacuum in the engine cover generated from the inlet manifold end would be prevented from sucking air from the turbo end by existing valving in the cover in the LHS end. So I'm puzzled as to whether this inline one-way valve is needed or not in my car.

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xantia_v6
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Re: THP155 engine breather one way valve

Post by xantia_v6 »

There is a non-return valve in the engine top cover.

For the PCV hose to the manifold there is a pressure regulator valve in the engine cover which closes to prevent excessive negative pressure in the crankcase, as that would increase blow-by and could cause problems for the oil pump. The crankcase does however run with slight negative pressure when the engine is off boost.

For the PCV hose to the turbo inlet, there is a pressure regulator valve that opens when the crankcase pressure is more than slightly positive, pushing the fumes into the turbo inlet, this only opens when the engine is on-boost. This valve also has a non-return action, to prevent air from the turbo inlet being sucked through the crankcase and other pcv hose directly into the manifold.