Yanmar diesel filter - valve between main and return

[__fdom__]

Hi there,
Is there anyone who knows about a yanmar diesel filter mounted to the engine. The engine is a 3jh40. I am in particular interested in the purpose of the valve which is apparently between the main diesel line and the return line. Can it be that the engine sucks air via this valve when not running and the diesel level in the tank is below the filter?

Any ideas appreciated.

Thanks
Frank

[skipperpete]

The valve has a primary function as a constant air bleed for the partially self priming fuel system but can also act as a non return valve..... very poorly because the flow through the valve is towards the tank which is the direction the fuel would drain if the tank return point was lower than the valve.
Because there are other return lines in that same circuit it is possible that if the valve failed and there was air in the system from the HP drain, common rail return or injector return, that air could get into the secondary filter........ but not likely.
If you are getting air in your system the suspect could be the manual priming pump on the water separator..... or any of the suction side connections.
This a the only fuel schematic I could easily find for your engine.

[__fdom__]

The whole installation is new. We are now checking and re-doing all connections on the suction side.

The schematics shows a diesel return where the exit into the tank is below the diesel level. Mine is above, i.e. the diesel "falls" into the tank, and if the engine is not running air can get into this exit.

There are is a loop in the return line, i.e. there is a whole section of the return line that is way below the filter and below the diesel tank. The fuel level in the tank is below the secondary filter.

[skipperpete]

Transparent fuel hose is a really good diagnostic tool, you don’t need a long length of it, just a 300mm piece with a barb fitting/joiner on each end where the supply goes into the secondary filter, you get an immediate visual indication of air bubbles in the line ,just keep tightening connections or re sealing joints till you see only clear fuel in the plastic tube.

[__fdom__]

The air came in via a leaky connection at the water separator. It was impossible to tighten the connection properly with the thick Vetus diesel hose and the short connectors at the water separator. Exchanged all diesel hoses and now everything is properly sealed.

Pete, thanks for your answers.

[skipperpete]

Well done fdom and thanks for posting the result.
Pete.