prv
Well-Known Member
Not necessarily, as in the previous post. Some engine manufacturers specify a dip tube on the return to minimise foaming, though of course not every installation will follow the spec.
Pete
Fuel supply - Tank/Engine
- Thread starter Yorkshire Exile
- Start date
Not necessarily, as in the previous post. Some engine manufacturers specify a dip tube on the return to minimise foaming, though of course not every installation will follow the spec.
Pete
Yorkshire Exile
Well-Known Member
Thanks to all for these replies. There's a current related thread which includes some good diagrams http://www.ybw.com/forums/showthread.php?518027-Fitting-a-diesel-bleed-to-fuel-tank-in-situ
Performance Sailor - I have checked for chafing and rectified (I do worry about the marine engineer who replaced these hoses!). My Mother always warned about the dangers of chafing.............
Following all your comments I am coming to the following conclusions:
Seems to me it's useful to have the fuel feed to have a stop valve, closing it limits any leakage that might happen at the engine end when one is not on the boat, it is easy to isolate the engine fuel system when working on the fuel filters etc and is an emergency isolation. That clearly would not be the case when my fuel return line was on that stop valve. My primary and secondary filters are both below the lowest point of the tank and therefore have a positive head.
The diagrams in the above referenced thread show 'pick-up' tubes on both the fuel supply and return lines. In my case that must be true or the engine would not have run when the fuel supply was connected incorrectly to the feed connection at the tank.
In the diagrams the return lines have a U bend in them. Is this to prevent syphoning back to the engine when it's not running? That's why I suspect the need for a non-return valve in that line.
Performance Sailor - I have checked for chafing and rectified (I do worry about the marine engineer who replaced these hoses!). My Mother always warned about the dangers of chafing.............
Following all your comments I am coming to the following conclusions:
Seems to me it's useful to have the fuel feed to have a stop valve, closing it limits any leakage that might happen at the engine end when one is not on the boat, it is easy to isolate the engine fuel system when working on the fuel filters etc and is an emergency isolation. That clearly would not be the case when my fuel return line was on that stop valve. My primary and secondary filters are both below the lowest point of the tank and therefore have a positive head.
The diagrams in the above referenced thread show 'pick-up' tubes on both the fuel supply and return lines. In my case that must be true or the engine would not have run when the fuel supply was connected incorrectly to the feed connection at the tank.
In the diagrams the return lines have a U bend in them. Is this to prevent syphoning back to the engine when it's not running? That's why I suspect the need for a non-return valve in that line.
prv
Well-Known Member
According to Beta it's exactly the opposite - to prevent fuel in the injector pump from draining back to the tank (presumably only if the tank is below the engine), meaning the engine won't start on the button because the lift pump needs to refill the injector pump first. I must admit I can't quite see how it achieves that, but I presume they know what they're talking about. Obviously a non-return valve wouldn't help since the direction of flow is the same for both the desirable and undesirable movement.
Pete
PerformanceSailor
Well-Known Member
Regarding (only) the fuel return line to the tank...
A mechanic friend with over 50 years experience with small diesels (and larger ones, too) tells me that our typical small sailboat diesels have very little fuel actually being "returned" to the tank. He sez it's more like a drip or a small dribble. The fuel just has to get there, somehow.
Back in the 50's, huge Catapiller 'dozers would leave it open to drip on the ground under the engine, the fuel return rate was so low. Of course in those unenlightened times a little pollution of the forest was not noteworthy.....
I see that Betamarine calls this function the "leak off" hose, so I surmise that their marinized Kubota engines actually return only a trickle when running. At the risk of proving that "a little knowledge is dangerous" my guess is that other small diesels behave similarly.
i.e. we all might, to some extent, tend to over-think this.
ps: my mechanic and my engine installer both could not figure out why the Betamarine diagram pictured a dip in the return line. My previous 1988 Universal engine (also a marinized Kubota block) did not have an sort of dip in that hose.
pps: Yorkshire, thanks for a chuckle about the problems of "chafing" !
A mechanic friend with over 50 years experience with small diesels (and larger ones, too) tells me that our typical small sailboat diesels have very little fuel actually being "returned" to the tank. He sez it's more like a drip or a small dribble. The fuel just has to get there, somehow.
Back in the 50's, huge Catapiller 'dozers would leave it open to drip on the ground under the engine, the fuel return rate was so low. Of course in those unenlightened times a little pollution of the forest was not noteworthy.....
I see that Betamarine calls this function the "leak off" hose, so I surmise that their marinized Kubota engines actually return only a trickle when running. At the risk of proving that "a little knowledge is dangerous" my guess is that other small diesels behave similarly.
i.e. we all might, to some extent, tend to over-think this.
ps: my mechanic and my engine installer both could not figure out why the Betamarine diagram pictured a dip in the return line. My previous 1988 Universal engine (also a marinized Kubota block) did not have an sort of dip in that hose.
pps: Yorkshire, thanks for a chuckle about the problems of "chafing" !
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