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Old 28-05-2010, 15:48   #1
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Fuel Line Check Valve

I know opinions vary about the use of check valve in the fuel supply line. I do not wish to open that debate. I would, however, ask if there are any recommendations for a reliable check valve to place in the fuel return line of a Yanmar 2gm. I plan to install an electric fuel pump/filter to "polish" the fuel while on shore power. Should the electric pump fail, I do not want the mechanical pump to pull fuel from the return line or risk air in the line.

Please forgive my inexperience and ignorance with fuel systems, but I am having trouble identifying a suitable check valve.

Yanmar 2gm with mechanical Fuel lift pump
Walbro FRB13 down stream of
Racor 500fg in series with Racor 120AS

All in a delightful Tartan 28 that unfortunately sits more than it sails.
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Old 28-05-2010, 16:05   #2
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Just one comment; a fuel polishing system should be completely independent from the engine fuel lines.
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Old 28-05-2010, 17:38   #3
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You wouldn't put a check valve in a returnline
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Old 28-05-2010, 17:39   #4
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It is not advisable to put an Electric pump inline with a mechanical fuel pump
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Old 28-05-2010, 20:29   #5
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Quote:
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You wouldn't put a check valve in a returnline
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It is not advisable to put an Electric pump inline with a mechanical fuel pump
I agree that for a fuel polishing system that the OP described this isn't the way to go, but as recommended by the installation manual for my 3GM30 the previous owner installed an additional electric fuel pump to the mechanical because the amount of rise from the tank in the keel.

As others have posted there are risks such as if the diaphragm in the mechanical pump breaks you will dilute the crankcase with fuel much quicker.

On the GM series there is already a check valve in the return line. It isn't used as a check valve. The excess fuel doesn't go through the injector pump. There is a tee banjo fitting at a high point where the fuel enters the injector pump. I believe this design is to help keep air out of the pump. To keep the fuel under pressure at the entrance point to the injector pump and to keep the fuel from just draining down the return line away from the tee point there is a check valve downstream of the tee.

Chief, what are the issues you were thinking of?

John
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Old 28-05-2010, 21:29   #6
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Quote:
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It is not advisable to put an Electric pump inline with a mechanical fuel pump
Chief: Please explain the physics here. I had both in line for 15 years and 3500 hours.
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Old 28-05-2010, 22:50   #7
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If you have a diaphagm failure at the lift pump.....or even a slight leak....you will fill the crankcase with fuel...............
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Old 28-05-2010, 22:52   #8
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Do you have a picture of this TEE

I am not sure of what you are describing.

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As others have posted there are risks such as if the diaphragm in the mechanical pump breaks you will dilute the crankcase with fuel much quicker.

On the GM series there is already a check valve in the return line. It isn't used as a check valve. The excess fuel doesn't go through the injector pump. There is a tee banjo fitting at a high point where the fuel enters the injector pump. I believe this design is to help keep air out of the pump. To keep the fuel under pressure at the entrance point to the injector pump and to keep the fuel from just draining down the return line away from the tee point there is a check valve downstream of the tee.



John
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Old 29-05-2010, 03:54   #9
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I agree that for a fuel polishing system that the OP described this isn't the way to go, but as recommended by the installation manual for my 3GM30 the previous owner installed an additional electric fuel pump to the mechanical because the amount of rise from the tank in the keel.

As others have posted there are risks such as if the diaphragm in the mechanical pump breaks you will dilute the crankcase with fuel much quicker.

On the GM series there is already a check valve in the return line. It isn't used as a check valve. The excess fuel doesn't go through the injector pump. There is a tee banjo fitting at a high point where the fuel enters the injector pump. I believe this design is to help keep air out of the pump. To keep the fuel under pressure at the entrance point to the injector pump and to keep the fuel from just draining down the return line away from the tee point there is a check valve downstream of the tee.

Chief, what are the issues you were thinking of?

John
I believe your speaking of the GM series with a model suffix of YEU, Ie; 3GM30F-YEU
the earlier units didn't have this.

I also wouldn't do what the OP is interested in doing.
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Old 29-05-2010, 07:35   #10
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I am not sure of what you are describing.
The fuel to the injecter pump is the silver rubber hose. The bleed screw is on top of the tee (so actually 4 ways the fuel can go). The bango tee is the junction where the fuel comes to the pump, goes into the pump, and excess fuel leaves. The metal hose coming out from behind the throttle linkage is the fuel return line. If you zoom in you can see it attaches to the banjo on the opposite side from where the rubber hose attaches. The check valve is downstream in the return line. Probably makes more sense to call it an overpressure valve, since it maintains a relatively constant pressure in the section of fuel line that includes the entrance to the injecter pump. The excess fuel never enters the pump, there is no separate fitting for excess fuel to leave the pump.

John
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