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Old 20-11-2011, 08:17   #1
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Fuel Lift Pump

Volvo 2003.My old Islander 36 came equipped with a Purolator 12S electric fuel pump.When it is switched on to run the engine it runs continuously.The engine only uses a small amount of the fuel pumped and the rest goes back to the tank through the return hose.So its also a fuel polisher as I have a Racor between the tank and the pump.But I have been unable to find if this pump is ok running continuously instead of cycling on and off.Does anyone know?
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Old 20-11-2011, 09:05   #2
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Re: fuel lift pump

The pumps I know are plunger pumps... they make this clicking sound. As you run your engine it should click slowly, like once every 2 seconds or so. It only moves little fuel because it just pressurizes the system up to 7 psi or so.

I guess the answer is that these pumps pump slowly instead of cycling. Exactly what is needed. When you would take the feed hose off the engine into a jug and switch on the pump, it will click like 5 times a second and provide full transfer capacity.

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Old 20-11-2011, 09:40   #3
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Re: fuel lift pump

No,like I said.The pump runs continuously.It clicks rapidly.It cannot build pressure because,apparently,it has no problem pumping past the injectors and back to the fuel tank.So I am trying to get an idea of how long this type of pump can last.
I have so much work to do on the boat I haven't had a chance to find out if the engine will run with the pump off...ie....can the INJECTOR pump suck all the way from the tank?
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Old 20-11-2011, 10:11   #4
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Re: fuel lift pump

Ok,I just took another look.This 3cyl engine has 3 individual injector pumps.So the fuel comes from the lift pump to the fuel bowl/filter and then to the injector pumps ,which are connected in line, and then it leaves the No3 injector pump and returns to the tank.So it looks like open pipe all the way.I guess if it had the mechanical diaphragm pump it would also pump at maximum .I think all the 2000 series must be this way.Anyone know?
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Old 20-11-2011, 10:19   #5
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Re: fuel lift pump

I believe the 2003 Volvo Penta does not have a lift pump other than the electrical one therefor it will not run without the Purolator /Facet pump which is a continous duty. I assume (We know how to spell that) the 125 you mention is the Max flow in liters? Here is a link.
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Old 20-11-2011, 12:02   #6
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Re: fuel lift pump

Thanks for the link Antares.That looks like the pump.
It looks like my engine can take a mechanical pump.I found a used one stowed with the spare engine parts.I have been eyeballing it and cannot see any defect and am wondering why they took it off.I guess I will have to try it when I get time.
With the electric pump I still cant help thinking I am missing something.Every other electric pump I ever saw clicked on and off with a pressure switch.
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Old 20-11-2011, 14:03   #7
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Our 2003 has a mechanical pump and nothing else.

Chris
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Old 20-11-2011, 14:07   #8
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Re: Fuel Lift Pump

My 1988 Volvo 2003 had a mechanical lift pump. I put an electric in-line one on as the motor was hard to start. Thought it might help. The only thing that helped was a Yanmar 3GM30F.
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Old 20-11-2011, 15:54   #9
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Re: Fuel Lift Pump

My Yanmar 54 has, as standard, only an electric lift pump that operates, as Nick says,continuously, when the ignition is on.
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Old 20-11-2011, 16:39   #10
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Re: fuel lift pump

Quote:
Originally Posted by nonam View Post
Ok,I just took another look.This 3cyl engine has 3 individual injector pumps.So the fuel comes from the lift pump to the fuel bowl/filter and then to the injector pumps ,which are connected in line, and then it leaves the No3 injector pump and returns to the tank.So it looks like open pipe all the way.I guess if it had the mechanical diaphragm pump it would also pump at maximum .I think all the 2000 series must be this way.Anyone know?
If this is your system;

You could put in a metering valve in the return line so it doesn't flow so fast but still allow it to bypass. The pump will not run so fast and if there is a demand for fuel the pump will speed up.

The drawing shows a mechanical pump which would only pump when the cam pushed against the pump lever. Not all the time.


You would have to experiment with meter hole sizes to know how big the hole would have to be. The pump only runs at 4-6 psi not enough to cause a problem with the injector pumps.
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Old 21-11-2011, 07:27   #11
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Re: Fuel Lift Pump

Good idea delmarrey.I think I will try that.
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Old 11-01-2012, 17:06   #12
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I have a 3gm30f with mechanical lift pump fed by an electric. The electric pump stopped working and the engine would not run. I can't usually hear the electric when the engine is running, but like yours, I think it runs at full speed most of the time due to the fuel return line. This is the way the boat was engineered and she ran fine for close to 500 hours. I just added a pump to the spares list. Mine isn't hard to change and the first lasted 15 or so years. I'd be a bit concerned about back pressure on the injectors with a metering valve. They were engineered for free flowing fuel.

Jim
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Old 12-01-2012, 12:30   #13
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Re: Fuel Lift Pump

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Originally Posted by JD.M View Post
I have a 3gm30f with mechanical lift pump fed by an electric. The electric pump stopped working and the engine would not run. I can't usually hear the electric when the engine is running, but like yours, I think it runs at full speed most of the time due to the fuel return line. This is the way the boat was engineered and she ran fine for close to 500 hours. I just added a pump to the spares list. Mine isn't hard to change and the first lasted 15 or so years. I'd be a bit concerned about back pressure on the injectors with a metering valve. They were engineered for free flowing fuel.

Jim
How much pressure is free flowing fuel?
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Old 12-01-2012, 15:24   #14
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Re: Fuel Lift Pump

Most diesel fuel systems use a pump sized for full throttle operation and an overflow/pressure regulation valve to control pressure at other times. In effect, this overflow valve is a metering valve. It diverts the correct amount of fuel to the return line in order to maintain an appropriate pressure input to the injection pump. If you put a restriction in your return line, you will raise the pressure to the injection pump.

In older diesels with mechanical injection pumps, they tend not to be too sensitive to the pressure input to the injection pump even though the pressure to the injectors will vary when they fire because it will still be above the popoff pressure. In theory, all of the components should be designed to be able to take much higher pressure but with older engines, raising the pressure is a great way to hurt seals and hoses.

With common rail engines, your lift pump feeds a high pressure fuel pump which will regulate the rail pressure. Having correct rail pressure on these engines is quite important.

The real question is, why do you want to change it from the way it was designed? You will not save yourself any fuel or maintenance.
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Old 12-01-2012, 16:46   #15
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Re: Fuel Lift Pump

Try this, variable frequency to maintain a certain output pressure.

Dickinson Marine - Low Pressure Fuel Pump

If you need a lower pressure then use a Holly regulator.

Holley Performance Products Two Port 1-4 PSI, Chrome*12-804
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