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Old 03-02-2013, 06:48 PM   #1
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FL 120 lift pump - flow through?

I'm planning on putting in a small electric fuel pump to prime my Racors. Is the engine lift pump of a flow through design so I can prime all the way to the injector pump?
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Old 03-02-2013, 07:07 PM   #2
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yes
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Old 03-02-2013, 09:17 PM   #3
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I would have said "No". Its a diaphragm pump with check valves in and out. Are you sure it will flow?
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Old 03-02-2013, 10:03 PM   #4
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I would have said "No". Its a diaphragm pump with check valves in and out. Are you sure it will flow?
well if it flows toward the engine but not the other way it would then flow through right? .....anyone know for sure?
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Old 03-03-2013, 12:26 AM   #5
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Yes. A small electric pump will prime through the lift pump.
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Old 03-03-2013, 06:54 AM   #6
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I don't know but wonder why you care. Wouldn't it be enough to simply fill the filter and let the lift pump do its job? Are you looking for a backup should the lift pump fail?

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Old 03-03-2013, 09:24 AM   #7
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If the lift pumps fails, with a leak in the diaphragm the backup electric could flood the crankcase with diesel.

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Old 03-03-2013, 10:51 AM   #8
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well if it flows toward the engine but not the other way it would then flow through right? .....anyone know for sure?
Yes. I had one on my last boat. Also when my tank is full on this boat the level is higher then the engine and it does self bleed with gravity.
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Old 03-03-2013, 02:20 PM   #9
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Yes. I had one on my last boat. Also when my tank is full on this boat the level is higher then the engine and it does self bleed with gravity.
That's actually why I posed the question because on my 43 the full tanks are at least 2 feet above the lift pump and I know they won't gravity feed through it. But its good to know that a primer pump would work. If I ever run out of things that I NEED to do and get to the list of things that would be NICE to do it may be on that list.
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Old 03-05-2013, 07:04 PM   #10
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If the lift pumps fails, with a leak in the diaphragm the backup electric could flood the crankcase with diesel.

JohnP
not if it has a check valve. Anyone know if they do?
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Old 03-05-2013, 07:06 PM   #11
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Yes. I had one on my last boat. Also when my tank is full on this boat the level is higher then the engine and it does self bleed with gravity.
So that means there is no check valve or if there is one the check valve leaks. right?
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Old 03-05-2013, 07:16 PM   #12
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The couple of people I know who have installed an electric pump to act as a backup pump or for bleeding the fuel system on an FL120 bypassed the mechanical lift pump. I do not know if the mechanical diaphragm pump will flow through or not. A call to American Diesel will get you the answer, though.

John's comment about fuel being pumped into the crankcase by an electric pump moving fuel through a mechanical pump with a failed diaphragm seems a valid one, however.
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Old 03-05-2013, 07:27 PM   #13
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Greetings,
I concur with Mr. Marin. Call AD. Assuming one installs an electric pump (EP) in addition to and in series with the mechanical pump (MP) it could be 1)before or 2)after the MP. It could also be installed in parallel with the MP and isolated by means of valves.
If 1) and a diaphragm failed, the EP would pump fuel into the crankcase? If 2) wouldn't the EP suck air through the holed diaphragm from the crankcase and cause engine stopage? Helluva thing to trouble shoot if you did get a stoppage.
I'd go with parallel myself.
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Old 03-05-2013, 10:02 PM   #14
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We had no bypass and pumped straight through as does gravity.
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Old 03-05-2013, 10:54 PM   #15
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I just read the section on the FL120s fuel lift pump in the Ford service manual for this engine which is on the Grand Banks forum. It would appear that it is NOT a flow-through pump. There are spring-loaded valves on both the intake AND the outlet side of the pump. The inlet valve is opened under vacuum from the movement of the pump's diaphragm.

When the chamber is full the pressure from the diaphragm against the fuel opens the spring-loaded outlet valve while at the same time the spring-loaded inlet valve closes.

When the pump is not developing alternatiing vacuum and pressure from the action of the diaphragm-- in other words when the engine is not turning over--- BOTH the inlet and outlet valves are closed under spring pressure.

This is obviously why the people I know who have installed an electric auxiliary pump on their FL120s plumbed around the mechanical lift pump. Priming the fuel system using the electrical pump without the engine turning over means the inlet and outlet valves on the mechanical pump will be closed.

If the diaphragm fails with the engine running, the inlet and outlet valves will not open since there is no pressure available from the diaphragm to open them. So the auxiiary electric pump must be able to send fuel to the injection pump around the mechanical pump, not through it.
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Old 03-06-2013, 01:32 AM   #16
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My reality is the opposite. I have had three Lehman 120s and they all feed through the lift pump, period. I give up on this one.
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Old 03-06-2013, 02:26 AM   #17
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I dunno..... My description was taken directly from the Ford service manual for this engine. According to it, the stock lift pump on the engine does not appear to be able to flow fuel directly through it unless the pump is physically operating because of the spring-loaded-closed valves on the inlet and outlet sides of the pump.

If you don't agree with that then I guess you'll have to take it up with the folks at Ford of England.

Or maybe your engine didn't have the stock lift pump on it.
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Old 03-06-2013, 04:08 AM   #18
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Or maybe the operating pressure of an aux pump is sufficient to open inline check valves.
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Old 03-06-2013, 06:58 AM   #19
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Are the spring valves set up like a Whale hand bilge pump (most diaphram pumps are)?...

Where they are held closed by springs yet the inlet opens in and the outlet opens out...the pump works and any reasonable presure (maybe not gravity but yes a lift pump) easily pumps straight through?
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Old 03-06-2013, 09:48 AM   #20
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The inlet check valve will open from either a vacuum applied downstream by the diaphragm or by pressure applied upstream by an external pump.

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