FL 120 lift pump - flow through?
- Thread starter meridian
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bobofthenorth
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- Gray Hawk
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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?
bfloyd4445
Guru
well if it flows toward the engine but not the other way it would then flow through right? .....anyone know for sure?
magicbus
Senior Member
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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?
Dave
Dave
Daddyo
Guru
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.
bobofthenorth
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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.
bfloyd4445
Guru
not if it has a check valve. Anyone know if they do?
bfloyd4445
Guru
So that means there is no check valve or if there is one the check valve leaks. right?
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.
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.
RT Firefly
Enigma
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.
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.
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.
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.
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.
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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bobofthenorth
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Or maybe the operating pressure of an aux pump is sufficient to open inline check valves.
:banghead
:banghead
psneeld
Guru
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?
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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I have a different engine, but that is what I do and it seems to work just fine.
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That makes sense to me. Unfortunately the FL120 service manual only describes how the mechanical lift pump works. It does not go into details like how much pressure is required to open the spring-loaded inlet and outflow valves.
But the accurate answer to the original question is easy enough to get by simply calling Bob or Brian Smith at American Diesel.
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bfloyd4445
Guru
Thanks Marin. Now that you explained it i can understand that when the engine is not running the presure on the check vbalve wont open it because the outlet side check valve is closed. If the pumpos valves are worn it may leak through but it would likely have to be really old. These thread are a cornicopia of information
psneeld
Guru
Just read the service manual and my guess is....
I don't think thats the way the check valves work...any pressure greater than a few psi on the inlet side should be enough to let fuel pass freely through this kind of pump. The diaphram would create a slight vacuum, inside the pump , then a slight pressure to open and close the valves...I think these diaphram pumps operate on very low pessures so any electric fuel pump would pump freely through it.
meridian
Guru
One of the reasons I'm doing this is to help flush my Racors. By having a shut-off valve after the filter, I can run the pump and open the Racor drain, flushing out the crud without having to open the filter or worry about air getting in the system.
RT Firefly
Enigma
Greetings,
Mr. meridian. Ahh....something I hadn't considered. GOOD idea although at one point in the recent past I had to mechanically agitate the crud at the bottom of my Racors, with a long plastic cable tie to unpack it in order to drain the crud. So you're planning to put this electric pump before the Racor? In series or parallel? If in series, the question arises is the mechanical pump strong enough to draw fuel through the, not used all the time, electrical pump?
Mr. meridian. Ahh....something I hadn't considered. GOOD idea although at one point in the recent past I had to mechanically agitate the crud at the bottom of my Racors, with a long plastic cable tie to unpack it in order to drain the crud. So you're planning to put this electric pump before the Racor? In series or parallel? If in series, the question arises is the mechanical pump strong enough to draw fuel through the, not used all the time, electrical pump?
RT Firefly
Enigma
Greetings,
So, 3 way valve, electric pump, 3 way valve in parallel before the Racor then? I concur, more frequent maintenance/draining would have eliminated or at least minimized my hardened crud.
So, 3 way valve, electric pump, 3 way valve in parallel before the Racor then? I concur, more frequent maintenance/draining would have eliminated or at least minimized my hardened crud.
FWIW I posed the question to the GB owners forum. This has been discussed there in the past and all the responses I recall had the electric pump plumbed around the mechanical pump, not through it.
However one fellow just responded to my recent question saying that he had installed an electric pump in series (before) the mechanical pump as part of his fuel polishing system and this setup pushed fuel through the mechanical pump with no problem. So it can be done.
However this same fellow said he had not considered the notion of the electric pump pushing fuel into the crankcase in the event of a pump diaphragm rupture and that it was a possibility worth taking into account if one was planning an auxiliary electric pump installation. To that end, he said routing around the mechanical pump was a better plan.
However one fellow just responded to my recent question saying that he had installed an electric pump in series (before) the mechanical pump as part of his fuel polishing system and this setup pushed fuel through the mechanical pump with no problem. So it can be done.
However this same fellow said he had not considered the notion of the electric pump pushing fuel into the crankcase in the event of a pump diaphragm rupture and that it was a possibility worth taking into account if one was planning an auxiliary electric pump installation. To that end, he said routing around the mechanical pump was a better plan.
Your filters must be different from mine. Mine (Racor) have a filter element and a plastic bowl on the bottom with a drain. I can open the drain and remove any water or sediment in the bowl, bit to remove "crud", I have to replace the filter.
I installed a Racor indicator that monitors the vacuum and indicates if the filters are clogged enough to need replacement.
