What fuel pump??

[Chotu]

Originally Posted by sailormed

“Though electrical components (such as a fuel pump) can spark and ignite fuel vapors, liquid fuel will not explode (see flammability limit) and therefore submerging the pump in the tank is one of the safest places to put it.”

Why reinvent the wheel when millions of cars drive with fuel pumps immersed in the petrol tank?

Yeah. The answer to this line of thinking is that when a pressurized fuel line on a car leaks, it drips on the ground.

When a pressurized fuel line on a boat leaks, it fills up the bilge. And it fills the boat with explosive vapors.

Boats and cars are not really equivalent.

[Searles]

Facet pumps on top of tank,one for each pick up,non return valve inc filter on the bottom of the pickup tubes , to small day tank ,to one facet pump to manifold ,have used this system on a couple of large cats ,quite successfully ,.⛵️⚓️

[Jlp0217]

I don't think your problem is the lift height, but rather the low fuel flow. Your pumps designed to pump gallons per hour are working really hard pumping fuel you are using at hours per gallon rates. As someone above said, the pumps rely on fuel flow to cool the pump. You need to either install a pressure switch to turn off the pump once the fuel line is pressurized ( a small accumulator tank will also help, just like in pressure water systems though the pressure is much less) or provide a fuel return line to return unused fuel to the tank like a diesel.

As is your pump is working har pumping fuel nowhere, against great resistance.

[Chotu]

Originally Posted by Jlp0217

I don't think your problem is the lift height, but rather the low fuel flow. Your pumps designed to pump gallons per hour are working really hard pumping fuel you are using at hours per gallon rates. As someone above said, the pumps rely on fuel flow to cool the pump. You need to either install a pressure switch to turn off the pump once the fuel line is pressurized ( a small accumulator tank will also help, just like in pressure water systems though the pressure is much less) or provide a fuel return line to return unused fuel to the tank like a diesel.

As is your pump is working har pumping fuel nowhere, against great resistance.

That’s actually a very good thought!

Makes a lot of sense. Now, I’d like to avoid return lines, of course since that’s a mess.

Is there a pump that’s small enough to be used properly in my setup? Brief periods of 6gph is possible, but typically it would max out at 3gph.

A single generator would use 1.4 quarts per hour.

[Simi 60]

I haven't read the whole thread but have you thought of day tanks?
Oversized pump from tank through 500fg to day tank on BD panel
Gravity feed from day tank down to engine.

[Chotu]

Day tanks are out. I have no place for them in the design. No room. Return lines, though also a nightmare, would be easier.

How do you set up a return line to say... a Honda eu2000 generator? Or an outboard? Anyone know?

[Chotu]

Wait a second. Return lines can’t work. Not without a return line tank selector manifold that you can’t rely on a human being to set properly.

Why is this so hard???

What have boats with inboard gasoline tanks and outboard engines been doing since the dawn of time?

[rslifkin]

Most setups I know of are plumbed directly tank to engine, maybe 1 selector valve in there. Usually not a ton of height difference and the onboard engine pumps draw fine.

Return lines wouldn't come from the actual engines and such in this case, but a regulator placed right after the pump. I think they do make valves meant to select feed and return source in one shot, but I don't know if there are any that support 3 tanks.

[Jlp0217]

I think probably most any small pump would work once the system is primed. The pumps on the outboards would probably work once primed, I don't know about the generators. Maybe all you need is a squeeze bulb to get the system primed initially, and then at most a small pump to feed the generators. The hard part of the 4 foot lift is trrying to suck the air out. Air is too compressable for small pumps to handle. Once they are pumping liquid its much easier.
This assumes that fuel will flow through the pump if it's not pumping. The electric pump I use to prime my diesel does. Maybe the big pumps you're using don't which is why your engines quit when the pump dies. Note, you never said just what fails when the pump dies. Does it run and not pump (failed valves or diaphragm), open or shorted wiring terminals, leak or what?

[Redline452]

Originally Posted by Chotu

These tanks are designed for big boats with
big engines. The pick up is like half an inch. Fuel lines are all oversized at 3/8 of an inch.

I think this is your problem. When I added an Espar heater in my sailboat, while my diesel tank already had a spare pickup tube, the installer ran a (very) thin section of fuel line down through the pickup tube, explaining that the Espar pump would not be able to lift the larger column of fuel when the tank ran low.

By my calculation, that 1/2" diameter column of gasoline 3 feet long (tank not even empty) is about 7 cu in, weighting about 3 oz. A 1/4" line would hold 1.76 cu in and weigh 0.76 oz - only a quarter as much. Size the line for what your engines need and your lift pumps will have less work to do.

[R Hutcheson]

You may want to look at Holley pumps. Also, consider buying direct from the factory or authorized dealer. I had an issue a last year where I was getting replacement fuel pumps from Amazon, they were the right part but were failing is an little as 10 hours. I suspect someone got hold of a bunch of factory rejects and listed them for sale as new parts. Finally paid a little more from the dealer and it has worked flawlessly.

[Dieseldude]

Originally Posted by Chotu

It took me a minute to fire up the CAD system. Ha ha ha.

The lift from the bottom of the tank to the pump is less than 48 inches.

Every component of the fuel system is located outdoors and on deck. For safety. This is gasoline.

The three fuel tanks and pick up fuel lines are the only things inside the hull.

The outboard engines are located lower than the fuel pump. The generators are located higher than the fuel pump. Even though it may be not drawn that way.

It seems that the layout cannot be changed due to the safety issues with gasoline. Otherwise it would make sense to locate the pump at the level of the tank bottoms. The faults experienced in previous pumps, may not be due to the pumps themselves, but the arrangement could be the cause of trouble. Each time it starts, the pump may have lost its prime. So it has to run dry a short time until flow is established. This causes a lack of lubrication and cooling of the pump, since the fuel provides these two functions.



If you cannot alter the height arrangement, does each suction pipe have a check valve at the bottom end? If not, fitting them would keep the lines filled at all times. Of course check valves rated for fuel are required. The check valves should be fitted with a strainer to protect them from failing to seat due to dirt lodging in them. The check valves and strainers should be fitted for easy access. Perhaps the suction pipe can be made for easy removal to withdraw the whole pipe, check valve and strainer as a unit. Not sure about where to source good fuel checks with strainers, other than check with a boat engine accessory supplier. Gear type pumps are typically used for fuel transfer, as they are quite rugged, though vane types can also be used. Vane pumps are generally more fragile.



Another thing to be mindful of is the filter arrangement and condition of the filter. The filter on the suction side of the pump ought to be a relatively coarse mesh to trap larger particles to protect the pump itself. It is quite difficult for a pump to suck liquid through the high resistance of a fine mesh filter. Your condemned pumps may have suffered cavitation damage due to filter resistance.



Of course it would be wise to fit a finer filter on the pump discharge to protect the engines. It is easier for the pump to push fluid through a fine filter than to suck it. The pump discharge filter should be slightly courser than the engines' own filters. This total arrangement will provide three stage filtration which will lower your total consumption of filters. Large particles are trapped by the courser filters, and this leaves the fine filter free of them. It would help to fit pressure differential gauges on your filters to monitor for when they require changing. A suction and discharge pressure gauge on the pump are also useful indicators. If your pump must be located above the tanks, this must be a vacuum gauge. If the pump is located at bottom height of the tank, it should be a compound vacuum/pressure gauge. Changing filters on running hours can be wasteful if they are changed before they really get clogged. They can also clog before "standard" running hours are reached. They are great troubleshooting aids too.



This may be gauge overkill for a small system out on the deck of a small vessel, so simplification could be in order. Even the suction filter may not be essential, since strainers could be fitted on the suction intakes inside the tanks that should protect the pump. This is a small system, and filters should not be too costly to change on a schedule, or just when a flow problem appears.



Selecting a pump involves some technical considerations. Of course discharge pressure and flow rate that meet requirements of supplied equipment are important. Suction head is often neglected. This is the maximum height that the pump is capable of drawing. If you will only be cruising on the sea, this will remain fixed. For inland waters, this will vary with altitude, so maximum altitude above sea level of any inland waters that you expect to sail must be considered. A good pump manufacturer should supply all this data. Suction specs are technically called net positive suction height or NPSH. Usually the spec's have a graph from which this can be determined for your particular situation.


One more consideration is discharge pressure relief. Fuel pumps are usually positive displacement pumps. So if the discharge pressure exceeds a certain value, the pump will be damaged. For example, if the pump is left running with a discharge valve closed. The seals could blow, and you have a dangerous fuel leak. Pumps may have an internal relief valve to prevent this. They are often adjustable so that you can set it for your requirements. But pumps that lack this will need an external relief valve in a pipe circuit that leads from discharge back to suction. A relief valve would have to be chosen and fitted in this return line These can be adjustable or fixed.



Pumping gasoline can be dangerous if the pump is lift running and a suction or discharge valve left closed. The gasoline may ignite due to heat build up inside the pump. Since this is intended to operate briefly as a transfer pump to top up engine tanks, this can be easily solved. Determine maximum time that you expect to run the pump and fit a shut off timer in the pump electrical supply. Example, if 10 minutes is the most that you will ever run it, then a timer set for 10 minutes will shut it down if forgotten, and you will not get a gasoline fire or explosion.

[s/v Jedi]

Like someone commented before: Walbro. Mine are 10 years old and just keep going. They pressurize to 6psi then just slow down or even stop when consumption stops.

[Chotu]

Originally Posted by s/v Jedi

Like someone commented before: Walbro. Mine are 10 years old and just keep going. They pressurize to 6psi then just slow down or even stop when consumption stops.

There have been a lot of guesses as to why this system shouldn’t work with any pump.

I’d certainly like to try a new pump before I make a lot of changes to the system.

Could you let me know the model of your pump? Also, what is doing in your fuel system? Is there a return line? Thank you.

[s/v Jedi]

Originally Posted by Chotu

There have been a lot of guesses as to why this system shouldn’t work with any pump.

I’d certainly like to try a new pump before I make a lot of changes to the system.

Could you let me know the model of your pump? Also, what is doing in your fuel system? Is there a return line? Thank you.

I have two in my fuel polishing/priming system. They are so old that they have been replaced with new models. These pumps are okay for continuous duty even against a closed valve. They are plunger pumps (the ones you hear ticking). I am not sure about life capacity, check the specs.