Installing electric fuel pump in series with on engine diaphragm pump

[StoneCrab]

Most engine mounted diaphragm fuel pumps have check valves going in and out of the pump housing. They both point toward the engine, so as the diaphragm is rising, it sucks fuel in from the supply line. The downstream (toward the engine) check valve stays closed, preventing fuel from being drawn from the engine side. As the diaphragm goes down, pushing on the fuel, the inlet check valve closes and the outlet check valve opens.

Since both check valves are pointed toward the engine, if you put an electric fuel pump between the tank and the diaphragm fuel pump, the fuel will flow through the diaphragm fuel pump freely.

I have a lot of diesel equipment and have mounted electric fuel pumps on all of my engines. I just tie it in with the ignition circuit. When the key is turned, the electric pump activates. The beauty of mounting a pump like this is that it makes it super easy to bleed the fuel system and to some degree, polishes the fuel. I say polish because any extra fuel coming from the electric pump, goes through the fuel filters and back to the tank.

[Chotu]

Lots of experience here with fuel pumps. I think my add on question is on topic.

I have 3 fuel tanks down in the hull of a catamaran. There are uninterrupted fuel lines from each tank to a set of valves to select the tank in use. These valves are located in the propane locker. (Gasoline)

Immediately after these tank selection valves is the Facet diaphragm fuel pump. After the fuel pump is a Racor fuel/water separator and filter.

From the filter, the fuel line is teed (again all is in the propane locker at bridge deck level) and a line runs to each outboard.

Problem:

Facet pumps are incredibly loud. Sounds like a machine gun. Is that normal?

Pump loses its prime very quickly when off and gasoline goes back to tanks.

Pump really struggles to get fuel to the engine. Takes 10-30 seconds to pull fuel up from the tanks.

Pump cannot push fuel up to bridge deck roof level.

What’s wrong with my installation?

[StoneCrab]

Originally Posted by Chotu

Lots of experience here with fuel pumps. I think my add on question is on topic.

I have 3 fuel tanks down in the hull of a catamaran. There are uninterrupted fuel lines from each tank to a set of valves to select the tank in use. These valves are located in the propane locker. (Gasoline)

Immediately after these tank selection valves is the Facet diaphragm fuel pump. After the fuel pump is a Racor fuel/water separator and filter.

From the filter, the fuel line is teed (again all is in the propane locker at bridge deck level) and a line runs to each outboard.

Problem:

Facet pumps are incredibly loud. Sounds like a machine gun. Is that normal?

Pump loses its prime very quickly when off and gasoline goes back to tanks.

Pump really struggles to get fuel to the engine. Takes 10-30 seconds to pull fuel up from the tanks.

Pump cannot push fuel up to bridge deck roof level.

What’s wrong with my installation?

I am not familiar with your particular diaphragm pumps. If they are of any size, I'm going to say that you have one of three problems:

1.) The ends / bearings on the pushrod that flexes the diaphram are worn causing the noise. This could also be the joint that connects the pushrod to the diaphram.

2.) The pump check valves are shot. They could be cracked, or have a build up of sludge on them causing them to not close entirely. This will affect the height that the fuel can pumped to and also explain the gas not remaining at the engine...leaking back to the tanks.

3.) Your diaphram may not be seated properly in the housing, causing some
of the push pressure to be lost as regurgitation.

If it was me, I'd do a quick tear down and inspection of all the bits and pieces. This is not a hard job if you have spares on hand.

I am asking myself why you have diaphragm pumps for this service. If I understand your system description, this is not an engine mounted pump, but rather a bulkhead mounted pump in a locker. You could get a rotary pump for this service. They would be quieter. Since it is gas, if you go rotary, you may want one that is magnetically coupled. Then you wouldn't have to worry about a shaft seal leaking.

If your diaphragm pump is one of the really small ones, the same problems may exist but you probably can't rebuild it. Just replace it.

[Chotu]

Sorry. I should have been more specific.

Everything o have described happens from new. I bought the fuel pump new it’s a new boat.

Also, the pumps have died almost once per year and stopped working. Then I have to buy another and another.

Do you have an example of a rotary vane pump that will lift the fuel from the tank, 5ft below the bridge deck? I thought I could only use a positive displacement diaphragm pump.

I have attached the type of pump as an image.

Yes, it’s a bulkhead mounted pump.

Originally Posted by StoneCrab

I am not familiar with your particular diaphragm pumps. If they are of any size, I'm going to say that you have one of three problems:

1.) The ends / bearings on the pushrod that flexes the diaphram are worn causing the noise. This could also be the joint that connects the pushrod to the diaphram.

2.) The pump check valves are shot. They could be cracked, or have a build up of sludge on them causing them to not close entirely. This will affect the height that the fuel can pumped to and also explain the gas not remaining at the engine...leaking back to the tanks.

3.) Your diaphram may not be seated properly in the housing, causing some
of the push pressure to be lost as regurgitation.

If it was me, I'd do a quick tear down and inspection of all the bits and pieces. This is not a hard job if you have spares on hand.

I am asking myself why you have diaphragm pumps for this service. If I understand your system description, this is not an engine mounted pump, but rather a bulkhead mounted pump in a locker. You could get a rotary pump for this service. They would be quieter. Since it is gas, if you go rotary, you may want one that is magnetically coupled. Then you wouldn't have to worry about a shaft seal leaking.

If your diaphragm pump is one of the really small ones, the same problems may exist but you probably can't rebuild it. Just replace it.

[jpendoley]

Just a quick follow up on my original question so I can close out my part of the discussion and we could talk about the fuel pumps on the cat. Launched the boat yesterday and was unable to get prime using the little diaphragm pump with the pumping handle on the pump. Switched on the electric and primed the entire system instantly and then bled the air and went on my merry way.Without the electric pump, I would have been manually pumping the diaphragm pump for hours to get prime and may never have been able to. Once the system is primed with the electric pump I was able to shut it off in the engine seems to run fine with the Engine mounted diaphragm pump only.

Don’t have much to add to the question about the fuel pumps on the cat, but I will say that my electric fuel pump makes a very loud hammering noise until the system is full of fuel and then it quiets down to a very low level tapping. It sounds like you might need a more powerful pump in the electric pump you have.

[Chotu]

Originally Posted by jpendoley

Just a quick follow up on my original question so I can close out my part of the discussion and we could talk about the fuel pumps on the cat. Launched the boat yesterday and was unable to get prime using the little diaphragm pump with the pumping handle on the pump. Switched on the electric and primed the entire system instantly and then bled the air and went on my merry way.Without the electric pump, I would have been manually pumping the diaphragm pump for hours to get prime and may never have been able to. Once the system is primed with the electric pump I was able to shut it off in the engine seems to run fine with the Engine mounted diaphragm pump only.

Don’t have much to add to the question about the fuel pumps on the cat, but I will say that my electric fuel pump makes a very loud hammering noise until the system is full of fuel and then it quiets down to a very low level tapping. It sounds like you might need a more powerful pump in the electric pump you have.

Thanks. And I can add a little tidbit to yours. On one of my old boat’s it used to take 30 mins to prime the fuel system with the standard yanmar priming pump on the engine. Your electric pump installation sounds a lot better!