School me on eletric fuel pumps

I was thinking about electric fuel pumps for carbed boats. They don't return the fuel like injected pumps do. So how do they work? Do they just keep pumping dead head against the already pressurized fuel? Is there a built in relay to turn them off when they reach full pressure?
If they just keep pumping against the full pressure, why don't they burn up fairly quick? Just trying to wrap my mind around how they actually work.

Re: School me on eletric fuel pumps

Be a little more specific as to what exactly you are referring to! What boat, what engine, what year, what HP. If someone is just inserting an electric fuel pump on an engine that is not designed for one, they are asking for very serious issues. KABOOM comes to mind.

Re: School me on eletric fuel pumps

I think he's referring to the general fact that once the float bowl is full, the needle closes and fuel cannot enter the bowl anymore. So he's wondering how the pump doesn't burn up since it is pumping but technically the line is "closed off".

Re: School me on eletric fuel pumps

It all depends on the kind of pump it is. some electric pumps (vane style) require a return line so when the float boal fills up the pressure has somewhere to go while other electric pumps ( "wobble pumps" ) usually only produce just a few pounds of pressure and the needle and seat can stop the flow

Re: School me on eletric fuel pumps

I understand that. My question about what the application was because some folks ask a question like this without providing any details and then go ahead and add an electric fuel pump thinking all is ok when in fact they created a potential bomb. And that "bomb" is not because of the fuel pump itself, but rather because of how it is incorporated. Unless an electric pump has a circuit to kill it if the engine isn't running,(besides turning the key off) it is possible for a malfunctioning fuel system to kill the engine, but not the pump. so the pump fills the engine with fuel and then the operator tries to restart and the resulting explosion and fire becomes the issue as the pump continues to feed fuel to the fire. On four strokes it is easy to wire the pump through the oil pressure switch. Lose oil pressure the pump quits. Two strokes do not have an oil pressure switch or any other switch that would serve this purpose.

Re: School me on eletric fuel pumps

Whooo there big fella. No need to go off there about boat, engine, prop, length of appendage. I just wanted to know about carbed electric pumps. There is no return on them. As said, the bowl fills,needle shuts off flow. Pump pumps against closed line. Why doesn't it burn up grinding away against pressure? I'm not talking any specific boat. Obviously an inboard motor, because thats what the manufacturers make them for. And I don't think they are out to kill a bus load of nuns. So therefor they make them for a carbed application with the intention of using them in a boat.

Re: School me on eletric fuel pumps

I think this will answer the OP re: the regulation and how the pump shuts itself off

once the pressure reaches the 5 or 7 psi for example specified on the pump, the diaphragm is held back as the electromagnetic coil is not strong enough to push against 7 psi..
see that switch built in...
Once the pressure drops below 2 or 3 psi, the diaphragm relaxes and contact is made again, powering the coil and the diaphragm starts pumping again. Each pulse delivers fuel until once again the diaphragm is held back by pressure.
This shows the pumping action of the diaphragm. The iron core of the pump is a permanent dipole magnet. The electromagnet pushes it as it has the N and S pole reversed the way the coil is wound.

Re: School me on eletric fuel pumps

rockdog57 said:

Whooo there big fella. No need to go off there about boat, engine, prop, length of appendage. I just wanted to know about carbed electric pumps. There is no return on them. As said, the bowl fills,needle shuts off flow. Pump pumps against closed line. Why doesn't it burn up grinding away against pressure? I'm not talking any specific boat. Obviously an inboard motor, because thats what the manufacturers make them for. And I don't think they are out to kill a bus load of nuns. So therefor they make them for a carbed application with the intention of using them in a boat.

Click to expand...

Ahhhh -- but many folks attempt to replace the primer bulb on OUTBOARDS with an electric fuel pump -- and non-marine rateed ones at that. And I didn't "go off". I merely asked a question just as you did. The title of your post said "School me on electric fuel pumps". Consider yourself schooled.

Re: School me on eletric fuel pumps

Ahhh-- but this forum is the non-repair I/O and Inboards forum. Hence, no outboards. I'm sorry if I ruffled your feathers. But I asked a simple question. I just wanted a simple explanation exactly like Howard gave me. And yes, now I am schooled. Thank you Howard, I understand how they work!