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-   -   another fuel lift pump question.... (http://www.sailnet.com/forums/diesel/87097-another-fuel-lift-pump-question.html)

Rockter 05-07-2012 09:30 AM

another fuel lift pump question....
 
I have a Volvo MD17C.
For many years now, I have been running a pressurised fuel system, effectively presurising the fuel delivery from the tank to the Racor filter, then from there the fuel feed runs to the engine-mounted lift pump and engine-mounted fuel filter.
The system has been very reliable, and I have never drawn air, or had a problem. It draws about 2-3 amp, at nominal 12V.
One thing concerns me though : if the engine lift pump fails its diaphargm, then the electrical lift pump will fill the sump of the motor with diesel and I have no feedback until it is too late and my motor is full of diesel.
The electrical lift pump is intermittent, with a rub-dub-dub vibration every 2 or 3 seconds. If the engine lift pump diaphagm failed, the electrical lift pump would run continuously.
I had the idea of rigging a bulb in series with it and running the bulb to a wooden bulkhead in the footwell. That might work, but if I wire the bulb in series it will corrupt the 12 V voltage drop needed through the pump.
I had thought of a fibre-optic, but I don't know how to do that.
Effectively I need to light a bulb at the moment that the pump is running. And the bulb needs to go out when the pump stops.
Can I do that with a bulb in series? How would that work, unless the bulb was very low resistance.
An in-series ammeter would do, I suppose, and I just watch for the needle wavering. If it stays on, then I have a problem. That would work, I guess, but i will have to watch the ammeter all the time.
I really need something to warn me if the electrical lift pump stays running continuously, and stays quiet if it operates intermittently. That's a not an easy call for me to design.


What do you think folks?

sea_hunter 05-07-2012 10:05 AM

Install a switch with an indicator light or add it to the preheat circuit of the start switch (if you have preheat) and use it only when you start. If the mechanical fails you can always leave it on if switched.

Faster 05-07-2012 10:25 AM

Re: another fuel lift pump question....
 
If you want a 'pump running' warning light wire it in parallel with the pump otherwise neither will have the voltage they require. Easy to do with a small terminal block.

Rockter 05-07-2012 02:08 PM

Re: another fuel lift pump question....
 
Faster :

I am smiling from ear to ear. Why the heck did I keep thinking in series wiring? You are absolutely right, just wire it in parallel and allow the pump motor switch to complete the circuit!!!!!

I will run a wee bulb and waterproof lens into the footwell bulkhead, or an LED into the instrument mount. It may get a wee bit annoying at night, as it will have to be seen during the day and at night, but it's better than a lost motor.

Thanks.

Rockter.

dabnis 05-07-2012 04:27 PM

Re: another fuel lift pump question....
 
Quote:

Originally Posted by Rockter (Post 868280)
Faster :

I am smiling from ear to ear. Why the heck did I keep thinking in series wiring? You are absolutely right, just wire it in parallel and allow the pump motor switch to complete the circuit!!!!!

I will run a wee bulb and waterproof lens into the footwell bulkhead, or an LED into the instrument mount. It may get a wee bit annoying at night, as it will have to be seen during the day and at night, but it's better than a lost motor.

Thanks.

Rockter.

I used an electric pump on an engine conversion, ran for years full time, no problems. You could just remove the mechanical pump and carry a spare electric pump. More on pump setups:

The Diesel Page, Electric Lift Pump and Racor Filter installation

Paul T

Rockter 05-08-2012 03:04 AM

Re: another fuel lift pump question....
 
Dabnis :

I have a spare electrical pump on board already. Perhaps its best simply to by-pass the engine lift pump and go directly from Racor filter to the engine mounter filter.

If the electrical lift pump failed, I could rig a temporary fuel supply with gravity feed to get me home in any case. Changing the electrical fuel pump in a lumpy sea would make me kinda seasick, methinks. It could be done fairly rapidly though. They are normally very reliable. The last one lasted 20 years.

In all the years I have owned the ship, the engine room electrical bus has never lost power so perhaps I am worrying too much.

Thanks.

Rockter.

dabnis 05-08-2012 09:43 AM

Re: another fuel lift pump question....
 
Quote:

Originally Posted by Rockter (Post 868581)
Dabnis :

I have a spare electrical pump on board already. Perhaps its best simply to by-pass the engine lift pump and go directly from Racor filter to the engine mounter filter.

If the electrical lift pump failed, I could rig a temporary fuel supply with gravity feed to get me home in any case. Changing the electrical fuel pump in a lumpy sea would make me kinda seasick, methinks. It could be done fairly rapidly though. They are normally very reliable. The last one lasted 20 years.

In all the years I have owned the ship, the engine room electrical bus has never lost power so perhaps I am worrying too much.

Thanks.

Rockter.

Right, that would simplify things. You could mount the spare with a switch and valve so you could use the spare in a minute or so.

Pasul T

Rockter 05-09-2012 03:28 AM

Re: another fuel lift pump question....
 
dabnis :

I would just ned to be sure that the electrical lift pump's 5 psi feed is enough to get fuel through two filters (Racor filter and engine mounted filter) and through to the injection pump.

I guess time will tell.

I will leave the engine-mounted mechanical lift pump in situ in case one day it will be needed again. Perhaps it's just better to take it off to save wear on the diaphragm and blank off the aperture?

Thanks.

Rockter.

dabnis 05-09-2012 09:22 AM

Re: another fuel lift pump question....
 
Quote:

Originally Posted by Rockter (Post 869030)
dabnis :

I would just ned to be sure that the electrical lift pump's 5 psi feed is enough to get fuel through two filters (Racor filter and engine mounted filter) and through to the injection pump.

I guess time will tell.

I will leave the engine-mounted mechanical lift pump in situ in case one day it will be needed again. Perhaps it's just better to take it off to save wear on the diaphragm and blank off the aperture?

Thanks.

Rockter.

Right, if you leave it on with no fuel running through it the diaphragm may get brittle and break. I would think 5 pounds of pressure would be plenty to get through both filters. One article I read recommended a filter between the tank and the suction side of the pump to protect the pump mechanism. Or, some pumps may have an integral filter?

Paul T


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