Electric lift Pump?

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neil1967

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Following on from the series of fuel/filter questions posed by pcatteral, has anyone replaced a mechanical lift pump with an electric one - i know oldsalt has, but would like to hear of any other experiences. The background to my question is that the diesel tank on my yacht is lower than the engine (Perkins 4108) and bleeding it can be a pain. I am going to replace the primary filter with a racor this winter and am considering fitting an electric lift pump immediately after the racor, and then bypassing the mechanical pump entirely.

I believe that the benefit will be easier bleeding (no need to turn the engine over and risk salt water suck back) and oldsalt reckons starting is easier too. Equally, if I leave the mechanical lift pump in place, I will have a fallback should the electric one fail (although if it is solid state there is no reason why it should - in fact it should be more reliable than the mechanical pump). Can any one see any problem with this approach, and can I just blank off the existing lift pump fittings, or would I need to actually remove it?

Thanks

Neil
 
If you by pass it I personaly would remove the old pump, as it would be working at full output pumping air, and I imagine the diaphram would soon fail as it rubbed itself to bits.(think leaving a shower pump on all the time but no water going through) Then oil & crancase vapours would have an escape path.


Remove and make a blank plate.

Others have fitted squeeze bleeding bulbs with sucess. probably cheaper, & better and more reliable. After all if the 4108 is stopped with a cable stop, why introduce the need for lecky to keep it running?

If it was me I woulndnt.
 
Quote from David "Others have fitted squeeze bleeding bulbs with sucess. probably cheaper, & better and more reliable."

But is the bulb all that more convienant than using the hand pump? I think that I could have made some sort of tool so as to work the hand pump with less contortion.
I found the hand pump difficult but acceptable for the filters and high pressure side but used the starter ( total 30 seconds) for the injectors. If I had to do extended cranking then I guess it would be simpler ( in my case) to disconnect the raw water hose just before it mixes and direct the water into the bilges.
I guess that an electric pump could be installed parrallel to the manual one ( yes more valves!!) and be used for bleeding and in the event of pump failure?
 
I didn't fit it but our new engine has one and it's an improvement, much easier to bleed fuel. Pressurises the fuel system as soon as the ignition is switched on so, quicker starting. Be careful what you buy, some are not suitable for high lift situations. Suggest talk to Thornycroft who can supply.

As already suggested, remove mechanical pump and blank off.
 
I have fitted a Thornycroft electric pump in line with the mechanical one. It has a non-return valve built-in, and doesn't impede the mechanical pump when switched off. This gives the best of both worlds - easy bleeding when changing filters, and an instant backup if the mechanical pump fails.
 
A related question.

Can a pump fitted after a filter be used to bleed that filter?

It seems fairly obvious to me that it cannot - if you're sucking fluid through a filter, then opening a bleed screw on that filter will pull air in, not let it out.

But in another thread about electric fuel pumps, someone who seemed credible (probably for the best that I can't remember who :) ) told me that this was incorrect, and it was possible to bleed a filter using a pump downstream of it.

If so, how? Or did he misunderstand the situation?

Cheers,

Pete
 
All bleeding is doing is replacing air with fluid. If the pump can suck air out, to be replaced by fuel, then the is no need to open any bleed screws. Just like sucking on a pipe to start siphoning fuel, wine, beer etc out of one container into another.

Neil
 
prv said:
Can a pump fitted after a filter be used to bleed that filter?
Click to expand...
Yes, but you may have to open a bleed further down the line. Depends on the engine setup and tank returns.

Ours bleeds OK without opening anything as long as I give it a few minutes to run the fuel through before trying to start the engine.
 
neil1967 said:
All bleeding is doing is replacing air with fluid. If the pump can suck air out, to be replaced by fuel, then the is no need to open any bleed screws. Just like sucking on a pipe to start siphoning fuel, wine, beer etc out of one container into another.
Click to expand...

Ok, that makes sense, so instead of bleeding air out of the filter the idea is to suck it into the fuel line and blow it onwards to the engine.

That relies on the pump being able to work effectively at pumping air - imagine how much air there is in the top of a filter that's just been changed, even if you tip a jug of diesel into it before screwing it on. Does the typical "solid state" cube pump air OK?

Not sure I particularly like the idea of shoving that much air into the engine, though with the bleed screw on top of the engine filter open I suppose I can't see a specific problem.

Pete
 
I too have a tank below engine installation The engine is a BetaMarine 28. When new all worked well but gradually the starting performance tailed off. After discussion with Beta I fitted a Facet solid state pump between primary and secondary filters leaving the original lift pump in circuit. All was well for a while then starting and performance really began to fail, resulting in my almost not getting up to my winter layup yard in the dark and rain last year.
I bypassed the mechanical lift pump this year and the result has been faultless performance.
With the tank being low it is important for the electric pump to be as low as possible (preferably level with the bottom of the tank) as their suction performance is not so good as on the pressure side. Also any air leaks on the suction side will really affect performance.
I also have a Racor primary filter with a hand primer incorporated and a Parker vacuum gauge on the outlet side before the electric lift pump to indicate when the primary filter needs changing. (well worth the money) I also fitted a non return valve between the primary filter and the tank even though the Racor has one incorporated, belt and braces.
 
prv said:
That's interesting - so where does the air go? Back through the fuel return, I suppose?

Pete
Click to expand...

Yes. The difference with the electrical pump is that it pumps all the time it's switched on, same output regardless of engine revs. Excess fuel and any air just goes back to the tank via the return so, in effect, it's scrubbing the fuel through the filters whenever switched on.
 
Originally Posted by pcatterall
If I had to do extended cranking then I guess it would be simpler ( in my case) to disconnect the raw water hose just before it mixes and direct the water into the bilges.

Simpler still to close the seacock, surely? Quote

Yes simpler but the OPs concern was excessive use of engine cranking and water consequently getting into the engine.
 
pcatterall said:
Yes simpler but the OPs concern was excessive use of engine cranking and water consequently getting into the engine.
Click to expand...

Sure - but if you close the intake seacock then that can't happen. It's standard advice, and in fact it's engraved on my engine panel directly under the start button ("Close seacock during prolonged starting attempts or when turning over without running").

Why would you go to the bother of undoing hose clamps and pumping water into the bilge instead? The only reason I can think of is if your engine seacock is completely inaccessible, which is a problem waiting to happen in itself.

Pete
 
Ello PRV !!
The reason for shutting off the seacock is clear.... prolonged cranking may draw water into the engine.
But if we shut it off and engage in prolonged cranking the impellor will eventually run dry and may be damaged ( so I am told).
In my own case I have one of those long life speed seal plus impellors which ( I'm told!) will allow the impellor to run dry longer.
I am happy to crank my engine with the sea cock shut for some time ( I can reach it quite well thanks!!) certainley in order to bleed my injectors but if I thought that there was a possibility of damaging my impellor it would be easier (for me) to disconnect the raw water hose AFTER the water has circulated around the engine and BEFORE it mixes with the exhaust.
I hope that this clarifies things?
 
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