Installing electric fuel pump in series with on engine diaphragm pump

[jpendoley]

I am putting my power plant together after a rebuild of the engine (Westerbeke40/Perkins 4-108) and replacement of the fuel tank. Really looking forward to operating with a clean tank and rebuilt engine.
I use a small electric pump for priming the on engine fuel filter and the Racor 500. I believe it was plumbed in front of the Racor-that is between the tank and the Racor. Racor advises to have it behind the Racor so it draws fuel through the Racor before sending it to the on engine filter. I had an incident last year with contaminated fuel where when priming with the electric pump, I filled my Racor with emulsified fuel and water that ultimately clogged my secondary filter. My question is this: can the on engine diaphragm pump pull fuel thru the Racor and the electric pump which will be behind the Racor even if the pump is normally off?
The install order I envision is new shiny tank to Racor to electric pump (which is normally off) to on engine diaphragm pump to secondary on engine filter to injection pump. Is that the ideal configuration? Any suggestions much appreciated.
Jim

[a64pilot]

I was going to say most, but actually all electric fuel pumps I’ve ever used, fuel will flow through them easily when the pump is off.
From a mechanical standpoint you would want the pump in the fuel tank and send pressurized fuel to the engine, It’s easier and more efficient to pump than to use a vacuum, max pressure differential possible with a vacuum is only one atmosphere. It’s the way fuel injected cars do it.
However I believe boats suck fuel through the system to include the primary fuel filter is for safety’s sake, a leak will just suck air in a vacuum system and the engine quit, where it would spray fuel in a pressure system and unless the leak was massive, you would never know as the engine would keep running.
Most I believe put the pump before the Racor. If it’s just a priming pump I don’t believe it matters where it is, cause it will be off when the engine is running. However if it’s after the filter and you drain the bowl when you change filters, the pump is going to have to suck a whole lot of air, and many wont, where if it’s before the filter it’s before the air and only has to pump fuel and not air.

[kmacdonald]

It should be tank - primary filter/water separator - electric lift pump. The electric pump will mix the water and fuel making it harder for the filter to separate the water so put the pump after the water separating filter. Supposedly if you suck the fuel thru the filter the water separation process works better. Its suggested by filter manufacturers to do it this way. Another note, a lot of electric lift pumps have a mounting orientation that should be followed. Failure to do so will cause frequent bleeding.

[Dalestr]

Focusing on Facet pumps of the cube style (UL Marine Listed), there are basically 3 configurations they can give while de-energized. 1. Acting as a free flow forward but with reverse check valve 2. Positive shutoff 3. Full free flow. Realize that "Free Flow" is relative -- there is surely some restriction dependent on flow rate and this spec is not at hand.
There are specs for pressure range and dry lift capability on these; flow rate is usually not a concern for small diesels. On my 2GM20F I just replaced the mechanical lift pump with a 40163 model based on similar pressure rating (about 2psi). It is placed after the primary filter too so that it does not emulsify fuel. For priming the primary filter I still use a primer bulb which of course is free flowing with check valve.
You can start looking at the Pegasus Racing website though some other specs like dry lift are found at the Facet website.
With the right pump placed upstream of the primary filter in series with the mechanical pump, you would seem to have the best of both worlds but you must supply a small automotive filter on the inlet of this pump to keep its valving happy (Facet sells one). The electric could then be used just for priming/bleeding unless something fails on the mechanical one. I prefer to remove the mechanical and keep it for spare to remove the slight risk of a failed diaphragm. I would not consider using an electric full-time with a mechanical pump installed and bypassed, except for emergency.
https://www.pegasusautoracing.com/gr...ID=FACETSIPHON

[roland stockham]

While at this stage have you considered adding a 'day tank'. Electric pump fills the day tank which then gravity feeds the engine with clean freshly filtered fuel. Very easy to flush the day tank regularly and acts as a reserve in case of any fuel feed issues. I did this when fitting a new engine and it both increased reliability and made priming a simple case of opening a bleed screw.

[motion30]

You can install 2 tee s a and connect both the inlet and Outlet of the electric pump. This will bypass the electric pump when it is not running it was still Prime fuel system when you hit the switch

[Scorpius]

I've had just such a set-up on Scorpius for 20 years - with the electric pump between the tank and the first filter (the Racor). I originally installed it thinking it would be needed to get fuel up from the lowest tank - way down in the bottom of the keel six feet below the engine fuel pump - but that turned out not to be the case. Now I only turn it on for re-filling the filters after changes, priming and bleeding - but for that it's fantastic - and, when it's off the engine (Isuzu C240) mechanical pump draws fuel through it no problem.

[JOHNMARDALL]

Your proposed system will work well, but put you at some risk of pumping fuel into the boat if a leak develops in the fuel line - not much of a problem if the only pump is the one on the engine that will pull air through a fuel line leak and stop the engine. I like having an electric pump to prime the fuel system and so control the electric pump through the glow plug connections on the ignition switch. The electric pump only works when you're energizing the glow plugs, which is usually coincident with any priming need.

I hope this helps
John Mardall
for
Vetus Maxwell Boat Equipment

[Locquatious]

We installed the electric fuel pump such that it draws from the filter housing. In our case the draw pipe is near the top of the filter housing. To avoid getting air into the engine after the filter housing is drained or a filter is replaced, we put in a diverter valve after the pump. The diversion flow goes back to the tank via the return line. This allows the fuel/air at the top of the filter housing to be pulled out of the filter housing before the diverter is put back to normal operation.
We have run into a fuel pump that blocks fuel flow when not energized. For example a replacement fuel pump for a Kubota tractor HD46645504WIN seems to block fuel flow when not energized. The pump is inexpensive and reliable (at least on tractors). In our case we have connected the pump to the fuel rack solenoid circuit which energizes the pump whenever the generator is started and running.

[Lepke]

I have a 4108 running a generator. I have a 12v pump before the lift pump, after the Racor. It has no problem pushing fuel thru the lift pump and the lift pump has no problem drawing fuel thru the 12v pump. 12v pump is normally off when the engine is running, but is large enough to supply fuel in the event of lift pump failure.

I have a 12v pump inline to both mains and 2 generators. No issues.
Each pump has built in check valves that allow fuel to flow toward the engine, but not back to the tank.

[B_Wieberdink]

I like to have the pump between dieseltank and the filters. Its running when the engine is on. When there is a leak, there is no air sucked in, just some leaking of diesel, which you can smell. Air will stop your engine.

[billgewater]

Originally Posted by roland stockham

While at this stage have you considered adding a 'day tank'. Electric pump fills the day tank which then gravity feeds the engine with clean freshly filtered fuel. Very easy to flush the day tank regularly and acts as a reserve in case of any fuel feed issues. I did this when fitting a new engine and it both increased reliability and made priming a simple case of opening a bleed screw.

Totally agree. After about 20 years on my boat with various typical fuel issues I installed a 70 L tank under the aft deck that gravity feeds both a small diesel gen set and also the main engine (80 hp ancient Ford). The day tank has a test drain valve. I use a large Racor filter/water separator for the pumped fuel entering the day tank from the main fuel tanks and also when the fuel leaves the day tank for either the gen. set or the main engine. Both engines have their own filters. No water issues, no extra pumps, no vacuum problems. Certainly makes injector bleeding easier. KISS

[Bundyon]

I have been running Facet cube style fuel P.p in my boat for a couple of years now. I run the P.p between the tank and the Racor Primary filter. I have had no problems with water getting into the engine, the primary filter seems to catch most water, the secondary filter, a CAV796 very rarely has water in the bowl. Prior to cleaning this 1000litre tank, we covered a 800nm journey. The electric P.p was on the whole time. My thoughts on this is that it takes the load off the mechanical lift P.p.
When I reassemble the fuel system on completion of scrubbing out the tank, I will install a sediment bowl between the tank and the electric P.p, This will minimise the risk of stirring the fuel and any moisture as well as any grit or paint chippings that may be sucked into the system.

[Dalestr]

Originally Posted by Locquatious

We installed the electric fuel pump such that it draws from the filter housing. In our case the draw pipe is near the top of the filter housing. To avoid getting air into the engine after the filter housing is drained or a filter is replaced, we put in a diverter valve after the pump. The diversion flow goes back to the tank via the return line. This allows the fuel/air at the top of the filter housing to be pulled out of the filter housing before the diverter is put back to normal operation.

I was intrigued by the notion of the 3-way diverter valve. Not clear if this was used without bleeding. Certainly a simple way to remove most air quickly but there is a potential caveat if you skip bleeding.
The method will pull air that is accessible, at or below the filter's pickup port leaving behind some air floating above, the amount dependent on the design. The air left behind may later get to the outlet port when the boat is bouncing about or healing in a seaway. Some larger engines have continuous self-bleeding and might not suffer from bubbles of air but most engines don't have this.
A Racor turbine type filter was not any consideration for this method, but they pull fuel (to the outlet port) at an elevation near the bottom of the filter element (from a hole bored in the central tube) and so this technique would leave the element almost dry in a huge air bubble. These should be close to full with fuel before sealing the lid.

[sanibel sailor]

It makes the most sense to me to place it in the same relative location as the mechanical pump it is supplementing/replacing.



On my Westerbeke W30, I ditched the on-engine pump as a risk (small) of fuel leakage into engine resulting in either oil dilution or catastrophic runaway. More problematic, new diaphragms were not readily available for it. The electric pumps are quite reliable. Now I have new tank/Racor/electric pump/engine filter. Replaced every hose and hose clamp and redid every connection.

My system has a fuel pressure switch so as designed the electrics (to which I added my pump) come on only when the engine is running. I added an on/off/on switch which normally is set to the fuel pressure switch, but I can also run the pump independent of the engine for bleeding. I added a small T valve so I can fill a small container to top off the Racor as needed. With a new tank and meticulous fuel cleanliness management however, I have not needed to change the filter in years and it looks perfect.