Racor Vacuum Gages and Electric Fuel Pump

[MauleOne]

I want to add electric fuel pumps to my fuel system. Right now I only have the engine mounted mechanical pump.* I am concerned that I will have no back up if the mechanical pump failed. also having an electrical pump will make bleeding and priming the system so much easier when changing filters.

However I am concerned about vacuum gauges on the Racor fuel filters. It seems the gauges show how much suction is coming from the engine driven mechanical fuel pump.

*

If I install the electric pump it will be at the fuel tank and that will place the Racor fuel filters between the electric pump (which will be pushing fuel to the engine) and the mechanical engine mounted pump (which will be sucking fuel to the engine).

Will this cause the Racor vacuum gages to read incorrectly?

 

[Marin]

If your objective is to have an electric pump to use in case the mechanical pump fails, I would think you would want the electric pump to be be in the same position (in the fuel schematic, not physically) as the mechanical pump. So if the mechanical pump fails the electric pump can be used to bypass the mechanical pump and feed fuel to the engine. Sort of like the electric fuel pump in an airplane (I assume you fly a Maule which I think uses a Lycoming engine?) which is there to supply fuel if the mechanical pump fails.

From your description of what you're proposing to do it sounds like the electric pump would be at the tank sending fuel to the Racor which is then supplying the mechanical pump. So if the mechanical pump fails, I'm not sure what the electric pump is going to do for you since it sounds like the failed mechanical pump will still be in the fuel line to the engine.

So logic tells me-- based on your description--- that you want the electric pump afer the Racor but plumbed around the mechanical pump and back into the fuel line going to the injector pump or whatever system you have on the engine that gets fuel to the cylinders. In this position, the electric pump will be pulling fuel through the Racor same as the mechanical pump and the function of the vacuum gauge on the filter will be unaffected.

I assume you would need valves in the lines so you could shut the feed to the mechanical pump and open the feed to the electric pump but advice regarding this is best left to someone like RickB who really understands fuel systems. I'm not the one you want to talk to about that sort of thing

 

[markpierce]

Aaaaaahhhhhhh!

*Somehow managed to use the polisher system to transfer*diesel fuel*from the port tank to the lower port tank today!* (Valve settings were altered from what is pictured above.)

*


-- Edited by markpierce on Friday 15th of July 2011 11:30:27 PM

 

[MauleOne]

Wow!

Nice installation. Makes me want to clean up my whole system when I put in the electric pumps.

I appreciate the response and the pictures.

 

[MauleOne]

Note:

As to your comment about the Maule (great airplane) with the Lyc engine.

It does have electric and mechanical pump. The mechanical pump is double diaphram design to prevent fuel from entering the crank case if the primary diaphram fails and to allow fuel from the electric pump to pass to the engine.

Different design than my diesel engine mechanical pump which only has one diaphram and might allow fuel to pass into the crankcase if the diapgram fails and the electric pump is operating.

I agree with your idea of providing a bypass in the even the mechanical pump fails.

 

[RickB]

MauleOne wrote:
Nice installation.

*You can do a lot better than that kluge with a little thought and planning.

 

[sunchaser]

Why not carry a*spare mechanical pump? I'd be very dubious about an off the shelf generic electric pump to be used on a 24/7 basis. What does the engine manufacturer say about and recommend for an electric pump?

 

[Marin]

MauleOne wrote:
Note:

As to your comment about the Maule (great airplane) with the Lyc engine.

The Maule is one of the planes I have always admired.* I came very close to buying one back in the early 80s.* I like STOL airplanes so another one high on my list is the Helio Courier although I'm not fond of geared powerplants (we have one at Boeing and it is a funky machine indeed).* I fly a de Havilland Beaver (on floats) which, while not a true STOL airplane, does a pretty good job of getting in and out of small lakes.* The attached photo was taken by my wife when we were trying to get a photo for a magazine article.* Location is in the Coast Range in BC.


-- Edited by Marin on Saturday 16th of July 2011 12:46:12 PM

 

[Forkliftt]

Duane,
Do you really live at the North Pole??:smile:

What type of engine do you have?
I have Lehman 135's and have a small electric fuel pump on one engine after the Racor and before the CAV twin filters on the engine. It operates on a toggle switch and can be a real joy to have when bleeding. As I understand- you would like to use it for this and in the event of a mechanical pump failure. I would think it would work placed like mine is for that purpose. One concern however would be the type of failure your mechanical pump had. Most operate with a diaphragm that is moved up and down by an arm that pivots on the pump housing and rides on a dedicated camshaft lobe. There are also two spri g loaded check valves opposing each other. If a check valve were to fail due to trash or a worn sealing area the electric pump should be able to push fuel through and keep you running. The other common failure would be a ruptured diaphragm. If this happens the diesel would push through the pump into to crankcase. That would be very bad!!
Possibly you would want to have a spare hose fabricated that ran from your electric pump to the engine fuel filter?

 

[Capn Chuck]

Racor filters are designed to have the fuel pulled through them and not pushed. In addition, you have no protection for the pump by having it before the filter. We ran an electric pump on our previous boat, after the filter, for 7 years and thousands of miles of motoring with no issues. Chuck

 

[RickB]

MauleOne wrote:
I want to add electric fuel pumps to my fuel system.

*Two small 3-way valves and the electric pump mounted close to the mechanical pump is all you need. It shouldn't take more than a couple short lengths of copper tubing.

In the event of a mechanical pump failure you just turn the two valves to place the electric pump online and the same action isolates the mechanical pump. Energize the pump and carry on.

 

[MauleOne]

Sunchaser

I do carry a spare mechanical pump but to install it I have to remove the exhaust. Not something I want to do at sea.

Forklift

North Pole, Alaska is right outside Fairbanks.

*

The Maule is a lot of fun but i never got it on floats. Now I have a Charokee 6 because the family likes being comfortable. I have flown a Beaver and they are certinally different.* Everything is done with flaps.

Thanks for all the advice. I never considered that Racor filters would not like fuel pushed through them. will change my plans.

The pump is an aircraft pump and will not run 24/7, only when needed.