Fuel Pump problem

Jimboscr · #1 10-19-2013, 10:12 AM

I have just done a fuel pump test and there is very little fuel being delivered by the electric fuel pump. It makes all of the right noises and after a couple of seconds sounds like it is loading up, and fuel is flowing out, but the amount of fuel being delivered is way below what is required and when I put my finger over the out flow I can easily hold it there as there is no pressure behind it.

I have sucked fuel through the system so I know there is fuel going through the fuel selector. However there seems to be a lot of bubbles. If I have an air lock somewhere how do I clear it?

My system is for a fuel injected engine. I have an Andair fuel selector and an Andair fuel pump and filter. The fuel comes from the chosen tank, through the selector and into the fuel filter. It then goes into the pump and on to the engine. After the fuel pump there is a "T" piece connected to a pipe with a non return valve which directs any excess fuel flow back to a point below the fuel selector, creating a circular flow for this excess fuel.

I would post a diagram of my set up, however it is in a word Document and I have no idea how to post it here. (I have enough trouble trying to post a picture)

I am open to the possibility I may have a design flaw in my system. For example should I have the pump before the filter rather than after?

Cheers

Jim

flyinga · #2 10-19-2013, 10:46 AM

Check for a suction leak prior to the electric fuel pump. Probably around the Andair valve. I had a similar situation due to some B-nuts that were not tight enough.

Jimboscr · #3 10-19-2013, 11:18 PM

O.k. I have managed to organise some pics. The 1st is the actual set up, the second is a diagram to explain the design and the third is a diagram of the whole system.

I would appreciate any suggestions as to why it is not pushing fuel at the required rate. wether it be the design or that I am overlooking something. I have checked all of the connections and they seem to be tight.

Thanks

Jim

P.S. why does the link rather than the photo come up on the page. I used the URL for the direct link?

flyinga · #4 10-20-2013, 09:43 AM

I assume that your "non-return" valve shown in your third picture is just a one way check valve. This needs to be some kind of pressure regulator that will not open until the required pressure is reached. The system will not reach required pressure until this pressure regulator is installed. Basically, as drawn, you are just circulating fuel from the pump through the T fitting back to the selector valve. If your "non-return" valve is a pressure regulator; forget the above.

Don at Airflow · #5 10-20-2013, 11:56 AM

I do not see why you need the check valve in this system. It's installed the wrong way anyway. If this is a fuel injected installation, remove the tee and check valve on the outlet side of the pump. The PX375-TC Andair pump has an internal check valve (allows fuel to free flow through the pump when it is off) and an internal pressure relief valve to set the pressure to the system when the electric pump is running.

Don

Jimboscr · #6 10-20-2013, 05:47 PM

I will remove the non return valve ( block the apprpriate lines too) and see what happens. However is it o,k, to have the fuel filter before the pump? I was thinking that this is perhaps part of the problem.

Jim

Robert Anglin · #7 10-20-2013, 05:58 PM

You can not build any pressure if you have an open return between the discharge of the pump and the engine. If you have return fuel it will come after the engine has regulated the upstream pressure and in most cases go's back to the tank through the bottom half of a douplex fuel valve. In some cases it is returned to the feed line side of the pump. I like it to go back to the highest point of the tank that you are feeding from at the time.
Yours as always R.E.A. III #80888

Jimboscr · #8 10-21-2013, 07:40 AM

Thank you for the replies. The collective wisdom on this forum is astounding. All of this information really gives me something to go and work on.

Cheers

Jim

RV8 Tom · #9 10-21-2013, 10:09 AM

Jim,
I had a similar problem so much that I could not get my mechanical pump to work. After trouble shooting for hours, I found the the top nut on my verticle fuel filter was not 100% tight and would allow just enough air to disrupt the fuel flow. I almost re-piped the whole system.
Hope things work out for you,

Tom Ellis
New Lenox, IL
RV-8
T-51
Rotorway162F