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Fuel pump question

R

Rivethead

Well Known Member
Does anyone know if when the airflow performance fuel pump is set up this way (see picture) and it is pumping in the overflow mode does it flow the fuel back through the line marked number 1 or does it also run fuel back through the line marked 2 which also would back flush the filter? also Does anyone know what the resistance to flow this type of filter places on the pump? (stock filter element)

fuelpumpquestion.jpg
 
Boost pump operation

Any time the boost pump is running you are returning fuel. On a 180 hp engine the return flow can vary from 35 GPH to 18 GPH depending on the power the engine is making. The return flow comes out of the blue colored valve and will go through the filter in the direction of normal flow through the filter. This is because the pressure on the outlet side of the filter is the same as the inlet pressure of the pump (a little lower), and the pressure at the inlet of the filter is the same as the tank feed pressure (a little higher). These two pressures are very close to one another but there has to be a pressure differential in order for the fuel to flow. It?s probably on the order of 0.04 PSID or less.

The filter flows over 200 GPH @ 2 PSID. Since your engine only will use 16-20 GPH at take-off power the pressure drop through the filter (when clean) will be less than 0.015 PSI.

Hope this answers your question.

Don
 
It exactly answered my question and shows me why I can't do what I was thinking of doing the way I was thinking of doing it. Don't ask I'm still thinking. Could be dangerous!
 
Rivethead

If Don at Airflow Performance can't answer your question on fuel systems--------there is no answer! The only connection I have with them is that I am a very satisfied customer! They are great guys there. I have been to their Facility to have a Bendix RSA-5 Fuel Servo worked on. They not only did the work while I waited, they bought me lunch. Customer service doesn't get much better than that!
 
Boost Pump

The gold valve is the swing check valve that allows free flow to the engine driven fuel pump when the boost pump is off. This valve closes when the boost pump is turned on to prevent back-flow through the boost pump. The blue valve is the pressure relief valve that sets the pressure to the system when the pump is turned on. Since the pump puts our a fixed amount of flow, the excess fuel flow that is not used by the engine is passed through this valve and re-circulates to the inlet of the fuel filter then back to the inlet of the pump (a pump loop if you will).

You should have had this explanation in the manual you received with the pump, with pictures too (which I don?t know how to post on here). If you don?t have this manual, just email me at [email protected] and I can email you a copy.

Don
 
Constant Use

Slightly off-thread but since Don is here........

I am contemplating dual Airflow pumps and eliminating the engine driven pump. Went through the effort of dual alternators for ignition so that concern is taken care of.

Question is, what sort of longevity could be expected for a single pump in continuous operation? Are they really rated for full time use or more for intermittant use as a backup?
 
Dual pumps

zav6a said:
Slightly off-thread but since Don is here........

I am contemplating dual Airflow pumps and eliminating the engine driven pump. Went through the effort of dual alternators for ignition so that concern is taken care of.

Question is, what sort of longevity could be expected for a single pump in continuous operation? Are they really rated for full time use or more for intermittant use as a backup?
Click to expand...

Give FRANKH a shout here. I believe he is already doing what you want to do. The pumps typically give good service. We have some that have over 2000 hours. Some give 50. It's hard to predict, but it has a lot to do with the installation and the filtration on the pump inlet. Also if your going to do a installation like Frank you have to get with us, because the pumps are configured special for that application.

Don
 
Picture which make things clear ... hopefully

Here is a picture, I hope it is this that Don mentioned:

AFP.jpg


Regards, Dominik
RV7A very slow
Switzerland
 
zav6a said:
Slightly off-thread but since Don is here........

I am contemplating dual Airflow pumps and eliminating the engine driven pump. Went through the effort of dual alternators for ignition so that concern is taken care of.

Question is, what sort of longevity could be expected for a single pump in continuous operation? Are they really rated for full time use or more for intermittant use as a backup?
Click to expand...

Duane,
These pumps were originally used on early fuel injected automobiles, so they are intended for constant operation. You are "good to go" with your intended use of them. I would "guesstimate" that their MTBF (mean time before failure) would be somewhere between 4,000 to 6,000 hours, based on constant use performance in automobiles. It may be even higher.
Charlie Kuss
 
Dueal electric pumps

Don at Airflow said:
Give FRANKH a shout here. I believe he is already doing what you want to do. The pumps typically give good service. We have some that have over 2000 hours. Some give 50. It's hard to predict, but it has a lot to do with the installation and the filtration on the pump inlet. Also if your going to do a installation like Frank you have to get with us, because the pumps are configured special for that application.

Don
Click to expand...

Hi Guys...I will post pictures of my system as soon a I get a minute.

I bought the presure relief valves from Don and I used NAPA pumps.

Built a pump/filter/pressure relief set up. Each one of these i instaled in each wingroot.

To run the left tank you run the left pump and vice versa. The Van's selector valve is used but it plumbed as an on/off valve...The valve has an extra port which allows you to do this.

To make the pump/relief manifold I simply welded a few fittings together from my local hydraulics store.

Pumps are rated to run continuously and have been doing so for close to 300 hours.

You will need two Andair non return valves from Van's and filter for each pump.

You could put both the pumps on the floor if you wanted to, but the engineer in me wanted a "hydraulically correct" solution...I.e pumps as lclose to the tank as possible.

I think Don and I were talking about specially configured pumps at one stage but I did'nt end up going that way...I.e I just used a standard NAPA pump.

I'll post my system pics ASAP...

Frank
 
Warning! DO NOT DISCONNECT THE WIRES !

I do not want to hijack this thread, but it is certainly related!

OK, call me stupid,...... I know!, I know! it is clearly stated in the manual that if you undo the electric wires to the pump, the warranty is void, but considering that these pumps normally do not break down and I am not going to send a pump back from Belgium to the USA to be repaired and the fact that I am stupid, I still undid the wires to make the connections without a splice, directly to the pump. Guess what happened? Right, I snapped one of the studs right off, beyond repair!

So, for anyone reading this, do not undo the wires, but make a splice. I thought my inspector would not like to see the splice if it is not really necessary, but this is going to cost me a couple of hundred $!

I hope this keeps others from making the same mistake.

Regards, Tonny.
 
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