Fuel pump question
 

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)

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!

So what does the valve on line two do (gold).

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 airflow2@bellsouth.net 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
 

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:



Regards, Dominik
RV7A very slow
Switzerland

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