| I’ll remove the pumps to confirm the model and do some testing. In old notes I see I thought they were GSL392’s. The real obvious is as you show in your calcs, the volume of fuel heading back to the tank with both pumps running is huge. With a piddly little 150hp stock unit that probably has quite a small orifice for bypassing regulation, quite large pressures are going to build up. I have the two problems though. 1. Flow capacity of the regulator if I want to be able to run both pumps simultaneously. 2. The difference between the pumps currently. Why does one draw more current and produce less pressure?
What is causing the 4psi pressure differential: One of the pumps draws more current but the pressure has dropped from 48 to 44psi. Now either one of two things could bring this about in my thinking. A. The higher current pump is delivering very low fuel flow and so measures a rail pressure drop, meaning not enough fuel pressure/flow to break the regulator seat. But I think I can remember hearing fuel returning to the tank when either pump is running. OR B. The other pump is delivering at idle more fuel pressure/flow than the the regulator can cope with so is higher than the regulation pressure. So as the engine begins to use fuel the rail pressure would drop back to the regulator pressure. (I cant remember seeing this during engine testing, but I wasn’t looking for it and Ive deleted some video of engine monitoring).
Have I missed something?
Steve
Steve,
Examining the Walbro pump specifications at: and looking at the data for the individual pumps enables the following speculation. It is only speculation.
If you have GSL392 pumps, as are almost all of the pumps listed now on Ebay, they have a flow rating of 255 L/hr (70 gal/hr) at 40 psi and 8 amps. If your engine could use 20 gal/hr, that would still leave 50 gal/hr returning to the tank. With two of those pumps running at 65 psi
they should be moving 60 gal/hr each with each drawing 10 amps. If your engine was using 20 gal/hr, 100 gal/hr would be returning to the tank. This would seem to be moving much more fuel than necessary. Depending on where you are measuring the fuel pressure and the details of the fuel flow path, the pressure at the pump outlet (and the current draw) could be much higher with flow rates this high.
At these flow rates, your whole fuel system could be a constriction and any fittings (tee's etc) may have significant effects.
That is why it would be good to establish which pumps you are using either by identifying them or measuring their flow rates. GSL393 pumps (45 gal/hr at 40 psi and 5 amps) might be more appropriate for your installation if your present pumps have high flow ratings.
Steve Boese
Hey Steve,
Just re-read your post with the measurements, & I'm not sure which had higher current draw. It was the bottom pump, right?
Thanks,
Charlie
On 3/24/2017 8:06 AM, Stephen Izett wrote:
Good idea Charlie. That would clear it up as far as the manifold flow characteristics. Just a pain in the but to get to. Thanks Steve
Have you tried swapping the position of the pumps & making the same measurements? It's hard to imagine it making that much difference, but the bottom pump does have a tight right turn and then a sharp edged 'T' turn to the left. I couldn't guess how much, but that would account for at least some pressure increase.
Charlie
|