Mailing List flyrotary@lancaironline.net Message #63259
From: steve Izett <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fuel Pump current and pressures
Date: Sat, 25 Mar 2017 08:23:05 +0800
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
I thought about reducing electrons but like you thought it just introduces another failure mode to a critical path.
Thanks for the feedback re mode of reducing the electrons. I could place a series resistance to drop voltage but we would be generating a bunch of heat.
Steve
On 25 Mar 2017, at 3:36 am, Charlie England <flyrotary@lancaironline.net> wrote:

Good point. The GSL393 (lower volume) is what RWS (Tracy) was selling before he retired. 

FWIW, I toyed with the idea of using electronic pump control (PWM) to eliminate the need for a mechanical regulator. I called Walbro's tech line & he said that we shouldn't use PWM (which is fine on turbine style pumps) with gerotor pumps because the constant square wave pulsed supply voltage 'hammers' on the gears in the pump & greatly reduces life. But he went on to say that it's perfectly ok to run the pump at lower voltage to reduce the flow. So it's possible to insert an adjustable DC power supply in the supply to lower its output. Not necessarily recommending this, since it might introduce other 'issues' (reliability being one), but there you go....

Charlie

On Fri, Mar 24, 2017 at 2:11 PM, Steven W. Boese <flyrotary@lancaironline.net> wrote:

Steve,


Examining the Walbro pump specifications at:

https://walbrofuelpumps.com/walbro-gsl-series-universal-inline-fuel-pumps

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


From: Rotary motors in aircraft <flyrotary@lancaironline.net> on behalf of Charlie England <flyrotary@lancaironline.net>
Sent: Friday, March 24, 2017 12:24 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Fuel Pump current and pressures
 
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



On 24 Mar 2017, at 8:56 pm, Charlie England <flyrotary@lancaironline.net> wrote:

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

On Fri, Mar 24, 2017 at 4:14 AM, steve Izett <flyrotary@lancaironline.net> wrote:
Hi Guys
Hi Peoples

Here is a photo of our parallel pumps plumbed with 3/8 aluminium lines feed from a 28 gallon header tank above to the right.
Fuel then passes through the firewall and race filter before feeding the rail and returning via the pressure regulator (4cyl toyota reg) 
back through the firewall to the header tank, again in 3/8.

I did further measurements today. 

1. Bottom Pump only ~8A and 48psi - Turning both pumps on this pump draws 9.9A and produces a rail pressure of 65psi
2. Bottom Pump only ~9.9A and 44psi - Turning both pumps on this pump draws 14.8A and produces the same rail pressure of 65psi

So bottom pump goes from 8.0 -> 9.9A (1.9A increase) under higher head pressure
Top pump goes from 9.9A -> 14.8A (5.1A increase) under same head!!

Clearly Pressure Reg bypass capacity is inadequate for both pumps, perhaps with even one pump running. 
(I don’t have data of fuel pressure under load to see if it drops as power is applied)
I think I modelled the pump layout/manifold after seeing someone else’s and not sure if it causes any problems?
The pumps came from eBay stating that they were genuine Walbro and now I’m wondering.

Cheers

Steve Izett
Glasair Super II RG Renesis 4 port RD1C EC3 EM3 





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