On 26 Mar 2017, at 10:05 pm, Charlie England <flyrotary@lancaironline.net> wrote:

I'm not aware of any made for inline use, since they won't self prime.

If your existing tank has a flat side or bottom surface, could you just cut a port big enough for a pair, and mount them on a cover plate? That's what I'd have done in the RV-7's wing tank, but there just wasn't room because of the tank's shape (wing leading edge).

Of course, the simplest thing is to 1st check that pump for proper operation, and then get a high capacity regulator. 

On Sun, Mar 26, 2017 at 8:16 AM, Stephen Izett <flyrotary@lancaironline.net> wrote:

Hi Charlie

In retrospect I’d seriously consider building the 18 Gal header tank to suit a couple of submerged pumps.

As my pumps live below the header tank perhaps I could use turbine pumps, but does anyone make them for inline use.

Cheers

Steve Izett

On 26 Mar 2017, at 3:52 am, Charlie England <flyrotary@lancaironline.net> wrote:

I'd say the Walbro is the 'gold standard', but there are plenty of others out there. If you could get into your header tank, or have room for an additional small 'sump', you could try this type:

http://www.ebay.com/itm/360843503639?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

(Not saying to use a $12 pump; just this style of pump.)

I considered this style for my in-tank pumps, but they must be mounted vertically, and would have interfered with the float of the fuel level sender.

Variations on this are in almost all new cars, but in the gas tank. That one is ~1.5 inches diameter & ~4.5 inches tall. Supposed to draw around 4 amps, so likely to be lower flow than any of the gerotor pumps. Walbro makes one that's about the same size, for typically around US $80-$90. They're turbine pumps, so the bottom must be in fuel to prime. No easy way to attach an input, except the purpose-made filter sock.

There are complete after-market assemblies (single pump, filter sock, surge housing, 40-240 ohm fuel level sender, and cover plate with both fuel & electrical connections, for around US $30-$50.

Charlie

On Sat, Mar 25, 2017 at 7:31 AM, steve Izett <flyrotary@lancaironline.net> wrote:

Thanks Steve

Really appreciate your helping me with this.

Is there an option other than the Walbro GSL393 or is this the recommended inline pump at present?

Thanks

Steve

On 25 Mar 2017, at 3:11 pm, Steven W. Boese <flyrotary@lancaironline.net> wrote:

Steve,

It is quite likely that getting your fuel system to behave would not involve looking at more than can be seen in the photo of the pumps that you posted.

Your item 1 would most likely be resolved if pumps of lower flow ratings were used.  The stock RX7 regulator is very similar to the one you are using and has worked well with those smaller pumps.

Item 2 may be a result of the pump with the higher current draw having more internal friction causing a load on the motor in addition to the load from pumping fuel. 

The additional load would slow the motor down resulting in less flow and lower pressure.  It is possible that the decreased flow allows the regulator to control the pressure at 44 psi.   Otherwise there may be a constriction either within the pump or in the flow path somewhere before the point where the flow of the two pumps are combined.

Item A is unlikely to be the case since if the seat in the regulator hadn't been broken, there would be no flow, thus stalling the pump and causing a current draw of over 20 amps.

In item B, you are likely correct that the regulator cannot support the flow from the high volume pump, thus causing the rail pressure to be above the regulator's pressure rating.  It seems unlikely, however, that the pressure would drop with the engine running since there is so much more fuel circulating through the system (~70 gal/hr) than what the engine could ever use (~20 gal/hr) even at full throttle.

All this discussion is directed toward the pumps or the system downstream of them.  Consider also the system between the tank and the pumps.  Trying to draw 140 gal/hr with the two pumps through a single -6 line, and also through a 20 to 40 micron screen if one is installed as required by the pump manufacturer, would have to involve a very low pressure at the inlet to the pumps.  This seems to be a very good recipe for vapor lock.

Steve Boese     

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From: Rotary motors in aircraft <flyrotary@lancaironline.net> on behalf of steve Izett <flyrotary@lancaironline.net>
Sent: Friday, March 24, 2017 6:19:23 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Fuel Pump current and pressures

 

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

On 25 Mar 2017, at 3:11 am, 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

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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 

<Fuel Pres Pumps.JPG>