Mailing List flyrotary@lancaironline.net Message #63734
From: Charlie England <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fuel system diagram
Date: Fri, 1 Sep 2017 17:09:40 -0500
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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A little late, but you could have simplified the system a little bit by plumbing the tip tank directly to the outboard aux, on the premise that if you're undertaking a truly long flight, you'd never want to fill just the mains and the outboad aux's, without filling everything. At that point, you could use the 'turbine' principle, as Tracy did, and I intend to use on my -7. One main tank feeds the motor through redundant injection pumps on the cockpit floor (no valves in the fuel delivery to the engine). Single return to main supply tank (or loop it to the pump input, if you want; that's what certified injection boost pumps do). If you keep the regulator in the cockpit, then bypassed fuel is never heated by the engine compartment. With only high pressure fuel in the engine compartment, it's virtually impossible to vapor lock (think every car on the road these days). No need for check valves or main fuel shutoff valve; the Walbro injection pumps completely block flow when not running. No need for Facet boost pumps; the pumps always have 'head'. A single Van's (Spruce) 3-in/1-out selector could select left outboard, right outboard, or 'main aux', and feed redundant transfer pumps.  

Purge solenoid valve: The Lyc guys use purge valves on one brand of dribble injection 9~20-30 psi), because of persistent vapor lock issues. Don't recall if it's solenoid or cable operated, but I'd consider a mechanical valve for this use a plus. :-) If you want, I'll try to find the source for it.

Something to consider if any of your low pressure stuff is forward of the firewall: Hot air from the motor itself will probably be cooler than a Lyc, but air around the exhaust is another story. *Many* RV's have issues with vapor lock due to having low pressure fuel lines forward of the firewall. (Want to hear about my incident with my carb'd, Lyc powered -4?) I just had a long conversation with my neighbor (A&P who has built an RV & multiple other a/c) about an RV-7 he's currently working on. The builder (apparently some Yankee who never saw hot weather  ;-)  ) mounted an Andair gascolator low on the firewall, followed by the Weldon (certified) injection boost pump, which then feeds the engine driven injection pump. The plane consistently vapor locks while on the ground when the cowl's on it. Boost pump doesn't help. He's about to rip out the fuel system for the owner, & move the boost pump & final filter into the cockpit, where they belong. Obviously not going to be cheap for the new -7 owner, but less expensive than scraping it out of the trees....

FWIW, and worth what you paid... :-)

Charlie

On Fri, Sep 1, 2017 at 3:09 PM, Todd Bartrim <flyrotary@lancaironline.net> wrote:
Good Morning;
I have considered a duplex valve and I think for those using only 2 wing tanks it's the best solution to return fuel to a tank. Unfortunately it doesn't really help me to easily draw from and return fuel to 6 tanks. There are creative ways that I could incorporate it into the system and I spent a lot of time thinking about it, but they all end up being complex.
    The main selector valves I used were these ones (#05-01033) from ACS
As they allow for selecting from 3 tanks with no "both" position. I used 2 of them, one for each wing. I'm able to select from 2 tanks (one from either side) but normally leave one in the "off" position while selecting one of the tanks from the other side. Functionally, it works great and I have my head wrapped around it just fine, however it may seem slightly confusing to others. But should I care? I never built this to sell. If I did I would have put a Lyc in it. I honestly can't see myself ever letting this plane go flying without me on-board. Which brings up another important topic for another thread, so I'll not go there now.
   Long ago I met an interesting guy with 6 tanks on his RV-6 and he machined his own 8 position selector valve. It can be seen here on this google drive link.
He gave me the CAD file that he'd drawn so that I could make my own. It can be seen at the link below for those who are interested. You will need a CAD program to view it.
This really would be the better solution, but you would need to be a machinist to make your own. I do have access to a machinist at work but I've used his services a lot already and try to save my favors for stuff that really matters... like the PM generator project. I also have long thought about buying my own small metal lathe and this would be a great project for that.
  I don't seem to have any good pics showing my valving arrangement inside the console so later today I'll open that up and get some pics. 

Andrew, I would like to see some pics of your header arrangement if you can post them. Not that I could copy that idea at this point, but I am interested in seeing it.

   I was going to agree with Andrew, in that if I was building today, then each tank would have it's own in-tank pump. But it just occurred to me that the problem with that, is that those pumps don't last long when run dry. So that would mean that you'd always have to switch from your auxiliary tanks before they were empty. So you'd be carrying around the extra weight of a pump in each tank as well as unusable fuel in each tank. And it would be hard to know just when the fuel was at it's lowest safe level. By having an optical sensor in the line right at the tank outlet, then you know the moment that tank is run completely dry with no unusable fuel at all. I should stress that this only applies to auxiliary tanks, as the main tanks should obviously never be run dry. Here's a couple of pics showing how I put the Gems sensors into the fuel lines at the tank outlet.

   Another way to do it would be to have an in-tank pump in one main tank having only that tank feed the fan, then each auxiliary tank transfer fuel to that tank via it's own facet pump. But for me that would bring back the concerns about transferring fuel, even though they may not be legitimate enough to worry about.

At this point, while I would love to improve my valving arrangement by building the 8-position valve, I am satisfied with it and my previous flight experience with it shows that it works fine with it's only weakness being it's confusing at first to others.
  The thing that concerns me is the new stuff that I've not flight proven, such as the new fuel filter/water separator, and my choice to return my regulator directly to this filter. Should I route this return fuel back to a main tank like the way Dave has done it. That's a good proven solution, that requires vigilance to ensure fuel isn't pumped overboard. But is it safer than this where I don't have to worry about fuel going overboard, but is there a reasonable chance of excessive fuel heating?
   And going to a single large filter. Previously, I had 2 separate filters for better redundancy, but I felt even that probably this single large filter was a better choice. And as a bowl type cartridge right at the low point of my firewall, it will be much easier to access to change filters.
   
  The fuel purge solenoid valve. I decided to use a double block valve arrangement for this, using one manual isolation valve and one automatic valve. The manual isolation valve is there in-case the automatic solenoid valve leaks by. The automatic solenoid valve is there as it's configured as a momentary-on so it can't be inadvertently left open. My concern with this is in the choice of solenoid valve. I don't want anything big & heavy. Small and light are prerequisites.
This is what I decided to use, based on personal experience with them. I had a couple of spares at work from some obsolete samplers. We had 6 effluent samplers with 2 of these valves in each of them, each valve cycling twice, every 15 minutes, 24/7 for at least the last 17 years that I've been an instrument mechanic there and possibly much longer and I only ever changed out one of these solenoids that I can remember. The pump was the common failure. They are meant for only air, but they were in a dirty environment and would occasionally see effluent through them and they seemed to tolerate it well. They are rated for up to 120 psi.

  But how well will they tolerate fuel? I can't find any info on that. But just because they are not rated for fuel doesn't necessarily mean they won't tolerate it. But it's an unknown. So this is one reason for the manual isolation valve. But there is still the concern of a leak through the housing. Many spool type solenoid valves can be easily disassembled to change the o-rings to a Viton o-ring, but these can't easily, without damage. These are a balanced spool design so pressure can't open them. So long as the seals don't wear, they hold well.
   So here I am experimenting again. If I could find a more suitable valve, I would, but the only 12v fuel selector valves I can find (and I even bought one that I have here) are only rated for a maximum 6psi and are meant to be on the suction side. What are the consequences of failure here? These valves can't blow apart, by design. I think any possible failure would come in the form of a slow leak through the top coil housing, but there are seals here as well.

 So to summarize, my biggest concerns are;
  • regulator return to filter inlet
  • solenoid valve on purge line
And just because I'm concerned doesn't mean it won't work well. Doesn't mean it will either. 
Thoughts' comments' criticisms?

Todd    -- I just can't stop experimenting....


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