|
|
The "check" valves you mentioned aren't actually check valves. Check valves have a very low cracking pressure (0.5-2psi) and are intended to basically free flow in one direction and block flow in the other. These valves are called secondary bypass valves and they open at 50psi, just a bit higher than our regulated pressure. They serve several purposes... first, without them when it's time to switch tanks and you turn on the pump you'll be switching to, that pump's full pressure is dead-heading against the body of the selector valve, not good for the pump, and if you don't switch immediately you'll blow the breaker (don't ask me how I know). Second, hi-pres pumps don't typically have an internal bypass, so the pump's full pressure pushing on the body of the selector valve makes it very difficult to switch tanks for anyone with less-than Popeye arms. Third, the pressure buildup against the valve without them causes a sudden spike in fuel pressure when the selector is actually switched and can cause a very-rich-followed-by-lean condition as the FP regulator deals with the spike and then its absence. The whole idea is to keep the fuel pressure on both sides of the selector valve within reasonable limits to facilitate the several things I've mentioned above (and probably more).
All I can tell you is that I wish I'd put them in in the first place.
<Marv>
"Barnhart" <dsbarno@vbe.com>:
Marv,
What is the function of the check valve between the feed and the return line?
I have my return line running straight back to the tanks from the regulator
on the fuel rail.
Barny
MGDQ 20bt
----- Original Message -----
From: Kelly Troyer
To: Rotary motors in aircraft
Sent: Thursday, November 11, 2004 7:21 PM
Subject: [FlyRotary] Re: EFI stuff
Marv,
Thanks a million .......My fuel system is now finalized.......The rest of
the
group could do themselves a favor and copy as much of your fuel system
as will work for their respective projects!! Very professional and well
thought
out . The JPG's print out very well.
Thanks again,
--
Kelly Troyer
Dyke Delta/13B/RD1C/EC2
-------------- Original message from "Marvin Kaye"
<marv@lancaironline.net>: --------------
> HI Kelly,
>
> No, I just accepted their 50psi number... our fuel pressure seems to run
> around 40-43psi (as set by the engine manufacturer) so even if they're
off by
> -10% we'll be ok.
>
> I've saved the picture as several JPGs... it still might be hard to
read,
> though, as the only print on it is very tiny. I hope you can piece it
> together so it makes some sense.
>
> keltro@att.net (Kelly Troyer):
>
> Marv,
> Did you opt to pay the extra $20.00 per valve to have them flow
> and pressure tested for the exact cracking pressure ? Also can you
> resubmit your fuel system schematic in other than DXF which I cannot
open ?
>
> Thanks,
> --
> Kell! y Troyer
> Dyke Delta/13B/RD1C/EC2
>
> -------------- Original message from "Marvin Kaye" :
> --------------
>
> > No problem, Kelly... sharing and solutions is what we're all here for.
BTW,
> > the valves that I ordered are their part number 3156. It's a hard
anodized
> > aluminum housing with -6 AN flares, looks just like a check valve.
Difference
> > is that check valves typically have cracking pressures from .5 to 2
psi...
> > this one opens at 50psi (to work with an EFI system that operates at
45.) You
> > can find it three items down the middle column at the top of page 35M
in
> >their
> > online catalog (better to download their complete PDF catalog, only
about 7mb
> > and pretty quick on broadband). They've got _WAY_ too many cool things
for
> > EFI to not include them in one's list of resources.
> >!
> >
> >
> > PS... if you'd like to see the fuel system schematic I'm attaching a
copy of
> > the DXF file for those of you who have some kind of cad capability...
Need
> > to get out to the airport and find out why the gearbox oil pressure
was
> > indicating zippo at the end of yesterday afternoon's run. Taxied the
IVP
> > around Deland airport a bit late yesterday afternoon... woo-hoo, wish
it were
> > mine.
> >
------------------------------------------------------------------------------
This message scanned for viruses by CoreComm
------------------------------------------------------------------------------
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
_____________________________________________________
This message scanned for viruses by CoreComm
------------------------------------------------------------------------------
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
_____________________________________________________
This message scanned for viruses by CoreComm
|
|