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Engine basics => Engine set up tips => Topic started by: RknRusty on November 07, 2013, 08:17:27 PM
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I recently made the switch from a wedge tank to a 4oz Dubro clunk tank to feed my OS FP 35. I have a pressure line from the muffler to the uniflow vent. It runs very well and I like it much better. But after I fill the tank, while I'm waiting my turn to fly, I don't want the fuel dribbling through the pressure line, so I've been clamping it, but wondered about putting in a check valve. I've seen people do this with backplate pressure lines on Tee Dees, but I wondered if the one way valve could cause too much pressure to build up in the tank. Of course, the volume of fuel is dropping as the engine runs. Does that completely offset the buildup? Will the valve affect my run, or should I see any difference with or without the valve?
Thanks.
Rusty
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I have this problem, too.
- Lots of people seem to feel that you don't need uniflow if you're on muffler pressure. Certainly the planes I have on Hayes tanks seem to work OK. So, you could use a 'conventional' tank.
- You can aim your uniflow upward and use a generous-sized pressure line, so that a siphon can't get established.
- You could unhook from the muffler until you're ready to fly
- You could leave the vent unplugged until you're ready to fly
- You can be vigilant, and make sure not to fuel until right before you fly
I use a combination of the loop in the pressure line and being vigilant. So far it mostly hasn't been an issue, but I've had problems with the fuel in the pressure line starting a siphon on a cool morning with the bright sun pushing a lot of fuel out and then the siphon taking over and filling my muffler with fuel that I needed to fly with. So far its only happened in practice and I could just squirt some more fuel in the tank.
I think a check valve would present all sorts of problems, starting with the fact that you'd need one with very little back pressure that could seal well, all while being very light and being able to withstand vibration and rough handling.
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......I think a check valve would present all sorts of problems, starting with the fact that you'd need one with very little back pressure that could seal well, all while being very light and being able to withstand vibration and rough handling.
Yep, that's kinda what I thought. I don't want to change the configuration since it works so well, from steady run to cutoff. I'll just get an inline clip for it so I don't have to mess with the hemostats. I'll swipe one from dialysis in the morning. :!
Thanks, Tim.
Rusty
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There's a little gizmo that is/was made specifically for this sort of dilemma. I attached a picture below. It seems to me that it was made by Fourmost Products, but their website is in limbo not having renewed their domain, funds due end of October 2013. I hope they just forgot, 'cause they made some neat stuff, including those little check valves... H^^ Steve
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Yep, that's kinda what I thought. I don't want to change the configuration since it works so well, from steady run to cutoff. I'll just get an inline clip for it so I don't have to mess with the hemostats. I'll swipe one from dialysis in the morning. :!
Thanks, Tim.
Rusty
Howard's idea of a loop is more-or-less what I have. I would never use hemostats on silicone fuel line. There's too much potential to nick the line. Although my World Champion buddy does it all the time.
Brett
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I use stubby toothless plastic hemostats. I have a bunch of them for my pressure bladder applications. Pinch it too close to the hard line and you'll rip the silicon tube anyway.
(http://i166.photobucket.com/albums/u116/rknrusty/Airplanes/708f553e-a971-4fb3-8161-400834ec8258_zpsfa75bad2.jpg) (http://s166.photobucket.com/user/rknrusty/media/Airplanes/708f553e-a971-4fb3-8161-400834ec8258_zpsfa75bad2.jpg.html)
That Fourmost clip reminded me, I could use a spring steel fishing leader clip like so many people connect their leadouts with.
Like this one:
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How about just waiting until you're ready to fly to fuel up? Just a thought...
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How about just waiting until you're ready to fly to fuel up? Just a thought...
When I'm flying for fun and fooling around, it's not an issue.
But at a contest, I want to have that out of the way and done when the judges are ready for me to carry my plane and lines onto the circle. Maybe when I'm more accustomed to the contest environment I can cut it closer. For now, my practice flights follow the same routine as when it counts.
Rusty
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I think you're being over-anxious, at least if you do the "loop up and over" thing on the muffler pressure line. When the guy in front of you starts flipping his prop you have time to recruit a pit crew (if necessary), fill the tank, walk your lines out for twist and dirt, and get a little bit bored before he lands. Your worst concern is that your pit crew may forget and wander off.
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There's a little gizmo that is/was made specifically for this sort of dilemma. I attached a picture below. It seems to me that it was made by Fourmost Products, but their website is in limbo not having renewed their domain, funds due end of October 2013. I hope they just forgot, 'cause they made some neat stuff, including those little check valves... H^^ Steve
They may be out of buisiness. My local hobby shop told me that the filters were no longer available.
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I think you're being over-anxious, at least if you do the "loop up and over" thing on the muffler pressure line. When the guy in front of you starts flipping his prop you have time to recruit a pit crew (if necessary), fill the tank, walk your lines out for twist and dirt, and get a little bit bored before he lands. Your worst concern is that your pit crew may forget and wander off.
Over anxious, probably so, since I've only been there once. I'll get the hang of it. I haven't gotten to the part about being bored yet.
They may be out of business. My local hobby shop told me that the filters were no longer available.
Someone mentioned that in another thread. I have a couple of Fourmost check valves, and use their filters on my smallest 1/2A bladders like the Li'l Satan where there's barely enough room to fit it all.
Rusty