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bubbles in the fuel line
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Anyone used the Orbit clunk? Was it OK?
I used one for the first time in a new own design model recently, feeding a Wren MW54 mk3 from a 2 litre tank. At all throttle settings it tended to draw bubbles, even when the tank was full. Where could they be coming from? I changed the tubing, I changed the brass fittings and the tank stopper, I wire locked all the connections, but still I was drawing bubbles all the time, and I had 3 or 4 flameouts in flight. Then I removed the Orbit clunk and fitted a pleated paper one from Mick Reeves and the bubbles stopped and I've had a dozen flights without a flameout. That made me think it could be the clunk, but where did it manage to find air bubbles in a tank that was full of fuel, and the pipe and clunk were wholly submerged, and there was no frothing in the tank????? |
RE: bubbles in the fuel line
ORIGINAL: alasdair Anyone used the Orbit clunk? Was it OK? I used one for the first time in a new own design model recently, feeding a Wren MW54 mk3 from a 2 litre tank. At all throttle settings it tended to draw bubbles, even when the tank was full. Where could they be coming from? I changed the tubing, I changed the brass fittings and the tank stopper, I wire locked all the connections, but still I was drawing bubbles all the time, and I had 3 or 4 flameouts in flight. Then I removed the Orbit clunk and fitted a pleated paper one from Mick Reeves and the bubbles stopped and I've had a dozen flights without a flameout. That made me think it could be the clunk, but where did it manage to find air bubbles in a tank that was full of fuel, and the pipe and clunk were wholly submerged, and there was no frothing in the tank????? there has been lots of disscusions about this particular clunck do a search.. |
RE: bubbles in the fuel line
Restricted fuel supply:
I was using one in my kero supply tank, worked fine when new..after a period of time pumping / air bubble problems showed up in the fill line. Cut it off added a different large port brass clunck added some nylon stocking material for filtering.. problem solved. I believe the orbit filter screen material causes too much restriction..which causes pumps to pump slowly and pumps don't like that!!! I never have used one in the aircraft fuel system...switch to a UAT for the final draw tank, use open brass clunck(s) in your tank(s)..your problem will go away. Lee |
RE: bubbles in the fuel line
http://www.rcuniverse.com/forum/m_7798607/tm.htm
Was a thread I started about the same problem from a felt clunk. Lots of opinions. - John. |
RE: bubbles in the fuel line
Cavitation can occur across a pressure differential; this condition can allow the entrained gas bubbles in the fluid to expand into the flow stream causing slug air bubbles.
In other words the clunk can be causing a restricted flow which can lead to cavitation. |
RE: bubbles in the fuel line
I had the exact same problem using an Orbit clunk with my Wren XL 200. Problem solved by changing to a felt clunk, Tillotson, from Digitech. Orbits work fine, very well, with small engines.
Regards, David Gladwin |
RE: bubbles in the fuel line
Thanks guys,
Sounds like I'm not the only one to have problems. From this and other threads I gather that the bubbles are from air/gas dissolved in the fuel and coming out of solution because of the drop in pressure. I'll try to stick to pleated paper pickups in future. Maybe that's why the full size use tank pumps submerged in the fuel. Alasdair |
RE: bubbles in the fuel line
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Hi!
Seems clear that the smaller surface area Orbit clunk is not suitable for large (over 20lbs?) engines - but how about the larger clunk, see attached pic. Asking your expert opinion because I have one already installed...also UAT...P200...not run with this setup yet... Btw. this larger Orbit clunk has over four times the membrane area compared to the clunk in question in previous posts! So what say you - GO or NO GO?? |
RE: bubbles in the fuel line
What say me? Me say U please test run it on the ground at full power and let us know if you had bubbles. If it does OK on that big ole 200 then it should be fine for the rest of us too!
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RE: bubbles in the fuel line
Roger that! Me test run. Will tell.
Unless someone else has already seen it, been here, done that!? Or something... |
RE: bubbles in the fuel line
Guys,
Be careful. It is not only the membrane that is restrictive on the smaller clunks. If you cut one up you will find that the holes in the metal core of the clunk are also very small and that contributes to the restriction that is causing the problem. I have not sectioned the larger one to have a look but it might be a good idea to sacrifice a pickup in the name of research rather than potentially sacrificing a jet. The membranes also clog up very quickly over time due to microbial growth within the membrane. Some of them run ok for a while but will quickly become sufficiently obstructed to cause a problem even if they do not create one immediately. Craig. |
RE: bubbles in the fuel line
ORIGINAL: Craig B. The membranes also clog up very quickly over time due to microbial growth within the membrane. Some of them run ok for a while but will quickly become sufficiently obstructed to cause a problem even if they do not create one immediately. Craig. Using fresh Jet A1 from nearby airport, oils like everybody else - Exxon, Aeroshell, DTE Ligth etc. |
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