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2 Klunk/Pump Setup

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Old 11-21-2005, 01:42 AM
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Shubova
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Default 2 Klunk/Pump Setup

2 Klunk/Pump Setup.
Has anyone heard of this? An old timer showed this to me but I haven’t tried it yet to see if it really works. He said he read it in a RC magazine and uses it on all he planes.
It’s easier to understand if drawn out on paper so here it goes, stay with me.
Set up tank vent line as usual. Take the tubing that connects to the muffler and plug/cap it off.
The next line is set up like a standard fuel line with klunk at the end. Connect the end of this tube to the muffler then cut the tube at a convenient location and insert a check valve between the muffler and tank. I think the idea is that the check valve (engine running) allows air pressure from the muffler into the tank. (Check valve only lets fuel run one way.)
Last, set up another fuel line with klunk at end. Add a fueling valve to this line and connect to the carburetor.
I was told this is like a pump with continuous fuel flow.
Again I am asking if anyone has heard of this. I have not tried it nor am I sure the set up is exactly correct. And no I am not nuts!
Sensible feed back will be appreciated.
Bern
[8D]
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Old 11-21-2005, 09:53 AM
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Default RE: 2 Klunk/Pump Setup

I think what you are getting at is called a Uniflow system.....

The way I have mine set up is ......

fill line.... capped off except for fueling...

clunked line to muffler pressure tap (no check valve)
clunked line to carb....

thats it... works perfectly...
The check valve might be an option to build up pressure...but you would need to unhook the fuel line somewhere while fueling....

Search for Uniflow... is that what you are refering to?
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Old 11-21-2005, 10:32 AM
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Default RE: 2 Klunk/Pump Setup

I also cap the fill line rather than the vent line. However, I only run one clunk in the tank. I'm so used to running lines to the top for vent and the lower corner as the fuel pickup in my boat tanks that it seems natural to do the same for airplane plane tanks. I always align the stopper so the fill is at the bottom, carb in the middle, and vent on top.

Edit: had to fix the tank color, I run Omega, not Cool Power.
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Old 11-21-2005, 04:53 PM
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Default RE: 2 Klunk/Pump Setup

I use the same arrangement as does Piper Chuck, with one exception. I use a fuel line and a clunk for the fill as it will hard to empty the tank without a klunked line.

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Old 11-21-2005, 07:21 PM
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Default RE: 2 Klunk/Pump Setup

Fuel line from carb into tank goes to the clunk.
Pressure line from the muffler goes to the clunk and is attached to it's side about 1/2" short.
Vent line goes to top of tank and is only uncapped when fueling tank.

Fairly simple and easy to make. And it's the simplest uniflow setup.

There are variations that create a better setup for fueling, like with a t-line connection with check valve or such. The way the above is worked for fueling is that you pull the "stopper" on the vent line, then pull the pressure line off the muffler and fuel into there. When the vent line spits fuel, the tank if full. Put the stopper back in the vent line, plug the pressure line back on the muffler and crank that puppy up. Needless to say, you have to have access to the pressure line and the vent line for this to be an easy-to-use setup. And also needless to say, you can make it easier to use with some t-connections etc.

Uniflow works great. Having the muffler pressure blowing very near the fuel pickup in the tank sounds bad, but trust me, they've been working great for years and years and years.

Only special detail you need to keep in mind is that both the pickup line and pressure line will be attached to the clunk so the clunk is going to have to move two hoses with gravity. So make the interior hoses SOFT ones.

But truth is, in most RC aircraft, you really don't need uniflow. but if you have a plane that won't work well with the normal setup, the uniflow is easy to try for a fix and will very often help.
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Old 11-21-2005, 08:09 PM
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Default RE: 2 Klunk/Pump Setup

ORIGINAL: DaveB

I use the same arrangement as does Piper Chuck, with one exception. I use a fuel line and a clunk for the fill as it will hard to empty the tank without a klunked line.
Not at all hard, just make sure the nose is pointed a bit down. The tubing to the corner will let you drain the tank better than you can with a klunk.
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Old 11-21-2005, 08:12 PM
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Default RE: 2 Klunk/Pump Setup

ORIGINAL: darock

Fuel line from carb into tank goes to the clunk.
Pressure line from the muffler goes to the clunk and is attached to it's side about 1/2" short.
Vent line goes to top of tank and is only uncapped when fueling tank.
What's the theory behind putting the pressure on a line that sits in the fuel rather than just anywhere in the tank?
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Old 11-21-2005, 10:03 PM
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Default RE: 2 Klunk/Pump Setup

Chuckle chuckle.... not only does it sit in the fuel very close to the pickup location, but if it's in a plastic tank you can see bubbles blowing out as you run it (like on the bench breaking in). It really blows your mind to see it in operation, especially if you are skeptical of the whole deal to begin with (which I was years ago).

I still don't believe it works, but it does in spades.

The idea is sorta twofold.
First, the theory is that the pressure the pickup experiences is lots more constant that if the pressure is entering the tank far away. Only problem with that theory is that pressure is supposed to be constant everywhere according to high school physics right.
Second, the theory is that if the pressure input is from some place in the tank that is covered by fuel awhile and not covered by fuel awhile, the pressure experienced by the fuel pickup opening will fluctuate. Seems that high school physics teaches other than that as well.
Truth is that it works great and for whatever reason it really simply works great.

I sorta feel that the covered/uncovered deal is why it works. But don't worry about the why.

It really helps control line stunters because they encounter way more g-force in their 5' radius turns than most RC planes ever feel. But it really isn't a big deal in RC planes. I use both and both work good for RC.
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Old 11-21-2005, 10:59 PM
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Default RE: 2 Klunk/Pump Setup

Hay thanks for the feedback.
The comment about Uniflow system, I think nails it!

I went to towerhobbies.com and found a check valve. Here is their tech comment.
COMMENTS: This resembles and is about the same size as a fuel filter.
It is a "one-way" valve. This means that fuel or air will flow
through it in one direction only.
The end with the notch goes closest to the fuel tank.
It is used in line between the fuel tank and the engine to maintain
constant pressure by not allowing the fuel to back-feed into the
tank. It can also be used in the pressure line between the
exhaust and fuel tank to maintain constant pressure in the tank.
In this case, the notch should be closest to the exhaust.
Also some of you missed the part were I said to insert a fill fuel valve (with fueling probe) in the line to the carb.
Thanks
Bern
[8D]

PS: Hay piper_chuck, how did you insert the picture (attachment) in you reply?
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Old 11-21-2005, 11:46 PM
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Default RE: 2 Klunk/Pump Setup

Rereading the last couple of comments I realize that is why you would want to use a check valve between the exhaust and fuel tank, to maintain constant pressure in the tank, no pressure fluctuation. Seems logical constant pressure in the tank should equal constant pumping of fuel. The faster the engine turns the more fuel is needed. That’s why the old time said it’s like a pump.
Am I full of it or have I been enlightened?
Bern
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Old 11-22-2005, 11:21 AM
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Default RE: 2 Klunk/Pump Setup

Hi!
A check valve is not necessary! Just use the Uniflow set up with two clunks, one shorter than the other. The shorter one is for pressure from the silencer...the longer goes to the carb.
This system has been used by control line stunt people for decades and very few R/C people seems to know about it.

Regards!
Jan K
Sweden
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Old 11-22-2005, 11:35 AM
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Default RE: 2 Klunk/Pump Setup

thats what I do......

2 clunks, no check valve...

I do have a third line just for filling the tank, but that is capped off while flying
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Old 11-22-2005, 11:45 AM
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Default RE: 2 Klunk/Pump Setup

jaka,
You don't actually need to use two clunks if you use flexible enough hose inside the tank. Matter of fact, using separate clunks can cause problems. Just make sure that the hose is flexible enough that two of them going to the same clunk isn't so rigid that the clunk won't fall around the tank back.

If you stick a short section of rigid tubing into the end of the pressure hose that's in the tank, it provides you an excellent "device" that is easily strapped to the clunk. I usually have that rigid tubing stick out of the pressure hose enough that only the rigid tube overlaps the clunk. Then it's easy to either wire it on the clunk or use wire-bundling-strap (the plastic things we use for so many different jobs). Or if you're still using brass inside your tanks (not the best idea) and your clunk is brass and the rigid tubing is brass, you could solder them together, another neat installation.

The idea behind the uniflow is to lock the pressure outlet into an unvarying distance from the fuel pickup point. Obviously, two clunks should follow the same general paths, but just using one heavy clunk and two adequately flexible hoses works great and gives you the opportunity to lock the pickup and pressure outlet together.

And btw, in the old days, the CL stunt guys didn't use clunks. Almost none of us used anything other than tin tanks with brass tubing and it was all soldered into place. Rigid setups for sure. And... chuckle... most of us would recoil in horror at the thought of putting TWO lumps of weight into our planes when one lump was enough. And we'd probably trim that lump of clunk some to reduce it's weight... lol at us..... We didn't even like to put too much solder into the tanks when converting them.
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Old 12-02-2005, 12:47 AM
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Default RE: 2 Klunk/Pump Setup

Has anyone noticed high fuel consumption when using the uniflow system on an RC engine? From my experience fuel from the tank backs-up into the muffler when the engine goes from high RPM to idle. This fuel is not burned in the engine but just goes out the muffler. Has anyone noticed this?

Bob P.
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Old 12-02-2005, 07:32 AM
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Default RE: 2 Klunk/Pump Setup

Nope. Actually noticed the opposite and in a situation where the engine runs were VERY well monitored.

Tank plumbing used to be a very hot topic in CL stunt. Guys argued the best plumbing arrangement for years. And they often swapped out tanks quicker than they changed their shorts. And they'd swap them out from one flight to the next, so the test proceedure was one in which for once there was REALLY only one variable changed with an immediate re-test. And the engine run time was super critical, so the testing included a very strict check for how long the engine ran. It was basically life-or-death to have the engine run long enought to get through the cloverleaf but not run over the maximum flight length.

It didn't always happen that a uniflow gave better "mileage", but they often did.

Like everything else, it seemed to depend on a number of other things. What was the "other" tank? Did the engine's carburation or fuel draw or centerline or color or age or timing or prop nut size or..... whatever "like" any tank's draw better than it liked the other tank's draw or whatever.

BTW, put a good fuel filter close to the needle valve and you'll often see less differences in mileage, and more uniformity in about every aspect of how your engine is running. The filter "combs" out any foaming that gets that far. Sometimes....
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Old 12-02-2005, 07:45 AM
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Default RE: 2 Klunk/Pump Setup

From my experience fuel from the tank backs-up into the muffler when the engine goes from high RPM to idle. This fuel is not burned in the engine but just goes out the muffler.
BTW, if you're seeing raw fuel coming out the muffler on idle, it really shouldn't be coming from the pressure line. For the fuel to back out of the tank would require a couple of things. First off, it's really a long way from the pressure outlet in the tank to the muffler. And it'd take some pressure to push that fuel that far. And it'd have to do it against the engine's pressure that's reduced on idle but still measurable. And that pressure would have to come from somewhere, and the only external force would be from the line to the needle valve and that's sucking when the engine is running. It's possible that at full throttle the muffler pressure blows up a plastic tank and when the muffler pressure drops at idle the tank shrinks back and provides pressure, but that's really improbable. And you can easily check that out on the bench.

Raw fuel is part of the exhaust of almost all model engines. They're designed that way so the unburned fuel carries off a high proportion of the heat that's blown out the exhaust. There's a good chance you don't see it at high throttle since the exhaust is at high velocity. And some of the heavier solids might collect inside the muffler during your middle throttle running in the pits. Or during high speed running in the pits. And when you then chop your throttle the different exhaust velocity actually works better to push out those droplets.

It's not odd to see drops of fuel blowing out the exhaust at idle for some engines.
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Old 12-04-2005, 05:34 PM
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Default RE: 2 Klunk/Pump Setup

Darock, Thanks for the reply. I don’t know anything about CL, by engines are on RC planes where the throttle goes up and down. Here is what I see happening. First, I do not see raw fuel coming out the muffler on idle. After WOT, when muffler pressure is high, I then cut the throttle to idle, and then I see fuel backing up the muffler pressure line and into the muffler. Then when I advance the throttle again to or near WOT is when I see large amounts of raw fuel blowing out the muffler. While at idle the raw fuel just collects and stays in the muffler and the engine continues to idle nicely. I think there is too much muffler pressure from my engines. I have now used the uniflow system on three different plane/engine setups with this same problem of blowing a lot of raw fuel out the muffler. Also when I ran these engines on my test stand, with a clear see-through tank and fuel lines, I can see this phenomenon happening very clearly. The more muffler pressure I see at WOT the more fuel I see blowing back into the muffler when I reduce the throttle to idle.

I have a fairly accurate monometer (reads muffler pressure to within .01psi) and my engine /muffler combos are producing between .3 and .6psi at WOT and .03 and .05 at idle. Is this too much muffler pressure differential for the uniflow system? Should I just forget about using the uniflow system or try to reduce my WOT muffler pressure so I do not get this fuel blowback into the muffler?

Bob P.
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Old 12-04-2005, 06:01 PM
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Default RE: 2 Klunk/Pump Setup

I have a fairly accurate monometer (reads muffler pressure to within .01psi) and my engine /muffler combos are producing between .3 and .6psi at WOT and .03 and .05 at idle. Is this too much muffler pressure differential for the uniflow system?
Kewl.... Not ever have I seen anyone with such a tool using it on a model a/c engine, and especially not seen anyone who had stuck it into their muffler pressure line with the engine running. Amazing.... and fun to talk to someone using that sucker (pun? intended). (Can I borrow it? )

I've read that muffler pressure is normally in the pounds range, not less than a pound. And it really looks like your WOT pressure is out of the norm for what the books said. Also, I'm fairly certain that most 2 cycle model engines produce sufficient muffler pressure at idle to easily keep the pressure line pressured. Are the engines giving you problems 4 cycle? I'd figure they'd be the only ones that'd be able to cause the problem from the engine side of it.

There is also the possibility that the pressure tap is located badly. Where do you have it? If it's in the OEM placement, then you really have a baffling problem, but the problem shouldn't be with the muffler or pressure tap location in the system.
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Old 12-04-2005, 11:31 PM
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Default RE: 2 Klunk/Pump Setup

Actually this makes sense if you think about it. The exhaust at WOT is pressurizing the tank to its max pressure but that same exhaust pressure keeps the fuel from blowing back into the vent line and into the exhaust. Then all the sudden you drop the throttle back, there is pressure still in the tank and it can't go in the carb so it flows back to the exhaust for a short period. This is because the vent line is in fuel at the bottom of the tank. There is only one place for the fuel/pressure to go, back to the exhaust. Makes sense to me.
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Old 12-05-2005, 07:17 AM
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Default RE: 2 Klunk/Pump Setup

Except, I think that in reality, the negative pressure in the ventury (even at idle speeds) is greater than the pressures aerosman recorded. So even if the tank was pressuring the pressure line into that pumped up tank, that pumped up tank would be pushing fuel into the pickup line and the ventury would be pulling on that line as well. Which ought to/might possibly/maybe/could almost instantly kill any flow back toward the muffler. And it seems that the tank would have to be pumped to fairly high pressure for that pressure to overcome the pressure the muffler SHOULD be pusing into the line, even at idle, and the negative pressure from the delivery line. And the WOT pressure aerosman recorded isn't really much pressure. But who knows what the theory is that actually applies.

Because.... theory suggests that if there was residual pressure in the tank sufficient to force fuel back up the line to a muffler that's pushing back (no matter how little it's pushing back) then that same pressure ought to be pushing fuel at the carb when the carb doesn't want much at all, and one would think that would cause obvious engine idle problems.

I'm looking forward to aerosman's next posts.

BTW, aerosman, how far from the pickup point is the muffler pressure outlet? Normal uniflow theory suggests the muffler outlet hole be something like 1/2" from the intake pickup hole.
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