ORIGINAL: allanflowers
The pressure from the exhaust is determined by the engine and exhaust system and will be exactly the same, regardless of where the tube ends up in the tank.
I'm not about to get into another huge physics debate, so I'll say my peace and be on...
Your correct, the pressure from the exhaust IS determined by the engine and exhaust system, and it WILL be exactly the same... THAT is in fact, the entire PRINCIPLE that the uniflow tank works on...
WHAT EFFECT! that pressure HAS on the fuel, is another story... I hate to do it because I'm really just repeating what has been said on the site i mentioned earlier, but I'll try to word it a little better.... It's important to note in this example that while I speak of having 15psi, it is also STILL OPEN TO THE ATMOSPHERE... Much like our normal fuel tanks are... This means that while there is 15 psi of pressure, it can still draw more air in, and even at a faster rate if need be, etc.. Now.. If I have a tank that has 1 inch of liquid in it, and is has 15psi of pressure on it... I will get a specific flow rate from the tank... It will be VERY close to 15psi.... IF we take that same tank, still pressurized at 15psi, but this time we have 10ft of liquid in it, we will now get MUCH more than 15psi coming out of it... The reason is because NOT ONLY do we have the 15psi of pressure forcing the liquid out, but we ALSO have the WEIGHT of the column of liquid, in this case 10ft of liquid, which is going to be a LOT of pressure... This pressure from the column of liquid will add together with the 15psi found at the top, and create an output that is much higher than 15psi.... In our NORMAL fuel tanks, say our muffler is supplying 15psi... There is also additional pressure being create at the output because of the column of fuel in the tank... This allows the pressure at the carb to be higher than the 15psi being fed in....
Now comes the uni-flow setup... In this case, the top of the tank is NOT open to the atmosphere... BECAUSE the clunk is submerged in the tank (at the same level as the output clunk), the pressure of the muffler has the weight of the fuel to work against as well!... This effectively means that the additional "pressure" that is created by the column of fuel in the tank, is "canceled" out, because it takes at least that much pressure "away" from the muffler pressure... So, no matter WHAT level the fuel column is at, nor how much pressure it in itself is exerting, if you supply 15psi from the muffler, you will ALWAYS have 15psi at the carb....
I hate to say this, and I'm really not being a jerk when I do, but this IS BASIC PHYSICS! The page that Nigel set up uses NOTHING but WELL KNOWN LAWS OF PHYSICS to define the use, and advantage of a uni-flow tank setup.... I don't think he was trying to act like a "big expert", nor was he on a "high horse"... He was simply trying to EXPLAIN in the simplist terms he could think of, exactly how this whole thing works... If he were trying to be a big expert, or on a high horse, you would have seen every single calculation, formula, etc, that goes along with his explaination. Instead he's trying to explain it in basic terms that most people can grasp. EVERY SINGLE THING mentioned about a uniflow tank is based on physics... not "guess of physics", not "we think this is right when it comes to physics", but LAWS! of physics...
Bottom line, if you do NOT believe me, or anyone else, then PLEASE print out Nigel's page... Take it to your local university or college... Find a physics professor and show him the info... He WILL tell you that all of the explainations are sound.... (I've also found that physics professors from most colleges are generally very helpful and can usually set demonstrations up quickly to "show" what is happening in a given situation)...
Last but not least... If you STILL don't believe it... Then don't talk about it... TRY IT!... Prove it wrong... Show that it doesn't work.. You say "there is no difference in pressure between a normal tank and the uniflow tank"... Show us the laws of physics you are basing that hypothesis on, explain to us WHY there is no difference... Since after all, we have attempt to explain to you why there IS a difference... OR! Do it in an even better way.... TEST IT YOURSELF!.... Take a plane, (i'm assuming you fly planks), tune the high side of the engine EXTREMELY RICH... Get it to the point where it's just coming in and out of the "two-cycle / four-cycle" sound... Now take off and fly around at full throttle... At first, you'll still hear it coming in and out of two-cyclic / four-cycle... As the tank empties out, you'll hear it STOP doing it... This is because as the tank empties, the mixture leans out because the pressure at the carb gets less and less....
Now, do the exact same thing with a tank set up for uni-flow.... Amazing isn't it? It will stay in the two-cycle / four-cycle sound throughout the whole tank...
In fact, you can do it even easier.... Start a plane with a full tank of fuel.... Get it just a little on the rich side and check it with a tach.... Now don't touch the needle... either let it run out most of the fuel, or kill it, drain most of the fuel adn start it again... Now tach it... Turning higher RPM huh? Now do the same experiment with a uniflow.... No change...
There is no difference in pressure between a normal tank and the "uniflow" tank, except for clunk problems, bubbling in the fuel right at the carburator clunk intake and backflow problems.
Not at all.. First, see above about the pressure.. Second, you will have no clunk problems... The fuel tubing is too stiff even on the clunk line to allow any sort of tangling or anything like that (unless your running ultra thin fuel line for the clunk, which can allow the clunk to fall to the front of the tank and other problems anyway... With a normal clunk line, it would be impossible for them to get tangled up in any way to cause problems.... You will not have bubbling in the fuel right at the carb clunk... The carb clunk will be longer than the exhaust clunk... This prevents any possibility of sucking "air" straight from the pressure clunk...
Now backflow problems your right about... If the pressure line from the muffler to the tank is TOO SHORT, AND you chop the throttle from full to idle, you CAN get a little fuel flowing out of the pressure line.... If you make the line long enough, (it really doesn't take much), you'll have no such problems... Generally most people are transitioning the throttle anyway, it's very rare someone CHOPS the throttle quickly like that... And EVEN IN THE WORST CASE SCENARIO, you'll just get a few drops of fuel leaking out the muffler.... BIG WHOOP...
I've said my peace, and as stated won't open my mouth again on the subject... There is plenty scientific fact that proves the function of a uni-flow tank... If you take the time to read it and understand it, you'll understand uni-flow.... If nothing else, just go over it with ANYONE with a physics background and perhaps you'll take their word for it...