Uni-Flow Tanks
 

I Must have mis-understood the Article in FLY RC.. It says that there's some advantage fuel flow wise to running a Uni-Flow system However after a brief seard I found what a Uni-Flow Does and it appears to me there would be no advantage unless you are running a Cowled set-up.. But just for Ease of Operation purposes.. Am I missing somthing?


I Just re-read the article to make sure what I was seeing was true and it says that it provides steady flow of fuel no matter aircraft attitude and that it decreases the engines tendancy to load up do to less that Ideal tank placement. But I just don't see how.. Can someone explain?

RE: Uni-Flow Tanks
 

they do work as intended. the main benefit is that your engine won't lean out during the flight, where you set it at a full tank is where it will stay until it runs out of fuel. it works because when the tank is full, the pressure inside will be less then what you would have otherwise, the muffler pressure is having to fight the column of fuel to push air into the tank. (imagine blowing bubbles with a straw deep in a cup vs at the top) when the tank is nearly empty the weight of the column of fuel is much less, so more pressure can build up, compensating for the lower fuel level and keeping the fuel pressure roughly equal.

just test ran my shrike with a irvine .53 and a uniflow setup. one interesting thing is that after running at full throttle for a little bit, you will get a little fuel going back into the pressure line when you suddenly chop the throttle. at that point the tank has excess pressure and it has to escape somewhere. (probably just going to add more pressure line in my situation so I'm not dumping fuel out the exhaust)

RE: Uni-Flow Tanks
 

I saw this topic header and my curiousity got the best of me. After reading the previous posts, I did a search and found the article espousing this idea of a "uniflow tank".
Sorry guys. This is another example of the plethora of bad information being spread around by misinformed "experts" who badly need to retake their high school physics.
On the otherhand, there are some actual problems with this design due to the backflow problem mentioned and especially the likelyhood of the clunks getting tangled up.
The answer is to hook up your tank like the manufacturers tell you to.
Allan Flowers

RE: Uni-Flow Tanks
 

The uniflow tank was invented by Edme Mariotte of Dijon, France, in the 1600's. A search for Mariotte Siphon or Mariotte Bottle will turn up more information. For example: http://www.uswcl.ars.ag.gov/exper/mariotte.htm Basically a uniflow or reguflow tank gives uniform flow in spite of changing fuel head. I do not know the the physics involved but I have success using the idea that the engine thinks the fuel is coming from the uniflow outlet in the tank. Many who use a clunk tank in control line tie the two clunks together. I've used uniflow tanks for many years in control line racing and stunt airplanes, with and without pressure, with great success. I would not build a serious airplane without a uniflow tank.

Incidentally, Edme Mariotte was the first person to test a model in a wind tunnel.

Jim

RE: Uni-Flow Tanks
 

I need more convincing. The article made it seem like this was a cure-all for tanks being above/below centerline. I don't see how the pressure would be any different through a fuel klunk vs the vent. Same amount of pressure going in = same amount of pressure going out. Any Hydro Engineers reading this?

RE: Uni-Flow Tanks
 

I would assume you would be referring to my post, as I was the only after the initial question... (finished 2 years of university physics, 1 year of university chem...) what part don't you agree with? here is an example for you. set up a aquarium, then put a bubbler in it and blow bubbles through the line. try blowing when the bubbler is at the bottom, and then try when it is near the top of the tank. it is MUCH easier when it is at the top, for your average 29 gallon tank it is quite difficult to actually get a decent stream of bubbles when the outlet is at the bottom.

your muffler pressure is you blowing into the tank. the overall effect is the pressure is the same when the tank is near empty, but when it is full the pressure the muffler exerts is decreased, much the same as how you aren't able to blow as many bubbles through the aquarium when the outlet is at the bottom. I would like to hear why or how this system does not work as I have outlined...

RE: Uni-Flow Tanks
 

I'll play devil's advocate for a min. I'm not sure if typical two stroke is even capable of pushing air through a full tank of gas. If this were the case, the air pressure from the muffler pushes only on the open surface area of the fuel tube, 1/8" If the same amount of pressure is applied to say 2 square in of surface area, the effective pressure on the fuel is several times greater. Hydrolic pressure is calculated by surface area x force.

Pressure = Force (Lbs)/Unit Area (sq. In) edited to insert formula.

I think, unless proven otherwise, that the Uni-flow type tank adds no measureable pressure to the fuel, thus fuel pressure is the same at the end of the flight as it was in the beginning.

Please don't take this as a personal assault smokingcrater. I have never tried a Uniflow tank, it may work fantastic. I am only trying to understand the physics behind it.

RE: Uni-Flow Tanks
 

That's EXACTLY the purpose of a uni-flow tank... it's not meant to ADD pressure to a tank.. In a normal tank it will always get leaner as the tank empties out... With uni-flow, the pressure stays equal throughout the duration of the tank, so the mixture stays more even throughout the tank...

Here's a link that explains the principles behind it... it's fairly easy to follow...

http://www.fraserker.com/heli/uniflo...flow_works.htm

RE: Uni-Flow Tanks
 

Hi!
Most fellows being into racing seem to have used this tank set up, but for many newcomers who haven't flown in competition this is tank set-up is a new "thing". I have used the Uniflow tank for decades and it sure works.
But an even better tank is the Tettra bubble less tank.
Regards!
Jan K
Sweden

RE: Uni-Flow Tanks
 

Smoking Crater, I was not referring to you but rather Nigel Fraser Ker, the "expert" who went to so much trouble to prepare the website mentioned by Rusirious. I think it is one thing to hold an opinion and another to get on a high horse and act like a big expert with a special website.
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.
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.
Allan

RE: Uni-Flow Tanks
 

Wow this got real complicatied really fast Haha!

I sat there last night after I posted this with a fuel tank and hardware in hand just trying to figure out what advantages there were to the Uni-Flow and how they were obtained.

I don't know how much exhaust pressure the engines build but with this setup I don't think the Uni-Flow will even work..

It's a 22 oz tank first of all and it's pretty hard to get fuel from it by blowing into the pressure line.. Second this is a 1.40 with a larg open exhaust that I know doesn't build nearly enough pressure.

jaka,
YOu say you know the tank "sure works" but what does it do for you and how does it do it?

I'm still not seeing the adantage.

RE: Uni-Flow Tanks
 

Ice Man, you need to pack it in and get a pump or use crankcase pressure and a Kline regulator. A Uniflow tank works by varying the low pressure above the fuel remaining in the tank. With the vent on the bottom, as fuel is used a partial vacuum forms. As it gets to a certain point, air is drawn through the vent. As fuel is used, it gets easier to pull air in. The effect is to keep fuel flow constant. Your engine has to be able to draw fuel from the tank by itself to create the low pressure.

Uniflow tanks work best when the tank is vented to the air and not pressurized as in CL stunt and some racing events, slow rat, for example. The engine run is characterized by a few seconds of rich running while the low pressure is built up, then a constant setting from then on. On my old racers, this took from 3/4 to 1 lap.

The Uniflow tank was not designed to supply fuel from a distance, only to maintain a constant fuel flow. A Uniflow tank will actually give you less distance that the tank can be removed from the engine since you are sucking fuel against a low pressure. Your situation with an open exhaust really needs a pump.

RE: Uni-Flow Tanks
 

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...

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...

RE: Uni-Flow Tanks
 

First of all, lets all take a breath....
Secondly, the suggestion "Find a physics professor and show him the info" is really really great advice. Just get a smart one please.
Thirdly, after you have talked to the physics professor, Please let us all know what you learned (what I already know...).
__________
I stand by my statement that the uniflow tank is bogus. Properly set up (NOT open-vented to the atmosphere), it will still provide muffler pressure and insure more even fuel feed during the flight, just not any better than the conventional plumbing arrangement (if vented to the atmosphere then you have accomplished absolutely nothing. Just because the tube comes out under the fuel surface doesn't change the pressure situation at all. Basic physics).
__________
Let me ask the uniflow advocates a simple question. How come SULLIVAN, DUBRO, HAYES, GREAT PLANES, ETC. ETC. Etc. all recommend the top vented muffler taps? Who the heck are the experts here. Them or Mr. Frasier Ker??

Respectfully,
Allan

RE: Uni-Flow Tanks
 

rusirius.
Ahh your staring to make sense! But then again so is allan:D

Looks like some one does need to take that info to their local college and see what they say!

RE: Uni-Flow Tanks
 

I swore to myself I wasn't going to post another message in this forum, BUT, i will address these two points, and hopefully you'll give them some consideration (especially since it seems ice man might be leaning towards the dark side... ;)

I'm sorry to be brash here, but this statement shows a complete lack of knowledge of basic physics. You ever go swimming? Take a nice big breath and dive deep under the water? What happens? Pressure on your chest is amazing isn't it? That's because of the PRESSURE the column of liquid your swimming in is exerting on your air filled lungs... By your statement above, you could dive as deep under water as you wanted, because WHERE you were under the "water" surface, doesn't change the pressure situation at all... Think about it... Or... do the experiment that someone else told you.. Surely you know someone that has a 29 gallon or more fishtank? Or go to a swimming pool... Take a long bit of fuel tubing with you... Put it just under the surface of the water and blow.. Not to bad heh? Now stick it way under the surface, towards the bottom... blow on it now... Pretty darn hard huh? Do this in a swimming pool, and you'll probably barely get a bubble out... of course WHERE the tube comes out under the fuel surface changes the pressure situation, because of the weight of the column of fuel sitting on top of it..

Can you IMAGINE what the world would be like if we had always lived by this principle? There would NEVER be ANY innovation... Because OBVIOUSLY anything that already exists is the "best way" to do it. Why try to improve anything, or come up with new or original ideas? Obviously everything out there is already the best it can be...

RE: Uni-Flow Tanks
 

The example of a person blowing into a tube while swimming deep in water is a nice argument for your case because everyone can relate to the fact that, as one goes deeper, one has to blow harder to get any bubbles to emerge.
However, bubbles or not, the over-pressure (that above atmospheric) is still transmitted to the fluid according to Pascal‘s law.
In the case of a model engine, running under prescribed conditions, rpm, etc. the pressure tap in the exhaust will have a given amount of over-pressure, no matter where the other end of the tube ends up. If this is, say 2 pounds at the muffler, it will be essentially 2 pounds on the other end of the tube. If 2 pounds is not enough to make bubbles in a deep tank of fuel, this doesn’t mean that the 2 pounds of pressure just disappears or goes somewhere else. It is still transmitted into the system. The air in the tube, and the fluid in the tank still transmit this pressure along. Of course it adds to the pressure in the bottom of the tank caused by the fluid “head” of pressure. This is a classic example of Pascal’s law which
I would suggest reviewing at the following link. http://www.engineersedge.com/fluid_flow/pascals_law.htm
The nice thing about this web page is it shows the pressure effect (equal on all surfaces) and shows how it combines with the pressure head effect.

To help visualize your example, here's my sketch of the situation you have described, where the over-pressure in the tube is fixed at a limited amount and insufficient to force a "bubble" into the fluid. Still it manages to displace some of the fluid in the tube, forcing the top surface of the fluid to rise, transferring the pressure to the air in the top of the sealed container. This pressure transfer is instant, complete and absolutely one-to-one. The pressure measured by the gauge at the top of the tank will MATCH the pressure at the input tube (at the RED arrow). The pressure measured by the gauge near the bottom of the tank will match the internal air pressure from above PLUS the fluid pressure caused by the "head" of fluid (it will be higher than the internal air pressure by the amount caused by the pressure head of fluid).

The reason that the companies I mention don’t suggest the uniflow design is not tradition but what they have found to be true and valid.

Regards,
Allan

RE: Uni-Flow Tanks
 

Oh believe me, I am VERY familer with Pascal's law... The problem is, you have taken his law and applied it backwards... Well, actually you haven't, but your only applying it to ONE side of the equation... (or tank in this case... ) Okay... look at it this way....

Your absolutely correct that if we have 2psi of pressure at the muffler it will STILL exert 2 psi of pressure at the exhaust clunk in the tank... ABSOLUTELY... and your right, that force IS transfered to the system... But in your example, your ONLY considering THIS pressure, not others involved in the system...

Now... Let's go back to my earlier example, and in fact, since you trust the information on the website you linked to, let's use information from their own page. Go review this link... http://www.engineersedge.com/fluid_f...h_pressure.htm . This shows the relationship that depth has upon pressure...

Now, if the pressure being exerted at 10 ft is 5 psi, (these are just random numbers pulled of my head, not actual figures) and the pressure at 20 ft is 10psi, and at 30ft is 15psi... Then if I blow on a tube with 10 psi.... If I place it at 10ft, it will bubble into the tank... If I place it at 30ft, it will not, but instead as shown in your example, liquid will actually enter the tube for some distance... if I put it exactly at 20ft, the pressure will equalize... I will not be putting bubbles into the tank, but I also will not have liquid entering the tube... Correct?

In this example... Of COURSE I'm still exerting a pressure on the entire system when I have the tube at 20ft... Just because I'm not putting bubbles in the tank, etc.. doesn't mean I'm not exerting pressure... I never said I was.... What I said, was that the PRESSURE I am exterting (10psi), now MATCHES the pressure the tank is exerting (from the weight of the fuel at the 20ft depth)... Therefore they cancel each other out...

If I take a sealed tank 30ft tall (and keep the figures from the above example)... Only in this case put a pressure gauge at the top of the tank... If I start with 0psi on the tank, and put my hose in at 10ft... (5psi) and apply 10psi of pressure.... Bubbles will enter the tank... This will BUILD to the pressure in the tank.... It will slowly start to rise... Now let's go back to 0psi... If I put the hose in the tank at 20ft, and give 10psi on it, the pressure in the tank will NOT go up to 10psi.. I will stay exactly where it is.... Never gaining, never losing.... Because the pressure i'm exerting on the tube is exactly matched to the pressure the weight of the fluid is exerting on it from the opposite direction...

I know I know... Pascal's law right? Pascal tells us that if we apply 10psi to a system, that 10psi will be applied to the entire system.... That's very true.... BUT your only considering the pressure applied to the tubing... You FORGOT about the pressure applied to the clunk by the weight of the liquid.... Remember? It is exerting a pressure JUST like we are... and just like pascal said, it gets applied to the entire system just as well.... Not JUST to the pressure line, not JUST to the exhaust line, but to BOTH EQUALLY! Think of it this way... Take a REAL close look at the example you provided of pascal's law.... Do you not realize, or did you not notice that the force being applied to all the pistons was completely different? Piston A has 50 pounds of force, B has 50 pounds of force, C has 60 pounds of force, D has 80 pounds of force, and E has 75 pounds of force...

Okay, one last example, then I'll give up... You'll either understand and agree, or disagree and we'll just let others read the discussion and they can make up their own minds (or better yet try it themselves and see the proven results...)

If I take a tube just the right diameter to fit a BB inside (so that air cannot get around the BB).... If I then blow with 10psi on one end, and a friend blows with 10psi on the other... The BB doesn't move right? Because the forces equalize on either end.. He's not able to displace any air, so the BB can't move... (assuming we're holding the tube horizontal).... First, in two parts... If we check the Pressure in the tubing, what is it? I'm exerting 10psi, he's exerting 10psi.. The pressure in the tube SURE AS HELL isn't 20psi!!! it's 10psi!!! Now, you said...
Yes, your right, it is TRANSMITTED to the system, but it's not ADDED to the system... There's a big distinction there... 10psi and 10psi doesn't make 20psi!
Second... If we then move the tube vertical... While still maintaining 10psi on each end, does the BB stay precisely in the middle? Of course not... The WEIGHT of the BB will now exert a force on the 10psi under it... it will also exert less force on the 10psi above it... Both ends are STILL at 10psi... but now the BB is exerting it's OWN forces.... JUST LIKE THE FUEL IN OUR TANK EXERTS IT'S OWN FORCES because it is a column of liquid...

RE: Uni-Flow Tanks
 

Well I think I learned more here than in science class!

So far the Uni-FLow argument is in the lead..

Rusirius,
Were you a prosecutor at some point in your life? Great work man!

Allan,
Can you argue with that last example? Or is this over with?

I'm gonna let my dad (High school teacher) read it and see if he can decide which one is better.. Then show it to a few people in the club.. I'd like to det ahold of a College physics teacher but you know..

RE: Uni-Flow Tanks
 

LOL, no, but I have had my fair share of college level physics classes. (physics 101, 111, and 112) (111 by the way is where we went in depth with mechanics, fluids, sound, and heat.) In fact, physics, trig, and geometry were my favorite subjects (in that order)... Oddly enough, despite my love of physics, I ABSOLUTELY HATED! algebra and calc...

Edit: You know... I MAY have been a prosecutor in a PAST life... [sm=bananahead.gif]

RE: Uni-Flow Tanks
 

Hi, Rusirius,
I will start at the end of your recent post and work forward, through just a few of your arguments.
Let's take your BB example. The internal pressure in the tube BEFORE the two people start blowing is atmospheric (14.7 lbs). The BB doesn't "feel" any pressure because it is on all sides. After you and your friend add 10psi to each end, the BB still doesn't feel any difference but the internal pressure in the tube is now 24.7lbs (plus 10 from before). I never said that my 2 lbs example would raise the pressure by FOUR pounds just the 2 being ADDED. This additional pressure is applied equally to all surfaces in the closed system.
The closed system equalizes by reaching equilibrium - at the higher pressure.
Let's look at another BB-in-a-tube example where one end of the tube is closed and that half is filled with noncompressible fluid. Your friend blows 10lbs of air pressure in his end. The fluid cannot go anywhere and it cannot compress so it has to exert the added 10lbs of pressure on everything it touches. The BB is happy, feeling no movement but the tube is getting ready to bust (this is a weak tube?).
This last example is more analogous to the situation in the muffler tap tube at the point where the exhaust pressure equalizes with the fluid pressure resisting it - reaching equilibrium at the higher pressure (assuming a closed system).
Lets look at your example of a tube ending at the 20 foot depth, where a 10psi pressure is presumed to exist.
BEFORE air pressure is applied, the tube will be full of liquid. That is the true "before" situation. The "after" situation requires the air to have displaced the liquid in the tube to the 20 foot depth.
_______
If this is a swimming pool, the water level will rise a tiny bit and the water pressure on the sides of the pool will not change (actually the tiny rise WILL cause the pressures to rise a tiny bit too but this is almost unmeasurable).
A swimming pool is open to the air, it is not a confined system and Pascal's law does not apply - just the pressure/depth situation you have so well described applies in a swimming pool.
_______
However, if this is a CONFINED system then the new pressures are added to the pressure/depth numbers at all points according to Pascal's Law.
Here is the link again to the page on this law. http://www.engineersedge.com/fluid_flow/pascals_law.htm
If you study it, you will find that the text starts with acknowledging the pressure/depth issues but then deals with an external pressure being added. The diagram clearly shows both the pressure/depth forces and the ADDED external force.
I urge anyone reading this discussion to click on this link, read the short explanation and look at the diagram. It proves my point beautifully.
________
Time to go fly. My new design overheated on its maiden flight two weeks ago and I am eager to see if the modification I made will do the job. See the Cyclone thread in the Scratch Building forum. It is not using a Uniflow tank arrangement by the way.
I will check in again in a day or two. Hopefully we will draw in some new blood to add fresh thinking and arguments, before we bore everybody to death.

Allan
(also took college physics classes and got A's and B's in them -at Illinois Institute of Technology, a leading engineering school)

RE: Uni-Flow Tanks
 

I agree... Honestly, at this point, let's just agree to disagree.. LOL... we can keep running around in circles forever.. ;) Hopefully if nothing else this will give anyone considering a uni-flow setup a little more knowledge so that they can make up their own mind for or against.

On a side note... This is twice now that I've been involved in physics debates (the other with fluid dynamics) on this site.... And in BOTH cases, it has actually been enjoyable.... No "that's stupid...", "your a moron for thinking....", "any fool can see...", "you must have got your degree from wal-mart..." etc.... comments! ;) In both cases it has been a very respectable debate. For that, I applaud not only the ones who have participated in the conversations, but the site in general for apparently, at least for the most part, drawing civilized people. Kudos for that...

RE: Uni-Flow Tanks
 

Awww poo i was enjoying reading the debate...

Allan when you get some fresh info be sure to dig up this forum and start the debate again... It'd be really interesting to see which one is actually the PROVEN better of the two[8D]

RE: Uni-Flow Tanks
 

Time to eat crow.
After reviewing all the posts and websites mentioned in this thread, I have decided to reverse my position on the uniflow tank. I now believe it to work as described in Nigel Frasier Ker's website. My apologies to Nigel. He was right, I was wrong.
_______
Now before anybody starts to gloat, let me bring you down to earth (a little). First of all, Nigel's site is not so well illustrated and it requires very close reading to truly grasp what he is saying as being true. It was only thanks to another site, referred to by Jim Thomerson that I was able to understand the physics properly. Of course then Nigel's site became understandable. This doesn't get me off the hook but I wish his graphics had included the excellent diagram from the other site which I shall attach herein for you all.
There are two forces involved in the tank. One is the pressure head force which varies with the depth of the fluid above the carb clunk. The other is the gas pressure provided by the muffler tap (and ambient atmospheric pressure).
MOST of the proponents of uniflow argued that the gas pressure from the muffler is reduced or eliminated by the depth of the pressure clunk under the fluid surface - and this is what makes the fuel flow more even - and that, as the fuel level drops, the muffler pressure transmitted is increased.
I argued that the gas pressure from the muffler tap was transmitted immediately throughout the tank with no losses.
I was right in this.
Where I was grossly wrong was in failing to understand that the two clunk locations (at the exact same depth) eliminates ANY pressure head forces, leaving only the gas pressures to act within the tank. We were arguing about the wrong forces.
Please look at the diagram and see how the "head" of pressure is NOT measured from the water surface. Now envision the vent tube being extended down a bit, to the same height as the outlet.
I hope you have all enjoyed this...
Ice man, I hate you.
(just kidding)

Allan

RE: Uni-Flow Tanks
 

One comment on the original diagram. I would cut the uniflow line about an inch shorter than the fuel pickup line. Fuel is being sucked (I know it is not being sucked, but cut me a little slack here) out the fuel pick up and it is possible that bubbles can be sucked out of the uniflow if it is too close.

I made C's and D's in two years of university physics 50 years ago[:o],, but B's in a three semesters of Chemistry:D, so don't ask me about the physics. There are a couple of articles on Mariotte Bottles in Science Magazine in 1934. I suspect the physics is explained there. I have done some more recent work with hydropower so I know about hydraulic head. In a Mariotte Bottle, uniflow tank, the head is between the end of the uniflow and the exit of the fuel at the carburetor. If this were not the case, a constant flow, as fuel runs out, would not be maintained. And it is.

If you have a Fox stunt 35 left over from your first childhood, run it up on the bench. By fiddling with the needle you can keep it running with the tank a foot below the engine. That tells you how much suck that engine has. Running muffler pressure will allow you to drop the tank another three or four inches. The point is that engine suction, with a reasonable size hole in the carb, is not to be sneezed at. I think the problem with some of the arguments above is that this has not been taken into consideration. Crankcase pressure is two or three times muffler pressure.

Some years ago my wife underwent chemotherapy. There was a little Mariotte Bottle in the IV line.

Jim