Alternative to a bladder tank?

Alternative to a bladder tank?
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Alternative to a bladder tank? - 4/10/2008 10:50:33 PM

happypappy

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Is there an alternative to a bladder tank using 3 lines and a check valve in the exhaust pressure line? How do you set it up and can you set the engine RPM at peak and leave it there with this set up? Thanks!

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RE: Alternative to a bladder tank? - 4/10/2008 11:51:09 PM

YUKONFLYR

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The bladder tank keeps air out of the fuel by never allowing the two to touch. Using a check valve will keep tank pressure up, however there is still air in the tank and the posibility of foaming fuel allowing the engine to go lean. One bubble or lots of little ones spell disaster for your expensive engine if the fuel foams.

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RE: Alternative to a bladder tank? - 4/11/2008 12:14:19 AM

garys

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The box that the Tetra tanks come in shows a 3-line setup, but I've never heard of anybody using it in a racing application. I've also never heard of any racers using a check valve in the muffler pressure line, and wouldn't recommend setting any engine at peak RPMs, although in some cases you can get close to it, depending on engine, ect.

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RE: Alternative to a bladder tank? - 4/11/2008 12:50:46 AM

rmenke

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Happypappy:

Sort of sounds like you are working with a YS engine? Have never used or sean a bladder tank setup used with 3 lines. Guess you could add another line inside the bladder to use as a sucker or vent line to help get rid of bubbles, but the approach not used in my experience. A additional line increases the odds of something going wrong by 33%. Enough happens to simple designs without adding unnecessary complications. Note that the Jett bladder tanks only have two lines. ENJOY

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RE: Alternative to a bladder tank? - 4/11/2008 3:33:51 AM

happypappy

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Should have explained myself a little better I guess. The plane is a club 40 plane with a simple ST GS-40 on it. I had heard about using a tank with the normal clunk in it then adding an additional clunk on the line that supplies pressure. The third line is simply a vent line while filling and gets closed off. The pressure line has a check valve in it to keep a constant pressure in the tank. By keeping the pressure line clunk submerged the pressure should never change as the tank level lowers as only what is being used is being replaced at a constant pressure. Anyone know anything about this set up? Obviously the advantage here is, if it is possible, to tune the engine to peak instead of 3-400RPM down and wait for the tank level to drop to lean the engine.

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RE: Alternative to a bladder tank? - 4/11/2008 3:58:26 AM

HighPlains

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quote:

A additional line increases the odds of something going wrong by 33%.

Actually no, all things being equal. Increasing the number of lines from two to three lowers reliability by 50%.

Assume a MTBF for single line to be 100 hours. With two lines the reliability drops to 50 hours, while adding a third line drops the MTBF to 33.3 hours.

Where MTBF gets interesting (and they pay you the big bucks) is when you do it for electronic systems.

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RE: Alternative to a bladder tank? - 4/11/2008 4:22:31 AM

Duane-RCU

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The first Tettra tank I used had three lines. I used my electric fuel pump to fill it. I could cycle the pump and get all the air out, once full I didn't want to just run the pump, in case it put too much pressure on the bladder. Other racers won't notice you are using one, since you won't fill it with a syringe. The system worked fine, I filled it several times on the bench to make sure it worked before putting it in the plane.

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RE: Alternative to a bladder tank? - 4/11/2008 5:47:34 AM

djlyon

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You are talking about a uniflow system. Common on aerobatic planes. The check valve really doesn't do much for you in your situation. No purpose in a discussion here on gas and liquid flow rates. Setting the rpm 3 to 400 rpm low for this kind of airplane is not primarily to accommodate the pressure head change as the fuel level goes down but rather to accommodate the fuel demand as the prop unloads as the plane gets up to speed. The ground rpm for each engine is going to depend on the fuel demand of that specific engine as it unloads assuming all else in the fuel system is correct.

and Highplains after all the MTBF calculations it's really all about controlling junction temps. Lord I'm glad I'm retired.

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RE: Alternative to a bladder tank? - 4/11/2008 6:24:11 AM

HighPlains

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I don't miss semi-log graphs either.

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RE: Alternative to a bladder tank? - 4/11/2008 1:26:57 PM

happypappy

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Djlyon - thanks for the corrrect terminology. The check valve should keep fuel fom running out of the tank and through the exhaust when I throttle down since the pressure clunk is now submerged. Remember that in this plane the engine will be run at WOT from the time it leaves the ground. Do you think I can set the needle leaner with this set up than with a standard two line tank? RPMs is speed after all !

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RE: Alternative to a bladder tank? - 4/11/2008 2:35:13 PM

daven

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You can set them leaner than you could a conventional tank, but you can't set them to full bore lean. Well you can, but they don't last too long that way.

Better to leave the motor a little room to unload.

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RE: Alternative to a bladder tank? - 4/11/2008 4:11:25 PM

Ed Smith

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I keep hearing reference to a check valce in the pressure line. IF this is a one way valve then do not do it. because there is no escape route it will create a very high pressure build up in the tank and flood the engine. Normal muffler pressure goes so high then escapes out of the muffler outlet. It is similar to crankcase pressure. It is almost impossible to get an engine to idle using crankcase pressure that pulsates and has no escape route

Ed S.

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RE: Alternative to a bladder tank? - 4/11/2008 9:27:05 PM

happypappy

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Actually, it looks like I can run the check valve as the pressure differential would remain the same and all I have to do is tune for it vs the conventional tank. The check valve would be there simply to keep fuel from rushing back up the pressure line when backing off the throttle. Take a look at this pretty simple explanation I found while researching this.
http://www.fraserker.com/heli/uniflow/how_uniflow_works.htm

< Message edited by happypappy -- 4/11/2008 9:30:01 PM >

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RE: Alternative to a bladder tank? - 4/12/2008 12:25:39 AM

Ed Smith

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You are not listening. fuel cannot run up the pressure line when muffler pressure is present, at idle or full throttle. When you are given sound advice, listen to it.

Ed S

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RE: Alternative to a bladder tank? - 4/12/2008 1:33:58 AM

gunfighter

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This "Uniflow" guy is all wet! That system would work fine to keep a header tank full for helicopters etc. but would flood a standard engine if the throttle is even slightly reduced.

Try this...with the system he (and you) are talking about. fill the tank, put your finger over the muffler outlet and flip the prop several times. Fuel will start running out the fuel line with ever increasing volume until the fuel is gone or the pressure is reduced / vented. Pressure built up inside the tank has no where to exit. therefore, it will continue to increase as the engine is run.

Now do the same with a bubble less (or a good standard clunk) tank. Fuel will come out in "spurts as the muffler puts pressure on the fuel. Then the flow will stop as the pressure is equalized.

You could NOT set the needle any leaner and expect it to last for an entire tank. With a check valve as you describe it, (and YES, I have tried them) the pressure keeps increasing in the fuel tank until the engine floods.

Just spend the $15.00 and get a Jet or Tetra bubbel less tank and your problem will be solved with out further experimentation.

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