Dogma
Forum Sage
Well technically you are correct that the steady state levels of the fluid in the tube are only based on the pressure differential and the amount of head produced by the column height differential (i.e. density of the fluid and height). However in the case of usability, if you blip the carbs, it will take longer to evacuate that larger volume over the ATV than if the tube was narrower and so you have longer to react (i.e. back off the throttle). With narrow tubes, it is virtually impossible (ask me how I know).
I worked out the equations recently and basically the ratio of volume in the standing tube to area of hose represents the electrical equivalent of capacitance (If I remember correctly; I'll post the results if i can find it) and given this works against some flow resistance in the line there is the equivalence of a RC filter which provides the dampening but also will delay the rise in the column according to the same linear filter theory.
Taking this to the extreme with a simple example, should make the effect more clear. If you basically have two large several cubic feet of air space above each column of ATF, yes the ATF level will approach the level required to balance the pressure above the fluid, but restrictions in the flow of either ATF fluid between the tubes and or air above the fluid in exhanging through a small tube will create the RC filter effect I have described and so it takes a while for pressures to equalize even though the ultimate levels are independent(your initial point) of the capacitance.
You will note that the fluid tubes and tee's below the manometer are much smaller than the standing tubes as well as the size of the vacuum hoses above the fluid. I suspect this has very good damping properties due to both forms of capacitance.
Posplayr
Are you a EE?
Makes sense to put a vacuum reservoir over the liquid. Not having balanced carbs yet, I didn't recognize the danger of getting the fluid moving with sudden throttle changes. This should tend to reduce bouncing too.
A similar stabilizing effect could be achieved by spooling some extra tubing on the ground to increase the total fluid inertance of the ATF, or using a larger reservoir. Maybe pull water from a filled gallon jug. I remember "Inertance" is the term for the fluid version of inertia, which is mathematically analogous to inductance, IIRC. So we're looking at something like an RCH filter if we ignore the, uh, elasticity of the vacuum above our liquid, right?
A few loops full of vacuum would make some vacuum reservoir too. I don't know if the extra tubing would be more or less cost effective than the fittings, etc. necessary for for adding flow restrictors, or those nice fat graduated cylinders, or connecting the lines together at the bottom.
Thanks for the heads-up on getting the liquid moving. I'll have to remember when the time comes (probably later this summer).
..."full of vacuum". What a concept.
