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George Ryals wrote:r90s, when you plumb the long and short tubes together with a tee, they become one tube. One tube, one pressure and one height in both tubes. The only way to have different liquid heights is to have different pressures on top of the liquid in each tube.

Excellent point, George. R90s, your whole math argument, while still flawed, is based on the premise that the two tubes have different total volumes of air, which, in your experiment, they do not.

Yes, that is why the level of the liquids in each column evens out when that vacuum stops changing.

But while the vacuum is changing, in equal value to each tube length, the effect of different lengths of tube is shown by the movement of the levels - short tube length rises, long tube length drops.

We are not talking about static situations here, but rather dynamic, as in , when the manometer is in use on the running engine.

Did you look at the video I posted? Did you see the levels changing relative to each other? How do you think that happen?

Cheers,
Jon-Lars

I watched the video. No one has said that the responce time of a long tube and a short tubr are the same. In your experiment, if you keep pumping until the vacuum quits changing (as each cylinder will do on an airhead at a steady rpm) you will see that it is a static situation and the fraction of a mm difference in liquid level you saw in your experiment will disapear.

Right, when the number of gas molecules is no longer being changed. In other words, when it goes back to a static state.
But when the manometer is in use, it is measuring a dynamic state.

Instead of arguing from your desk, put up some formulas to prove your assumption and test it with your equipment.

So I tested my balancer as per Jon's method.

One tube is 15" longer than the other. I have about 12" of 40w motor oil as a medium.

The short tube does pull up before the other. At about 25" of vacuum they are about 4mm apart. They slowly equalize after I stop pumping.

Two things are obvious to me:

The damping action of the oil takes a long time for the difference to settle, meaning the short tube will always show higher on my scale.

The difference between the two is within my normal margin of error. After I rebuild my balancer it will be inertesting to see if I can feel the difference in smoothness. I will do a before and after test on the bike.

BTW, engine vacume is never static. It fluctuates with every power pulse, so the shorter tube will allways read higher as it moved first and is never allowed to recover till the engine is shut off.