Water level accuracy revisited

[stryped]

Is there any difference in accuracy with using a resivoir vs just the tube? I want to acurately level the torque boxes on my car on jackstands so i can make frame measurements.
Thanks

 

[Baluncore]

Depending on what you mean by a reservoir, if the density of the fluid is the same throughout and exposed to the same atmosphere, the water level will settle to the same level. A tube of water will settle quickly because waves are damped. A large body of water will slosh around, but in the end give a level result, if you are prepared to wait.

 

[stryped]

I was thinking a gallon jug with a nipple and tubing filled with windshield washer fluid.
I am not against using just a tube but I will be working by myself and not quite sure how just a tube is used. What I need to do is level as perfectly as possible 4 jackstands, placed under the 4 torque boxes under the car. Then set the car on these stands. With the 4 torque boxes leveled, i can take measurements to ensure squareness of frame as well as weld on door braces. (Because there are no doors on the car currently)

 

[Baluncore]

I was thinking a gallon jug with a nipple and tubing filled with windshield washer fluid.

Density must be the same throughout the system. Use clean fresh water to eliminate any density gradient that may develop. The volume of water and the volume of the reservoir and tubing will depend on the temperature so you will need to check the level at both ends every time. Avoid sunlight falling on part of the tube.

I would use a clear vinyl tube, CVT, laying on the floor with the ends vertical, tied or taped to the vehicle or stands at the reference points. Keep the reference end fixed, move the other between the points to check. Note the difference between reference and water level, then apply that offset as a correction to the points being checked.

Using the same CVT at both ends, shapes the meniscus the same at both ends, so it should cancel some reading errors. Look at the level through the wall of the clear tube, with plenty of spare empty tube going upwards to prevent spilling water while moving.

 

[stryped]

Cvt?

 

[Baluncore]

I would use a clear vinyl tube, CVT,

google; 'clear vinyl tube ebay'

 

[Nugatory]

I would use a clear vinyl tube, CVT, laying on the floor with the ends vertical, tied or taped to the vehicle or stands at the reference points. Keep the reference end fixed, move the other between the points to check. Note the difference between reference and water level, then apply that offset as a correction to the points being checked.

with respect, I'm going to disagree with baluncore here. With four points to level, and needing to maintain the level reference through the very fiddly process of getting the height of each jackstand exactly right (by the way, how are you going to do that? Pads of appropriate thickness under each stand? Or weld up something that let's you adjust a threaded rod?) it's easier to start with a large reservoir, at least a gallon and preferably several gallons. Fill it to the level of your final reference height, then run four separate lengths of the clear tubing baluncore recommends (it's cheap, no reason to skimp) from reservoir down to floor then up to reference point. Make sure that the end of tubing is above the reference height (otherwise you'll start a siphon that will drain your reservoir - ask me how I know!), then suck on the end of the tubing to fill it with water. You'll end up with the water level in each of the four tubes exactly equal to the level in the reservoir, and you can add or remove water from the reservoir to adjust the level slightly up or down.

Oh... and use plain ordinary water. It's cheap, non-toxic, easy to handle, and being able to suck on the tubes to fill them safely is a huge advantage.

 

[sophiecentaur]

Using the same CVT at both ends, shapes the meniscus the same at both ends,

A small quantity of detergent in the water would probably 'tame' the meniscus and avoid it 'sticking' by wetting the plastic surface.
It would be good to know the actual accuracy that you need for your measurements. Baluncore's query about how to achieve your adjustment is relevant to the steps in thickness of your 'shimming' required.
A conventional 'spirit level could possibly give greater accuracy as the curved tubes magnify the effect of the angle from the horizontal. The only disadvantage with a conventional bubble level is when there is stuff in the way between the levels of interest but that is easy to take care of with equal length pins on stands, to offset the measurement.