We wanted to survey the slope of the drive - and so we got a long hosepipe and fixed a yard of clear plastic tube to each end - and filled the whole thing with water.
But when we held the two clear tubes together the levels differed by about a centimetre!
How on earth could this possibly happen? We've been unable to think of any explanation - and are totally nonplussed!
Two spring to mind (assuming your hose was wide enough to ignore surface tension effects):
The less likely: There may have been some flow resistance in the hose (even a slight obstruction / kink) that would have required a minimum pressure differential to overcome. Nett result being once the column heights were closer than the required differential they could no longer force movement through the pipe. You could test this by blowing gently on the pipe with the taller column of water, until the imbalance was by the same margin in the oposite direction. Once you stopped blowing on the pipe your would see the imbalance remain in its new direction.
The second more likely, was that your connecting hose contained an air bubble. This would have to fall in one side or other of your manometer. The side with the air bubble would then have a very slightly lower average density (and hence higher volume) than the other. Hence balance would be archived with the less dense side sitting higher. To verify this you could try the same blowing experiment as above. This time however once you stopped blowing you would expect the imbalance to return to its original direction.
(note also you could have many variations on this density differential theory, caused by say a temperature rise due to one section of the hose being exposed to more sun than the other, or a water impurity etc)
The fix: buy a laser level!
Bubbles or contamination within the hosepipe.
Surface tension.
Chris
Were the ends plugged? You've got air in it somewhere.
Did you have the ends of the clear tube plugged? Or one end?
How long did you let the water run for?
Could be air bubbles, but more likely the water in the pipe near the tap was initially quite warm and the hose was warm so when the water arrived at the far end it was warm. As you filled up the hose you drew cold water from the mains and the hosepipe lost its initial warmth, so the water at the tap end was colder and therefore denser. I would guess that that end had the lower water level. Laws of physics obeyed!
When I used clear plastic tube in a home made level I found I had to use a larger diameter piece of pipe at each end to avoid surface tension effects.
Michael Chare
Invest £30 in one of the spinning laser levels: try defining a vertical plane using the hosepipe!
Works just fine. If you spin it fast enough.
Vertical planes crash.
Anyway a spirit level works for that, or a plumb line.
A bit more involved if you want to put a vertical line on two opposing walls (and perhaps the ceiling) though.
I held off getting one of these spinning laser levels for a long time. On the first job I used it on I had the thought "how have I managed without one of these for all these years?".
I still carry a spirit level with me at all times, but the spinning level goes out on jobs where I'm expecting to line something up.
Andrew
A spirit level isn't accurate enough over a long distance - like for say a suspended ceiling.
A plumb line isn't an alternative for setting horizontals.
Just got a simple laser level. One of the cheap, tripod, rotating adjustable base, couple of "prisms" (line and 90deg) and the level.
Walls in the current room I'm papering are anything but a) flat b) vertical. One wall is 4" (four inches) further back on the 5' length of my plumb line. Trickly to transfer accurate marks to the wall. Doddle with the laser in line mode, transfer one mark via a square at the bottom of the plumb line. Align laser to that and the suspension point mark wall along line of laser light. Much more accurate than a level in vertical mode or transfering plumb line marks. I'm pleased with it and it will make setting a plane for a mid wall border a POP.
Say 10 degrees difference, that would give about 0.3% change in density by my reckoning - NAH
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Beware of doing that in a room thats not level though :) Genuinely level things look.... on the wonk.
NT
But you can set the plane so it looks right, thats pretty tricky with just a rule and a level.
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