For some reason, I feel unduly proud of myself for having constructed a
manometer for soundness-testing my recent gas installation. Total time -
just over an hour.
In case anyone wants to do the same (as they cost about 25 quid in the
shops) this is what I did. As I had the materials lying around anyway, this
cost me nothing.
White contiboard offcut - about 60cms by 5 cms
Clear plastic flexible tube - about 1.5 metres long - I used 3/8ths of an
inch outside diameter, but this was a bit narrow
Some wire like you would use in the garden for tying back plants
A 30 cm school ruler
Pair of pliers
Warm the end of the tube in hot water and expand one end of the tube to
about 3/8ths of an inch inside diameter and shove something in to stop it
shrinking back - you might be better off with wider tube but this is what I
had lying around.
Arrange the tube on the contiboard in a U-shape, with about a foot of the
expanded end loose. Drill holes in the contiboard and secure the tubing in
place with the wire. It does not matter what is happening at the U-shaped
end, as long as the two straight parts of the tube are parallel to each
other. I arranged them so they were side by side, rather than leaving a gap
between them. I screwed the ruler to the contiboard with the centimetre
scale next to one of the straight bits of tubing - in fact tucked slightly
under for accuracy of measurement.
Use a hook in the end of the contiboard or a loop of wire, so that the whole
thing will hang vertically.
Add water to fill the bottom of the U and bring the water level up to the
bottom of the ruler. If you are being feisty, you could cut slots in the
ruler for the fixing screws, so it can be moved up and down to zero it.
Otherwise, you just have to make a note of the starting level, so that you
can subtract this from the ending level. I found no need to add ink to the
water but you could add this if you want the fluid to be more visible.
You can read the pressure in millibars off the ruler - 1 cm = 1 mb. This is
accurate to 3%, ie the correct conversion is 1.03cm = 1 mb.
I measured the movement in the water of just one of the sides of the
manometer. In other words I just measured the rise in the water in one half
of the U. I assumed that the other side had dropped by an equal amount but
did not measure it. This means that I needed to double whatever difference
in level I found.