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.
Materials:
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
Tools
Small drill
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.
HTH
Geoff