Question about "water gauge"

[Dave]

Am I right in thinking that a "water gauge" pressure measurement is just how far a column of water gets moved in a U shaped tube, measured in inches?

Dave

[Set Square]

Yes, provided the sides of the U are vertical. It's the difference in levels of the 2 sides.

If you're measuring the pressure in In.Wg, just take a direct reading in inches. If you need millibars, you'll need to do a conversion. [The burner pressure table for my boiler specifies both mbar and in.wg]

[Dave]

Thanks, no need to spend money on a manometer then :-)

Dave

[a]

same idea with mm or inches of mercury - but it obviously needs higher pressure to move mercury than water :o)

[Set Square]

It's quite easy to make your own manometer for checking boiler gas pressure - using a length of plastic tube bent into a U, a strip of wood and a sheet of graph paper. [Come back Blue Peter - all is forgiven!]

[Rob Morley]

The tubes don't need to be vertical, as long as your measurement is.

[Set Square]

Whilst that is true in pedantic terms - it doesn't really add much to the fund of human knowledge in practical terms! [Would you *really* want to devise a means of measuring the vertical distance when the tube was *not* vertical?!]

[Rob Morley]

I was just pointing out that you don't need to worry about whether the tube is perfectly aligned in order to get an accurate measurement - obviously the two sides should be somewhere near vertical to make life easier.

[Ian Stirling]

Spirit (or laser) level, plumb-line, ruler (or tape measure.)

You have to be careful if the distance is long enough for the curvature of the earth to become a factor.

[Set Square]

It would have to be a *bloody* big manometer!

[Ian Stirling]

True :) I suppose at that level, tides might be important.