How to Read a Water Column Manometer
- 1). Define the terms. The pressure in column A that is exposed to the open air is P(A). This is the reference pressure which we will assume to be approximately 101,325 pascals of pressure. The pressure in column B that is connected to the test is pressure source P(B). Assume that P(B) > P(A) for this experiment.
- 2). Read the height of the water in column A and double it to get the height differential h between the two columns. Remember that the water in column A must rise by the same distance that the water in column B is lowered. By measuring the height of the column of water that P(B) is supporting against the reference pressure of 1 atm, you can later calculate P(B).
- 3). Use h as a relative measure of pressure. You can use the height differential directly to compare the measurements between two different pressures. This may be sufficient for some experiments even though you don't have an absolute measurement of pressure at this point.
- 4). Convert the manometer reading to pressure in pascals. This is given by the standard formula P(B) -- P(A) = dhg where d is the density of water in kilograms per cubic meter (1,000 kg/m^3), h is the height differential in meters and g is the acceleration of gravity in meters per second squared (9.8 m/s^2). Therefore, P(B) = P(A) + dhg = 101,325 pascals + (1,000)(9.8)h pascals = (101,325 + 9,800h) pascals of pressure.