M.Sc-I (Electronics)DOES – PC (UOP)

Manometer

Manometers are devices in which one or more columns of a liquid are used to determine the pressure difference between two points.

U Tube Manometer:

U- Tube Manometer:• A manometer is comprised

of a bulb containing a gas and a U-shaped tube.

• The U-shaped tube is partially filled with mercury. The weight of the mercury puts pressure on the gas.

• If the U-tube is OPEN there is also air pressure acting on the gas.

• The gas molecules put pressure on the mercury.

PHg

Closed Manometers:

• There is a balance between the weight of the mercury on the left (PHg) and the pressure of the gas on the right (Pgas).

• The difference between the heights of the mercury on each side of the tube is a measure of the pressure of the gas.

Pgas = Dh

vacuum

PHg

Open Manometers:• When gas pressure is greater than

atmospheric pressure, the mercury is pushed toward the open end.

• The balance is between the gas on the right, and the air plus mercury on the left.

Pair + PHg = Pgas

• The weight of the mercury is measured as the height difference:

PHg = Dh

So Pgas = Pair + Dh

Pair

PHg

Open Manometers:

• When gas pressure is less than atmospheric pressure, the mercury is pushed toward the gas reservoir.

• The balance is between the air on the left and the gas plus mercury on the right:

Pair = Pgas + PHg

• The weight of the mercury is measured as the height difference:

PHg = DhSo Pair = Pgas + Dh

Or Pgas = Pair- Dh

PHgPair

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