U Tube Manometer: Manometers are devices in which one or more columnsof a liquid are used to determine the pressure differencebetween two points.
• A manometer is comprisedU- Tube Manometer: 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 PHg there is also air pressure acting on the gas. • The gas molecules put pressure on the mercury.
Closed Manometers: • There is a balance between the weight of the mercury vacuum on the left (PHg) and the pressure of the gas on the PHg 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
Open Manometers: • When gas pressure is greater than atmospheric pressure, the mercury is pushed toward the Pair open end. • The balance is between the gas on the right, and the air plus mercuryPHg on the left. Pair + PHg = Pgas • The weight of the mercury is measured as the height difference: PHg = Dh So Pgas = Pair + Dh
Open Manometers: • When gas pressure is less than atmospheric pressure, the mercury is pushed toward the gas reservoir. • The balance is between the air PHg on the left and the gas plusPair mercury on the right: Pair = Pgas + PHg • The weight of the mercury is measured as the height difference: PHg = h So Pair = Pgas + h Or Pgas = Pair- h
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