A manometer is a general term for any device that measures pressure. A U-tube manometer is a specific type of manometer that measures the difference in pressure between two sources of gas. It typically compares a gas source with an unknown pressure to the atmosphere, which has a known pressure. A U-tube manometer is so-named because the primary component is a tube in the shape of a “U.” It’s frequently the subject of school science projects.
- Tube fasteners
- 4-foot length of plastic tubing
- 2-foot length of wooden board
- Plumb bob
- 100 ml of water
- Red food coloring
- Gas source
Use the tube fasteners to attach the plastic tubing to the board in the shape of a “U.” The tube fasteners must not impede the free flow of water through the tube. Ensure the “U” shape of the tube is smooth, without any sharp breaks or kinks.
Suspend a plumb bob to provide a vertical reference. Position the manometer so that the two halves of the “U” shape are vertical and fasten the plumb bob to the board securely with a nail.
Mix water in a beaker with sufficient red food coloring to make the water red. Pour about 100 ml of the water into one of the open ends of the manometer.
Position a ruler vertically on one side of the manometer. Adjust the ruler’s position so that its zero point is level with the surface of the water in the manometer. Secure the ruler firmly in place with tape without obscuring the ruler’s scale.
Insert one of the open ends of the manometer over the nozzle of a gas source to make a gas-tight seal. Measure the height of the water in the tube next to the ruler to obtain the pressure of the gas source relative to the atmospheric pressure in inches of water.
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