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Question
Explain the principle, construction and working of manometer.
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Solution
A manometer is a device used to measure the pressure at any point in a fluid, manometers are also used to measure the pressure of gas and air.
Pressure or the intensity of pressure is defined as force per unit area, or P=FA, where P is measured in Nm2. Fluid pressure is measured with respect to varying individual reference that is a device or procedural specific. When it is measured with respect to absolute zero (or complete vacuum), it is called absolute pressure. When it is measured either above or below atmospheric pressure, it is called gauge pressure.
The term manometer is derived from the ancient Greek words 'manós', meaning thin or rare, and 'métron'. A manometer works on the principle of hydrostatic equilibrium and is used for measuring the pressure (static pressure) exerted by a still liquid or gas. Hydrostatic equilibrium states that the pressure at any point in a fluid at rest is equal, and its value is just the weight of the overlying fluid. In its simplest form, a manometer is a U-shaped tube consisting of an incompressible fluid like water or mercury. It is inexpensive and does not need calibration.
As seen in the figure, the U-shaped tube filled with liquid measures the differential pressure, i.e., the difference in levels 'h' between the two limbs gives the pressure difference (p1−p2) between them. When pressure is applied at limb 1, the fluid recedes in limb 1, and its level rises in limb 2. This rise continues till a balance is struck between the unit weight of fluid and the pressure applied. If the pressure applied at one opening; say limb 1 of the U-tube, is atmospheric pressure, the difference gives the gauge pressure at limb 2.
h=(p1−p2)ρg
where, ρ= density of the liquid used in the manometer
Hence, ρg= specific weight of the liquid
Pressure or the intensity of pressure is defined as force per unit area, or P=FA, where P is measured in Nm2. Fluid pressure is measured with respect to varying individual reference that is a device or procedural specific. When it is measured with respect to absolute zero (or complete vacuum), it is called absolute pressure. When it is measured either above or below atmospheric pressure, it is called gauge pressure.
The term manometer is derived from the ancient Greek words 'manós', meaning thin or rare, and 'métron'. A manometer works on the principle of hydrostatic equilibrium and is used for measuring the pressure (static pressure) exerted by a still liquid or gas. Hydrostatic equilibrium states that the pressure at any point in a fluid at rest is equal, and its value is just the weight of the overlying fluid. In its simplest form, a manometer is a U-shaped tube consisting of an incompressible fluid like water or mercury. It is inexpensive and does not need calibration.
As seen in the figure, the U-shaped tube filled with liquid measures the differential pressure, i.e., the difference in levels 'h' between the two limbs gives the pressure difference (p1−p2) between them. When pressure is applied at limb 1, the fluid recedes in limb 1, and its level rises in limb 2. This rise continues till a balance is struck between the unit weight of fluid and the pressure applied. If the pressure applied at one opening; say limb 1 of the U-tube, is atmospheric pressure, the difference gives the gauge pressure at limb 2.
h=(p1−p2)ρg
where, ρ= density of the liquid used in the manometer
Hence, ρg= specific weight of the liquid
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