A simple manometer consists of a glass tube having one of its  ends connected to a point where pressure is to be measured and other end remains open to atmosphere. Common types of simple manometers are:

(1)    Piezometer
(2)    U-tube Manometers
(3)    Single Column Manometers

•    It is the simplest form of manometer used for measuring gauge pressures.

•    One end of this manometer is connected to the point where pressure is to be measured and other end is open of the atmospheres as shown in.


•    The rise of liquid gives the pressure head at that point. If at a point A, the height of liquid s h in piezometer tube, the pressure at A

P_A = ρ x g x h

•    It consists of glass tube bent in U-shape, one end of which is connected to appoint at which pressure is to be measured and other end remains open to the atmosphere as shown in


•    The tube generally contains mercury or any other liquid whose specific gravity is greater than the specific gravity of the liquid whose pressure is to be measured

(a)    For Gauge Pressure:

Let  A be the point at which pressure is to be measured, whose value is P. The datum line is x-x.

Let      h₁ = Height of light liquid above the datum line
           h₂ = Height of heavy liquid above the datum line
           S₁ = Specific gravity of light liquid
           S₂ = Specific gravity of heavy liquid
           ρ₁ = Density of light liquid
           ρ₂ = Density of heavy liquid

As the pressure is the same for the horizontal surface, hence pressure above the horizontal datum line A-A in the lift column and in the right column of U-tube manometer should be same.

For static equilibrium

Pressure above A-A in the left limb = Pressure above A-A in the right limb

P + ρ₁ g h₁ = ρ₂ g h₂

P = (ρ₂ g h_{2 -} ρ₁ x g x h₁)

(b)    For Vacuum Pressure:

For measuring vaccum pressure, the level of the heavy liquid in the manometer will be as shown in.

Then

Pressure in the left limb = Pressure in the right limb

ρ₂ g h2 + ρ₁ x g x h₁ + P_A = 0

P_A = - (ρ₂ g h2 + ρ₁ g h₁₎

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