•    A pitot tube is the simple device used for measuring the velocity of the flow at the required point in a pipe or a stream.

•    It is also called as impact tube or stagnation tube.

•    It is based on the principle that if the velocity of flow at a point becomes zero, the pressure is increased due to conversion of kinetic energy into pressure energy.


•    In its simple form, a pitot tube consists of a transparent glass tube bent through 90( ) and with ends unsealed.

•    Diameter of tube is larger enough to neglect capillary effects.

•    One leg called as the body is inserted into the flow at upstream and aligned with the direction of flow whereas the other leg, called as stem, is vertical and open to atmosphere.

•    The liquid is raise in the tube due to changes in energy.

•    The velocity is determined by measuring the rise in the tube.

Consider a section 1 and 2 at a same level just in front of inlet of the tube

Apply Bernoulli’s equation

P₁/ γ + V₁² / 2g + Z₁ = P₂ / γ + V₂² / 2g + Z₂

Z₁  =  Z2 as they are at same level

V₂  = 0 because flow of particle is comes to rest at point 2.

h  = rise in tube

H = head of pressure at

h + H = stagnation head

Substitute above value in Bernoulli’s

H + V12 / 2g = h + H               h = V12 / 2g

V1 = √2gh

Actual velocity   V =  C_v V _theoretical

V = C_v √2gh

Where C_v = Coefficient of velocity

Where

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