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Ali Hamza
Ali Hamza
25 Jan 2019

What is U-tube Manometer??


The U-tube gauge can be used to measure the pressure of either liquids or gases. The bottomof the U-tube is filled with a manometric liquid Q which is of greater density 𝜌man and isimmiscible with the fluid P, liquid or gas, of density ρ, whose pressure is to be measured.

What if the fluid is a gas?

𝜌man >> 𝜌


can be neglected

PA = 𝜌man gh2


For the left-hand limb,

PXX = PA + ρ1 ga

For the right-hand limb,

PXX = PB + ρ1 g(b - h) + ρ2 gh

Thus PB − PA = ρ1 ga - ρ1 g(b - h) - ρ2 gh

or, if A and B are at the same level, X X 


PB − PA = ρ1 ga - ρ1 g(a - h) - ρ2 gh

PB − PA = (ρ1 - ρ2 ) gh 

The “U”-tube manometer can be connected at both ends to measure pressure difference between these two points.