# Manometers

Manometers are the devices used for measuring the pressure difference

Different type of manometers are there they are

·         Simple manometer

·         Differential manometer

·         Inclined manometer

Simple manometer

• This manometer is the most commonly used one

• It consists of a glass U shaped tube filled with a liquid A- of density

ρA kg /meter cube and above A the arms are filled with liquid B of density ρB

• The liquid A and B are immiscible and the interference can be seen clearly

• If two different pressures are applied on the two arms the meniscus of the one liquid will be higher than the other

• Let pressure at point 1 will be P1 Pascal's and point 5 will be P2 Pascal's

• The pressure at point 2 can be written as =   P1+ (m + R ) ρ B g

(m + R ) = distance from 3 to 5

Differential manometers

• These manometers are suitable for measurement of small pressure differences

• It is also known as two – Fluid U- tube manometer

• It contains two immiscible liquids A and B having nearly same densities

• The U tube contains of enlarged chambers on both limbs

• Using the principle of simple manometer the pressure differences can be written as

∆P =P1 –P2 =R (ρc – ρA) g

Hence smaller the difference between ρc and ρA larger will be R

Inclined tube manometers

Many applications require accurate measurement of low pressure such as drafts and very low differentials, primarily in air and gas installations.

In these applications the manometer is arranged with the indicating tube inclined, as in Figure, therefore providing an expanded scale.

This enables the measurement of small pressure changes with increased accuracy.

P1 –P2 = g R (ρ A - ρ B) sin α

Measurement of rate of flow of fluids

Whenever fluid are used in a process it is necessary to measure

The rate at which the fluid is flowing through the pipe

Methods of measurement are

1. Direct weighing or measuring

2. Hydrodynamic methods

·         Orifice meter

·         Venturi meter

·         Pitot meter

·         Rotameter

3. Direct displacement meter