Manometers

Manometers are one of the oldest type of pressure measurement.

Manometers can be used to measure gauge pressure,differential pressure and absolute pressure.

Various types of Manometers
1.U tube Manometer
2.Well type or reservoir manometer
3.Inclined manometer
4.Float type manometer

U tube Manometer.

U tube is made of glass.The tube is filled with a fluid known as Manometer fluid.

Manometer fluid may be  mercury , water etc…

If the manometer is connected to same pressure source (P1 = P2) the level of the manometer will be same.

If the manometer is connected to two different pressure source there will be a difference in level of the manometer fluid in both the limps.

If P1>P2 the differential pressure P2-P1=@h
@=density of the fluid

h=height difference

While choosing the manometer fluid for a particular application we need to remember following things.
Manometer fluid should not wet the wall
Manometer fluid should not absorb gas
Manometer fluid should not react chemically
Manometer fluid should have low vapor pressure
Move freely

In a well type manometer,one leg is replaced by a large diameter well.Since the cross sectional area of the well is much larger than the other leg,when pressure is applied to the well,the manometer liquid in the well lowers only slightly compared to the liquid rise in the other leg.As a result of this,the pressure difference can be indicated only by the height of the liquid column in single leg.

For static balance,

P2-P1= @(1+A1/A2)h

 where

A1= area of smaller-diameter leg

A2= area of well

If A1/A2 << 1 then P2-P1 = @h

If the area of well is 500 or more times larger than the area of vertical leg,the error involved in neglecting the area is negligible.