Manometer

Pharmaceutical Engineering

1. Manometer are device used to measure the pressure difference values. Types of Manometer 1.Simple Manometer 2.Differential Manometer 3.Inclined tube manometer Manomete r

2. A simple manometer is a tube gauge for measuring high as well as negative pressures. It is the simplest form, having a U shaped bent tube, one end of which is attached to the gauge point and the other end is open to the atmosphere. The construction of a simple manometer is shown in Fig. The U shaped glass tube is filled with a liquid (A) of density, ρ A , kg/m3. Above liquid A, the tube arms are filled with a lighter liquid B of density ρ B, kg/m.

3. Both the liquids are immiscible and the junction interface is clearly visible. Generally, liquid A is mercury which is 13.6 times denser than water and therefore, suitable for measuring high pressures also. When two different pressures are applied to the arms of manometer, the liquid A shows a movement so that the meniscus in both the arms is at different levels. Consider various This manom points (1 to 5) in the center of the lumen of U tube at different distances as shown in Fig. 1.3.

4. Let us suppose that the pressure at point 1 is P1 (Pa) in the left arm of the figure and at point 5 is P2 (Pa) in the right arm of the figure. pressure at point 2 can be written as: pressure at point 2 = P1+h. ρ .g................................1 Here h is height of liquid above the point 2 i.e. ( m+R )and density is . gB So Pressure at point 2= P1+( m+R ). ρ B.g .......................................2 Pressure at points 2 and 3 are at same level,pressure at point 3 is Pressure at point 3= Pressure at points 2=P1 +( m+R ). ρ B.g ............3 Now pressure at point 4 in terms of P2 can be written Pressure at point 4= P2+m. ρ B.g .......................................4

5. In another form, the pressure at point 4 can also be written in terms of P1 from the left arm as: Pressure at point 4 = P1+( m+R ). ρ B.g - R ρ A.g .............5 Since both the points are same, both these equations 4 and 5 should be equal, Hence, the pressure at point 4 can be re-written as: P1 +(m + R). ρ B.g -R. ρ A.g = P2 + m. ρ B.g P1- P2 = m. ρ B.g - (m + R). ρ B.g + R. ρ A.g ∆ P = m. ρ B.g -m ρ B.g -R ρ B.g + R. ρ A.g ∆P =R.( ρ A- ρ B ).g Thus the value of ∆P is independent of the distance m and dimension of U tube with a condition that P1 and P2 are measured in the same horizontal plane

6. Inclined Manometer It is a kind of modified simple manometer used to measure small difference in pressure. In this type, one limb of the manometer is inclined in such a way that for a very small value of actual reading R, the meniscus moves a considerable distance (inclined reading) so that it can be noted easily. The inclined distance is equal to the actual reading R divided by the sine of angle of inclination α (sin α ). Thus by making α small, the value of inclined reading R, can be increased. ∆P = P1- P2 = Ri ( ρ a - ρ B ). g ∆ P = P1- P2 = ( R/sin α ) ( ρ a - ρ B ). g