TITLE.PM5

BASIC CONCEPTS OF THERMODYNAMICS 37

dharm
M-therm/th2-1.pm5

The principle of the inclined manometer is explained in Fig. 2.19. If pressure p 1 = p 2 , then

the level of liquid is shown by LM. However, when p 1 is slightly greater than p 2 , the level is the

reservoir sinks by h 2 , whilst level in the tube rises by a greater distance h 1 as shown in the

diagram. If h is the vertical distance between the two surfaces due to difference of pressure, then

Fig. 2.19. Principle of inclined manometer.

h = h 1 + h 2

also h 1 = d sin θ

and h 2 × A = d × a

or h 2 = d × Aa

where A = Area of cross-section of the reservoir, and

a = Area of cross-section of the inclined tube.

Also the pressure difference ∆ p i.e., (p 1 – p 2 )

= hw = dd

a

×+×A

F

H

I

sinθ Kw

= dw sinθ+

F

H

I

K

a

A

where w is the specific weight of the liquid.

The sensitiveness of the instrument can be varied by changing the slope of the inclined

tube. The position of the inclined tube is so arranged thatsinθ+

F

H

I

K

a

A is round figure.

The multiplication factor of the gauge is dh =^1

sinθ+Aa

Thus the multiplication factor depends on θ and Aa. The smaller the values of θ and (^) Aa,
the greater the multiplication factor.
Advantages and disadvantages of manometers :
Advantages. The manometer claims the following advantages :

1. Relatively inexpensive.


2. Easy to fabricate.


3. Requires very little maintenance.


4. Good accuracy and sensitivity.