Page 306 - Introduction to Marine Engineering

280 Instrumentation and control

System Atmospheric
pressure pressure

1 i

i
h ^ 'Scale
*
1 ^
\
\
^ ^ s
Liquid — * I ;
>H

h a system pressure (gauge value) Figure 15.1 U-tube manometer

Barometer
The mercury barometer is a straight tube type of manometer. A glass
capillary tube is sealed at one end^ filled with mercury and then inverled
;
in a small bath of mercury (Figure 15.2). Almost vacuum conditionsexist
above the column of mercury, which is supported by atmospheric

Vacuum •Scale

Glass
•** capillary
tube

Adjusting
screw Figure 15.2 Mercury barometer