Page 100 - Introduction to Marine Engineering

Boilers 87

Flange
connected
/ to boiler
shell

Packing ring

Glass tube

Drain pipe
led to
bilge
Figure 4.11 Tubular gauge glass

up as a 'sandwich' of front and back metal plates with the glass plates and
a centre metal plate between. Joints are placed between the glass and the
metal plate and a mica sheet placed over the glass surface facing the
water and steam. The mica sheet is an effective insulation to prevent the
glass breaking at the very high temperature. When bolting up this
assembly, care must be taken to ensure even all-round tightening of the
bolts. Failure to do this will result in a leaking assembly and possibly
shattered glass plates.
In addition to the direct-reading water level gauges, remote-reading
level indicators are usually led to machinery control rooms.
It is possible for the small water or steam passages to block with scale
or dirt and the gauge will give an incorrect reading. To check that