Gauge glasses

General

The requirements are that there must be two independent means of reading the boiler water level. Normal practice for propulsion plant boilers are the fitting of two direct reading level gauges and a remote display readout.

Low pressure boilers( up to 17.5 bar)

Small vertical boilers may be fitted wit a series of test cocks to ascertain the level, this is deemed unsuitable for boilers above 8.2 bar and/or 1.8m in diameter.

Tubular gauge glass

Tubular guage glass

Tubular guage glass

Medium pressure boilers

reflex guage glass

Reflex glass is used due to the fact that light falling on the glass is reflected by the steam but not by water, and so the glass appears bright where there is steam and dark where there is water.

High pressure boilers

Gauge glass suitable for high pressures

A ball is located in the water side to prevent large quantities of water entering the engineroom in the event of the glass failing and the subsequent large expansion of the water as it flashes off to steam. An orifice restrictor is fitted to the steam valve.
Mica is placed on the water side of the glass to protect against erosion and chemical attack of the high temperature water.

General gauge glass faults

Due to the evaporation of water leaking through the cock joints a build up of deposits can occur. This leads to restriction and eventual blockage of the passage. If this occurs on the steam side then the level tends to read high as the steam condenses.
Another reason for blockage is the cock twisting, hence the cocks are all arranged so that in their normal working positions, i.e. steam/water open , drain shut, the handles are all pointing downwards. Possibility of the sleeving rotating on the cock has led to the use of ribbed asbestos sleeves which must be carefully aligned when fitting.
For tubular gauge glasses the length of the tube is critical and should be checked before fitting

Bi-color gauges

refraction through water of different colors

Igema remote reading indicator

Fitted in addition to gauges required by statute and not in place of them. The red indicator fluid does not mix with the water

Igema remote indicating water level indicator

Equilibrium condition is when H= h + rx where r is the specific density of the indicator fluid.

If the water level rises h increases and x reduces. Therefore H will be reduced and water will flow over the weir of the condenser to maintain the level constant. If the water level were to fall h would be reduced, x increase and H would be increased. Water therefore must be made from condensing steam in order to keep the condenser level constant.