1.9 Domestic fresh and salt water
systems
? Open systems using gravity tanks,etc.,are rarely met
nowadays and Figure 1.8 shows a characteristic
arrangement of pressure tanks,calorifiers and pumps for
a large ship,The fresh water pumps are self-priming,
drawing from storage tanks and discharging through
filters to a rising main,branched to give a cold supply and
a hot supply in closed circuit through a calorifier,A tank
kept under pressure by an external supply of compressed
air rests on the system and provides the head necessary
for constant supply throughout the ship.
1.9 Domestic fresh and salt water
systems
? The pump starters are controlled by pressure switches
which operate when the pressure in the tank varies within
predetermined limits as water is drawn off,Distilled
water in now largely used in board; this may be corrosive
(due to the presence of dissolved CO2) and flat to the
taste,It is not unusual to provide for the introduction of
certain chemicals,e.g,Calcium Chloride (CaCl2) and
Sodium Bicarbonate (2NaHCO3) which,in solution are
converted to Calcium Bicarbonate (Ca(HCO3)2) and
Sodium Chloride (2NaCl) to render the water neutral and
palatable,It may then be chlorinated to ensure
bacteriological purity and subsequently de-chlorinated,
Figure 1.9 shows such a system diagrammatically.
1.9 Domestic fresh and salt water
systems
? It is not unusual to provide for the introduction of
certain chemicals,e.g,Calcium Chloride (CaCl2)
and Sodium Bicarbonate (2NaHCO3) which,in
solution are converted to Calcium Bicarbonate
(Ca(HCO3)2) and Sodium Chloride (2NaCl) to
render the water neutral and palatable,It may
then be chlorinated to ensure bacteriological
purity and subsequently de-chlorinated,Figure
1.9 shows such a system diagrammatically,
1.9 Domestic fresh and salt water
systems
? The salt water pump(s) need not be self-priming,
nor are heating nor treatment required,otherwise
the system is identical.
Domestic fresh and salt water systems
End of Chapter 1