Describe a sprinkler system and explain how it operates. Describe the control valve and
explain how it is reset after use or testing of system.
The sprinkler system is an automatic fire detecting alarm and extinguishing system that is
constantly "on guard" to deal quickly and effectively with any outbreak of fire that may occur in
accommodations or other spaces. The system is composed of a pressurized water tank with
water pipes leading to various compartments. In these compartments the water pipes have
sprinklers heads fitted which come into operation when there is an outbreak of fire. The
pressure tank is half fitted with fresh water, through the fresh water supply line. Compressed air
is delivered from the electrically driven air compressor raises the pressure in the tank to a
predetermined level, this should be such that the pressure at the highest sprinkler head in the
system is not less than 4.8 bars. Sprinkler heads are grouped into sections with not more than
150 heads per section and each section has an alarm system. Each sprinkler head is made up of
a steel cage fitted with a water deflector.
A quardtroid by which contains a highly expansible liquid is retained by the cage. The upper end
of the bulb presses against a valve assembly which incorporates a soft metal seal. When the
quartizoid bulbs are manufactured a small gas space if left inside the bulb, as the bulb is
subjected to heat the liquid expands and the gas diminishes. This will generate pressure inside
the bulb and the bulb will shatter once a predetermined temperature (and hence pressure) is
reached. Generally the operating temp range permitted for these is 68C to 93C, but the upper
limit of temp can be increased this would be depending upon the position where the sprinkler
head or heads is the rated. Quartriod bulbs are manufactured in different color the colors
indicate the temp rating for the bulb.
rating
68C = red
80C = yellow
93C = green
Once the bulb is shattered the valve assembly falls, permitting water to be discharged from the
head, which strokes of the deflector plate and sprays over a considerate area. When a head
comes into operation the non-return alarm for the section opens and water flows to the
sprinkler head. This non-return valve also uncovers the small bore alarm pipe to a rubber
diaphragm and then operates a switch which causes a break continuously live circuit. Alarms
both visible and audible fitted in the engine room, bridge, and crew spaces are then
automatically operated. Stop valves, A and B are locked open and if either of these valves are
inadvertently closed a switch will be operated that brings the alarms into operation. The alarm
system can be tested by opening valve C, which allows a delivery of water similar to that of one
sprinkler head to flow to drain.
An electrically operated pump with a direct suction to the sea comes into operation when the
fresh water charge in the pressure tank has been used up. This arranged to operate
automatically through the pressure relay. A hose connection is also provided so that water can
be supplied to the system from shore when the vessel is in dry dock. This connection must be an
international shore hose connection. Any part of the system which might be subjected to
freezing must be protected.
Some sections may be of the dry pipe type, where considered necessary. The dry pipe extends
upward from the section valve which also acts as the link between the sprinkler system water
pressure and the dry pipe pressurized with air. Water pressure is contained by the water clapper
which is held on its seat by the centre valve. The space above the centre valve is fitted to the
level with water and the pipe above that is filled with air under pressure. The center valve is
made watertight by a joint and intermediate sprinkler is dry. When operation of a sprinkler a
sprinkler head releases the pressure in the dry pipe, the centre valve is pushed by the force of
water under the clapper. The clappers lifts and rotates on the yoke being swing to one side by
the effect on the water flow on the skirt. The water floods up through the dry pipe causing the
centre valve to lock open, and in filling the intermediate chamber pressurizes and operates the
alarm.
Pressure gauges for air and water are required. The section valve opens when air pressure drops
to 1/16th that of water pressure. The cover has to be removed to reset the valve. The clapper
valve alarm is tested by opening a testing valve on the dry side of the suction valve alarm
allowing water to flow through the valve as though the sprinkler had been operated. After
resetting the clapper the water is admitted on top of the centre valve through a water
connection for that purpose and water brought to the correct level. The water is necessary for
maintaining a good seal on the clapper.
