Question

With reference to an automatic water sprinkler, fire detecting, alarm and extinguishing system for accommodation spaces:

(a) (i) Sketch a typical system; (8)

(ii) Describe the operation of this system. (4)

(b) State the sources of water available. (3)

(c) Describe the sprinkler head and its operation. (3)

(d) State how the temperature rating of the sprinkler head is determined. (2)

Answer 1

Part (a)

The automatic water sprinkler system is an automatic fire detection, alarm, and extinguishing system that can quickly and effectively deal with any outbreak of fire that may occur in accommodations or other spaces on ships.

A tank (half filled with fresh water) initially charges the entire system with fresh water at a pressure of about 8 bar and maintains it under pressure with compressed air.
It is also connected to an independent seawater pump with its own seawater suction. Each sprinkler head has a quartzoid bulb, which retains a diaphragm seal in the outlet of the water pipe.
When the sprinkler head comes into operation, the non-return alarm valve for the section opens, and water flows to the sprinkler head. This non-return valve also uncovers the small bore alarm pipe lead, and water passes through this small bore alarm pipe to a rubber diaphragm. The water pressure acts on this diaphragm, and this operates a switch, which causes a break in the continuously live circuit. Alarms, both visible and audible, fitted in the engine room, bridge and crew space are then automatically operated.
When the system pressure drops to 5 bar, the seawater pump will start automatically and continue to supply with seawater. A hose connection is also provided so that water can be supplied to the system from shore when the ship is in dry dock

Part (b)

The Source of water available is Sea water and Fresh water.

Part (c)

Operation of Sprinkler head:

Each sprinkler head is made up of a steel cage fitted with a water deflector.
A quartzoid bulb, 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 quartzoid bulbs are manufactured, a small gas space is left inside the bulb so that, if the bulb is subjected to heat, the liquid expands, and the gas space diminishes. This will generate pressure inside the bulb, and the bulb will shatter once a predetermined temperature is reached.
Once the bulb shatters, the valve assembly falls, permitting water to be discharged from the head, which strikes the deflector plate and sprays over a considerable area.

Part (d)

Generally, the operating temperature range of quartzoid bulbs is 68°C to 93°C, but the upper limit of temperature can be increased. Quartzoid bulbs are manufactured in different colours, which indicate the temperature rating of the bulb.

Rating colour

68°C Red

80°C Yellow

93°C Green

✓ Verified Model Answer (Text Solution)

The Source of water available is Sea water and Fresh water.

Operation of Sprinkler head:

Generally, the operating temperature range of quartzoid bulbs is 68°C to 93°C, but the upper limit of temperature can be increased. Quartzoid bulbs are manufactured in different colours, which indicate the temperature rating of the bulb.