MAGAZINE SPRINKLER SYSTEM
LEARNING OBJECTIVES: Recall the purpose, components, and functioning of shipboard magazine sprinkler systems. Identify the various control valves, gauges, and alarm systems.
Sprinkler systems are used for emergency cooling and fire fighting in magazines, ready-service rooms, and ammunition- and missile-handling areas. A magazine sprinkler system consists of a network of pipes secured to the overhead and connected by a sprinkler system control valve to the ships saltwater firemain. The pipes are fitted with sprinkler head valves that are arranged so that the water forced through them showers all parts of the magazine or ammunition- and missile-handling areas. A modern sprinkler system can wet down all exposed bulkheads at the rate of 2 gallons per minute per square foot and can sprinkle the deck area at the rate of 4 gallons per minute per square foot. Magazine sprinkler systems are designed to flood their designed spaces completely within an hour. To prevent unnecessary flooding of adjacent areas, all compartments equipped with sprinkler systems are watertight. Upper deck-handling and ready-service rooms are equipped with drains that limit the maximum water level to a few inches. Magazines are completely encloses if flooded, they would be exposed to the full firemain pressure. The firemain pressure on most ships is considerably higher than the pressure magazine bulkheads could withstand therefore, magazines are equipped with exhaust ventilators located in the bulkhead near the overhead. An exhaust ventilator is a pipe with a check valve that permits pressure release (usually to topside). Since the diameter of the pipe is large enough to allow water to flow out as fast as it flows in, no excess pressure can build up in the magazine compartment.
On newer ships, magazines are also equipped with small, capped drainpipes located in the bulkhead near the deck. The caps may be removed in the adjacent compartment to drain flooded magazines.
In their complexity, the sprinkler system control valve and associated components vary with the type of ammunition intended for stowage in the magazine.
The basic type of hydraulically controlled saltwater/seawater-operated sprinkler system is the dry type. The dry type is normally installed in gun ammunition magazines and in missile magazines. For this reason, only the dry type is covered in this chapter. Technical information on other types of sprinkler systems is contained in Magazine Sprinkler System, NAVSEA S9522-AA-HBK-010.
The remaining coverage of sprinkler systems is presented as follows:
Magazine sprinkler control valves (commonly refereed to as main valves)
Hydraulic (saltwater/seawater) control systems
Automatic (thermopneumatic) control systems
Sprinkler alarm systems
MAGAZINE SPRINKLER CONTROL VALVES
Magazine sprinkler valves are normally closed, globe-type valves that are designed to open wide upon actuation and supply seawater to the sprinkler system. They are diaphragm operated and manufactured by either the CLA-VAL or Bailey Company. Both valves open on a minimum operating pressure of 40 psi. Each of these valves is held closed by the combined force of the valve spring and the firemain pressure acting on top of the valve disk.
The diaphragm-operated control valve (fig. 2-14) is held closed by firemain pressure acting against the valve disk and the valve spring force acting against the upper diaphragm washer. When the control system is actuated, seawater from the firemain (operating
pressure) enters the diaphragm chamber and acts against the lower diaphragm washer. The area of the lower diaphragm washer is larger than the area of the valve disk Accordingly, the magnitude of the resultant upward force is sufficient to overcome the downward forces of the valve spring and the firemain pressure acting against the valve disk. When the control system is secured, the operating pressure is bled from the diaphragm chamber and the valve is closed by the force of the valve spring.
The test casting or test fittings for the Bailey and CLA-VAL models are NO T interchangeable.
Figure 2-14.-Diaphragm-operated magazine sprinkler control valve.