SYSTEM OPERATION.- Now that the injection system is activated, the other components begin to function. As the freshwater continues to shoot out the detector nozzle, the flow switch actuates. Freshwater pressure decreases and, in a matter of seconds, the main check valve opens. The system continues to operate, discharging the fire main supply from the (one) activated nozzle. When the emergency is over, personnel turn off the fire main supply to secure the system and replace the detector nozzle. The system is then flushed, refilled, and charged.
A word of caution worth remembering-Use extreme care when working around a water injection nozzle. The gold-wire spring pin is sensitive. A dropped tool or a misplaced foot can result in a tremendous surprise !
Actual GMLS Water Injection Systems
All GMLSs have a water injection system. Each system operates on the same principle. Only the physical location and number of components differ.
The Mk 13 GMLSs (fig. 8-26) have a total of 96 detector nozzles (48 on the inner ring and 48 on the outer ring). Since the Mk 13 GMLS RSR rotates, the RSR cells (16 inner and 24 outer) can be indexed and stopped at over 96 different positions. The Mk 26 GMLS has one detector nozzle at each RSR hanger rail position. The Mk 41 VLS has a deluge system for each cell canister, which floods the canister during rocket motor ignition without the missile leaving the canister.
The Mk 13 GMLSs use a special valve in their water injection systems. It is called a restart valve. In the typical water injection system schematic (fig. 8-24), this valve would replace the manual shutoff valve above the main check valve. The restart valve may be operated manually or by a remote-controlled solenoid. The solenoid is actuated by a switch located inside the launcher control room.
Initially, the injection system must still be activated automatically. However, the restart valve may be used to secure the system. It can also be used to reactivate (restart) the system in an emergency situation (such as a flashback).
A special feature of the Mk 26 GMLS is that a sensing line connects the water injection system to the
Figure 8-26.-Mk 13 GMLS magazine base; injection system arrangement inside magazine area.
sprinkler system (fig. 8-27). Should a rocket motor ignite, the detector nozzle activates the injection system. Additionally, the blast pressure pushes the blow-in plate down, causing it to fall into the plenum port of the RSR station. Loss of a blow-in plate releases the drop-away plunger of a sprinkler-actuating valve assembly. Water pressure in the sensor line decreases and starts zone sprinkling. The operation is unique to the Mk 26 GMLS.
DRY-TYPE SPRINKLER SYSTEMS
A dry-type sprinkler system is one in which the piping from the outlet side of the main sprinkler control valve up to the sprinkler heads contains no water in a normal or ready state. This piping remains "dry" until the system is activated.
The sprinkler system may be activated automatically or manually. A thermopneumatic system, using HSDs, performs the automatic function. Manual control valves, located at separate local and remote control stations, are used to activate the system manually.
Once the system is activated, it must be secured manually. System design permits it to be activated at one station and be secured from another station.
The Mk 13 GMLS and Mk 41 VLS have dry-type magazine sprinkler systems. A dry-type sprinkler system can be divided into four main equipment areas:
1. Automatic control system
2. Hydraulic control system
3. Main sprinkler control valve
4. Sprinkler alarm system
Figure 8-28 is a general schematic arrangement of the major sprinkler components. Take a moment to study it, as we will refer to it frequently. Locate the four equipment areas.