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All LM2500 GTE modules have some method for detecting and extinguishing a fire in the enclosure. The sensors used to detect a fire are identical on all classes. The detection system has three ultraviolet (UV) flame detectors, a flame detector signal conditioner, and two resistance temperature elements (RTEs) used as temperature switches. The use of these sensors and the fire- extinguishing systems vary with ship classes.

Figure 2-6 shows a block diagram and an exploded view of a UV flame detector. This detector senses the presence of fire in the enclosure and generates a photoelectric signal. This signal

is transmitted to the signal conditioner to alert the operator of fire in the module. On the LM2500 GTE of the twin-shaft ships and on the Allison 501-K17, it also activates the fire stop sequence and releases fire-extinguishing agents to extinguish the fire.

The signal conditioner (fig. 2-7) is contained in a metal box. The box is attached to the underside of the base enclosure on the LM2500 GTE. On the Allison 501-K17 GTE, the unit is located in the alarm terminal box on the generator end of the base. Identical detector cards (one for each UV sensor) are located in the signal conditioner. The detector card amplifies, rectifies, and filters the current pulses from the UV sensor. This provides an output voltage level proportional to the UV light level at the UV sensor. The signal conditioner processes the input from the UV flame detector and completes the alarm control circuitry outside of the gas

Figure 2-8.—Fire system temperature switches and manual switches.

turbine module (GTM), which results in the alarm indication.

The two temperature switches are mounted on the enclosure ceiling and generate an alarm signal if the temperature reaches a preset level (fig. 2-8). The output of the RTEs, which generate a fire signal only, is an input to the free standing electronic enclosure (FSEE).

CG-, DD-, and Class Ships

Since we discussed the components of the fire detection system in the previous section, we will not discuss them here. The alarm system also has a manual fire alarm push button (shown in fig. 2-8) besides the electrical signal generated by either the temperature switch or the flame detector signal conditioner. The extinguishing system has two CO2 discharge nozzles. When

manually activated, the CO2 fire-extinguishing

agent is discharged into the enclosure. It also has an extinguish release/inhibit switch and a CO2

release/inhibit switch mounted to the outside of the enclosure, next to the side access door.

Figure 2-9.—CG, DD, and fire stop sequence flow chart.

Two CO2 discharge nozzles are located inside

the enclosure. They are mounted on the crossbeam under the compressor front frame. One is for initial discharge (primary) and the other for extended discharge (secondary). The fire extinguish release/inhibit switch is mounted above the fire alarm push button. It is a two-position switch (ACTIVE/INACTIVE). When in the INACTIVE position, this switch prevents discharge of the CO2

extinguishing agent.

Figure 2-9 is a signal flow chart of the fire stop sequence. Fire is sensed by the flame detectors or temperature switches. The fire may also be discovered by watch station personnel who would operate the manual CO2 release

switch. In either situation, the sequence of events are the same after the fire is discovered. Electrical contacts close to activate the fire- extinguishing system and the following concurrent actions occur:

1. The fire alarm signal sounds.

2. The system conducts a self-check to see if battle override has been selected at the propulsion local control console (PLCC) or the propulsion auxiliary control console (PACC) or if the module cooling system has failed. Either event will terminate the fire stop sequence.

3. The GTE fuel shutdown valves close, shutting down the GTE.

4. The fuel supply to the GTM is shut off in the ship’s service system.

Figure 2-10.—FFG fire system block diagram.

5. The module cooling air fan is shut down. 6. The module vent damper is closed. 7. The bleed air valve is closed.

8. The enclosure lights flash (only if lights were previously on).

9. After a delay of 20 seconds, the initial CO2

discharge occurs.

To prevent CO2 discharge, position the release

inhibit switch to the INACTIVE position during the 20-second time delay. The initial discharge delivers 150 pounds of CO2 at a rate of 50 lb/min.

If required, the extended CO2 discharge is

manually activated. The extended discharge delivers 200 pounds of CO2 at the rate of

10 lb/min.

FFG-Class Ship

Like the other ship classes already discussed, the fire detection system of the FFG-class ship has three flame detectors, a flame detector signal conditioner, and two temperature switches. The manual alarm system has a fire alarm push button. The extinguishing system has a single Halon discharge nozzle, connecting tubing, and an extinguish release inhibit switch.

The UV flame detectors of the FFG-class ship are identical to the type on the other class of GTE-powered ships, but provide only an alarm. The RTE fire sensor will also sound that same alarm, indicating a fire is present.

The manual fire alarm push button is mounted on the outside of the enclosure, next to the side access door. When activated, a contact closure signal is provided to the ship’s system which

sounds an alarm at the propulsion control console (PCC) to notify the engineering officer of the watch (EOOW). Fire may also be sensed by the flame detectors (fig. 2-10) or either of the two temperature switches may detect enclosure temperature above preset limits.

The Halon discharge nozzle is located inside the enclosure. It is mounted on the underside of the crossbeam under the compressor front frame. This one nozzle provides both initial (primary) and standby (reserve) Halon discharge. The fire extinguish inhibit switch is mounted above the fire alarm push button on the outside of the module. When in the ACTIVE position, this switch will allow automatic or manual discharge of the Halon. When in the INACTIVE position, this switch provides a signal to the ship’s system that is used to prevent discharge of the Halon, However, this switch does not override manual activation locally.

You can extinguish a fire in either enclosure by filling the enclosure with Halon. The PCC has a FLAME DET ALARM/HALON FLOOD push button for each enclosure. To prevent an enclosure from being flooded with Halon while personnel are inside, place the fire extinguish inhibit switch in the INACTIVE position.

Activation of the FLAME DET ALARM/ HALON FLOOD switch on the PCC will provide the initial Halon discharge of 60 pounds at a rate of 1.45 lb/sec. An additional 60 pounds, with the same rate of discharge, is available on standby (manually activated).