THEORY OF OPERATION
The TFFT contains the same functional base systems as the M977 vehicles, with some modifications. The TFFT
firefighting systems are described in the following paragraphs. Refer to TM 9-2320-347-10 for base M977A2
vehicle systems not contained in this manual.
WATER PUMPING SYSTEM
Water pressure is supplied to the water pumping system by a Darley PSE, single stage, engine driven, centrifugal
pump. Water flows from the pump discharge manifold to roof turret, bumper turret, ground sweeps, window deluge
system, two (2) pre-connect discharges; and two (2) driver side and passenger side discharge valves.
The water pumping system can be operated from both cab instrument panel or pump operator's panel. Controls
are interlocked to ensure single operator control. In pump and roll mode, system can only be operated from cab
instrument panel. In structural mode, system can be operated from pump operator's panel.
In pump and roll mode, water is supplied to the pump from the water tank. Pump must be disengaged when water
tank is emptied.
In structural mode, water is supplied to the pump from either the water tank or alternate source(s). Alternate
sources may be fire hydrants, remote pumping units, or an open reservoir. If water is drawn from tank for structural
firefighting, water must be continuously supplied through automatic direct tank fill valve.
WATER PUMP ENGINE
The water pump engine is a Deutz, six cylinder, turbocharged, auxiliary diesel pump engine. The water pump
engine is water-cooled and has 198 HP to drive the water pump. The water pump engine is installed in the pump
house in a "crossmount" configuration. This allows for water pump modulation in accordance with NFPA 414 for all
vehicle speed ranges, in all directions of travel, without any loss of pump discharge rates and ranges. The water
pump engine draws fuel from the chassis fuel tank.
Water pump pressure can be increased or decreased by changing water pump engine RPM.
WINDSHIELD DELUGE SYSTEM
Windshield deluge system is operated from cab instrument panel. Nozzles are mounted below windshield and
receive fluid from a 24 VDC electric pump. The windshield deluge system draws water from the 1,000 gal (3,785 l)
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