Two check valves in the AFFF piping prevent the
valve floods the inlet or suction side of the main water
back flow of water/AFFF into the AFFF side of the
pump. Water is prevented from flowing back into the
AFFF proportioning system. There are also two shutoff
tank by water tank check valve. The water pump has a
valves, which isolate the AFFF and water sides of the
hydraulic motor which is driven when the
proportioning systems. When closed, these ball valves
0/150/250/500 gpm joystick is moved off the "0"
allow the operator to shoot water only from the turret
position with the engine running.
and/or handline by shutting off the AFFF flow from the
The water pump output is coupled to a manifold to
AFFF side of the proportioning system. To shoot water
which the turret and handline are connected. However,
only, the operator must also place the STANDBY/OFF
the water must be mixed in the correct proportion with
switch to the OFF position. The operator then must
the AFFF to obtain an effective fire-fighting agent. The
manually actuate the isolation control valve by lifting
AFFF concentrate is pumped from the AFFF tank by a
and turning its knob clockwise. This opens the water
gear-type foam pump. The AFFF pump is hydraulically
pump isolation valve to flood the water pump without
driven and operates at a constant speed as it draws
energizing the electrically actuated PTO pump solenoid
AFFF from the AFFF tank. The AFFF concentrate
valve in the AFFF pump control valve.
passes through a Y-suction strainer designed to capture
There are two flushing valves located on the AFFF
contaminates in the AFFF before reaching the AFFF
side of the proportioning system. One is a flushing inlet
foam pump. A 1-1/2 inch pressure-relief valve controls
valve and one is a flushing outlet valve. They provide
pressure in the AFFF system by dumping excess
the means for connecting a freshwater supply to the
pressure back to the AFFF tank. Water and AFFF are
flush inlet valve and a drain line at the flush outlet
combined in the ratio controller (TRC & HRC). The
valve. Then, with the AFFF tank suction shutoff valve
TRC is a 3-inch ratio controller for the turret and the
and AFFF tank return valve closed, all AFFF
HRC is a 2-inch ratio controller for the handline. Both
proportioning system piping including the handline can
are sized by the manufacturer to ensure that water and
be flushed with freshwater by operating the turret and
AFFF on the input side are mixed in the proper ratio and
handline in a normal manner. However, prior to
discharged on the output side. The amount of AFFF
flushing the system, the proportioning system should
agent available at each ratio controller is regulated by
be completely drained. All AFFF concentrate drained
the back pressure regulating valve. This is
from the AFFF side of the system should be returned to
accomplished by controlling the flow of AFFF from the
the AFFF tank. AFFF/water mix should never be added
AFFF foam pump back to the AFFF tank. The valve is
to the AFFF tank.
setup to maintain equal pressure on the water and AFFF
side of the system. A pressure sensing line taps into the
Nursing can be accomplished by via line
water side just downstream of the water pump while
connections. There are two 2 1/2-inch National Fire
another taps into the AFFF side downstream from the
Hose threaded fittings and valves that permit the unit's
AFFF foam pump. The pressure-sensing lines act on
fire-fighting system to nurse from the ships
opposing sides of a diaphragm located in the top of
fire-fighting stations. By opening the nursing line
back pressure regulating valve. When the two sensing
control valves, the nursed agent is piped into the unit's
pressures are equal, the flow of AFFF concentrate back
water pump suction inlet. When running, it is pumped
to the tank is maintained at a preset rate in proportion to
to the turret and/or the handline. The STANDBY/OFF
the pressure sensed. When the sensing pressures are not
switch must be in the OFF position to prevent damaging
equal, the diaphragm moves up or down to either
the AFFF foam pump.
increase or decrease the flow of AFFF concentrate back
The water tank quick-fill connection consists of
to the AFFF tank.
one 2 1/2-inch connection for servicing the vehicle's
The AFFF proportioning system has two pressure
water tank. It has a quick-fill control valve/lever that
relief valves. The 1-1/2 inch pressure relief valve opens
opens the water tank fill piping to allow for tank
when the pressure in the AFFF side of the
servicing. You must pull to open it, and it is closed
proportioning system exceeds its preset. The valve
under normal conditions.
relieves pressure by dumping AFFF concentrate back
to AFFF tank. A 3 by 2 1/2 inch valve pressure-relief
Fire-Fighting System Safety Precautions
valve relieves any built up pressure at the turret flow
control valve by opening and dumping water/AFFF to
Before opening the turret flow control valve and
the deck.
actuating the 0/150/250/500 gpm joystick, be sure
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