Hydrostatic Wheel Drive Circuit
With this switch ON and the engine running, the valve
remains closed and charge pump pressure is held at the
The hydrostatic wheel drive pump assembly is
solenoid valve. Moving the parking brake switch to
engine driven via power transfer. It provides hydraulic
OFF, opens the valve and circuit pressure is directed to
flow (drive) and charge pump pressure (control) to
the brake modules, overcoming the spring applied
drive and control the hydrostatic wheel drive system.
The wheel drive motors receive flow through the
The brake release hand pump is used to manually
freewheel manifold from the wheel drive pump to turn
apply pressure to release modular brakes and free flow
the wheels and move the vehicle.
hydrostatic pressure in the drive circuit in case of an
The freewheel manifold splits and directs equal
engine or hydraulic failure. The pump has an integral
fluid flow to the wheel drive motors and back to the
shuttle valve and a lever actuated pressure relief valve.
wheel drive pump. Flow through the manifold is
The freewheel control valve is manually opened
dependent on flow received from wheel drive pump.
and closed to apply hydraulic pressure from the brake
The flow direction is dependent on whether the F-N-R
release hand pump to shift the freewheel valve. The
(Forward-Neutral-Reverse) lever is in forward or
freewheel valve is located on the freewheel manifold
reverse mode. The hydrostatic wheel drive pressure test
and is opened by pressure from the brake release hand
point is located in port A1 on wheel drive pump.
pump. The valve releases the hydrostatic lock on both
the drive motors by allowing fluid to flow freely be-
Water Pump Drive Circuit
tween the motors. The modular service/parking brakes
consist of self-adjusting, pedal-operated service brakes
The water drive pump assembly is also engine
with a master cylinder. The parking brakes require
driven via power transfer and provides hydraulic flow
hydraulic pressure to over come spring pressure.
(drive) and charge pump pressure (control) to drive and
control the water pump drive system. (4350-psi max.
The accelerator pressure control valve releases
output). The water pump drive motor receives flow
hydraulic pressure in proportion to movement of the
from the water drive pump and the fluid flow powers
accelerator pedal to the gear select valve. The farther
the motor to mechanically drive the water pump via the
the pedal is depressed the more pressure that is sent.
water pump transmission. The water drive hydraulic
The gear select valve directs the fluid pressure to fwd or
pressure test point is located in port B1 of the water
reverse ports of the spool valve located in the main
drive pump assembly.
wheel drive pump assembly.
The 0/150/250/500/ gpm joystick controls the
Hydraulic System Safety Precautions
operation of water pump drive motor by directing
hydraulic charge pressure to spool valve in water drive
Ensure the hydraulic system is depressurized prior
pump and AFFF foam pump drive motor solenoid. The
to performing work on any component or system.
motor speed is controlled proportionally by the joystick
Hydraulic fluid MIL-H-83282 (or MIL-PRF-83282) is
position (0-500 gpm).
toxic. Ensure that you wear chemical splash goggles,
rubber gloves, and an apron when feasible. Keep the
The isolation control solenoid valve is an
fluid off the skin, eyes, and clothing. Wash affected
electrically operated hydraulic valve controlled by the
STANDBY/OFF switch. It directs the charge pressure
to the isolation valve hydraulic cylinder, which opens
and closes the isolation valve located between the water
tank and the water pump inlet. It also has a manual over
The P-25 fire-fighting vehicle is an important part
ride knob, which opens and closes the valve in case of
of the ship's fire control systems. Knowledge of the
an electrical power failure.
fire-fighting system is necessary to properly operate
The isolation valve cylinder opens and closes the
and maintain the vehicle.
isolation valve located between water tank and water
pump inlet to allow water from the tank to flood the
suction side of water pump in preparation for water
There are several components within the
pump operation. It also closes the isolation valve to
fire-fighting system that you must become familiar
allow the system to be drained to prevent the pipes from
with to understand how this system operates. Once