258 Hydraulic System
Dual Vane Pump
EXPERT™ vehicles with automatic loading arm are equipped with a dual vane pump. Both sections of
the dual vane pump are activated by two electric solenoid valves. One is mounted on the pump and
the other on the chassis (see Figure 5-3). The electrical signal that activates the solenoid is sent by the
pump switch on the control panel.
Figure 5-3
Vane pump solenoid valve on the pump (1) and on the chassis (2)
When the truck is started, various multiplex modules start monitoring the vehicle and the engine
speed, and allow the vane pump to engage (or not). If the vehicle is going faster than 15 mph (25 km/
h) or if the engine speed exceeds 900 RPM, the vane pump will not engage.
The first section of the vane pump, known as the body vane pump, located closer to the pump shaft,
powers all body functions (tailgate, body hoist, and packer) through the directional control valve (see
Directional Control Valve on page 258). It is capable of delivering a flow of 20 GPM at 700 RPM. A
dump valve located on the chassis (see Figure 5-2) limits the flow to the valve to 45 GPM. All excess
flow is sent back to the hydraulic tank. When the pump is turned off, the oil returns to the hydraulic
tank.
The second section of the vane pump, known as the arm vane pump, powers lifting arm functions and
other options through the proportional valve (see Proportional Valve on page 260). It is capable of
delivering a flow of 16 GPM at 700 RPM. A dump valve located at the pump outlet limits the flow
(see Figure 5-3) to the valve to 20 GPM. All excess flow is sent back directly to the pump inlet. When
the pump is turned off, all the oil returns to the inlet.
Directional Control Valve
EXPERT™ vehicles are equipped with a directional control valve (see Figure 5-4), as part of the body
vane pump, that powers all body functions (tailgate, body hoist, and packer).
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