2008 25 DSTOPTRS
gutter broom operation but is reduced to 1500 PSI for the pick-up head and the
dump door. The control valves are solenoid actuated meaning that they are shifted
from inside the cab by use of electric switches. These switches are located on the
sweeper control console panel with the exception of the dump switch which is
located externally on the left side of the sweeper just above the fender well.
2. BAH Control Valves
BAH Hydraulic Circuit - Flow from the fixed displacement vane type pump is sent
to a single tandem center series control valve mounted on a manifold subplate found
on the left-hand side of the sweeper frame just under the blower housing. When the
solenoid actuated control valve is not in use, oil passes through the valve and is
routed back to a filter manifold and then into the reservoir. When the BAH switch is
shifted 'on’, electrical current shifts the control valve and opens an electric lock valve
(located on the BAH sequence manifold) used to lock the broom in the “UP” position.
Oil is diverted by the control valve to the BAH sequence manifold where the pressure
differential created as the oil passes through the sequence valve is sent to the base
end of the two BAH cylinders causing the broom to be lowered to the pavement.
The amount of hydraulic down force exerted on the broom can be increased or de-
creased by adjusting “in” or “out” the BAH sequence valve adjustment screw. (When
the oil is reversed through the circuit, the sequence valve serves as a check valve
diverting oil to the rod end of the two BAH cylinders causing the broom to raise.)
Once the BAH cylinders are fully retracted, the circuit is dead headed causing the
pump relief to blow over at 2500 PSI. Once through the sequence valve, oil flows to
torque motor inside the pick-up head on the left-hand side which is directly linked to
the broom. Rotational speed of the broom is determined by the output flow of the
pump. Maximum flow of the pump is limited to 8 GPM and is achieved at 1900-2000
auxiliary engine RPM which results in a broom speed of 230 RPM. Oil leaving the
torque motor returns to the BAH sequence manifold then back to the control valve,
back to a filter manifold and then into the reservoir.
BAH Pressure Switch Circuit - A safety circuit designed specifically to protect the
BAH pump from overheating is accomplished using a pressure switch located on
the left-hand pick-up head lift cylinder rod end port. Should the pick-up head be
raised before raising the BAH broom, the pressure switch interrupts current to the
BAH control valve and shuts off the system. This prevents the BAH cylinders from
shoving the broom forward and jamming it against the back of the blast orifice caus-
ing the torque motor to stall. Upon stalling, the BAH pump relief blows over creating
heat that if not corrected quickly can burn up the pump. Once the pick-up head is
lowered, the pressure switch returns current to the BAH circuit allowing the broom to
function normally.
Check this system by lowering the pick-up head and turning on the BAH switch.
Raise the head with the BAH switch still on and observe the broom to stop rotation
without jamming against the blast orifice. Lower the head and observe the broom to
start rotating again.
D. CONTROL VALVE SERVICE
Should the switch fail to activate the component, manual override buttons are provided
on top and bottom of each valve segment. Use the following procedure to engage the
manual override buttons:
1. Locate valve segment not functioning.
2. Set auxiliary engine RPM at idle.
3. Use a screwdriver or similar device to push manual override button into valve
(considerable force must be exerted to overcome springs inside valve).
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