Broderson IC-250-3D, Operation And Maintenance Manual

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3-15
HYDRAULIC SYSTEM
The IC-250 hydraulic system consists of two subsystems, driven by a double pump with a single
inlet port. The 29 GPM (110L/min) vane pump supplies the hydrostatic steering function and
the boom and outrigger functions. The hoist and brake booster are powered by the 34 GPM
(129L/min) vane pump.
The boom, outriggers, hoist and optional front winch are controlled by one valve assembly. The
29 GPM (110L/min) pump flow enters the steering flow control valve first and then flows into the
left-hand section of the control valve assembly supplying the swing, telescope, boom and out-
rigger sections. The flow from the 34 GPM (129L/min) pump enters the brake booster flow con-
trol valve first and all but 4 GPM (15L/min) is directed to the inlet section to the left of the hoist
valve. Adjustment procedures for the crane hydraulic functions are given on page 3-22 through
3-24. The schematics of the hydraulic system are shown on pages 3-16 and 3-17.
STEERING SYSTEM
The steering system is shown in the schematic on the next page. The IC-250 steering system
is a load-sensing, demand-type system that takes only as much flow as is needed when steer-
ing and directs the excess flow to the control valve for boom and outrigger functions. The pri-
ority flow-control valve is in the line between the 29 GPM (110L/min) pump section and control
valve.
Oil from the 29 GPM (110L/min) section of the pump goes into the priority valve at port "P."
When no steering is required, the entire flow goes through the priority valve and leaves through
port "EF" to the crane valve. The crane operating speed is not affected since there is no loss of
volume passing through the priority valve.
When the steering wheel is turned, the load-sensing line signals the priority valve to divert the
required amount of oil to the steering control unit to meet the steering system requirements.
The excess oil, not required for steering, flows to the crane control valve as usual. Since the
amount of oil required for steering is usually a small portion of the pump output, the crane con-
trol valve is always operational while the unit is being steered. Crane operation speed is re-
duced such a slight amount it is usually not noticed.
The steering control unit is non-load reactive. This means that bumps, curbs, and obstacles
cannot change the steering angle and are not felt in the steering wheel. It also means that the
wheels do not recenter when the steering wheel is released. The steering wheel must be
turned back to center at the end of a turn.
There is a check valve in the pressure line between the priority valve and the steering control
unit. This prevents pressure in the steering cylinders from venting back into the pressure line
when the pressure is low. This eliminates steering wheel kickback when the steering wheel is
released.
The steering system pressure was set at 1800 PSI (124bar) at the factory, and this should not
need adjustment.