Operator`s manual

Extension System - the Proportional Valve (16) that controls ladder extension and retraction operates in
the same way as the Proportional Valves for ladder elevation and rotation. When the directional control
valve in the Proportional Valve is opened in either direction, oil passes through the pressure compensated
flow valve. The relief valve in the Proportional Valve (16) is set at approximately 1300 psi and protects the
ladder from an overload in the event the ladder strikes an obstacle during ladder extension. From the flow
valve, oil passes through the directional control valve and overcenter valve (25) to the Winch Motor (18),
causing the winch to turn and the ladder to extend or retract, depending on the direction of oil flow to the
motor. Extension and retraction are controlled by cables which are payed in or out on the winding drums
of the winch. Oil leaves the Winch Motor, passes through the directional control valve in the Proportional
Valve (16) and returns to the reservoir (1) via the filter (4). The directional control valve also directs oil, via
a check valve, to the Relief/Unloader Valve (14) at the same time that oil is directed to the Winch Motor
(18). The check valve prevents the return flow of oil to the directional control valve in the Proportional
Valve (16). The Relief/Unloader Valve (14) will close permitting the Winch Motor to turn. The valve will
remain closed at this point until the hydraulic pressure changes.
A by-pass valve (17) serves as an oil by-pass. When open, the ladder can be extended or retracted using
the hand crank. The by-pass valve is always closed during normal operations.
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