Operator`s manual

From the flow valve, oil passes through the directional control valve to the overcenter valves (21) and
passes via the check valve in each overcenter valve to the upper portion of the hydraulic cylinders (22). At
the same time, the oil in the lower portion of the cylinders flows via the Proportional Valve (16) and
hydraulic return lines to the reservoir (1). The check valves in the overcenter valves prevent the oil from
draining from the upper portion of the cylinders when there is no pressure in the hydraulic lines to the
overcenter valves. When it is necessary to lower the ladder, the relief valve section of the overcenter
valves open, allowing oil to flow out of the upper portions of the cylinders as oil flows into the lower portion
of the cylinders.
When elevating the ladder, oil also flows through the check valve in the Proportional valve (16) and then
flows to the Relief/Unloader Valve (14) at the same time that oil flows to the overcenter valves. The check
valve prevents the return of oil to the directional control valve. The Relief/Unloader Valve will close,
permitting the ladder to elevate. The valve will remain closed at this point until the hydraulic pressure
changes. If the pressure to the Relief/Unloader Valve (14) exceeds 1550 psi the pressure relief valve of
the Relief/Unloader Valve will open and the oil will flow to the reservoir via the filter (4).
The overload indicator (23) measures the pressure in the upper portion of the elevating cylinders and
indicates when the ladder is operating within safe limits.
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