Operator`s manual

The Bourdon Tube (24), which is connected to the right elevating cylinder, measures the pressure in the

elevating cylinders. The Bourdon Tube operates a micro switch (see Figure 6-6, number 25). When the

pressure in the elevating cylinders exceeds 1050 psi, the micro switch opens and the Automatic Stop

Lamp (see Figure 6-6, number 26) lights. Current is cut to the depression solenoid of the Elevation Valve

(see Figure 6-6, number 20) and to the extension solenoid of the Extension Valve (see Figure 6-6, number

18). When the pressure is again below 1050 psi the Bourdon Tube micro switch will close and all ladder

movement is restored. Refer to paragraph 6.4.7. for an explanation of the ladder electrical circuits above

the turntable.

Rotating System - the Proportional Valve (16) that controls ladder rotation operates in the same way as

the Proportional Valve for ladder elevation. 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 900 psi and protects the ladder from an overload in the

event the ladder strikes an obstacle during ladder rotation. From the flow valve, oil passes through the

directional control valve to the hydraulic motor (20) causing the turntable to turn in either direction,

depending on the direction of oil flow to the motor. After leaving the hydraulic motor, the oil passes through

the directional control valve in the Proportional Valve 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 hydraulic motor. 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 hydraulic motor to turn. The valve will remain closed at this point until the hydraulic

pressure changes.

A by-pass valve (19) serves as an oil by-pass. When the valve is opened the ladder can be rotated with

the hand crank. The by-pass is closed during normal operations.