BT OE35, Service Manual

Page: 244 / 332

PS M6.0 6000
001 OE35
Version no T-code
F-code Section C-code
Hydraulic System
242 Service Manual 1997-10-23
2. General Information
The hydraulic system consists of a compact hydraulic pump
unit, including a electric solenoid valve, pressure relief valve
and a cylinder(s) for lifting the platform.
2.1. Lift/lower
During lifting the duplex pump is turned by a single electric
motor. Oil is drawn from the reservoir into the inlet ports of
both pumps.
Oil flow from the pump outlet goes into the lift/lower control
valve block. For low speed lift, the oil entering the lift/lower
control valve block passes through a normally open solenoid
valve, a restrictor, and one way check valve and is directed
out of the valve block through hoses to the lift cylinders. For
high speed lift the normally open solenoid valve is electrically
closed and the normally closed solenoid valve is electrically
opened, the oil entering the lift/lower control valve block
passes through the normally closed solenoid valve and one
way check valve and is directed out of the valve block through
hoses to the lift cylinders. Oil flowing into the lift cylinder acts
upon all the internal surfaces of the cylinder. The pressure of
the oil forces the cylinder rod to extend out the top of the
cylinder. All lift cylinders are the positive-displacement type.
The only seals are in the cylinder head (gland nut). There are
no seals on the cylinder rod piston.
Equal oil pressure is applied to both the freelift and the
staging cylinders. The freelift cylinder rises first because it
has less weight to lift. The staging cylinder must raise the
same thing as the freelift cylinder plus the weight of the freelift
cylinder and the mast rails. The cylinders will continue to rise
as long as the pump motor is turned on and the oil is flowing
into the cylinders.
A nitrogen filled accumulator is used to soften the effects of
sudden pressure changes within the system. The lift/lower
control valve block contains a pressure relief valve. In the
event that pressure from the pumps exceeds the relief valve
setting then the excess pressure and flow is diverted back tot
he hydraulic reservoir.
When the pump motor is turned off lifting stops. The oil in the
lift cylinder is trapped by a check valve and two lowering
valves in the lift/lower control valve block.
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