Upright AB38, Service & Parts Manual

Page: 58 / 133

Maintenance
Section
4-28 AB38 Work Platform
4.20
4.20 Adjustment of Overcentre
Valves on AB38 Lift Cylinders
(Figure 4-22)
The valve supplier delivers the Overcentre valve
preset to specification and
SHOULD NOT be
adjusted by the user.
In the event of the valve having been tampered with
the advisable course of action is to fit a replacement
cartridge.
A short term solution is to temporarily adjust the
valve as follows :-
a)
Place the max. SWL (Safe Working Load),
evenly distributed, in the cage.
b) Raise the boom to 50 mm stroke on the
cylinder.
c) First loosen the Locknut, then using an Allen
Key adjust the spring setting screw on the valve
cartridge. Turning the screw clockwise
increases the pressure setting. Turning the
screw anticlockwise reduces the setting and
allows the boom to creep downwards. Adjust
the spring setting until the boom just begins to
creep downwards.
d) Screw the adjuster 1 (one) further turn
clockwise and secure Locknut.
This operation should only be carried out by
suitably qualified and/or experienced personnel.
An incorrectly adjusted valve may cause
one of the following:-
Cylinder drifts down under load less than the
SWL (Safe Working Load).
Jerky motion in cylinder & boom when lowering.
Pump under high load when lowering.
Valve does not hold load if hose connections
are loosened or broken.
Damaged seals in cylinders due to high
ambient temperature rise.
High pitched sound from hydraulic system when
lowering.
CAUTION
Figure 4-22: Overcentre Valve
The Overcentre Valves are located towards the Rod End
of the Lower Lift and Upper Lift Cylinders.