The overload warning device is offered as an attachment. In some areas it is required if the excavator is used to lift loads. (See the local accident prevent regulations for earthmoving equipment.)
For use in lifting loads, turn shutoff valve (3) (Fig. 728) by 90° into position "open" (note symbols on shutoff valve). When exceeding the permissible load, the fault lamp in the operator's compartment will light and a buzzer (alarm) will sound at the same time.
In this case, either reduce the load or the reach of the boom.
1. All hoisting work should be carried out with the crane hook only.
2. When using the sling lug at the bottom of the backhoe bucket, the connection is to be made by means of a shackle.
3. The cam plate (4) (Fig. 728) features 3 different curves on account of the difference in stability during various operating conditions, e.g. unsupported - 2-point support and 4-point support, etc.
Choose the appropriate curve for the current condition or application.
4. For further information, see also the topic Adjustment of the Overload Device.
If the machine is not on level ground, load capacities will vary. To prevent personal injury, do not exceed the rated capacity of the machine. Use short slings to prevent excessive load swing.
Deactivating the Overload Warning Device
If the excavator is used for work other than hoisting, the overload warning device must be deactivated.
For this purpose, rest the working implements on the ground. (The piston head side of the boom cylinders is now unpressurized.).
Turn the lever of the shutoff valve (3) (Fig. 728) by 90° into position "Excavator Service". The shutoff valve is closed.
If the device signals an overload, although it is deactivated, leakage in the shutoff valve has caused pressure to build up in the measuring system of the pressure switch.
The pressure switch can be relieved by opening and closing the shutoff valve, the implements being set down on the ground.
Make reference to WARNING on first page of the TESTING AND ADJUSTING Section.
NOTE: Make these tests when the hydraulic oil is at normal temperature of operation. (1 Bar is equal to 100 kPa; 1 Bar is equal to 14.5 psi; 1 psi is equal to 6.9 kPa)
Adjustment of Overload Warning Device
1. Connect a pressure guage having a scale range from 0 to 400 bar (0 to 40 000 kPa) and a connecting facility for a miniature measuring system to the miniature measuring screw coupling (7) (Fig. 728) in such a way that reading can be observed from the operator's compartment.
2. Move the stick or the implement cylinder into its steepest position (steep position = boom cylinders completely extended) and adjust the cam plate on the carrier (5) (Fig. 728) so that the roller of the pressure switch is exactly on the mark.
3. Open the shutoff valve (3) (Fig. 728) between the warning device and the cylinder supply line on the boom cylinder, ("Crane Service" position) and extend the boom cylinder against the stop (fully extended). Move against the stop carefully until the pressure corresponding to the load moment has been reached (punched marks on the cam plate).
If the warning device fails to trip at this pressure, adjust the response pressure on the pressure switch (1) (Fig. 728).
4. Lower the stick or the implement cylinder until a further point marked on the cam plate is reached. This point is a check point. Close the shutoff valve in the operator's compartment and actuate the boom cylinder downward (retracting cylinder = lowering the implement) in order to build up pressure on the piston head side. The warning device should now trip at the pressure indicated on the cam plate.
In case of higher response pressure, a correction must be made.
5. Check the warning device every day for proper operation by fully extending the boom cylinders and building up their maximum operating pressure. In this case, the warning device should trip.
All moving parts of the protection device must be checked for free movement and lubricated at regular intervals.
The adjustment described above is required for one load moment only, i.e. the two other load moment conditions are thereby adjusted automatically. It is advisable to make the adjustment for the load moment in the "unsupported" condition.
Under item 4, if the excavator is equipped with boom relief and check valves, a blocked union connection is to be made from the pilot control line (9) (Fig. WH 199) to the boom relief and check valves unit instead of closing the shutoff valve. The connection from the pilot control line to the control valve bank must not be interrupted.