Dumpmaster - Adjusting the pressure relief valve

NOTE! Authorization must be obtained from the manufacturer, before any adjustment is made to the pressure-relief valve setting. Unauthorized adjustment will result in the warranty being voided.

The pressure-relief valve limits the maximum hydraulic pressure flowing to the ram, and thus the maximum weight that can be lifted.

If the bin is heavier than the setting will allow, the motor and pump still run but the oil just bypasses straight back into the tank. While this does not do any harm to the machine, oil passing through the relief valve generates a lot of heat; for this reason, if the relief valve is ‘blowing’ frequently, either the setting should be increased, or the bin weight reduced.

The standard Dumpmaster is factory set to accommodate at least 250kg in a vertical lift test. If you are tipping a bin that weighs close to 250kg it is possible that as the bin starts to tip (at the point where the tipping track has a bend), the machine will stall. This is because there is more force required to start the tipping action than is required to lift the bin. 

It is permissible to increase the pressure relief valve on a standard Dumpmaster so that a 300kg bin can be lifted off the ground. This article provides the steps how to do this.

Procedure

1. Remove the outer powerpack cover.
2. The relief valve adjustment screw is located near the back of the left-hand side face of the centre housing. (Circled green)
3. Loosen the locknut (on current machines this is 22mm, on older machines it could be either 13mm or 17mm)
4. Using a 6mm Allen key, adjust the pressure-relief screw.
   1. Turn the screw clockwise to raise the overflow pressure and increase the lifting capacity.
   2. Turn the screw counter-clockwise to lower the overflow pressure and decrease the lifting capacity.
5. Test the capacity using a full bin. In general, the most pressure is required just as the bin starts to tip, so check it at this point.
6. When pressure setting is correct, tighten the locknut.
7. Replace the powerpack cover and return machine to service.