Pumping concrete is the unit’s main job, and hydraulics help to get it done. But concrete placement only happens successfully if the truck is firmly planted on the ground. The boom may reach out 100 ft or more. To keep the unit from tipping, a set of outriggers reach out from the truck much further than on most cranes. These long-reach outriggers typically need telescopic cylinders to extend them and later to tuck them away. High quality, pilot-operated check valves keep the down-cylinders locked against the ground.
The operator’s remote pendant gives them control of the pumping rate described earlier, and also fine control of the various sections of the boom as well as swing motion. A separate open-loop piston pump is configured with a load-sensing (flow compensated) controller, which limits the pump to a pressure margin just higher than the most demanding boom function. The pump flow path for this circuit is open loop (tank to tank), but the control of flow rate and pressure is closed-loop. The load sense shuttle valve network inside the electro-proportional valve bank sends the highest function pressure back to the pump compensator/controller to make continuous adjustments. Pre-spool compensators in each section of the valve bank help to keep flow steady to lighter loaded boom cylinders already in motion, as the pump up-strokes in response to a heavier loaded boom section. This well-designed and tuned system gives the operator the ability to make smooth motions with the boom to move the placement hose to where it is needed during a pour, without wasting extra energy.