Hydraulic Pressure Transmitter in Hydraulic Crane Use

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Helping Hydraulic Crane Parts Work Together

When thinking of hydraulic cranes, we tend to think of the enormous objects being moved by a large arm with very little effort. What we do not see is what goes into the moving of these “immovable” objects. The key to this process is hydraulics. The fully functioning hydraulics system depends on the proper distribution of an incompressible fluid to drive the pistons, usually oil. This distribution of proper fluid pressure relies specifically on the proper instrumentation applied.

WIKA offers the MH-2 special purpose mobile hydraulic pressure transmitter to ensure effectiveness of the operation and safety of the crane. When lifting and/or lowering these heavy construction materials, the efficiency and safety of the process will depend on the crane’s stability in carrying the loads. Operators and engineers must realize the importance of the load moment indicator, understand what it is used for, and recognize its value to the operation of their cranes and the success of their construction project.

Hydraulic Crane Basic Parts

  • Boom: the steel arm that lifts and holds the load    
  • Counterweights: weights placed on the back of the cab to prevent tipping during lifts    
  • Jib: lattice structure that extends out of the boom    
  • Load Moment Indicator: display of lights located in the cab that notify the operator when the crane’s lifting limits are reached    
  • Outriggers: supports that extend to balance and support the crane    
  • Rotex Gear: large gear under the cab that allows the boom to be rotated    
  • Two-Gear Pump: hydraulic pump system that uses two rotating gears to pressurize oil

The load moment indicator determines the stability of the load and whether it can be carried by the boom. Since the boom carries the load, the counterweight must provide an opposite force to prevent the crane from getting outbalanced. Load moment indicators make use of special pressure sensors, the WIKA HP-2 pressure transmitter for high pressure applications, to provide the operator with crane’s actual and correct working state.

This hydraulic pressure transmitter provides overload and breaking weight monitoring of the hydraulic arms under existing load conditions. It indicates the moment of force applied on the boom, the hook amplitude as the height of the load increases, the crane rating, and the actual hoisting capacity of the crane. The device for monitoring the load moment includes the load sensor that is capable of producing an electrical signal representing the instantaneous actual load moment on the crane boom.

Two pressure sensors are connected to a control and alarm box. The first pressure sensor is adjusted to react to a pressure corresponding to 90% of the pressure corresponding to the maximum permissible loading moment by sending a signal to the control and alarm box. The second pressure sensor is adjusted to react at the full value of the pressure and by sending a signal along a separate line to the control and alarm box.

Cranes lift heavy loads to tall heights, so the truck must be completely stable during the lifting operation. All hydraulic crane parts must work together. To assure the truck’s stability, outriggers are used to act as balances that keep the crane from leaning too much to one side or the other. The outriggers consist of the beam (the leg) and the pad (the foot) and use hydraulics to lift the entire truck, including the tires, off the ground. As shown in the diagram above, these outriggers use pressure transmitters to make sure the proper pressure is distributed evenly to each side.

Accuracy is critical in dealing with load moment indication, to make certain the lift is performed properly.  If the proper instrumentation is not used, the crane can possibly be pushed beyond its maximum capability. This, in turn, could jeopardize the safety of the operation and those involved. WIKA’s MH-2 hydraulic pressure transmitter maintains full control throughout the process, ensuring safety and accuracy.

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