The shaking system uses two 75-cc/rev hydraulic pumps, which have electronic displacement control (EDC) that is regulated by electronic amplifiers set by dials in the cab. We use low power potentiometers to communicate EDC pump position to the amplifiers. The amplifiers are voltage-controlled current drivers, so they can provide a constant current as specified by a constant voltage from the potentiometers. Because the EDC pumps use a constant current as a setpoint in their internal closed-loop displacement control system, this helps us stay load and temperature independent.

Each pump drives a hydraulic motor piped in parallel, and each motor drives an eccentric weight through a belt drive. Nielsen revealed, “The reason we use two pumps is because we need to control the speed of each motor independently to produce the most effective shaking pattern. We wanted completely isolated control with closed-circuit operation. A single, larger, open-circuit pump would have required more complex valve circuitry. We tried this — with some success — but it was far more complicated and didn’t have some of the nice features, such as braking with the closed-circuit system.”

The clamping system uses two 41⁄2-in. bore hydraulic cylinders piped in parallel to push the arms of the head together, providing positive contact force at the trunk. The duration of the shake is dictated by an electronic timer, which provides an on-off signal to a hydraulic valve to initiate or terminate the shake. The timers send an on/off signal directly to solenoid valves to initiate the shake. Feedback to the operator is provided by pulse counter displays to monitor the motor speeds from the sensors built into the hydraulic motor cases.”

Endorsement of hydraulics

Nielsen continued, “Hydraulics have become the industry standard for this type of machinery, due to its rugged and reliable nature. Electric motors, on the other hand, have a tendency to become fouled in the dusty, dirty conditions, occasional pressure washing, etc.”

For more information, email Erick Nielsen Enterprises Inc., Orland, Calif., at or visit