What should be considered when hydraulic motors are connected in series?
Series connection of Hydraulic motors are used when a constant high speed is required in an application. In contrast to the parallel connection the volume flow of the Hydraulic pump not divided among the hydraulic motors connected in series. Due to the series connection, the oil flow remains constant, as the return of the first motor is fed into the inlet of the second motor, the return of the second motor is fed back into the inlet of the third motor, etc. In our example, 3 motors are connected in series. The oil flow is 60 l/min, so each hydraulic motor achieves a speed of approx. 300 rpm.
With a series connection , it should be noted that the available torque of the individual motors is reduced.
The pressure effective in a hydraulic motor is the so-called differential pressure (difference between inlet and outlet pressure).
If the inlet pressure is 140 bar and the return pressure is 100 bar, the pressure drop (difference between inlet pressure and outlet pressure is 40 bar. This means that the input pressure for the second motor is 100 bar, and the return pressure is 60 bar (the pressure difference is also 40 bar). The third motor has an inlet pressure of 60 bar and a return pressure of 20 bar. The available pressure for all 3 motors is 40 bar, which corresponds to a torque of approx. 70 Nm for a CPRM200CD hydraulic motor.
When connected in series, the return pressure is highest for the first hydraulic motor . For this reason, the leakage oil line should always be connected when connecting in series.
Areas of application for parallel circuits of hydraulic motors
The series connection of hydraulic motors is used in conveyor belts or in the scraper floor drives of loader wagons. The series connection can be combined with a parallel connection by means of suitable hydraulic valves. parallel connection combined by means of suitable hydraulic valves. If there is a high torque requirement, you can switch from series connection to parallel connection.