Gear-Type Hydraulic Flow Divider

The gear-type flow divider functions like two gear motors with their shafts rigidly attached. We will consider first the case in which both motors have the same displacement. Since their shafts are attached, they both have to turn at the same speed; consequently, the same flow goes through both sides. Except for leakage, which is always a little different for the two sides, the flow is equally divided, and the cylinders extend simultaneously.

Pressure intensification is a potential problem with a gear-type flow divider. In Fig. 7.1, suppose that the load is removed from one cylinder, say Cylinder 2. The no-load pressure to extend Cylinder 2 is 65 psi, and the pressure to extend Cylinder 1 is 10 times higher at 646 psi. Suppose the pressure drop due to flow restriction through the flow divider is ?P = 9 psi. The pump will build pressure to

P = 646 + 9 = 655 psi

The pressure drop across the Cylinder 2 side of the divider is 655 – 65 = 590 psi. The side-2 motor torque due to this pressure drop is delivered through the coupled shafts to side 1. The side-1 motor has a torque delivered “into” its shaft; thus, it functions like a pump and builds pressure on side 1. This pressure is higher than the 646 psi needed to move load at the desired velocity. Under certain circumstances, it could get to a level that causes damage. When using a gear-type flow divider, the designer must always analyze the circuit to ensure that pressure intensification will not cause a safety problem.


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