Speed control with motor-type flow dividers

Figures 11-30 through 11-33 show a different type of motor-type flow-divider circuit for variable speed. This circuit uses a smaller pump, electric motor, and tank to give the same speed but less high-speed force. Notice there is a 3-gpm pump supplying one section of the flow divider. As the fed section of the flow divider turns, the other two sections also turn and pump fluid directly from the tank. Thus, in Figure 11-30, the two right-hand sections of the flow divider are only circulating oil. All pump flow is going to the cylinder, which is operating in slow-speed mode. In this condition, the cylinder is capable of generating its highest tonnage. Notice that the cylinder requires 300 psi to move it and the pump is showing 300 psi.

Figure 11-30. Meter-in flow-control circuit with motor-type flow divider to minimize heat generation. (Shown with cylinder extending at slow speed.)

The cylinder speeds up when solenoid C2 on the left-hand 3-way valve is energized as in Figure 11-31. Now, one flow divider section sends its oil to the cylinder along with pump flow. The cylinder goes to mid-speed mode and pump pressure climbs to 600 psi.

Figure 11-31. Meter-in flow-control circuit with motor-type flow divider to minimize heat generation. (Shown with cylinder extending at medium speed.)

To get full speed from the cylinder, solenoid C1 on the right-hand 3-way valve is energized as shown in Figure 11-32. Now all three sections of the flow divider feed the cylinder. The cylinder is at fast-speed mode and pump pressure climbs to 900 psi.

Figure 11-32. Meter-in flow-control circuit with motor-type flow divider to minimize heat generation. (Shown with cylinder extending at fast speed.)

If the pressure required to move the cylinder to the work is relatively low, this circuit works well. There is enough flow to move rapidly at low pressure, and enough pressure at low flow to do the work.

Note: The gears in standard motor-type flow dividers are noisy. In the above two systems, the flow divider turns continuously. The noise level may be unacceptable in low-noise areas.

Figure 11-33. Meter-in flow-control circuit with motor-type flow divider to minimize heat generation. (Shown with cylinder retracting at fast speed.)

Motor-type flow divider in full-time regeneration circuit

Figures 11-34 through 11-44 picture a unique regeneration circuit using a motor-type flow divider. Normally flow-divider circuits use the split flow to synchronize actuator movement. This circuit uses a flow divider to intensify flow for regeneration. This circuit works best on cylinders with small rods; and gives exactly twice speed on double-rod cylinders and hydraulic motors.

Figure 11-34. Full-time regeneration circuit using a motor-type flow divider. (Shown at rest with pump running.)

Figure 11-34 shows the circuit in the at-rest condition. Equal-outlet motor-type flow divider C is piped between the cylinder rod-end port and the directional valve. The flow divider’s normal inlet port connects to the cylinder; one outlet connects to the directional valve; and the other outlet is teed into the cylinder cap-end line.

Figure 11-35. Full-time regeneration circuit using a motor-type flow divider. (Shown with cylinder extending under regeneration.)

Figure 11-35 depicts solenoid A1energized so that flow from the pump goes past the teed-in flow divider line to the cylinder cap end. As the cylinder extends, oil from the rod end enters the flow divider. The flow divider splits this oil. Half goes to tank at 0 pressure and half goes to the cylinder cap-end tee at pressure high enough to mix it with pump flow. As the cylinder starts to extend, speed quickly increases to almost twice the original speed. Maximum cylinder speed directly relates to the rod size: the larger the rod, the slower the speed. With a double rod-end cylinder, speed exactly doubles. As with any regeneration circuit, speed increases but force decreases.

Figure 11-36. Full-time regeneration circuit using a motor-type flow divider. (Shown with cylinder retracting.)

Figure 11-36 shows the cylinder retracting. Energizing solenoid B1 of the 4-way directional valve sends pump flow to one outlet of the flow divider. Both of the motors in the flow divider turn at the rate of flow from the pump. During this part of the cycle, the motor that has its inlet teed into the cap-end line becomes a pump. Pump flow plus the same flow from the second motor makes the cylinder retract twice as fast as a conventional circuit. (However, cylinder thrust is only half that of a conventional circuit.) This flow-divider regeneration circuit doubles the cylinder speed without making the pump work harder. Size the pump, valve, tank, and piping up to the regeneration circuit according to pump flow. The only high flows are at or very near the cylinder.

Using a motor with a higher displacement on the left-hand side of the flow divider increases speed even more. The limit is reached when pressure to run the cylinder at the faster rate exceeds the relief valve setting. When using unmatched motors, make sure the line from the cylinder cap-end to the motor will handle the higher suction flow.