BOOK 2, CHAPTER 11: Flow divider circuits

Motor-type flow divider as an intensifier

As noted earlier, a motor-type flow divider intensifies pressure at one outlet when the other outlet is at a lower or 0 pressure. In the case of a 2-outlet motor-type flow divider with equal displacements, if the inlet pressure is 1000 psi, one outlet can be at 2000 psi while the other outlet is at 0 psi. While pressure doubles, flow from the intensified outlet is one half that at the inlet. The energy from the outlet motor with 0 pressure transfers to the other motor via the common shaft, thus intensifying the pressure.

With more than one section going to tank — say a 4-outlet divider with three outlets to tank — intensification would quadruple the pressure. While the intensified fluid reaches that pressure, volume is only one-fourth of inlet flow.

Using motor-type flow dividers with unequal sections is another way to get high intensification. If the motor in one section discharges 3 gpm to tank and the other section discharges 1 gpm. Intensification is still 4:1.

Figures 11-45 through 11-48 depict how to use this feature of motor-type flow dividers in a circuit. This circuit has equal-outlet flow divider C and 3-way directional valve D in the cylinder cap-end line. In the at-rest condition, shown in Figure 11-45, both outlets of the flow divider connect to the cap-end port.

In Figure 11-46, the cylinder is extending at full speed and low thrust. Energizing solenoid A1 shifts the directional valve to pass oil through one side of the flow divider and the 3-way valve to the rod-end port. Fluid from the other side of the flow divider goes directly to the cylinder rod-end port. The pump and valves must be sized to handle enough flow for the speed required during the fast-forward portion of the cycle. (Normally, motor horsepower is low for a cylinder moving a light load.)

When the cylinder contacts the limit switch, as in Figure 11-47, the switch energizes solenoid C1 on the 3-way valve. The valve shifts and oil from one section of the motor-type flow divider then goes to tank. Pressure doubles while cylinder speed drops to half what it was before solenoid C1 was energized.

This circuit works best on actuators that are not required to stall. Using this setup for a fast advance followed by a clamping operation might result in excess heat because internal leakage in the flow divider while the cylinder is holding.

Energizing solenoid B1, as in Figure 11-48, makes the cylinder retract. Oil from the cap-end port goes through both sections of the flow divider and back to tank through the directional valve.

When using a motor-type flow divider as an intensifier, make sure it is capable of operating at the elevated pressure. The pressure rating of an inexpensive gear-motor-type flow divider may be only 2000-psi intermittent and 1500-psi continuous. On the other hand, some gerotor-type flow dividers handle as much as 4500-psi intermittent and 3000-psi continuous — at a higher price.