What is in this article?:
- BOOK 2, CHAPTER 10: Flow control circuits
- Types of flow-control circuits
- 3-speed meter-in circuit
- Meter-in flow control of a running-away load
- When meter-in circuits are necessary
- Action of a meter-in air circuit with a varying load
- Meter-out flow controls
- Three-speed meter-out circuit
- Meter-out pneumatic circuit with a variable load
- Bleed-off or bypass flow controls
- Three-speed bleed-off circuit
- Different locations for flow controls
- Heat generation in hydraulic flow-control circuits
- Motor-type flow-divider speed control
- Another motor-type flow-divider speed control
- Controlling speed of hydraulic motors
- Three-port flow control
Three-speed meter-out circuit
The schematic diagram in Figure 10-31 shows a 3-speed meter-out flow-control circuit using modular valves. Energizing different combinations of solenoids changes speeds at will. To get additional speeds, add more tandem-center directional valves and flow-control modules like station DV02. The limiting factor would be pressure drop through the valves’ tandem centers. Using a bar manifold and modular valves eliminates many fittings and possible leak sources. As in all meter-out circuits, the pressure-compensated pump shown here generates less heat than a fixed-volume pump.
Fig. 10-31. Three-speed meter-out flow-control circuit using modular valves on bar manifold – at rest with pump running.
Figure 10-32 shows the cylinder extending at fast speed. Solenoid A1 of directional valveDV01 shifts and fluid from the cylinder passes through the meter-out flow-control module directly under it. This flow path will always produce the fastest speed.
Fig. 10-32. Three -speed meter-out flow-control circuit using modular valves on bar manifold – cylinder extending at fast speed.
By energizing solenoid B2 on directional valve DV02, as in Figure 10-33, return flow from the cylinder passes through the left flow control in the module underneath it. This will produce a slower speed -- here called middle speed. Either solenoid A2 or B2 could be assigned to middle speed (making the opposite solenoid produce slow speed). As with fast speed, the rate of cylinder movement is variable, except it can never be faster than fast speed.
Fig. 10-33. Three -speed meter-out flow-control circuit using modular valves on bar manifold -- cylinder extending at middle speed.
By actuating solenoid A2 on directional valve DV02, Figure 10-34, oil from the cylinder passes through the right flow control in the modular valve underneath it. This will be a different speed --here called slow speed.
Fig. 10-34. Three -speed meter-out flow-control circuit using modular valves on bar manifold -- cylinder extending at slow speed.
The cylinder can retract at fast speed or at any of the same slower flow settings as above. By energizing solenoid B2 of directional valve DV01, flow will pass through the opposite meter-out flow control. This means fast speed can be different when the cylinder extends. The middle and slow speeds will be at the same flow rate as extend. Cylinder speed during these reduced flows will be somewhat slower due to increased area on the cap end.
When changing from a faster to a slower speed, the action will be abrupt. This is because the meter-out circuits control the flow exiting the cylinder.
Note: A simple manifold can set multiple speeds inexpensively while eliminating plumbing leaks. Also, be sure to use a valve for DV01 that can withstand tank-line backpressure.