What is in this article?:
- Book 2, Chapter 10: 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 (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
3-speed meter-in circuit
The schematic diagram in Figure 10-11 shows a 3-speed, meter-in flow-control circuit using modular valves. Energizing different combinations of solenoids changes cylinder speed at will. To get additional speeds, add more tandem-center directional valves and flow-control modules like station DV01. 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-in circuits, the pressure-compensated pump shown here generates less heat than a fixed-volume pump.
To extend the cylinder at fast speed, shift the valves as shown in Figure 10-12. Energizing solenoid A2 on directional valve DV02 sends fluid through the meter-in flow-control module directly under it to the cylinder’s cap end. This condition is always set for the fastest extension speed. Solenoid A2 stays energized for all extension speeds.
Energizing solenoid B1 on directional valve DV01, Figure 10-13, sends pump flow through the right-hand flow control in the module underneath it. This will produce a slower speed -- here called middle speed. Either solenoid A1 or B1 could produce middle speed, making the opposite solenoid produce slow speed. As with fast speed, the cylinder speed is variable, but never faster than fast speed.
By actuating solenoid A1 on directional valve DV01, fluid passes through the left-hand flow control in the module underneath it. This will produce a different speed here called slow speed.
The cylinder can retract rapidly or at any of the same slower-flow settings as above. By energizing solenoid B2of directional valve DV02, flow will pass through the opposite meter-in flow control. This means fast-speed retracting can be different from the extending speed. The middle and slow speeds will be at the same flow rate as extension. Cylinder speed during these reduced flows will be somewhat faster due to the decreased rod-end area.
A simple manifold can give multiple speeds inexpensively, while eliminating potential plumbing leaks.
Note: Select a valve for DV01 that can withstand tank-line backpressure.
Speed changes with this meter-in circuit will be smooth because the cylinder can coast while slowing down. (It also is possible that the cylinder could cavitate when slowing down, so an anti-cavitation check valve may be needed.)
Fig. 10-14: Three -speed meter-in flow-control circuit using modular valves mounted on bar manifold – extending at slow speed.