Positioning Cylinders: Circuit Setup
Order of Activation
The geometries of the fixture and workpiece may dictate that the positioning moves be carried out in some sequence. Chapters 1 and 3 explained control valves that are used to accomplishing sequential operation of cylinders. The three most commonly used are:
- Directional control valves are multiport valves that can be used to direct hydraulic fluid to cylinders in sequence.
- Sequence valves are activated by a sensed pressure. When one part of the hydraulic circuit reaches a preset pressure, the sequence valve opens to permit hydraulic fluid to flow to another part of the circuit.
- Flow control valves control the operating speed of hydraulic components. Cylinder travel speeds must be matched to the nature of the workpiece, but adjustment of travel speeds is also a way to accomplish sequencing.
Parallel vs. Series Plumbing
The cylinders in a hydraulic circuit can be supplied with fluid in either parallel or series fashion. Parallel feed is the method of choice. When supplied in parallel, all cylinders receive pressure and flow simultaneously, so there are no inequities of pressure or delays in activation other than those intentionally incorporated in the circuit design. On the other hand, a series arrangement takes the least space and may be the best choice for a tight fixture.
Tubing vs. Manifold
Whether to supply hydraulic fluid to cylinders and other components by means of external plumbing (rigid tubing) or a machined manifold is a classic tradeoff of upfront cost vs. long-term cost. Tubing has the attraction of lowest upfront cost. A drawback is the extra cluttering of the fixture by the tubing and fittings. In addition to taking up space on the fixture, the external plumbing tends to collect chips
A manifold approach results in a “cleaner” fixture with less chip-catching hardware. Additionally, manifold-mounted components can be easily removed and replaced. Clearly, the length of a production run is a major factor in choosing between external plumbing or a manifold..
 |
 |
|
A tubing setup.
|
A manifold setup.
|
Why Use Hydraulic Positioning?
Properly implemented, hydraulic positioning provides these benefits:
- Increased safety
- Vastly reduced setup time per part
- Accuracy and repeatability
- Less scrapped parts
| |||
 |  |  |  |
TM and © Enerpac 2011
All rights reserved. Reproduction of any materials without Enerpac's permission is strictly prohibited.