Single-Acting vs. Double-Acting Clamps

Single-acting clamps are ideal for many clamping systems. Single-acting components are simpler and slightly less expensive to install, because they require fewer fluid lines and have simpler controls. In addition, Roemheld Power Workholding clamps are designed with faster, more-reliable spring returns than those of any other manufacturer, so the need for double-acting clamps is not very obvious. Beginning users can usually get excellent results using only single-acting clamps.

There are some situations, however, where double-acting systems are better suited or even mandatory. Most professional fixture builders always consider double-acting clamps as an option in the appropriate circumstances. With a little experience, building double-acting systems can be almost as simple as building single-acting systems. The increased fixture reliability in high-production applications is well worth the small additional cost. The following are examples where double acting is the best choice.

1. Flood Coolant

Double-acting clamps are better suited for machining applications using flood coolant. Unlike double-acting clamps, which have hydraulic fluid on both sides of the piston, single-acting clamps have a small air chamber for the spring on one side of the piston. This air is exhausted during the clamping stroke, then new air is sucked in during the unclamping stroke. The use of coolants and cutting fluids has to be considered in the fixture design. Although all single-acting clamps have sintered-metal air filters to prevent contaminants from entering, there is still a chance that aggressive fluids can enter the spring area (especially with flood coolant), eventually causing malfunctions. One alternative is to continue using single-acting clamps and add air-vent lines to reach outside the coolant area, but switching to double-acting clamps usually provides a simpler solution.

1) Machine control
2) Hydraulic power unit
3) Swing clamp
   4) Machine tool
   5) Workpiece

2. Automated Systems

Double-acting clamps should be used in systems that have automated load/unload, or any other machine-tool interlock, so that all functions can be easily timed and coordinated. When clamps are returned by fluid pressure, clamp status can be monitored by pressure switches on both the clamping and the return sides.

3. Moving Linkages or Heavy Loads

Double-acting cylinders are the best choice for moving linkages or any loads attached to the plunger. When using custom Swing Clamps arms that are extra-long and/or heavy, a double-acting system is often the best choice.

4. Large Fixtures

Double-acting clamps are often better for large fixtures with long tubing lines or other flow restrictions. Return speed is adversely affected by several factors: 1) the pressure drop in tubing and hoses; 2) the pressure drop in valves; 3) fluid viscosity, which is higher at lower temperatures; 4) frictional force at piston seals, especially when clamped for an extended time, which displaces the fluid film on cylinder walls.