Putting a regenerative hydraulic circuit on a double-acting piston reroutes the flow exiting the rod side of the cylinder from the reservoir to the piston side of the cylinder. It merges with pump flow and increases the piston speed, but not the force it exerts. That's because both sides of the piston are exposed to system pressure, so the maximum force the piston exerts depends on the differential area between the cylinder's rod and piston sides.

Engineers at Sherex Industries Ltd., Lancaster, N.Y., have overcome the problem of limited force by adding a switch into the circuit of its Iversen automatic speed valves. It lets the full force of the cylinder be applied once a certain pressure level is reached, and increases piston speed during portions of the stroke in which little or no work is being done. When the valve closes, return flow goes to the reservoir and the cylinder applies full force. The valve can double the speed of double-acting cylinders.

In the past, these types of hydraulic circuits were only available by custom order. Iversen valves, however, are mass manufactured as individual, compact, self-contained components. They handle pressures up to 5,000 psi and flow rates to 11 gpm. Future models will handle flows of up to 79 gpm. The valves retrofit into older equipment using in-line mounting, and no external controls are required.

Speed valves increase cylinder speeds, which can reduce cycle times on injection-molding machines, hydraulic presses, and die-casting equipment. In the example graphed, the 80/50 mm cylinder has a 800-mm stroke and pump output is 20 liter/min.