Hydraulic clamping is usually fast, but not instantaneous. To estimate clamping time, consider the two phases of clamping:
- Extending time, under low-pressure free flow
- Pressure-building time
Extending time is fairly easy to calculate, knowing fluid required by each clamp and the power units flow rate, using the formula below. One obvious way to reduce clamping time is to set clamps as close to the workpiece as possible, to use as little stroke as possible.
After extending, an additional volume of fluid must be pumped into the system to build pressure. This is due mainly to:
- Compressibility of the hydraulic fluid (add about 4% of total system volume to build to 7500 psi)
- Volume expansion of hydraulic hoses (.066 cu. in. per foot)
- Charging an accumulator, if used
By calculating fluid required for each of the above factors, you can estimate pressure-building time. Using Sequence Valves lengthens clamping time, because each sequence step requires extending time and pressure-building time. To reduce clamping time, set Sequence-Valve trigger pressure as low as possible. With multiple Sequence Valves, set trigger-pressure differences at their minimum allowables value.