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"Sid" explains

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Spring base

Due to their design principle, SITEMA Safety Catchers can only be released if their clamping system is not under load – which is generally in accordance with the relevant safety regulations. If, however, the load overshoots after switching off the pressure, or moves slightly downward for any particular reason, the Safety Catcher is subjected to a partial load. In practice, this means that the load must first be raised before the Safety Catcher can be opened and before a movement in load direction is possible.

This effect, often found to be disturbing and time-wasting, can be avoided by not bolting the Safety Catcher directly to the machine frame, but rather on top of a spring-base. For its working principle, see the Simulation with spring-base.


  1. Even if the load slowly sinks down during normal operation, e.g. due to a small leakage at the lifting actuators, it is not necessary to lift the load before any downward movement.
  2. The crucial safety criterion “Safety Catcher can only be released if the rod is free of load", is satisfied without restriction.
  3. The spring-base also compensates for any lateral misalignment between the load guide elements and the clamping rod. Therefore, other compensation techniques are not necessary.


The spring-base is factory-mounted on the Safety Catcher, ready for use. Special mounting instructions are supplied for retrofitting.

For the compressive load versions, there are two alternatives for attaching the Safety Catcher to the machine frame, either by using threaded holes arranged identically to the ones on the Safety Catcher or via the shoulder which fits to the coupling flange FL/FS (see mounting flanges).
The tensile load versions are fixed to the machine frame by screws.