Sitema Safety Devices KNowledge Base


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SITEMA Frequently asked questions

How Far Does the Load Sink When the Safety Catcher is at Zero Pressure?

Typical travel without the optional Spring Base is between 5 and 15 mm…with the spring base, an additional 6-10 mm depending on the size. Full travel with the spring base option can range between 10-25 mm depending on type and size. If the catcher does not bottom out/compress the Spring Base fully, then release pressure can be applied and unlock the catcher without an upward movement.

How Do You Unlock the Sitema Safety Catcher?

If the safety catcher is holding a load? You must first apply release pressure and then move the axis upward. At this time, you should be monitoring the “Unlocked” proximity switch indicating the status condition.

What is the Typical Reaction Time of the Safety Catcher?

The typical reaction time of the SITEMA safety catcher is approximately 150 m/sec.

What is the Maximum Force Mounting Components Should Be Designed For?

All mounting bracketry should be designed for 4 x M in the event of an overload condition.

What Happens if Oil Gets on the Shaft? Do I Lose Holding Capacity?

No, the influence of mineral oil on the shaft is insignificant and you will not lose holding capacity.

How Do I Size the Safety Catcher?

Admissible Load (M) sizing is determined by the platen weight + tooling weight and anything mounted to the platen.

What is the Safety Factor of the Safety Catcher?

Factor of 100% is included. Minimum holding is 2 x M (admissible load) max holding is 3.5 x M. Force test required is 1.5 x M.

Are Safety Catchers Used for Accurate Positioning?

No, the clamp system requires approximately ½ inch of downward movement to develop full holding. The safety catcher’s are single acting and only hold against gravity.

What Control Circuit Do You Recommend for the Sitema Safety Catcher?

SITEMA Knowledge Base & FAQs

* In case impact noises due to excess pressure are audible when pressurizing the safety catcher, these can be suppressed by means of a flow control valve in the p-line.

** In case the pressure is not sufficiently constant (e.g. pressure drop at the beginning of a downward stroke), we recommend a check valve in the p-connection of the valve.


To keep the clamping permanently open, safety catchers mostly are hydraulically actuated. Pneumatic versions are also available for smaller units.

  • Hydraulic Actuation:Hydraulic oil (HLP) in accordance with DIN 51524-2:2006 must be used as pressure fluid. Please consult SITEMA before using any other fluids.
  • Pneumatic Actuation:The compressed air must be dried and filtered. SITEMA recommends compressed air according to ISO 8573-1:2010 [7:4:4].


In most applications an actuation as suggested in Fig. 2 is used. During every operational cycle, the 3/2-way valve is actuated electrically and releases the safety catcher.

In all other operational conditions, as well as in cases of power-failure, pressure line breakage, emergency stop, etc. the safety catcher becomes effective, secures the rod and/or stops the load. If necessary the valve can also be switched by another safety signal, e.g. speeding, contouring error, etc.


Proximity switch 1 “load secured” signals the secure state and is used to authorize entrance to the danger zone.

Proximity switch 2 “clamping release” is used to activate the movement of the drive in the load direction.

For automatic detection of failures both signals are compared. In case both switches indicate the same state—apart from minor overlapping periods—there is a defect present.
SITEMA Knowledge Base & FAQs
AMLOK Rod Locks & Press Safety

Want to learn more?

Check out the Complete Guide to Power-Off Clamping