FAQ Safety technology

If a failure or incorrect behaviour of a function can lead to a possible injury, it is a safety function. In pneumatics, operating functions often fulfil the safety aspects. For this reason, the components required in the safety function must be validated in accordance with ISO 13849-2.

Yes, because pneumatic actuators such as cylinders can also lead to serious injuries, they must also be assessed acc. ISO 12100 and if necessary safeguarded through constructive or control-related measures. Pneumatic or electro-pneumatic controllers are to be assessed and implemented acc. to ISO 13849-1 and 2.

In principle, protection against restart is to be considered with every safety function. This is regarded as one of the basic safety principles of ISO 13849-2. In pneumatics protection against restart means the following: after an energy failure (compressed air supply, compressor breaks down, or hose rupture) and subsequent recovery, the machine must not start up automatically without a separate start command. The detection of a primary side pressure drop, which must lead to a system interlock, is often sufficient.

In the ‘ISO 13849-2’ list of proven safety principles, there is the point ‘secured position’, which safety - oriented products and systems must fulfil. This term means, that the moving element of a component (the spool valve) is held mechanically in one of the possible positions. Friction alone is not sufficient. However, a bistable valve is only held in one position by friction and therefore does not fulfil this proven principle. These principles are to be fulfilled from the category 1 upward. Bistable valves are permitted if they have a detent (mechanical lock) in the end positions. Steel spool valves and soft-sealed special valves from SMC have such a detent and can therefore be used in safety-related control systems. The basic and well-tried safety principles of ISO 13849-2 must be observed, in particular, the application of the principle of energy separation (closed-circuit current principle). The safe state is achieved by disconnecting energy. This means that the last switching position before release is the safe state. Furthermore, in the event of use, it must be checked whether unexpected and/or additional hazardous movements can occur due to power failure and recovery.

A two-channel solution must be at least ‘one fault safe’, meaning that one single fault in the safety chain (e.g. a valve not switching) must not lead to the loss of the safety function. That is not the case with the pilot-controlled valve because a fault in the main valve’s spool (e.g. a chip that blocks the spool valve) leads to the failure of the entire system.

Yes, both systems are linked by the probability of failure and can be converted accordingly. In general, SIL / PL can only be calculated for complete systems. A single product cannot have a SIL / PL.

In principle it is possible to say that safety functions that can be implemented electro-pneumatically can also be designed purely pneumatically. In this case the cost-effectiveness of purchasing one’s own safety PLC depends on the complexity of the desired safety functions and the operating functions required for this. Special attention is on the sensors required by ISO 13849 to fulfil the degree of diagnostic coverage from category 2 upward. Realizing this purely pneumatically represents considerable extra expense in the conceptual design of the circuit, component quantity, and the costs resulting from that. The acquisition of a safety PLC compared with a purely pneumatic version of the safety function therefore often represents the more cost-effective solution.

SMC will gladly provide you via email with all the safety-relevant key figures, such as B10 and MTTF. Furthermore, SMC offers a Sistema library online. Sistema is a program for calculating your safety functions. It is provided free of charge by the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA).

Maintenance safeguards (lockout/tag out, LOTO) are technical facilities that lock control elements of a technical system, in other words switches, shut-off or ball valve, and so forth, in a particular position. They are used to protect against unauthorized access or unintentional activation, for instance during a maintenance procedure. They are used to protect against unauthorised access or unintentional activation, for example during a maintenance operation. If the adjustment or maintenance operation can be carried out in a depressurised state, it is possible to lock the SMC manual shut-off valve (VHS series) in the vented position.