• ISBN: 978-1-4249-6190-0
  • Issued: May 2004
  • Content last reviewed: June 2009

Moveable Guard General Requirements:

The moveable guard selected for guarding the point-of-operation of:

The moveable guard requires compliance with ISO 14120 "Guards-General requirements for the design and construction of fixed and movable guards" and the interlocking of the guard requires compliance with ISO 14119 "Interlocking devices associated with guards - principles for design and selection".


The preferred interlocking method is a dual-control system interlocking with cross-monitoring. Dual-control system interlocking without cross-monitoring would be acceptable if the guard interlocking system, selected and designed for its hostile environment, is checked and tested on a regular basis. The channels in this application would need to be in different media (hydraulic and electrical) to obtain an improvement in integrity due to the reduced probability of common cause failure. The guard interlocking devices are required to be fitted in opposite modes. The two switches (valve) are operating in opposite modes, each actuated by its own cam arrangement.

(This arrangement covers common cause failures due to cam failure or guard misalignment and the improvement in safety of the interlocking system outweighs the reduction in integrity of the channel with a non-positive mode device, see 5.41 of ISO 14120.)

Routine inspection and testing should be carried out at a frequency appropriate to ensuring the continued integrity of all safety related control functions. This applies as well to all hydraulic components/systems (i.e. cylinders and valves) effecting safety functions. It is recommended that all hydraulic systems are in conformance with ISO 4413 "Safety requirements for fluid power systems and components".

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