Fluid Control Systems - Reduced Speed
The European Machinery Directive and EN ISO 12100 place the following requirements when setting up, converting, troubleshooting and cleaning/maintenance work on machines must be carried out with the safety guard open or switched off:
- all other control types are switched off,
- operation is permitted only by continuous actuation of an enabling device, a two-hand control or a control device with automatic reset,
- operation is only permitted under conditions of reduced risk, for example reduced speed.
- further requirements of the Machinery Directive and EN ISO 12100 for the control or control unit and the command device must be fulfilled.
These requirements apply irrespective of the energy supply used (electrical, electronic, hydraulic, pneumatic).
The exact control requirements and any reduced speeds required can be found in the C-type product standards for the respective machine. Depending on the industry and type of machine, different max. values from 10... 33 mm/s for the reduced speed are permitted. For this reason, a drive should comply with the required reduced speed or circular speed for the corresponding safety solution.
Fixed orifice plates or flow regulators (see EN ISO 13849-2 Annex B ff.) should be used to reduce the volume flow and thus also to reduce the speed of a fluid drive. Depending on the cross-section of the fixed orifice or fixed flow regulator, a certain velocity can be achieved. With vertical movements, changes in speed are also present with greatly differing load weights. Furthermore, with different cylinder sizes with the same fixed orifice or fixed flow regulator, changes in speed must be taken into account.
Particularly in the case of pneumatic drives, the physical properties; compressibility of the pressure medium, must be taken into account when fulfilling the "reduced risk" requirement.
Integration in practice
Based on feedback and from practical experience, it can be determined that in many cases a reduced speed such as for setup operation is not yet realized. However, we have found that even with little additional effort in terms of control technology and by means of commercially available fluid technology components, a reduced speed can be achieved. This also applies to the application of pneumatically driven linear axes, where the compressibility of the medium must be taken into account when meeting the requirements of reduced speed.
The other requirements for fluid power equipment according to EN ISO 4413:2010 for hydraulics and EN ISO 4414:2010 for pneumatics must be observed. The European Machinery Directive, the design guidelines according to EN ISO 12100, the requirements from EN ISO 13849-1:2015 and -2:2012 as well as other applicable standards must always be observed by the machine manufacturer.