Rodless cylinder has ATEX dust approval

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ATEX dust certification has been achieved by Hoerbiger-Origa rodless pneumatic cylinders; it is claimed that this is the first time such actuators have been certified in this way. This approval for use in dust-laden atmospheres complements the existing ATEX gas approval that the cylinders already hold.

ATEX is the legislative framework for installing equipment in explosive atmospheres, the final stage of which has just been introduced. It treats dust and gas separately but, for both cases, equipment now needs to be certified if it is to be use in Zone 1 or 2 for gas and Zone 21 or 22 for dust environments that have been assessed as having a risk of explosion.

Rodless pneumatic cylinders differ from conventional cylinders in that the load is connected directly to the internal powered piston instead of via a rod running the length of the barrel. This allows installations to be very much more compact, often leading to significant cost savings and machine design advantages.

However, rodless cylinders need to have a slot along their barrel so that the yoke connecting the load and piston can move back and forth. This is pneumatically sealed with a special piston seal and a uniquely profiled stainless steel inner sealing band. An outer sealing band, also stainless steel in construction, prevents ingress of particles from the environment into the pressurised area. The effectiveness of the combined sealing system on the Hoerbiger-Origa cylinders, combined with the fact that the inner and outer stainless steel sealing bands are held together with magnetic force, enabled the dust approval to be readily achieved.

Airborne particles, even of apparently stable substances like flour or cement, can oxidise virtually instantly and therefore form a flame path, allowing sparks to propagate and lead to an explosion. Rodless cylinders are often used in dry environments where dust may be present and so may now require ATEX certification.

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