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Peace of mind in hazardous areas

09 September 2014

Piston air motors can offer many advantages over their electric equivalents, including energy efficiency, simple installation, easy maintenance, longevity and precise controllability. However, they really come into their own in hazardous area installations.

Piston air motors consume up to 80% less air than vane air motors, which can provide significant energy cost savings even when running at maximum torque. Because there is no electrical supply required for air piston motors, there is no possibility of sparking, which also makes the motors intrinsically safe for use in explosive atmospheres or close to flammable materials.

With piston air motors power is related to the supply pressure and speed to the air-flow, with an adjustable inlet valve providing control of the motor’s output. Motors can also be fitted with torque sensors for closed-loop feedback, allowing the motor to hold its set speed almost indefinitely. To achieve this with an electric motor would require a variable speed drive, which is expensive, requires installing on site, has to be programmed and commissioned – and could cause dangerous sparks. 

Less energy use
Piston air motors are different from their rotary vane type counterparts, partly because they hold their set speed and partly because they use only around 20% of the energy. They stop and start with no ill effects and this makes them suitable for constant stop/start duties under load, perfect for the hazardous or sensitive environments found in the hydrocarbon engineering, paper converting and wood working industries. The piston air motor’s inbuilt efficiency makes them very cost-effective.

Examples such as the Huco Dynatork range feature three free-floating pistons, driven by compressed air at up to 100psi, which transmit maximum torque on start up and can be adjusted via a pressure regulator, with maximum torque outputs of up to 16NM, or up to 550Nm being achievable using reduction gearboxes. Speed can be finely adjusted and pulse counters can be specified to programme direction of rotation, speed and number of revolutions.

A further benefit, in washdown areas, Dynatork motors are also available with an acetal outer housing so that they are impervious to the caustic fluids and chlorinated sanitisers used in hygienic washdowns.

Of interest in the nuclear industry is a new non-magnetic model which combines stainless steel shafts and ceramic bearings enabling the motor to be used safely where electro-magnetic interference and high magnetic fields are design issues. This makes them suitable for use in applications involving particle acceleration or in medical equipment such as MRI scanners.  

Mining applications
Dynatork piston air motors can be used in ATEX Equipment Group I Mining applications within the Protection Category 2 Gas & Dust rating, because they can be manufactured free from aluminium content, in stainless steel or Acetal. Above-surface applications fall in to Equipment Group II applications which do not, as a rule, have the same material constraints as Group I, but the Protection Category 2 Gas & Dust rating would still apply. Materials used in construction may still be of concern on above-surface applications, but these concerns are usually driven by environmental conditions, other than those included within the ATEX regulations.

It is always the buyer’s responsibility to specify the ATEX rating requirement for equipment to be used on their plant, bearing in mind that different areas within the plant can have different hazard ratings and as a result may need equipment with different protection category ratings to suit. 

In conclusion, piston air motors are efficient, offer cost and energy savings, have very low noise levels, can operate in clean environments, can be ATEX approved and are so corrosion-resistant they can even be used fully submerged. 

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