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08/04/2010
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Designing in lower compressed air use to pneumatics applications could mean considerable financial savings. Paul Fanning looks at some of the options.
 The need to control costs and conserve energy has tended to focus on cutting power usage. Pneumatic actuation, however, is an area that has often tended to escape scrutiny.
SMC Pneumatics' control system design engineer Mark Brinsley outlines the problem: "Because people are breathing air, they tend to assume it's free, but obviously you've got to compress it, which takes a huge compressor motor. It's thought of as a cheap form of energy, but not by the accountants."
Quite how significant compressed air usage is can be seen from the fact that its generation is equivalent to about 10% of industry's total electricity usage, rising to 30% in some sectors. This highlights why companies have compelling reasons to pursue energy saving initiatives in this area.
One type of air-saving solution that has existed for some time, but is starting to see increased interest as these costs are examined is SMC Pneumatics' ASR and ASQ air-saving valves, which work by simply reducing the pressure required to operate the return stroke of a cylinder but without compromising the speed at which the cylinder operates.
In the same size as a conventional flow controller, the ASR pressure valve incorporates a miniature integrated regulator with check valve and speed controller, whilst the ASQ comprises a quick supply and exhaust valve with speed controller. Says Brinsley: "If users are sending pneumatic cylinders out and in they're generally using one control pressure. If they're doing that, then they're using the same force on the out stroke as on the in stroke and we've found that most applications don't need that same force. So what we've done is reduced the pressure where we can. It's a question of 'right pressure, right force'."
The savings that can result are considerable. In fact, tests undertaken by SMC as a rule demonstrate a 30-40% air saving over a standard control set-up.
Another approach is the use of improved process valve control techniques, which can lead to reduced compressed air use through the adoption of on-actuator or in-actuator pneumatic solenoid valves.
At present, the majority of pneumatically piloted valves on production and process lines centralise pneumatic control around valve islands in a control cabinet or enclosure. This arrangement means that the pipework carrying the pilot pressure to the actual valve from the valve island can travel for many metres before it reaches the valve head. As a result, the venting cycle of the valves operation will exhaust proportionately more air than is necessary.
Burkert's type 8690, 8691 and 8695 valve control heads. Developed for use in the food, beverage and pharmaceutical industries, these units provide a decentralised method of opening and closing of process valves automatically, eliminating the need for the wasteful venting of control air normally associated with pneumatic tubing between the process valve and its related control solenoid valve.
The control heads integrate electrical and pneumatic control components as well as position feedback units and, optionally, field bus interfaces for AS-Interface or DeviceNet. They are mounted directly above the valve body, and, because there is little or no distance between the actuator and the valve that it is piloting, there is no air bleed: it is sealed. With this system the pressure feed goes directly into the valve head and the control signal is supplied either from a local closed loop control sensor or switch; or from a PLC / machine controller via a control bus - AS-Interface or DeviceNet – or multipole (parallel) directly into the valve.
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Author
Paul Fanning
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