Air motors: they're a gas!
01 May 2012
Dagmar Dubbelde offers four examples that demonstrate the versatility of air motors, from a device that turns waste process gas into useful electrical energy, to an ATEX-compliant brake motor at the heart of a system that empties toxic products from barrels.
'Furore' is one of the latest innovations to come out of Deprag's research and development lab. This 'Green Energy Turbine' (GET) generator is able to use small quantities of ‘waste’ process gas to generate a local electricity supply. The project is now sufficiently far advanced for it to be tested in conjunction with partners. The unit is based on the expansion turbine principle and comprises a turbine and generator sharing a common shaft. Excluding the control housing, GET is not much bigger than a shoe box, and can be used locally on a 'plug and earn' basis wherever gas at pressure either exits from an industrial process or where pressure levels must be reduced by exhausting the gas from the process.
Meanwhile, Helmut Pfeifer, an applications technician at Bodenbender GmbH, who has worked as a drainage repair expert for some 30 years, is totally convinced of the merits of air motors in his particular line of work. Hitherto, work on main drainage systems meant road surfaces had to be dug up, but these days they can be repaired - in situ and without excavation - using modern liners.
The air motor in this particular application - a Deprag vane motor - powers a BRM milling robot's cutting head, which removes deposits inside old drains, smoothing out casing crossovers, cutting away any protruding sockets, and removing invasive plant roots. The motor, which Mr Pfeiffer claims never fails even under the most difficult of working conditions, is only 118mm long and 57mm diameter. With an output power of 600W, rated torque of 0.95Nm and a speed of 12,000rpm, this motor has proved its worth in tight spaces. Once the milling work is complete the liner is introduced into the defective pipe.
In another application, an air motor is deployed in such a way that it enables a single person to move huge rolls of paper weighing several tons using just one hand, or effortlessly push railway carriages back and forth - or even manhandle an aircraft into its parking spot inside a hangar. The ‘Easy Roller’ - an inconspicuous roller transporter gives a single operator the power to manoeuvre weights of up to 100 tons without little exertion.
Take the case of a cable roll weighing several tons. In order to move this, Easy Roller is simply placed in position in front of the cable drum. It travels on two rubber rollers and the device's rubber drive roller is positioned above these. Springs press the front roller against the drive roller, and initially there is empty space at the rear one. The worker now actuates the manoeuvring valve handle and the air motor begins to turn, setting the drive roller in motion via a chain drive.
The drive roller transfers the movement to the front roller and the Easy Roller now moves towards the cable drum. At the same time, the manoeuvring device is pressed down, and this also creates contact from the drive roller to the rear travelling roller, where the forward rotation torque is transferred. When the contact pressure on the rubber drive roller (which is pushed with increasing pressure against the object) is high enough, the torque transfers to the cable roll, which subsequently moves.
The Deprag stainless steel vane motor used in this application produces 1.2kW of power from a unit just 218mm in length and 100mm diameter, weighing just 9.1kg. It rotates in one direction only with an idle speed of 100rpm and rated torque of 500Nm.
In our fourth application, an air motor has been integrated into a system along with holding brake and gearbox by bulk goods handling specialist, Beer Fordertechnik to provide a low-dust barrel emptying system for toxic loads of up to 200kg. The ATEX-compliant brake motor places the barrel in motion, and the tipping and emptying process begins. When the highest point is reached, the air motor switches off, the brake comes into action, and holds the barrel in position.
The integral holding brake consists of three brake discs, a pressure spring and a piston. It is triggered separately via a compressed air line. When the pressure is above 3bar, the spring tension is less than the pressure force - the brake discs have no load and the air motor can rotate freely.
If the pressure falls below 3bar, the spring tension is greater than the pressure force - the brake discs are pressed together and the air motor is blocked. A safety valve prevents any remaining compressed air in the line from causing any inappropriate friction on the brake discs. A compact planetary gear system, sized to suit the customer's torque and speed requirements, completes the system.
Air motors are a well-proven technology, on the basis of which pioneering and innovative products, such as the energy recovery turbine generator have been derived. Moreover, these robust units can be put to use wherever an overload-safe, high performance drive is required and where conventional motors would simply not be capable of operating.
Dagmar Dubbelde is with Deprag Schultz GmbH