Piston air motors offer huge energy savings

A UK-based automotive painting plant has reduced its compressed air consumption by 85% after replacing its 68 vane type air motors with an equivalent number of piston type air motors. According to Huco Dynatork's joint managing director David Lockett, total air consumption in the factory from the vane motors was 4,000m3/hour. But after installing 68 Dynatork air piston motors, this figure was reduced to around 630m3/hour - an 85% drop. "The overall cost savings to the factory were tens of thousands of pounds per year," he stated. The results are impressive, even if you take into account the purchase costs of piston motors, which are usually two to three times more expensive than equivalent vane motors. The figures are based on a Dynatork 3 Air Motor running at 350rpm, which consumes around 9 m3/hour of air, compared with an equivalent vane motor with reduction gearing to achieve the same speed and the same torque output. The vane motor consumes around 36m3/hour, around four times as much air than a piston motor. Of course, not all applications are suited to air motors, whether they are piston or vane. Generally, air motors are specified when electric motors cannot be used. Hazardous areas or electromagnetic interference are the usual problem areas for electric motors, but air motors perform well in these environments, even in underwater applications. With air motors, the two types are vane and piston. Vane type air motors (manufactured by the likes of Gast, Ingersoll-Rand and Parker Hannifin) generally run much faster than piston motors and so require gearing to reduce the output speed. The units are pretty noisy (even with silencing) and not very efficient, since the air runs out through the vanes and is difficult to control. Also, if the air volume supplied is too low or there is a sudden pressure drop, the motor can stall. Dynatork's piston motors are very different. They use three cylinders with a crank and rotor with air pushing the piston down. The volume of air needed is much less, there are less air leaks and so efficiency is better when compared to vane motors. Overall, you get more precise control with piston motors which makes them ideal for low speed-high torque applications such as paint stirring. Piston motors can stop-start and drive under load with characteristics similar to a stepping motor. Speed of the motors can be adjusted to fine limits using restrictors on the exhaust ports. Reversing is also possible using 5-port control valves, giving near-instant response even under load. Potential applications for piston air motors are vast. Valve modulation, heavy vehicle drive systems, food samplers, lead screw drives, winding machines, conveyor drives, process control and rotary brushes are just a few examples. Dynatork was acquired by power transmission couplings specialist Huco Engineering Industries in August 2005. Huco will use its vast network of global distributors to sell the Dynatork range.