All-pneumatic control maintains constant air motor speed

However, if the motor drives the impeller too fast then cavitation occurs, resulting in bubbles in the paint that give a poor finish. And if the paint is metallic, the suspended metal flakes will be damaged, leading to an aesthetically flat and therefore equally unacceptable finish. Conversely, if the speed is too low, the paint simply settles out.

Huco Dynatork says its piston air motor is excellent for such an application because, unlike a vane motor, it is eminently controllable. Its free-floating piston design transmits maximum torque on actuation, which can be regulated to fine limits by a self-adjusting control valve set on the air inlet.

Pulse counters can be used to program direction of rotation, speed and number of revolutions. This means the motors can provide near-instantaneous stop/start/reversal and drive under load, with characteristics similar to those of a stepper motor.

An electronic controller used to be the obvious choice for these motors but now Huco Dynatork has introduced its own pneumatic regulating valve set that ensures constant speed regardless of load. This new Huco Dynatork controller comprises two control valves: the first controls air pressure and the second adjusts flow rate. The controller works by sensing pressure drop across an orifice. Any reduction in pressure is proportional to flow rate and, by feeding back this value to the flow control valve via a diaphragm, air flow is adjusted accordingly. This enables a constant speed to be maintained automatically.

The controller is available in two sizes to suit different air motors.