Powered by compressed air (or nitrogen), air motors are simple in design, offer variable speed and are relatively inexpensive compared to electric motors. A key feature is the fact that they are explosion-proof.

Blue Earth Technology LLC has developed a new air-driven motor it says offers a few new twists on this venerable old technology. Inventor Roy Rafalski says the speed range of a proof-of-concept model, bench tested for maximum rpm with no load and simple use of magnetic switches to control valves located at the head and cap end of each cylinder to time pressure pulses, is in the 100 to 850 rpm range.

Rafalski says he believes a maximum speed of 4,000 rpm could be maintained with an electronic-valve timing controller and alternative valves, allowing the motor to compete with a gas engine of similar output.

Design News was not given a description of the proprietary internal structure of the motor, only a photo (right) showing the motor's exterior and the following explanation: "It is simply straight-line motion produced from the cylinder at the full force being transferred into the rotary crank mechanism."

Rafalski claims it is the first air motor design to use air cylinders to provide rotary motion. Based on the presence of the two silencers it appears they are used in a single-acting mode. By operating the cylinders in a double-acting mode, whereby air pressure is delivered to the cap end of one cylinder and the head end of the opposite, Rafalski claims the output torque increases by approximately 88 percent, but air consumption also rises.

Asked about the intended method of sensing shaft position and controlling the air valves, Rafalski says air delivery could be controlled several ways - electronically or mechanically. In order to maintain a constant speed, torque output, for industrial applications, the system would require constant pulse-width modulation.

The specific control scheme, however, would be up to the manufacturer. Blue Earth Technology does not plan to manufacture the motor; it is currently offering licensing agreements for the air motor technology to parties interested in manufacturing the technology.

Contact Rafalski at[email protected]or visit Blue Earth Technology's website atwww.blueearthtechnology.com.