By employing rotary solenoids instead of conventional linear solenoids, design engineers from the Aerodyne Controls Division of the Circle Seal Corp. say they are creating smaller and faster pneumatic valves.
The valves, which can move from fully-open to fully-closed in as little as 30 msec, reportedly can fit in a fraction of the package space ordinarily needed for comparably-rated valves using a linear solenoids. The new custom-designed butterfly valves are currently being employed in angina treatment machines and in military helicopters, where their speed and small size is said to be critical.
Aerodyne engineers say that the solenoid's rotary design is the key to making smaller, faster valves. "By going to rotary, we can apply the power directly to the operation of the valve, so we improve its speed," says Hugh O'Brien, chief engineer for Aerodyne Controls. In contrast, he says, linear solenoids must typically transfer their motion through mechanical linkages in order to operate a butterfly valve.
To date, O'Brien says, rotary solenoids have not been widely used in butterfly valves because their motion envelope is limited to 90 degrees, whereas linear solenoids can offer multiple 360-degree turns. Aerodyne engineers contend, however, that multiple-turn capabilities aren't critical in every application. More important, they say, linear solenoids tend to be bulkier and draw more power as a result of their attached linkages, which convert the linear motion to the rotary motion that's needed to operate the butterfly valve. "Linear solenoid designs take up significantly more space and require more power to overcome the friction of the linkages," O'Brien says. "With a rotary design, the power goes directly into driving the butterfly, and that maximizes the speed of the valve."
Aerodyne employs a three-way version of rotary solenoid butterfly valve to inflate and deflate rubber bladders in an angina treatment machine for hospitals. The machine, which helps force blood through patient's arteries and veins, incorporates the rotary solenoid design as a means of opening and closing the butterfly in less than 38 milliseconds. The design also provides a solenoid life of 100 million cycles, which is needed in the medical application.
Similarly, Aerodyne engineers say they have also used the rotary design to open and close a cockpit ventilation duct in military helicopters. The rotary solenoid, they note, enabled OEM engineers to place the butterfly valve in a tight packaging envelope. In contrast, a linear solenoid or motor-driven valve wouldn't have fit in the same envelope, they add.
Because the new design requires no external motor or pneumatic actuators, Aerodyne engineers expect it to catch on in other similar, space-limited applications.
"It requires no power source other than electrical current," O'Brien says, "so it can be used in all kinds of applications, including fly-by-wire."