Pneumatic Valve Cuts Size, Weight of Handheld Medical Devices

Targeted at applications ranging from infusion pumps to oxygen concentrators to medical simulation mannequins, the new solenoid valve employs a latching feature that enables it to draw current in very short pulses. “With this valve and a standard AA battery, you could open and close a valve more than two million times,” Robert Irwin, principal engineer for Precision Fluidics Division of Parker Hannifin Corp., told Design News. “If you didn’t have the latching feature, you would consume the battery in a fraction of those cycles.” Irwin said the design would not only extend the time between battery charges; it would enable designers to employ smaller, lighter lithium batteries in their handheld devices.

Used with a standard lithium AA battery, Parker Hannifin’s tiny LX valve could be opened and closed more than two million times.
(Source: Precision Fluidics Division of Parker Hannifin Corp.)

The key to the new pneumatic valve, known as the LX Series, is the latching feature. By balancing the forces between an onboard spring and a permanent magnet, the latching mechanism shuttles a plunger back and forth, opening and closing the valve. To accomplish that, it applies only a momentary pulse of electrical current to a solenoid coil. “By applying just the right amount of flux from that coil, it will tip the balance, so the spring has more force and the plunger moves in one direction,” Irwin told us. “Or the magnet has more force, and the plunger moves in the other direction.”

That technique represents a stark departure from the way such valves normally work. Typically, conventional valves apply current for as long as the valve needs to remain open. So if the valve is taking a 30-second sample, current must be applied to the coil for the full 30 seconds. In contrast, the LX’s latching feature draws a brief current pulse -– about 5 to 10 msec. After that, the balance of forces keeps the plunger in place without additional current draw.

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”When you remove the pulse, it stays in its position,” Irwin said. “So the part doesn’t consume power in either the opened or closed state.”

Because the LX is targeted at handheld devices, it’s small -– less than 8 mm in diameter -– and therefore can be integrated directly onto a PC board or mounted on a manifold. It operates at 0.4bar (about 6 psi) and accepts common input voltages from 3V DC to 24V DC.

Parker’s Precision Fluidics Div. said that about 80% of the applications for the new technology will be in medical and life sciences. In addition to infusion pumps, it could be employed in wound therapy, anesthesia, and respiratory devices. Outside of the medical arena, it could be used in small fuel cells to recharge hearing aids or in automotive lumbar support systems.

"In most of the applications, they would otherwise have to use a bigger battery,” Irwin said. “So this becomes a driver of both size and weight.”

Senior technical editor Chuck Murray has been writing about technology for 31 years. He joined Design News in 1987, and has covered electronics, automation, fluid power, and autos.