Hollis, NH--As medical equipment designers continue their furious efforts to downsize bench-top instruments, one looming problem stands in their way: pneumatic valves. Medical instruments often house as many as 40 such valves. And designers can't reduce the size of the instruments without smaller valves.
Now, however, there may be a solution to their dilemma. A new three-way, two-position pneumatic valve measures just 8 X 9 X 23 mm--about half the size of today's smallest valves with similar flow capabilities. Developed by engineers at Pneutronics Division of Parker Hannifin Corp., the X-Valve, as it's known, could see use in portable oxygen concentrators, non-invasive blood pressure instruments, and blood analysis systems. Pneutronics engineers believe it could also serve in HVAC and maybe even factory automation applications. "When you try to pack 45 or 50 valves in a machine, real estate becomes an issue," notes David Cross, engineering manager at Pneutronics. "It ends up being a tangle of valves and plumbing."
With the introduction of the X-Valve, however, Pneutronics engineers hope to change that. The reason: The X-Valve is not only smaller than competitors; it offers relatively high operating pressures--up to 50 psig-- and flow rates--30 liters per minute at 30 psig.
It accomplishes that by employing a unique solenoid-operated configuration. Unlike most solenoid-operated valves, the X-Valve is not simply a solenoid with a valve attached to it. Rather, it's an integral unit. As such, air flows right through the unit's pole piece.
During operation, users apply electrical current to the solenoid coil, just as they would on a conventional solenoid valve. The current produces a magnetic field, which in turn creates a magnetic force between the pole piece and armature. As the armature moves, it seals off one of the valve's ports while uncovering another. By energizing and de-energizing the valve in this way, the user's application can toggle flow back and forth between the ports. Pneutronics engineers say that this use of magnetomotive force is the key to producing high pressures and flow rates within the valve.
The key to its small size, however, is the fact that it drives air flow right through the magnetic half of the valve. That's a dramatic departure from conventional valve design. It's also a difficult feat to accomplish, because it inherently reduces the amount of magnetic material that can be used in key locations within the valve. But Pneutronics engineers accomplished it, mainly through careful design and computer analysis of the valve's performance. "In the interest of downsizing the valve, we had to balance the flow rate with the amount of magnetic material and the space that was available to us," Cross says.
To accomplish that, Pneutronics engineers incorporated several design innovations, including:
A unitized solenoid bobbin and valve body. The single integral structure enabled engineers to shave space, because it means that the valve is no longer connected to the end of the solenoid. The integrated component incorporates internal flow channels, tightly controlled press-fit regions for assembly, external mounting features, and tubing connectors for each port.
Multiple interference zones that permit O-ring-less assembly. Whereas a typical three-way valve may have four O-rings and two or three epoxy sealing points, the X-Valve has none of either. Instead, it uses patent pending interference zones to create seals. That, says Cross, was one more enabler in minimizing the valve's size. The precision fit of the zones also allows the flow to be redirected perpendicular to the valve body. That, in turn, facilitates manifold mounting and tubing installation.
An integral flux conductor. By using a one-piece flux conductor, instead of a conventional three-piece unit with an end washer, engineers were better able to deal with the magnetic material-for-flow tradeoff. The one-piece conductor is smaller than conventional conductors, yet just as efficiently directs the magnetic flux created by the solenoid.
The valve, introduced in the first quarter of 2000, is already being used in a portable oxygen supply system produced by Transtracheal Systems, Englewood, CO. The system, which uses two X-Valves, weighs less than a pound and is portable, thus giving patients the freedom to travel while they use it.
Pneutronics engineers say they expect the valve to see continued use, especially as medical designers seek ways to downsize their designs. "This could have been done previously, but there wasn't as much demand for it as there is today," Cross concludes. "The reason we introduced it now is that designers are asking for it."
Additional details...Contact William Nissim, Parker Hannifin Corp., Pneutronics Div., 26 Clinton Drive, Unit 103, Hollis, NH 03049; Tel: (800) 525-2857; Fax: (603) 595-8080.