Originally Published MPMN September 2008

PRODUCT UPDATE

Suppliers Shrink Valves for Small and Portable Devices

As portable and minimally invasive devices increase in number, the size of valves continues to decrease for gas and liquid applications.

Stephanie Steward

Providing more mobility to patients who suffer from long-term illnesses or who are recovering from surgery can free up hospital resources and increase treatment options. As such, a demand for more-flexible and less-invasive medical devices and remote patient-monitoring equipment has driven the industry to continue to decrease the size and increase the capabilities of their products. As the push for portable and minimally invasive devices gains steam, OEMs require smaller valves that can accommodate these design demands while still meeting flow-control requirements. In response, suppliers have employed creative thinking and strategic use of design tools to produce new valves that offer the tiny size and high throughput that OEMs seek.

Small Valve, Large Orifice

Solenoid valves direct the flow of air and gases in a fluidic module that typically incorporates miniature diaphragm pumps, compressors, or vacuum pumps. Over the years, as portability has become a more-common factor in device design, the challenge for suppliers has been to produce smaller, lighter components, including miniature solenoid valves, to fit in these medical devices, according to Dan Schimelman, director of business development at Hargraves Technology Corp. (Mooresville, NC; www.hargravesfluidics.com).

In trying to meet this challenge, Hargraves realized that simply reducing the size of the valve resulted in a smaller orifice, which restricted throughput, effectively sacrificing higher performance for a smaller package size. To address this design problem, the company focused instead on reducing the overall size of the valve while maintaining a large orifice. The result is its Magnum 10-mm series of miniature solenoid air and gas valves designed with an orifice up to 1.9 mm that the company claims can outperform many larger solenoid valves.
The positive impact of a much larger orifice and corresponding higher flow rate translates to an advantageous drop in the differential pressure that a pump must work against in a fluidic system, according to Schimelman. Potential advantages gained by incorporating a Magnum valve into a device include utilizing smaller, lighter pumps; less noise; and extended pump life. "Portable medical devices benefit from the high flow and high efficiency of Magnum valves that are optimized in conjunction with a miniature diaphragm pump or compressor," Schimelman says.

For applications that require fluidic modules to perform as efficiently as possible, the ability to optimize the power required to operate the solenoid valve that controls flow, pressure, or vacuum provides the added benefit of reducing current draw and heat generation. Since extending battery life is an important criterion to a portable medical device's market success, configuring a fluidic module with higher-efficiency and higher-flow solenoid valves has become a key technology driver, Schimelman says.

The large orifices of the solenoid valve also can benefit device applications that have chambers or cuffs to fill, pressurize, or evacuate in a timely manner, such as deep-vein thrombosis therapy or other compression-therapy devices. When equipped with a Magnum valve, these devices can provide a more-responsive therapy by pressurizing and evacuating the cuff faster, according to Schimelman. "Some of the applications can see this time reduced [by as much as] one-third the typical fill or evacuation [rate]," he adds.

Burkert Fluid Control Systems (Irvine, CA; www.burkert-usa.com) has also been paying attention to how portable and point-of-care devices are driving OEMs' demands. It has reengineered its 10-, 16-, and 22-mm valves with larger orifices to achieve higher pressures while consuming less power.

"The industry continues to look for [characteristics such as] smaller size, proven reliability, lower-power, higher throughput, and less waste," says Burkert microfluidics market segment manager Craig Occhiato. "Our Type 6650 'Flipper' solenoid valve [has the] mechanical advantages to meet or exceed the life science industry requirements," says Occhiato. The valve is only 4.5 mm wide, and is designed to be mounted directly above 96 and 384 microtiter plate instruments and other applications requiring tiny valves.

Analysis Tools Speed Up Time to Market

When designing the large orifice of its solenoid valves, Hargraves used finite element analysis (FEA) to analyze the flow throughput and flux efficiency of the magnetic field created by the valve in order to increase the valve's flow capabilities. Vernay Manufacturing Inc. (Yellow Springs, OH; www.vernay.com), which provides standard and custom precision fluid-control components, has also benefitted from using tools like FEA and computational fluid dynamics (CFD) when developing valves for liquid applications. Vernay used FEA and CFD to respond to a request from a customer to make its Supra-Valve line of elastomeric check valves smaller and capable of holding to tighter functional tolerances, according to John Madewell, Vernay's director of sales.

"We can model the valve using the FEA and CFD tools [to predict] how the valve will work in its intended application," Madewell says. "This benefits the OEM by reducing the time to market [by allowing] our customers to bypass the traditional route of multiple prototypes."

Although the company has been developing miniaturized parts for years, it is noticing the increased demand for even smaller valves more recently, Madewell says. To fulfill this need, the company offers a valve, approximately 3-4 mm in diameter, that is used in minimally invasive surgical applications.

Stick with Standard, or Get Customized?

Even with these advances in valve technology, however, some OEMs may still struggle with weighing the benefits of choosing a standard valve that will work for their needs versus opting to customize a valve to meet specific application requirements.

South Bend Controls Inc. (South Bend, IN; www.sbcontrols.com), a developer of fluid-control components, offers flexible options to OEMs in this situation. To help its customers, the company provides core technologies and products that can be easily modified to meet customers' application-specific requirements. For example, it offers a proportional solenoid valve, the PSV-PB, that is designed for medical ventilator applications, specifically those that require operation at multiple pressures or low pressures. However, the valve's orifice size, coil resistance, and spring rates can be modified to meet specific needs, according to the company's vice president and general manager, Peter Hutchings.

Flexibility and customization are crucial to advancing valves used in medical devices. But the biggest concern is still keeping up with the industry's demand for smaller and more-efficient components for the increasingly miniaturized and portable device market. "The requirements for mobility, both for ambulatory and sustained treatment, are moving away from the hospital," Hutchings says. "This shift is driving the need for smaller components for more-portable devices that require less energy than their predecessors, yet maintain the same reliability requirements."

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