TECH UPDATE EXCLUSIVE
Back to Basics: Valve Advice from the Experts
The VHS microdispensing valves from The Lee Co. can last a minimum of 200 million cycles if used correctly.
Selecting the right valve for an application requires a great deal of research--and it doesn't hurt to have a bit of guidance, either. Ralph Buck, electrofluidic systems product manager for The Lee Co. (Westbrook, CT; www.theleeco.com), and Samantha Miller, quality manager for Rheodyne LLC, an IDEX Health and Science Company (Rohnert Park, CA; www.rheodyne.com), address factors that OEMs should keep in mind when purchasing valves.
The finished product. When selecting a component, it can be easy to forget how this particular part fits into the bigger picture. OEMs must make sure that their goals for the finished device carry over to the components as well. For example, many portable devices demand low power consumption for use in the field. To achieve this, power consumption of the valve must be taken into account, along with the power consumption of additional components, according to Buck. When building a bed-side monitor, on the other hand, a primary concern when selecting a valve could be noise emission. Thus the valve's operating noise must be evaluated to assess the noise levels of the entire product.
Compatibility. Like in dating, the key to valve selection for medical applications is compatibility. "There are many different materials--a lot of different material options--and if you select the wrong material, that will affect the lifetime of the product," cautions Miller. OEMs must think about the fluids that will come in contact with the valve. Is the media aggressive? If so, it could cause corrosion or destroy the polymer in the valve, Buck says. Leakage could be a serious consequence. "On the flip side, you may have either tests or liquids that are very sensitive to things; a lot of proteins are very sensitive to metal ions, so you're going to need a valve that has no exposed metal," Buck says. "If you are flowing something that is sensitive to metal, you may need a chemically inert valve that uses something like PEEK or Teflon, or some of the more-exotic elastomers."
Supplier Capabilities. The more a supplier knows about requirements and intended use, the more it can help reduce time-to-market and offer better solutions. Miller cites the Rheodyne Titan series of valves, which comes equipped with an integrated PCB, as an example of such helpful solutions. "In the past and from other manufacturers, you might have to buy it separately or there may not be a PC controller available and you would have to develop your own motion profile and control language," she explains. "So, by giving them the PCB technology, it means [OEMs] don't have to have their own electrical engineers and their own development teams for that kind of technology; they can work with valve manufacturers to design exactly what they want."
Maximizing valve life. Once a valve has been selected for an application, it is important to maximize operation potential. It may sound obvious--silly even--but the best way to prolong a valve's lifetime is to use it in the context and in the conditions for which it was designed. However, OEMs may test the limits of valves or unintentionally use them incorrectly, thus expediting wear. "We have some microdispensing valves that will last a minimum of 200 million cycles," Buck says. "But they're designed to run wet. If you were to run them dry, you might only get 100,000 cycles." He also points out that running a valve at a higher voltage than intended can burn out the product quickly.
Reducing wear rates could also be as easy as meeting requirements--it's not always beneficial to be an overachiever. For example, Rheodyne's standard valve products have a pressure rating to 15,000 psi, Miller says. However, she points out that if an OEM only needs the valve to achieve 6000 psi, reducing the torque or pressure of the valve may help extend its life. "Having a clear understanding of their requirements, we can choose a design that will meet and not exceed those requirements," Miller says. "A lot of times where you see people go wrong is by trying to exceed requirements."