By Josh Cosford, Contributing Editor
There are a lot of pneumatic directional valve options on the market. There are the big players in the game who take up half the market under only a couple of brand names, but the remaining half of the industry contains hundreds of players with myriad options. When selecting valves for automation, there is a lot to choose from, so it helps to understand the basics as well as the common threads that tie them all together.
In high-demand, high-volume production factories, the number one criterion for a valve system is performance. Performance can entail many things for a pneumatic valve: flow rate, response time, service life and Fieldbus connectivity, for example. Each of these considerations is important to the engineer or designer selecting a valve package for their machine.
The Holy Grail of pneumatic valve technology is making a small valve flow big, and manufacturers are constantly looking for ways to improve their valves’ flow rates. You may find it listed by actual flow rate expressed in liters/min (or scfm), but also Cv or even described by how quickly a given bore of cylinder will travel. Cv is an odd unit described as gallons per minute of water at 60°F at 1 psi pressure drop, but what’s important is that more flow is better.
Response time describes how quickly the valve can shift, and the upper echelon of products lists how their valves perform. Response time is important for automation functions working at blinding speeds, such as packaging machines, textile air-jet looms and sorting machines. Although pneumatic valves are already quick, you can expect high-performance versions to be 20-30% faster still.
Any high-volume production line will lose bags of money during machine downtime, so you can expect the big players to offer sensational claims of hundreds of millions of possible cycles over a valve’s lifetime. Whether such claims are smoke and mirrors or based on lab results, you won’t go wrong choosing one of the big players with solid reputations. Even if said valve fails, their valve systems often make the replacement of valve sections within a bank or manifold quite quick and easy, reducing any downtime to minutes rather than hours or days.
Fieldbus connectivity makes the identification of failed valves a breeze. There are a dizzying number of possible control systems, so expect the ease of automation that comes with your preferred method of serial transmission — DeviceNet, PROFIBUS, EtherNet/IP and every other combination of acronyms and contractions electronics engineers dreamed up because they thought they had the better mousetrap.
Fieldbus systems are important for automation because they ease the installation, operation and diagnostic functions of a control system. By running a single cable to a valve bank, you reduce wiring complexity, ease the integration of subsequent valves, improve diagnostic capability, and reduce cost.
Automation through pneumatics has come a long way since the days of cam and roller lever days when dozens of sequentially activated valves were coordinated to achieve complex functions. It’s never been cheaper and easier to automate machinery, and with the proper selection of pneumatic valves, you can achieve previously unmatched performance as well.
