Canadian Plastics

Hot air about pneumatics

Using air to clamp, draw or move small objects is as old as the industry itself, and for something as conceptually as simple as blowing pressurized air into a cylinder to move a piston, it's amazing t...

November 1, 2001   By Jim Anderton, technical editor



Using air to clamp, draw or move small objects is as old as the industry itself, and for something as conceptually as simple as blowing pressurized air into a cylinder to move a piston, it’s amazing to me how many experienced personnel have no idea how it all really works. Experts tell me that with “air logic”, it’s possible to construct computer-like circuits with pneumatics, but on my lines, they’ve generally been restricted to clamping, pushing, shearing and other “brute force” labors.

I’ve made a few observations, usually by trial and error, that might be relevant to your operations. One seems self evident, but for some reason is difficult for even many engineers to understand: pressure does not equal force. Neglecting friction and any mechanical advantage in a given system, cylinder pressure times piston area equals the parameter you’re really interested in: force.

You can get by with pressure, maybe for years, but when the occasional glitch fouls up your lightning-fast transfer equipment, tracing the problem by pressures can be frustrating. One reason is that the problem won’t reappear while your technician or engineer is watching. I’ve seen this occur when the pressure fluctuation is triggered by the occasional simultaneous operation of multiple machines on a branch line. Depending on the operation, everything may fall into phase once or many times per shift, resulting in an apparent pressure drop that goes away with the next machine cycle.

What you need here is either more capacity, which is expensive, or maybe an accumulator to store a little reserve pressure for that critical machine. It’s possible to do a lot of complex math to calculate the correct reserve capacity, but for smaller equipment, I’ve found success by adding a substantial coil of hose in series with the affected machine. If the problem goes away, consider more air, rerouted lines or a dedicated accumulator in the system. If you plan to use the hose trick, however, remember that it adds substantially to the effective piping run, so it will only work if the equipment is running at significantly lower than line pressure.

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Of course, if you’re running at max p, then you’re asking for trouble anyway. What are the most common problems I’ve discovered when troubleshooting pneumatics? Water in the lines, leaks, and lack of proper lubrication (meaning less oil than you think) in the system. And that’s really about PM, not repair. I’ve ignored most pneumatic PM chores at one time or another, a topic about which I’ll say more next month.


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