Canadian Plastics

Blowing the budget with compressed air

Regardless of your process, I'll bet that somewhere in your shop you're using compressed air. For most of you, it's everywhere, and it's also far from the top of your priority list. That's too bad, be...

January 1, 2002   By Jim Anderton, technical editor

Regardless of your process, I’ll bet that somewhere in your shop you’re using compressed air. For most of you, it’s everywhere, and it’s also far from the top of your priority list. That’s too bad, because whether you’re using it for process automation or just as a blowgun, there’s money to be saved, or wasted here.

Most large operations source turnkey, compressed-air systems developed by specialists with software (and hopefully experience) to deliver a smooth-running, evenly distributed supply. Many smaller operators, in my experience, run off to their industrial supply house and buy a compressor. They then add plumbing as necessary and off they go. Usually it’s off to the industrial supply once again to replace the valves and actuators that failed ten minutes into that just-in-time run.

Here’s one symptom you have “pneumatic fever”: If you’re blowing off, kicking out or cooling moldings with an air jet duct-taped to the machine, you’ve probably let your air distribution system slide into critical condition.

Don’t be ashamed, you do what you have to do to get the product out the door. What happens, however, after the run? Chances are nothing, at least as far as compressed air is concerned.

Consider this: eighty percent of the electricity going into generating compressed air is wasted as heat. System improvements can generate electricity savings of 20 to 50 percent. Getting those savings, however, can take considerable human and capital investment, so here’s a few low-cost preventative maintenance methods for reducing pneumatic costs and downtime.

Step one is to look at the airflow around the outside of the compressor. Most small to medium sized units use a cooling fan integral with the flywheel/drive pulley, and if the cylinder cooling fins are clogged, then heat builds up. Heat is bad for the moving parts, but it also dissolves more moisture in the air, making your aftercooler/dryer/separator equipment work harder. Have you enclosed the compressor to reduce noise? I once built a beautiful sound-insulated booth for an ancient, noisy DeVilbiss and found temperatures around the unit to be astronomical. The air was saturated, but the plant was quiet!

Ducting cold outside air into the box helped. If you do this, please accept another piece of advice: screen the opening. It’s warm in there, and the local rodent population will thank you for the opportunity. The same airflow logic applies to aftercoolers (or intercoolers if you have a multi-stage compressor).

Inside the compressor, some airflow tips can also be useful. Cold, winter air is a good source, but hot, muggy Southern Ontario summers (no “dry heat” here) would sometimes overwhelm desiccant dryers in my small plant. The solution may be to simply increase the drain intervals and watch desiccant levels more closely. And if you go to a desiccant drying system, don’t forget to add a filter immediately downstream of the tower or towers, regardless of the quality of the supply air. Microscopic “fines” can be incredibly hard on seals and bores.

Another pet peeve is the use of plumbing valves instead of proper pneumatic equipment. Many small shops (and some larger ones) use water valves, which is bad enough, but a lamentably common mistake is to use them for flow regulation. Most plumbing valve gear is designed to operate either fully open or fully closed. Play with the settings and the stem packing will eventually surrender, leaving pressure-killing leaks everywhere. And unlike the black oil that spurted out of the overhead valves in those bad WWII submarine movies, you can’t solve it by turning a wheel. CPL

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