Electrical and electronic devices such as logic circuits, programmable controllers, and PCs normally control fluid-power and fluid-handling circuits. Such systems can also operate with “air logic,” controls that function like relays, switches, time delays, and counters. However, while the circuitry is similar, compressed air is the control medium instead of electric current.

Air-logic controls are often preferred in wet or dusty environments because they pose practically no danger of explosion or electrical shock. Likewise, air controls cannot ignite explosive or flammable gases and vapors. And they’re rugged. Water can splash on the controls without affecting operations, and they tolerate dust and dirt. Air logic can also be used on machines with fluid-power components but no electrical supply.

Air logic does have disadvantages. Most common is a lack of understanding among maintenance personnel on how to read schematics and troubleshoot problems. Also, air logic with long control lines responds noticeably slower than electronics. That’s because control lines longer than 10 to 15 ft fill and exhaust slowly compared to near-instantaneous electrical signals. In addition, it takes a high-quality, filtered air supply to ensure long life.