What Are Pneumatic Systems Used For?

Pneumatic Systems comprise a huge number of technologies and integrations that use pressurized air to either power or drive them. In the case of pneumatic controls and instrumentation, pneumatics are used to communicate process variables commands to control valves. Pneumatic logic is used in many machine applications. While being explosion proof and intrinsically non-hazardous for dangerous areas such as in refineries and chemical plants, pneumatics are relatively easy to install and maintain since the signals are carried through simple low pressure tubes.

Driving Force

Pneumatic systems of all types are powered by compressed air supplied by air compressors filling large air capacity tanks under a pressure of about 100 to 150 pounds per square inch. Most systems now add air dryers to the lines extending to point of use of the compressed air. An air dryer lowers the relative humidity of air flowing from the capacity tank to the system using the compressed air, which improves their performance and service life.

Pneumatic Controls

The first process controllers were pneumatic control systems which used a proportional pneumatic signal to communicate process variables and control valve signals. At first, 0 to 30 psi signals were used to convey 0 to 100 percent analog signals which could represent a scaled variable such as 0 to 200 degrees F, or 1-100 gallons per minute, or 0-60 inches of liquid level. Later, the standard process signal became 3-15 psi which bore a 3 psi live zero point, and a 12 pound full range span. The live zero eliminated hysteresis effects or free lash of zero pressure on moving components within the mechanisms. Later, 3-15 psi analog signals would correspond to 4-20 milliamp signals in electronic instrumentation. Simplified pneumatic control systems are used to control heating, ventilating and air conditioning in large buildings as well.

Control Valve Actuation

With pneumatic controllers sending 3-15 psi proportional output signals to air actuated control valves, it was a relatively easy matter to add proportional valve positioners. The valve positioners detected exact valve position between fully closed and fully opened and adjusted the position to be exactly equal to the percentage of the 3-15 psi proportional signal.

Intrinsic Safety

For years pneumatic controls were the system of choice for oil refineries and other plants where volatile, flammable, and explosive gases or fumes could be present. Whereas electrical and electronic systems had to be isolated and use extensive barriers, pneumatic systems was as easy as laying down tubing, connecting the control systems and starting the plant.

Simplicity

Pneumatic systems consist of tubes, castings, diaphragms, and gaskets that last decades. They are among the most reliable systems ever conceived.

References

• Pneumatic Systems
• Pneumatic Controls
• Pneumatic Maintenance