Driving medium

A driving medium is a pressurised gas or liquid that sets something in motion, for example by moving, opening or pumping it.

In industrial installations, many devices are not moved by an electric motor, but by the pressure of a gas or liquid. The driving medium is that gas or liquid. It is neither a product nor a raw material itself; it simply provides the force needed to do the work.

The most commonly used driving media are:

• compressed air, the most popular because it is readily available and safe,
• nitrogen, when the product must not come into contact with oxygen because it would oxidise, or when there is a risk of explosion in the surrounding area,
• water,
• hydraulic oil, in equipment that needs very high force, such as presses.

Typical applications include:

• pneumatic valves and actuators, which open and close under the pressure of compressed air,
• pneumatic pumps, such as diaphragm pumps, which transfer product using compressed air instead of an electric motor,
• pigs in pigging systems, which move through the pipe driven by gas or liquid and push the product ahead of them.

The driving medium must be at the correct pressure and properly cleaned, especially if it may come into even indirect contact with the product. That is why compressed air in food and cosmetics plants is filtered and dried.

Example: In a laundry detergent plant, several dozen valves operate on the pipes between the tanks. Each of them has an actuator supplied with compressed air. When the controller sends the “open” command, compressed air flows into the actuator and switches the valve. Without compressed air, the valves would stop working and the whole installation would come to a standstill, even though the power would still be on.