Factories move things with air rather than electricity

What pneumatics offer that motors do not.

Factories move things with compressed air because a pneumatic cylinder is mechanically simple, cheap, robust against dirt and moisture, and safe to run where an electrical spark would be dangerous, and because a single central compressor can supply dozens of cylinders through a network of pipes, sidestepping the wiring, controllers and individual motors an electric solution would need at every point of use.

One bellows, hundreds of pipes

A pipe organ can hold hundreds of pipes, and not one contains its own source of moving air. Each is a simple mechanical object that sounds only once wind reaches it from a single central bellows through shared ducts and valves. Pressing a key opens a path for air that was already pressurised and waiting, routed to wherever it is needed at the moment it is needed.

A factory floor full of pneumatic cylinders is organised on the same principle. An electric motor at every station on a line needs its own wiring back to a power supply, usually its own controller for speed and direction, and some protection against the vibration, dust and splashes a factory floor throws at everything. A pneumatic cylinder at the same station needs only a pipe of compressed air and a simple valve directing that air to one side of the piston or the other. The compressor elsewhere in the building has done the hard work once for the whole plant, and extending or repairing the line means adding pipe and a valve, not running new cables and wiring up another controller.

The previous two articles in this set dealt with where compressibility causes trouble. This one turns to the jobs where a compressible, centrally distributed fluid is exactly the right tool.

Nothing at the cylinder to burn out or spark

A pneumatic cylinder contains no windings, no magnets, no electronics and nothing that generates meaningful heat in normal use, which makes it much harder to damage through the ordinary hazards of a factory floor, dust, splashed coolant, an accidental knock, than a motor and its control electronics. It is also intrinsically safer around flammable dust or vapour, since no electrical current reaches the point of use and so there is no spark to ignite a hazardous atmosphere. In plenty of industrial settings that is a deciding factor.

The two technologies solve overlapping problems with very different failure modes, so a factory choosing between them is often choosing which set of risks and maintenance demands it would prefer to manage.

Holding a load for free

An electric motor asked to hold a load still against gravity or resistance often has to keep drawing current the whole time, since a motor produces torque only while current flows, and cutting that current lets the load drift back unless a separate brake is fitted. A pneumatic cylinder resting against one of its hard end stops needs nothing of the kind. The compressed air already in the line keeps pushing the piston firmly against the stop for as long as the valve stays put, holding the load without spending any energy beyond what it cost to get there. A cylinder can sit clamped against a part for an entire shift and use almost no more air than the stroke that brought it into position, which is one of the quieter reasons compressed air suits so many clamping and gripping jobs.

Where air gives way to motors

The advantage disappears once a task needs the fine, repeatable mid-stroke positioning the previous article showed compressed air struggles to deliver. At that point the simplicity has to be traded away for added valves, sensors and control loops, or for an electric motor suited to the job from the start. The choice comes down to which job a station actually needs: simple, robust, centrally powered motion between fixed points, or precise, individually controlled positioning. Each technology answers one of those comfortably and the other only at added cost.

Most working factory floors run both side by side, air handling the blunt, repetitive pushing and clamping across dozens of stations, and electric motors reserved for the smaller number of places where position control was always going to be worth the extra wiring.