Both pneumatic and hydraulic systems transmit power through pressurized fluid, but their working media — air vs. oil — create fundamentally different performance envelopes. Choosing wrong costs you money, safety margin, or both.

Pneumatics (compressed air)

• Pressure range: Typically 80–120 psi (550–830 kPa). Air is compressible, which limits force output but provides natural compliance — a pneumatic gripper won't crush a part if it meets unexpected resistance.
• Speed: Fast actuation. Cylinders easily reach 1–2 m/s stroke speed because air has very low viscosity.
• Infrastructure: Exhaust vents to atmosphere — no return lines needed. Leaks waste energy but don't create hazardous spills.
• Best for: Pick-and-place, clamping, blow-off, packaging lines, dental tools, air brakes on trucks.

Hydraulics (oil)

• Pressure range: Commonly 1,500–5,000 psi (10–35 MPa), with some systems reaching 10,000 psi. Oil is nearly incompressible, so position control is precise and force output is enormous.
• Speed: Slower actuation but with smooth, controllable motion under heavy loads.
• Infrastructure: Requires a reservoir, return lines, filters, and heat exchangers. Leaks are messy and can be fire hazards near hot surfaces.
• Best for: Excavators, hydraulic presses, aircraft flight controls, injection molding machines.

The force calculation is identical for both: F = P × A. A 4-inch bore cylinder (area ≈ 12.57 in²) at 100 psi pneumatic gives you about 1,257 lbf. That same cylinder at 3,000 psi hydraulic delivers 37,700 lbf — roughly 30× more force from the same physical package. This is why excavators don't run on air.

Real-world example: A factory automation line uses pneumatic cylinders to sort packages on a conveyor (fast, clean, low force) but hydraulic cylinders on the stamping press at the end of the line (slow cycle, 50-ton forming force). Mixing both systems in one facility is completely normal — each does what it does best.

Rule of thumb for selection: If you need less than 2,000 lbf and speed matters more than precision, start with pneumatics. If you need more than 5,000 lbf or precise position control under load, go hydraulic. The gray zone in between is where cost, cleanliness, and maintenance complexity break the tie — pneumatics wins on simplicity, hydraulics on power density.

One underappreciated factor: energy efficiency. Compressed air systems are notoriously inefficient — only about 10–20% of input electrical energy reaches the actuator. Hydraulics run closer to 40–60%. If your air system runs 24/7, the electricity bill may justify switching to electric actuators entirely.