Hydraulic and Pneumatic Systems
Hydraulics
The pump produces flow, not pressure; pressure is the resistance that flow meets. Force equals pressure times area, and cylinder speed follows flow divided by area. A relief valve sets maximum system pressure and should be treated as a safety device, not a pressure regulator. Directional control valves route flow, flow-control valves set speed, and check valves enforce one-way flow. Accumulators store pressurized fluid - they are stored energy and must be blown down and isolated before any work.
Most hydraulic failures are contamination failures. Know ISO cleanliness codes, filter micron ratings, reservoir breathers, and the difference between aeration (air entrained, foamy, spongy response) and cavitation (vapor pockets collapsing, noise, damage).
Pneumatics
Air is compressible, so pneumatic systems are fast but imprecise. The FRL unit - filter, regulator, lubricator - conditions the air. Compressors need dryers and traps; dew point matters. Cylinders use cushions to absorb end-of-stroke impact.
Safety traps
Never search for a hydraulic leak with your hand; a pinhole stream can inject fluid under the skin. Depressurize before cracking a fitting. Hose ratings must match pressure and temperature, and fittings must be the correct type (JIC, ORFS, NPT).
Worked example
A 3 in bore cylinder at 1,000 psi: area = π × (1.5)² ≈ 7.07 in². Extend force = 1,000 × 7.07 ≈ 7,070 lb. On retract, subtract the rod area - a 1 in rod removes 0.785 in², leaving about 6,283 lb.