Hydraulics & Pneumatics
From transcript: 20ME551 Hydraulics & Pneumatics (A)
Cheat sheet
Formulas
Pascal: P = F/A ; force multiplication F2 = F1 (A2/A1)
Flow continuity Q = A V ; actuator speed v = Q / A
Hydraulic power P = p Q (consistent units; η overall)
Pump displacement → Q = V_d · n · η_vol
Bernoulli/orifice: Q = Cd A √(2 Δp/ρ)
Accumulator energy ~ gas law polytropic storage
Pneumatic: compressible — use free air volume & pressure ratios
Pascal: Δp transmitted undiminished in confined fluid
Force: F = p A ; Flow continuity Q = A v
Hydraulic power: P = p Q (consistent units)
Pneumatic: compressible — use isothermal/adiabatic approximations carefully
Definitions
- Hydraulic fluid
- Transmit power, lubricate, cool, seal — viscosity grade matters
- Pump types
- Gear, vane, piston — pressure & efficiency ranges
- Directional valve
- Routes flow — 4/3, 4/2 spool designations
- Pressure relief
- Safety limit system pressure
- Flow control
- Meter-in / meter-out / bleed-off speed control
- Actuator
- Cylinder or hydraulic motor — linear/rotary
- Pneumatic FRL
- Filter–regulator–lubricator unit
- Compressibility
- Oil ~0.5%/100 bar class; air highly compressible
- Directional control valve
- Routes flow paths (e.g. 4/3)
- Accumulator
- Stores pressure energy; dampens shock
Topic-wise short notes
Fluid power circuits
- Symbols ISO 1219 — read schematics like electrical ladder.
- Open center vs closed center systems.
- Regeneration circuits for fast extend with differential areas.
- Counterbalance valves for suspended loads.
Pneumatic systems
- Fail-safe spring return; exhaust mufflers; soft-start.
- Vacuum generators (Venturi) for pick-and-place.
- PLC sequencing of cylinders — sensors at ends of stroke.
Maintenance & safety notes
- Contamination #1 hydraulic killer — filtration ISO codes.
- Lockout/tagout; support loads before cracking lines.
- Air in oil → spongy actuators; bleed procedures.
Exam traps & quick notes
- A grade — speak to circuit symbols (ISO 1219) and safety (lockout).
- Hydraulics: high force density; pneumatics: clean/fast, lower force.
- Farm automation: solenoid valves, pressure regulation, fertigation loops.
- Never check hydraulics with hands — injection injury risk.
- Meter-out better for overrunning loads (controlled).
- Cavitation at pump inlet from clogged strainer / high suction lift.
- Pneumatics: soft & fast; hydraulics: high force & stiff.
- Seal material compatibility with fluid & temperature.
Comprehensive notes
Fluid power circuits
Meter-in/out, regeneration, sequencing, pressure relief vs reducing valves.
Pneumatic systems
FRL units, actuator cushioning, vacuum generators; ladder logic interface.
External: SMC pneumatics guide ↗
Hydraulic circuits
Pascal’s law; F=pA; power pQ. Relief vs reducing valves; meter-in/out; regeneration; accumulators. ISO 1219 symbols.
External: NPTEL ↗ Engineering Toolbox ↗
Pneumatics & control
FRL units; compressibility; vacuum; actuator cushioning. PLC/ladder interface. Farm automation: valves, pressure regulation, fertigation.
External: NPTEL ↗ Engineering Toolbox ↗
Interview Q&A for this subject
Q: Hydraulics vs pneumatics?
A: Hydraulics: high force, stiff; pneumatics: cleaner/faster, lower force, compressible.
External: ASQ / quality ↗ MIT OCW ↗