Pneumatic and Hydraulic Systems - Exam Notes

Safety Precautions

• Wear PPE (safety goggles, shoes, gloves, overall) in the lab.

• Ensure tight line connections and undamaged lines.

• Never service the system while the pump is running (unless bleeding).

• Be aware of the system's function before operating.

• Check for leaks or damage; don't disable safety features.

• Handle hydraulic fluids carefully and follow equipment rules.

• Lift heavy objects safely; stay away from moving parts.

• Turn off and release pressure before fixing.

• Know emergency shutdown procedures and how to handle spills.

• Get trained for safety and efficiency.

Importance of PPE

• Safety Glasses: Protect against fluid leaks and high-pressure hazards.

• Gloves: Required when handling hydraulic fluid.

• Overall: Protect against high-temperature fluid burns.

Hazards and Risks

• Static electricity from fluid flow can create sparks.

• High fluid temperatures can burn skin.

• Fluid injections can cause severe tissue damage.

Basic Concepts

• Pneumatic Systems:

  • Function: Convert fluid pressure (air) into mechanical motion.

  • Working Fluid: Air.

  • Applications: Manufacturing, automotive, packaging.

• Hydraulic Systems:

  • Function: Use incompressible fluids (hydraulic fluid/oil) to transmit force.

  • Working Fluid: Hydraulic fluid (oil).

  • Applications: Construction, aerospace, heavy machinery (high-force).

• Common applications: Cranes.

Pneumatic Systems Principles

• Compressed air as working fluid.

• Function: Air pressure to mechanical motion.

• Advantages:

  • High energy efficiency.

  • Clean operation.

  • Low initial cost.

  • Suitable for most environments.

  • Fast operation.

Hydraulics vs. Pneumatics

Core Components: Pneumatic Systems

• Compressor: Pressurizes air (Power Source).

• Control Valves: Regulate air flow, pressure, and direction.

• Actuators: Convert air pressure to motion (Cylinders for linear, Motors for rotary).

• Filters: Remove contaminations from air.

• Pressure regulator: Used to regulate the pressure in both Hydraulic and Pneumatic systems.

Pneumatic System Elements Arrangement

• Energy supply element: Compressor, receiver, air service unit.

• Input element: Push button valve, roller lever valve.

• Processing element: Logic valves, flow control valves.

• Control element: Directional control valves.

• Power component: Pneumatic cylinder.

Single Acting Cylinder Operation Using 3/2 DCV

• Extend:

  • Pushbutton pressed; air connects to port A.

  • Compressed air flows into the cylinder.

  • Piston rod extends.

• Retract:

  • Pushbutton released; valve returns to original position.

  • Port A connects to exhaust port R.

  • Spring force returns cylinder to the initial position.

  • Air is pushed out through port R.

Pneumatic Component Symbols

• Air compressor, air receiver, air dryer, air lubricator, air filter, pressure regulator, pressure gauge, air service unit, directional control valve, pneumatic cylinder (single and double acting), air motor.

Control Valves

• Different types (2/2, 3/2, 4/2 way) with normally open/closed positions.

• Actuation methods: Manual, push button, solenoid, foot pedal.

Shuttle Valve

• Accepts pneumatic signals from two different locations.

• OR function: Gives output if any input has compressed air.

Two (Dual) Pressure Valve

• AND function: Output only if all inputs have compressed air signals simultaneously.

• Used in machines with hazards to ensure operator uses two hands.

Shut-Off Valve

• Controls fluid flow by completely stopping or allowing passage.

• Used for isolation during maintenance or emergency shutdowns.

Core Components: Hydraulic Systems

• Fluid (oil), reservoir, pump, electric motor/engine, hoses/tubing, valves, actuators (cylinders/motors).

Functions of Hydraulic Components

Hydraulic Fluids

• Transmit force, lubricate, provide sealing, protect against rust/corrosion, remove heat, prevent foaming.

Directional Control Valves

• 3-port and 4-port valves. Ports: P (pressure), T/R (tank/return), A/B (working lines).

• One, two, three positions.

Activation Methods

• Push-button, lever, manual, foot pedal, mechanical (roller), solenoid, spring, detent, pneumatic/hydraulic pilot.

Accumulators

• Store energy (gas-charged, spring-loaded, weight-loaded).

Relief Valves

• Direct-acting and pilot-operated.

Flow Controls

• Fixed orifice, needle valve, adjustable pressure-compensated valve.

Actuators

• Motors (uni-directional, bi-directional, semi-rotary) and Cylinders.

Troubleshooting: Pneumatics

• Common issues: Cylinder not retracting, pressure loss, slow operation, component failure, sensor malfunctions, air leaks.

Troubleshooting: Hydraulics

• Common issues: Fluid leaks, pressure inconsistencies, overheating, component wear, contamination, system noise.

Electro-Pneumatics Sensors

• Used to detect piston rod position, workpiece presence, and monitor pressure/flow.

• Types: Limit switches, proximity switches (reed, inductive, capacitive, optical), pressure switches.

Limit Switch

• Interlocks mechanical motion/position with an electrical circuit.

• N/O, N/C, changeover types.

Displacement-Step Diagram

• Represents the relation to the sequence step.

• Abbreviated notation (example): 1A+ 2A+ 1A- 2A-

Force and Pressure Calculations

• Formulas:

  • Force: $F = P × A$

  • Pressure: $P = F ÷ A$

• Units: Force (N), Pressure (N/m² or Bar), Area (m²).
  Q: The force (F) in a pneumatic cylinder is directly proportional to b) Area (A) over which the pressure is applied

Torque Calculations

• Formula: $Power = 2 * π * N * T$

  • $N$ = revolution per sec, rps

  • $rps= rpm/60$

  • $1kW= 1000W$

  • $T$= Torque Nm

Efficiency of Pump

• Power Output = Pressure x Discharge = P x Q = Pa x m^3/s

• 1kW =1000W

• 1L =10^{-3} m^3

• 1W= 0.00134102 HP

• Efficiency = Output power/Input Power

Conversions

• $P (hp)= P(W) / 746 W/hp$