title: MMME2044 // Pneumatics and Hydraulics

lecture_slides: [ ./lecture_slides/Lecture 4 Pneumatics and Hydraulics.pdf ]

uuid: 9df953f9-13bc-40df-916a-dccaf9a338cf (permalink)

tags: [ uni, mmme2044, pneumatics, hydraulics ]

written by: Akbar Rahman

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I don’t think I ever finished these notes.

Actuation Systems

Actuation systems are the elements of control systems which are responsible for transforming the output of a control system (such as a microcontroller or microprocessor) into a controlling action on a machine or device.

Typical Hydraulic Power System

The pump pumps oil from a sump through a non return valve and an accumulator to the system, from which it returns to the sump.

Advantages and Disadvantages of Hydraulic Power Systems

Advantages:

Disadvantages:

Components of the System

Hydraulic Pump

This provides the pressure and flow of the liquid in the system.

More information about pumps

Pressure Relief Valve

This is a safety system that safely let’s out the fluid of a pressurised system if the pressure exceeds a specified safe pressure.

Non-return Valve

Accumulator

The accumulator is a container in which the oil is held under pressure against an external force. This smoothes out any short term fluctuations in the output oil pressure of the pump.

Types of Pumps

Gear Pump

A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications.

They are also widely used in chemical installations to pump high viscosity fluids.

Vane Pump

A rotary vane pump is a positive displacement pump that consists of vanes mounted to a rotor that rotates inside of a cavity.

In some cases these vanes have have variable length and/or be tensioned to maintain contact with the walls as the pump rotates.

Radial Piston Pump

The working pistons extend in a radial direction symmetrically around the drive shaft to take in fluid and output it at the outlet port.

Axial Piston Pump with Wash Plate

An axial piston pump is a positive displacement pump that has a number of pistons in a circular array within a cylinder block. It can be used as a stand-alone pump, a hydraulic motor or an automotive air conditioning compressor.

Typical Pneumatic Power System

  1. (Filter, Silencer) The air inlet to the compressor is likely to be filtered silenced to reduce the noise level.
  2. An electric motor drives the compressor
  3. The pressure relief valve protects the system against rising above a safe level
  4. (Cooler, Water Trap) Since the compressor increases the temperature of the air, there may be a cooling system and filter/water trap to cool the air and remove contaminants from the system.
  5. An air receiver increases the volume of air in the system, to smooth out short term pressure fluctuations

Advantages and Disadvantages of a Pneumatic System

Advantages:

Disadvantages:

Actuators

Actuators generate a Force or Moment. Both hydraulic and pneumatic actuators have the same principles, but differ in size. Cylinders are the principal actuators for pneumatics:

A double acting single rod cylinder
BS ISO 1219 Symbols of a double acting, single rod cylinder

Terminology

Supply to compressed air to one chamber requires exhaust from the other chamber.

Positive Stroke

Extends and pushes to + position.

Negative Stroke

Retracts to - position.

Single Acting Linear Actuator

The control pressure is applied to one side of the piston.

When pressure is applied the piston moves along the cylinder.

When pressure is no long applied the piston reverts back to its initial position and the air is vented from the cylinder.

Double Acting Linear Actuator

Double Acting Linear Actuators are used by applying pressure to one of two sides to move a rod in one of two directions.

Rotary Actuator

These produce a rotary motion.

A linear cylinder can be used to produce rotary motion with angles less than 360 degrees with the correct linkages:

You can also have vane type semi rotary, where the difference in pressure causes rotation:

Control Valves

Pneumatic and hydraulic systems use directional control valves to direct the flow of fluid through a system.

They may be activated to switch the fluid flow direction by means of mechanical, electrical, or fluid signal pressure.

Valve Flow Symbols

Valve Actuation Symbols

Solenoid Operated Spool Valve

Spool Directional Control Valve

Move horizontally within the valve body to control flow:

Poppet Valve

This valve is normally closed.

Pressure Control Valve

Servo Valve

An electrohydraulic servo valve is an electrically operated valve that controls how hydraulic fluid is sent to an actuator.

Servo valves are often used to control powerful hydraulic cylinders with very small electrical signal.

Servo valves can provide precise control of position, velocity, pressure, and force with good post movement characteristics.

Process Control Valve

Used to control the fluid flow rate.

A common form of pneuma

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