Department of Mechanical Engineering

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For prices and dates, please visit the Course Overview

Mrs Gillian Elsworth
Centre for Power Transmission and Motion Control
Department of Mechanical Engineering
University of Bath
Claverton Down
Bath BA2 7AY


Tel: +44 (0)1225 386371

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This course is run in conjunction with the IMechE.


FP1 - Introduction to Hydraulic Circuits and Components

This introductory course provides a good working knowledge of hydraulic circuits and components by introducing their principles of operation, their performance characteristics, and standard ISO symbol representation. On completion, participants will be able to draw circuit diagrams, and design simple circuits for linear actuators, hydrostatic transmissions and velocity control. They will also appreciate the characteristics of hydraulic fluids, the need for contamination control, and understand the functions of auxiliary devices such as accumulators and coolers. A number of tutorials and extensive laboratory work strengthen the material and show how the new theoretical knowledge can be applied in practice.


Who should apply

Professional engineers, graduates, technicians, managers and supervisory staff, particularly those new to the field of hydraulic fluid power systems. Although the course material is more descriptive than mathematical, a basic mathematical knowledge is helpful.


Further details

Upon completion, participants should be able to do the following:

  • Understand the operation of a wide range of hydraulic components and circuits, and be aware of the underlying principles
  • Analyse hydraulic circuits from schematic drawings and draw diagrams using standard ISO notation
  • Design and analyse simple linear actuator and hydrostatic transmission circuits
  • Understand different methods of velocity control, and evaluate circuits for given applications
  • Select hydraulic fluids based on their classifications and properties
  • Be aware of the effects of contamination, and achieve, monitor and maintain appropriate system cleanliness levels
  • Have knowledge of the construction, operation principles, and uses of auxiliary equipment, such as filters, oil coolers, and accumulators.

Fundamental principles

  • Comparison between hydraulic, mechanical, electrical, and pneumatic systems in terms of performance, reliability, efficiency and versatility
  • Units for hydraulic and mechanical quantities
  • ISO symbol representation of hydraulic components and circuits
  • Causes and effects of pressure generation, pressure losses, heat generation, fluid leakage, cavitation, noise, and vibration
  • Mathematical relationships between:
    1. linear actuators: pressure, piston area and transmitted force; flow rate, cylinder dimensions and rod velocity
    2. valves: orifice area, pressure losses, fluid viscosity and flow rate; flow rate, pressure differential and thermal power
    3. pumps: displacement, shaft speed and flow rate; flow rate, operating pressure and hydraulic power
    4. hydraulic motors: pressure, displacement and motor torque; flow rate, displacement and motor speed

Hydraulic actuators

  • Construction of linear actuators - cylinder tubes, piston assembly, seals, bearings, end covers, mounting arrangements, cushioning, position transducers
  • Actuator sizing - force, velocity, buckling, side loading
  • Rotary actuator types (rack and pinion, vane, helical) and applications.

Directional control valves

  • Applications for 2-position 2/3/4-way valves and 3-position 4-way valves in open/closed/tandem centre configuration
  • Construction of DCVs - stand alone, sub-base, stacking, cartridge designs
  • Operating forces and valve actuation
  • Logic elements, poppet valves.

Pressure control valves

  • Construction, characteristics, and applications of single- and dual-stage relief valves
  • Description of sequence valves, unloading valves, and pressure reducing valves including practical circuit examples
  • Use of counterbalance valves for braking overrunning loads and winch applications.

Positive displacement pumps

  • Types of pumps - external and internal gear pumps, fixed/variable displacement vane pumps, fixed/variable displacement radial and axial piston pumps
  • Flow and pressure control, constant power compensators
  • Limitations on pump performance - cavitation, mechanical strength, lubrication, bearings, heat dissipation
  • Flow, power, and torque equations, pressure/flow characteristics.

Linear actuator circuits

  • Principle of operation and function of components in basic circuits, incl. actuator, directional control valve, pump, and pressure relief valve
  • Circuits for single and double acting actuators, incorporating 2-position 3-way and 3-position 4-way valves in open-, tandem-, and closed-centre configurations
  • Methods for dealing with leakage - use of pilot operated check valves and counterbalance valves
  • Over-run protection, dynamic braking and decompression.

Velocity control circuits

  • Relationship between piston areas, pressure, and flow on retraction and extension to force/velocity for symmetrical and unequal area actuators
  • Influence of relief valves
  • Velocity control with simple restrictor valves - flow control and effects of load change
  • Circuits with pressure compensated flow control valves
  • Meter-in, meter-out, and bleed-off systems
  • Deceleration control, transient behaviour.

Modulating valves

  • Characteristics and operating principles of proportional, direct drive and servo valves
  • Spool characteristics (overlap, underlap) and valve flow ratings
  • Valve actuation and open/closed-loop control, time responses
  • Multistage valves.

Hydrostatic motors

  • Description and comparison of high-speed low-toque motors (e.g. axial piston swash plate, bent axis) and low-speed high-torque motors (e.g. orbit, radial piston, radial piston cam)
  • Ideal motor equations
  • Causes and effects of volumetric and mechanical inefficiencies
  • Motor specifications and selection criteria.

Hydrostatic transmissions

  • Open and closed loop systems - example circuits for mobile and industrial applications
  • Output speed control
  • Performance - power availability and efficiency.

Hydraulic oils and fluids

  • Functions, properties, performance classification, and fluid selection
  • ISO viscosity grades, effects of temperature
  • Fire resistant and biodegradable fluids.

Contamination control

  • Sources, types, and effects of solid contaminants; prevention of contamination
  • Contamination related failure modes
  • Specification and monitoring of system cleanliness levels; establishing, achieving, and maintaining cleanliness targets
  • Filter types, rating, location, and performance.

Oil coolers

  • Construction and characteristics of oil-to-water and air-blast coolers
  • Thermodynamic principles of surface heat exchange
  • Energy losses, effects of oil temperature
  • Cooler selection and circuit considerations.


  • Types and construction of pneumatic accumulators (piston, bladder, diaphragm)
  • Application examples - supplementing pump flow, leakage compensation, emergency supply, shock alleviation, suspension, etc.
  • Accumulator cycles.
  1. Linear actuator circuit computer animations
  2. Velocity control computer animations
  3. Velocity control tutorial
  4. Linear actuator circuit design exercise.
  1. Velocity control circuits
  2. Proportional valves
  3. Relief valve characteristics
  4. Contamination examples
  5. Hydrostatic transmission
  6. Circuit design and build exercises
  7. Linear actuator circuits
  8. Gear pump characteristics