FP2 - Component Selection for Hydraulic Systems
Brief description
This module covers the selection and sizing of actuators, valves, pumps as well as associated equipment like oil coolers, accumulators, and filters. It introduces the theoretical background of orifices, pressure losses, hydraulic stiffness, and component efficiency. Worked examples, design exercises, computer simulation classes, and lab sessions demonstrate how to select commercially available hydraulic units to be used in practical open- and closed-loop hydraulic circuits, taking into account the constraints imposed by application-specific design requirements.
Who should attend
The course is suitable for engineering professionals and graduates concerned with the design, development, installation, maintenance, or simulation of fluid power systems. It is essential that participants have taken the FP1 module or have some work experience and knowledge of hydraulic systems equivalent to CETOP Level 3 before taking the course. Reasonable mathematical skills are needed.
Course objectives
Upon completion, participants should be able to do the following:
- Have a thorough understanding of the fundamental hydraulic principles.
- Appreciate factors which influence the specification and performance of hydraulic components and circuits.
- Understand technical specifications of components and use this information to select and size actuators, valves, pumps, motors, filters, coolers, and accumulators for given applications.
- Know the principles of system design taking into account duty cycles, system efficiency, and reliability issues.
- Have knowledge of pipework and component installation, and follow good design practices for pipework and reservoirs.
- Be aware of computer simulation methods for predicting the functionality and performance of hydraulic systems.
Course contents
Fundamental principles
- Causes, effects, and quantitative description of pressure generation, pressure losses, heat generation, fluid leakage, cavitation, noise, and vibration.
- Effects of fluid compressibility on component and system performance.
- Relationship between Reynolds number, laminar/turbulent flow, and flow resistance.
- Thermodynamic properties of fluids and gases, and principles of heat transfer.
- Duty cycles for hydraulic systems.
- Nonlinearities and their influence on system design and analysis.
Orifice characteristics
- Orifice equation - relationships between flow and pressure difference, orifice area, fluid density, discharge/flow coefficient.
- Variation of flow coefficients with Reynolds number.
- Flow control characteristics in meter-in and meter-out systems, force/velocity relationship during extension and retraction.
Velocity control using modulating valves
- Relationship between valve opening, available force, and velocity for equal and unequal area actuators.
- Effects of pump capacity, relief valve settings, and actuator geometry.
- Graphical methods for determining and understanding system performance.
Central bypass valves and load sensing circuits
- Central by-pass valve construction and principle of operation.
- Tandem, parallel, and series circuits.
- Characteristics of systems with single and multiple load sensing valves.
Pressure losses
- Influence of fluid properties (density, dynamic and kinematic viscosity) and pipe parameters (length, diameter, roughness).
- Laminar and turbulent flow conditions.
- Calculation of losses in straight pipes, bends, fittings, and valves - Poiseuille's and Darcy's equations.
Actuator stiffness
- Effects on fluid compressibility, expansion/contraction of pipes/hoses, and mechanical compliance of mountings on static position accuracy and dynamical response.
- Stiffness for interconnected volumes; combination of mechanical and hydraulic stiffness.
- Nonlinear relationship between bulk modulus and pressure, and influence of entrained air.
- Stiffness of rotational systems.
Pump and motor characteristics
- Linear and nonlinear pump and motor models; steady-state flow and torque characteristics.
- Influence of leakage and friction losses, and effect of fluid compressibility.
- Optimisation of efficiency.
Hydrostatic transmission design
- Review of performance characteristics, volumetric/mechanical efficiency, and principle of power transfer.
- Transmission design procedure - load, flow, and power requirements, motor/pump selection, motor/pump sizing, selection of additional transmission components.
- Analysis of operating characteristics.
Oil cooler sizing
- Principle of return flow, leakage flow, and purge system cooling.
- Basic theory or thermodynamics and heat exchange - motor/pump flow/power balance, heat generation due to friction and leakage.
- Practical design and cooler selection example for a hydrostatic transmission.
Accumulator sizing
- Basic pressure/volume relationship for pneumatic accumulators - isothermal and adiabatic gas expansion/compression.
- Refinements - compressibility factor and variation of adiabatic index with pressure and temperature.
- Design procedure for given duty cycles.
System component selection
- Overview of design process - specification, design, check, selection.
- Selection of operating parameters - system pressure, flow requirements, thermal effects.
- Component selection - actuators, valves, pumps, pipes, and auxiliary equipment.
System filtration
- Filter construction (housing, element, media), filtration mechanisms, and filter test methods.
- Filter location - pressure/return/suction line, bypass, off-line
- Filter selection - contaminant sensitivity and performance degradation, BFPA guidelines.
Pipework, connectors and reservoirs
- Pipe and hose materials and construction, types of couplings and fittings.
- Pipework layout - vibration, external/internal stresses, maintenance considerations.
- Reservoir design - size, location, instrumentation, fillers, breathers, baffles, connections.
Workshops
- Wave generator tutorial (system component selection)
- Computer simulation exercise with the LMS AMESim package.
- Forklift truck design exercise (linear actuator circuits and components)
- Marine engine loading system design exercise (hydrostatic transmission circuits and components)
Laboratory sessions
- Central bypass valve
- Pressure losses
- Hydrostatic transmission
- Pump characteristics
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This course is run in conjunction with the Institution of Mechanical Engineers. |