HYDRAULIC AND PNEUMATICS
Learning outcomes of the course unit
The course main goal is to give to the student the comprehension and the possession of the fluid power basic principles. The course presents the analysis of both fluid power components and systems; few elements of pneumatics are also introduced.
The main components of hydraulic circuits are presented, focusing on the working principles and the design criteria. Several hydraulic circuits are analyzed, taking remark from the most common industrial applications. Many numerical exercises are solved, some of them by means of numerical computer simulations.
Course contents summary
Introduction to fluid power: hydraulic and pneumatic systems
Power transmitting fluids
Physical properties of hydraulic fluids (density, viscosity, bulk modulus). Contamination of the fluid (in form of liquid, gas or solid).
ISO fluid properties classifications.
Basic types of filtering methods used in hydraulic systems: filters and strainer. Location of filters in hydraulic circuits.
Hydraulic symbols. ISO1219 specifications: basic symbols and combinations. Representation of pumps, motors, actuators and control elements.
Accumulators. Basic types of accumulators and working principles.
Pump classification. Positive displacement pumps. Different designs and main ideal characteristics. Pump torque and actual characteristics: volumetric and hydro-mechanical efficiency. The pump flow and pressure ripple.
Control components in hydraulic systems
Types of drives.
Directional control valves. Rotative spool control valves. Overlap: definition and effects on the valve behaviour. On/off and proportional control valves. Check valves.
Pressure control valves. Direct acting and hydraulically piloted relief valves. Actual and ideal flow characteristics. Sequence valves. Differential and proportional valves. Pressure reducing valves. Piloted valves: different solutions. Flow control valves. Orifices, compensated flow regulators, flow dividers and combiners Two ways and three ways flow control valves.
Constant flow rate pump group. Flow-pressure characteristics. Alternative solutions.
Discrete values variable flow rate pump group. Flow-pressure characteristics and evaluation of the group efficiency. Use of a remote piloted relief valve.
Variable flow rate pump group. Flow-pressure characteristics.
Fixed pressure pump group. Flow-pressure characteristics. Pump group with accumulators.
Linear actuators. Resistive and dragging load. Basic circuit for simple effect and double effect linear actuators. Choice of different types of control valves (closed centre, open centre, ….). Force – speed charts. Control of the dragging loads: counterbalance and overcentre valves.
Control of the actuator speed by regenerative circuits. Automatic transition to the regenerative solution.
Multiple load systems. The series, parallel and tandem configurations. Synchronism between several actuators.
Compensating and metering orifices. Flow dividers: a few examples. Multiple actuators with priority systems.
Load Sensing Systems
Load sensing system controlling several units: advantages and drawbacks. LS systems with fixed and variable displacement pumps. Energy saving and controllability of LS systems . Pressure compensators.
Working principles and application field. Open circuit and closed circuit hydrostatic transmissions. Elements of a closed circuit HT.
Pneumatics main principles and applications. Examples of pneumatic circuits. Pneumatic actuators. Control and regulation. Accessories.
The course includes several hours about numerical examples, an activity about the analysis and simulation of hydraulic circuits by computational software is also planned
N. Nervegna, “Oleodinamica e Pneumatica”, Politeko, Torino
H. Speich, A. Bucciarelli, “Oleodinamica – Principi, componenti, circuiti e applicazioni”, Tecniche nuove, Milano
Autori vari, “La Pneumatica e le sue applicazioni”, ASSOFLUID
J.S. Stecki, A. Garbacik, “Design and Steady-state Analysis of Hydraulic Control Systems”, Fluid Power Net Publications
G.L. Zarotti, “Circuiti Oleodinamici – nozioni e lineamenti introduttivi”, CEMOTER – Quaderni Tematici
G.L. Zarotti, “Oleodinamica termica – nozioni e lineamenti introduttivi”, CEMOTER – Quaderni Tematici
J.F. Blackburn, G. Reethof, J.L. Shearer, “Fluid Power Control”, The M.I.T. Press
Mannesman – Rexroth, “Basic Principles and Components of Fluid Technology”, Rexroth Hydraulics
D. McCloy, H.R. Martin, “Control of Fluid Power: Analysis and Design” John Wiley & Sons
Lessons are focused on topics described in "Contents". Numerical examples are carried out on calculators at the laboratories of the Dipartimento di Ingegneria Industriale
Oral test and presentation or discussion of a numerical example or of a simulation model.