How to Interpret Hydraulic Control Diagrams. Brendan Casey Marian Tumarkin

Transcription

1 How to Interpret Hydraulic Control Diagrams Brendan Casey Marian Tumarkin

2 How to Interpret Hydraulic Control Diagrams 2 Copyright 2006 Brendan Casey & Marian Tumarkin All rights reserved. No part of this electronic book may be reproduced or transmitted in any form or by any means, electronic, mechanical, photocopying, and recording or otherwise, without the prior, written permission of the publisher. The contents of this book reflect the author s views acquired through his experience in the field under discussion. The information in this document is distributed on an As is basis, without warranty. Every effort was made to render this book free from error and omission. However, the author, publisher, editor, their employees or agents disclaim liability for any injury, loss, or damage to any person or body or organization acting or refraining from action as a result of material in this book, whether or not such injury loss or damage is in any way due to any negligent act or omission, breach of duty, or default on the part of the author, publisher, editor or their employees or agents. First published in 2006 by HydraulicSupermarket.com PO Box 1029 West Perth WA 6872 Australia info@hydraulicsupermarket.com Web: About the Authors Brendan Casey is the founder of HydraulicSupermarket.com and the best-selling author of 'Insider Secrets to Hydraulics' the most comprehensive guide to reducing hydraulic equipment operating costs ever published. A fluid power expert with an MBA, he has more than 18 years experience in the design, maintenance and repair of mobile and industrial hydraulic equipment. Dr Marian Tumarkin has over 35 years of experience in the field of Fluid Power with a Ph.D. from the National Academy of Science in Moscow. He is an accomplished scholar in the field with over 50 published papers and 10 patents to his name. A highly experienced Fluid Power engineer, Marian has designed electro-hydraulic systems for Russian and Australian Air Forces, Australian and American automotive industries, as well as developing special purpose machines. In this role, he was responsible for concept design and problem solving, calculations and component selection, system testing and troubleshooting. Marian has extensive teaching experience both in Europe and Australia, delivering basic and advanced Fluid Power subjects to undergraduate and post-graduate students as well as engineers and technicians.

3 How to Interpret Hydraulic Control Diagrams 3 HYDRAULIC SYSTEM DIAGRAMS A variety of diagrams can be used to explain the function, operation, and assembly of a hydraulic power system. These include: Circuit diagram Piping diagram Pictorial diagram Cut-away diagram Combination diagram Step diagram Block diagram 1.1. The hydraulic circuit diagram (schematic) is the main drawing relating to the actual hydraulic system and is used in all stages of system design, installation, and troubleshooting. To aid understanding of the hydraulic system function and operation, mechanical, electrical, cutaway, and graphical symbols can be included in the circuit diagram. For installation and maintenance, a piping diagram should be supplied separately from the circuit diagram. EXAMPLE 1.1. Hydraulic system of a forklift truck A pictorial diagram (Fig. 1.1) shows the general location of each component and interconnecting piping. The main purpose of this diagram is to guide installation and assembly. Component locations are shown without any information about operation, parameters, and manufacturer or supplier. Hydraulic Power Unit Hydraulic Cylinder DCV Flow Control Valve Fig Pictorial diagram of a forklift

4 How to Interpret Hydraulic Control Diagrams 4 The hydraulic circuit diagram of the forklift is shown in the Fig The circuit does not provide enough information to understand cylinder retraction. Therefore, it should be modified with the cylinder shown in a vertical position and include a graphical symbol showing weight of the load (see Fig. 1.3) Fig Hydraulic circuit diagram Fig Combined circuit diagram Piping diagram for the forklift hydraulic system gives information about pipes/hoses location, sizes and fittings. 3-Cylinder DCV Flow control Pressure relief valve Pump Filter Reservoir Fig Piping diagram

5 How to Interpret Hydraulic Control Diagrams For sequential control, a displacement-step diagram provides information about the sequence of steps. Whereas a displacement-time diagram provides information not only about the sequence of steps, but also about the required stroke and speed. EXAMPLE 1.2. Molding press The main specifications for press operation are shown in the Table 1.1 Table 1.1. Specification for molding press Parameters S t F No Step m ft sec kn lbf 1 Fast approach ,000 2 Final pressing Holding ,000 4 Return ,000 5 Reload A displacement-step diagram provides information about the sequence of steps. However, no information is provided about the required flow rate. Therefore, preference should be given to a displacement-time diagram. A3 A Displacement, m Steps Time, sec Displacement, ft A1 Start A2 A3 Time A1 Fig Displacement-step diagram A displacement-time diagram provides information about the sequence of steps and the required distance and speed. Fig Displacement-time diagram

6 How to Interpret Hydraulic Control Diagrams A block diagram shows the transmission of signals, energy, or power. EXAMPLE 1.3. Power transmission in a hydraulic system A hydraulic power system converts mechanical power into hydraulic power, transmits it over a distance, and converts it back into mechanical power by means of a liquid (mainly mineral oil). The general function of the system can be shown graphically using a block diagram Fig HYDRAULIC POWER SYSTEM MECHANICAL POWER SOURCE mechanical input POWER CONVERSION hydraulic power POWER TRANSMISSION LOAD mechanical output POWER CONVERSION hydraulic power CONTROL output control Fig Block diagram for hydraulic system power transmission EXAMPLE 1.4. Simple level regulator The function of the regulator is to support a constant level of liquid (water) in the tank: H = constant control input VALVE water supply Fig Simple level regulator level LEVEL SENSOR RESERVOIR water consumption Fig Block diagram of the level regulator Block diagram of the regulator shows the regulator operation from the signal transmission point of view (Fig. 1.9). The functions of the main components are shown independently of their design: level sensor may not be a float valve, but rather an electrical transducer; water control valve could be a solenoid operated DCV, etc. This type of diagram is a standard tool for proportional control functional description and analysis.

7 How to Interpret Hydraulic Control Diagrams 7 FURTHER READING Advanced Hydraulic Control by Brendan Casey & Marian Tumarkin Available second half of 2007: