The drawing and reading method of hydraulic system schematic diagram
1) Notes on Drawing Hydraulic System Schematic
When using graphic symbol standards to draw hydraulic system diagrams, there are generally the following precautions.
① The size of component graphic symbols can be increased or decreased in proportion to the size of the drawing, based on the principle of clarity and aesthetics.
② The component and circuit diagrams are generally drawn in non working states without excitation (for example, the electromagnetic directional valve should be in the working position after power failure).
③ On the premise of not changing the initial state meaning defined by the standard, the direction of the components can be drawn by flipping horizontally or rotating 90 ° according to the specific situation, but the hydraulic oil tank must be drawn horizontally with the opening facing upwards.
2) Requirements, methods, and steps for reading hydraulic system schematics
① The significance and requirements of reading comprehension
Correctly and quickly analyzing and reading the hydraulic system schematic plays an important guiding role in the design, research, use, maintenance, adjustment, and troubleshooting of hydraulic systems. However, in order to read the hydraulic system schematic correctly and quickly, it is necessary to first master the construction, principles, characteristics, and comprehensive applications of various hydraulic components and basic circuits, understand the control methods, graphic symbols, and related standards of the hydraulic system.
Secondly, based on actual hydraulic equipment and its system schematic, read and practice as much as possible, accumulate analysis experience and skills, and master the characteristics of various typical hydraulic systems. This can play a role in drawing analogies, applying analogies, and becoming proficient in reading new hydraulic system schematics in the future.
② Reading Method Steps
The general method and steps for reading hydraulic system schematics are as follows.
a. Fully understand the functions, structure, working cycle, and main requirements for hydraulic systems of hydraulic machinery (main engine). For example, the schematic diagram of the hydraulic system for the power sliding table of a combination machine tool is mainly based on speed conversion. In addition to achieving the basic working cycle of fast forward → work forward → fast backward of the sliding table, special attention should be paid to the smoothness of speed conversion and other indicators. At the same time, it is necessary to understand the conversion of control signals and the electromagnetic action table.
For example, in the schematic diagram of the hydraulic system of a press, it is a hydraulic system mainly based on pressure transformation and control. In addition to achieving basic cycles such as waiting for the slider, fast forward, deceleration and slow pressurization, pressure holding and relief, and fast retreat, special attention should be paid to the reliability of pressure holding and whether the pressure relief method will cause vibration and noise. It is also necessary to understand the interlocking relationship between the slider and the ejection mechanism.
b. Refer to all components and their connection relationships in the schematic diagram of the hydraulic system, analyze their functions and the functions of the circuit they make up. Special attention should be paid to the structure and working principle of some specialized components represented by semi-structural diagrams (such as hydraulic control boxes composed of mechanical hydraulic directional valves in grinding machine hydraulic systems), and various control devices and variable mechanisms should be understood.
c. Analyze the working principle of the hydraulic system, carefully analyze and write down the action cycle of each actuator and the oil flow path of the system under various working conditions. For ease of reading, it is best to first code each oil circuit in the hydraulic system separately, and then divide the reading units according to the executing components. Each reading unit first looks at the action cycle, and then at the control circuit and main oil circuit. Special attention should be paid to the signal components when the system transitions from one working state to another, as well as which control components are activated and implemented.
d. Analyze and summarize the characteristics of hydraulic systems.
On the basis of understanding the schematic diagram, further analysis of the system should be conducted to evaluate the advantages and disadvantages of the hydraulic system, so as to continuously improve the hydraulic system used or designed. When analyzing and summarizing, the following aspects should be considered.
ⅰ Whether the basic hydraulic function circuit meets the action and performance requirements of the host.
ⅱ.Is there any contradiction or interference between the main oil circuit and the control oil circuit.
ⅲ.Is the substitution, transformation, and merging of hydraulic components reasonable, feasible, and economical.
ⅳ.Improvement direction of hydraulic system performance.
3) Precautions when reading hydraulic system schematic diagrams
① Have a basic understanding or familiarity with the structural principles of hydraulic pumps, actuators, hydraulic control valves, and hydraulic auxiliary components.
② You can use the host action cycle diagram and action cycle table, or describe the oil flow route in text.
③ Distinguish between the main oil circuit and the control oil circuit. The starting point of the oil inlet of the main oil circuit is the hydraulic pump pressure oil port, and the ending point is the oil inlet of the actuator; The starting point of the return oil circuit of the main oil circuit is the return oil port of the actuator, and the ending point is the oil tank (open circulation oil circuit) or the oil inlet of the actuator (hydraulic cylinder differential circuit) or the hydraulic pump suction port (closed circulation oil circuit). The control oil circuit should also clarify the source (such as the main pump or the control pump) and the control object (such as hydraulic one-way valve, directional valve, and electro-hydraulic directional valve).
④ For hydraulic systems composed of plug-in valves, it is necessary to analyze the oil flow path under each working condition based on the connection relationship between the plugs and the combination of the related pilot control valves (directional valve, pressure valve, or flow valve).
⑤ For a hydraulic system composed of multiple valves, the connection mode of the directional valve oil port in each valve should be identified one by one (parallel, series, series parallel, composite oil circuit, etc.), and then the oil flow path of each actuator under each working condition should be analyzed one by one.