How to design a hydraulic system, hydraulic system design ideas!

The hydraulic transmission system is a component of hydraulic machinery, and its design should be carried out simultaneously with the overall design of the main engine. When designing, it is necessary to start from the actual situation, organically combine various transmission forms, fully utilize the advantages of hydraulic transmission, and strive to design a hydraulic transmission system with simple structure, reliable operation, low cost, high efficiency, easy operation, and convenient maintenance.

1.1 Design steps
There is no strict sequence in the design steps of hydraulic systems, and each step often needs to be interspersed with each other. Generally speaking, after clarifying the design requirements, the following steps are roughly followed.

1) Determine the form of hydraulic actuators;
2) Conduct operating condition analysis to determine the main parameters of the system;
3) Develop a basic plan and draft a hydraulic system schematic diagram
4) Select hydraulic components
5) Performance verification of hydraulic system
6) Draw working diagrams and prepare technical documents

1.2 Clearly define design requirements
There is no strict sequence in the design steps of hydraulic systems, and each step often needs to be interspersed with each other. Generally speaking, after clarifying the design requirements, the following steps are roughly followed.

1) Determine the form of hydraulic actuators;
2) Conduct operating condition analysis to determine the main parameters of the system;
3) Develop a basic plan and draft a hydraulic system schematic diagram
4) Select hydraulic components
5) Performance verification of hydraulic system
6) Draw working diagrams and prepare technical documents
7) Requirements for dust, explosion, cold, noise, safety and reliability
8) Requirements for efficiency, cost, and other aspects

1.3 Develop a basic plan
1. Develop a speed control plan
After determining the hydraulic actuator, the control of its movement direction and speed is the core issue in formulating the hydraulic circuit.

Direction control is achieved through directional valves or logic control units. For general small and medium flow hydraulic systems, the required actions are mostly achieved through an organic combination of directional valves.For high-pressure and high flow hydraulic systems, a logical combination of plug-in valves   and   pilot control valves is commonly used.
Speed control is achieved by changing the input or output flow rate of hydraulic actuators or by utilizing changes in the volume of sealed spaces. The corresponding adjustment methods include throttling speed regulation, volumetric speed regulation, and a combination of the two - volumetric throttling speed regulation.

Throttle speed regulation generally uses a quantitative pump to supply oil, and uses a flow control valve to change the flow rate of the input or output hydraulic actuator to regulate the speed. This speed regulation method has a simple structure, but due to the need for flash valves in this system, it has low efficiency and high heat generation, and is often used in situations with low power.
Volume speed regulation is achieved by changing the displacement of hydraulic pumps or motors to achieve speed regulation. Its advantages are no overflow loss and throttling loss, and high efficiency. But in order to dissipate heat and replenish leaks, an auxiliary pump is needed. This speed regulation method is suitable for hydraulic systems with high power and high motion speed.

Volume throttling speed regulation generally uses a variable displacement pump to supply oil, and uses a flow control valve to regulate the flow of input or output hydraulic actuators, and make the oil supply amount adapt to the required oil amount. This type of speed regulation circuit has high efficiency and good speed stability, but its structure is relatively complex.
There are three forms of throttling speed regulation: inlet throttling, return throttling, and bypass throttling. The starting impact of oil inlet throttling is relatively small, while return throttling is commonly used in situations with load. Bypass throttling is often used in high-speed speed control circuits, and once the circulation   form of the circuit is determined, it is also determined accordingly.
Throttle speed regulation generally adopts an open cycle form. In an open system, the hydraulic pump draws oil from the tank, and the pressure oil flows through the system to release energy before being discharged back to the tank. The open circuit structure is simple and has good heat dissipation, but the fuel tank has a large volume and is prone to air contamination.

Volume speed regulation mostly adopts a closed cycle form. In a closed system, the suction port of the hydraulic pump is directly connected to the discharge port of the actuator, forming a closed loop. Its structure is compact, but its heat dissipation conditions are poor.

2. Develop a pressure control plan
When hydraulic actuators work, they require the system to maintain a certain working pressure or operate within a certain pressure range. Some also require multi-stage or stepless continuous pressure regulation.   Generally, in throttling speed control systems, oil is supplied by a quantitative pump, and the required pressure is regulated by an overflow valve and kept constant. In the volumetric speed control system, variable displacement pumps are used for oil supply, and safety valves are used for safety protection.
In some hydraulic systems, high-pressure oil with low flow rate is sometimes required. In this case, a   booster circuit can be considered to obtain high pressure instead of a separate high-pressure pump. When   hydraulic actuators do not require oil supply for a certain period of time during the working cycle and it is inconvenient to stop the pump, it is necessary to consider choosing an unloading circuit.
When the working pressure in a certain part of the system needs to be lower than the main oil source pressure, it is necessary to consider using a pressure reducing circuit to obtain the required working pressure.

3. Develop a sequential action plan
The sequential actions of each executing mechanism on the host vary depending on the device type, with some running according to a fixed program, while others are random or artificial. The control mechanism of construction machinery is mostly manual, generally controlled by manual multi way directional valves. The sequential actions of various actuators in processing machinery are often controlled by stroke control. When the working part moves to a certain position, an electrical stroke switch sends an electrical signal to the electromagnet to push the solenoid valve or directly press the stroke valve to control the subsequent actions. The installation of the travel switch is relatively convenient, while using a travel valve requires connecting the corresponding oil circuit, so it is only suitable for situations where pipeline connection is relatively convenient.
In addition, there are time control, pressure control, etc. For example, when a hydraulic pump starts without load, after a period of time, when the pump runs normally, the delay relay sends an electrical signal to close the unloading valve and establish normal working pressure. Pressure control is commonly used in machine tools with hydraulic fixtures, extruders, presses, and other applications. When a certain actuator completes a predetermined action, the pressure in the circuit reaches a certain value, and the next action is initiated by sending an electrical signal through the pressure relay or opening the sequence valve to allow the pressure oil to pass through.

4. Choose hydraulic power source
The working medium of the hydraulic system is completely provided by the hydraulic source, and the core of the hydraulic source is the hydraulic pump. The throttling speed control system generally uses a quantitative pump to supply oil. In the absence of other auxiliary oil sources, the oil supply of the hydraulic pump should be greater than the system's oil demand. The excess oil flows back to the oil tank through the overflow valve, which also controls and stabilizes the oil source pressure. Most volumetric speed control systems use variable displacement pumps to supply oil and limit the maximum pressure of the system with safety valves.

To save energy and improve efficiency, the oil supply of the hydraulic pump should match the required flow rate of the system as much as possible. For situations where there is a significant difference in the amount of oil required by the system during each stage of the work cycle, multi pump or variable pump oil supply is generally used. For situations where the required flow rate is low for a long time, an accumulator can be added as an auxiliary oil source.
The purification device for oil is indispensable in hydraulic sources. Generally, the inlet of a pump should be equipped with a coarse filter, and the oil entering the system should be filtered again through the corresponding fine filter according to the requirements of the protected components. To prevent impurities from flowing back into the oil tank in the system, magnetic filters or other types of filters can be installed on the return oil line. According to the environment in which the hydraulic equipment is located and the requirements for temperature rise, measures such as heating and cooling should also be considered.

1.4 Draw hydraulic system diagram
The hydraulic system diagram of the entire machine is composed of a predetermined control circuit and hydraulic source combination. When combining various circuits, redundant components should be removed to strive for a simple system structure. Pay attention to the interlocking relationship between each component to avoid misoperation. Efforts should be made to minimize energy loss. To improve the efficiency of the system and facilitate the maintenance and monitoring of the hydraulic system, necessary detection components (such as pressure gauges, thermometers, etc.) should be installed in the main sections of the system.

The key parts of large equipment should be equipped with equipment components so that they can be quickly replaced in case of accidents, ensuring continuous operation. Each hydraulic component should use domestically produced standard parts as much as possible, and be drawn in the normal position of the hydraulic component functional symbols specified by national standards in the diagram. For self-designed non-standard components, structural schematics can be used to draw them.
The system diagram should indicate the names and actions of each hydraulic actuator, the serial numbers of each hydraulic component and the codes of each electromagnet, and be accompanied by action tables of electromagnets, stroke valves, and other control components.