Selection taboos for hydraulic system principles
1. Safety design of hydraulic system
The taboo hydraulic system and components need to limit (set) the maximum pressure, that is, they need to be used at or below the rated pressure or the maximum working pressure, nominal pressure. In addition to hydraulic power sources using pressure compensated variable displacement pumps, one or more relief valves should generally be installed on the system to limit the pressure of all parts of the hydraulic system, especially at the rod chamber of the hydraulic cylinder, to prevent pressure increase caused by piston area differences from exceeding the rated pressure limit of the hydraulic cylinder.
The overflow valve is used to control the pressure value inside the chamber. When the pressure exceeds the set pressure, the overflow is used to reduce the pressure, and the overflowing hydraulic oil generally flows directly back to the oil tank.
It is forbidden to have pressure limiting devices and pressure display (indication) devices missing in hydraulic systems.
2. Practical design taboos for hydraulic systems
No extra circuits can be set in the hydraulic system. The control function of hydraulic systems, including control accuracy, can only be selected and designed within the range that existing components can achieve. Excessive control design may be "redundant".
Taking the throttling speed control circuit as an example, generally, the inlet throttling speed control (inlet throttling control), return throttling speed control (outlet throttling control), and bypass throttling speed control cannot appear simultaneously in a hydraulic system, and two identical throttling valves cannot be installed on a single pipeline.
Except for improving the safety design of hydraulic systems, it is forbidden to design hydraulic systems with "redundancy".
The applicability of hydraulic systems should also be demonstrated in terms of inspection and maintainability, and necessary instruments and meters such as pressure, flow rate, and temperature must be set up; Necessary testing and inspection of oil ports must be reserved; The necessary disassembly and assembly space must be sufficient.
The taboo hydraulic system cannot be inspected or repaired.
Hydraulic transmission and control are not omnipotent, and they also have many drawbacks, such as speed range, response time (speed), control accuracy, hydraulic shock, environmental temperature, noise, and vibration. Therefore, when necessary, it is necessary to consider combining other transmission and control forms to optimize and improve the practical performance of the entire machine.
Avoid designing hydraulic systems and circuits that are unstable (operating conditions or working conditions).
3. Taboos in Economic Design of Hydraulic Systems
In addition to the simplicity and practicality of hydraulic system and circuit design, the selection of hydraulic components should also be based on meeting the functional requirements, and lower priced components should be chosen. For example, gear pumps should be preferred for hydraulic pumps, throttling valves should be preferred for throttling speed regulation, and one-way valves should be preferred for backpressure circuits.
The connection form between hydraulic components is very important. In addition to the preferred two-way plug-in hydraulic valve for high-pressure and high flow hydraulic systems, other types of valves such as plate valves, tube valves, stacked valves, threaded plug-in valves, etc. should have fewer pipelines, fewer bends, shorter lengths, smaller oil block volumes, simple design, processing, and manufacturing, and be easy.
The brand of hydraulic components is also important and should generally be clearly stated in the contract between the supply and demand parties. It is best to use domestically produced hydraulic products of independent brands to support the development and progress of national industries. Choosing simple connection forms and easy to purchase hydraulic components can shorten the manufacturing period of hydraulic systems, reduce costs, and improve economic benefits.
Do not neglect the design of hydraulic systems that prioritize cost and efficiency.
4. Taboos in reliability design of hydraulic systems
On the premise of ensuring the completion of required functions, the simpler the hydraulic system, the better. The more complex the hydraulic circuit design, the higher the failure rate may be; The simpler the hydraulic system and circuit, the higher the reliability.
The function of the hydraulic circuit (local) should be clear and preferably single, otherwise safety and reliability may be affected. If the hydraulic power source safety valve doubles as an overflow valve in the oil inlet or return throttling speed control circuit, the safety and reliability of the hydraulic system may be reduced. The various functional circuits in the hydraulic system cannot interfere with each other. The hydraulic pump may reverse due to circuit interference or external load, and the actuator may also move or rotate beyond the preset due to circuit interference or external load, even uncontrollably.
A reliable way to prevent hydraulic pump reversal is to design and install a one-way valve at the outlet of the hydraulic pump.
In the reversing circuit, an actuator such as a hydraulic cylinder should be controlled by a reversing valve to reverse its direction; If two or more directional valves are used in series to control one hydraulic cylinder, it may cause the hydraulic cylinder to "move randomly". Except for special hydraulic devices or hydraulic presses, it is forbidden to use pipelines or circuit crossover directional valves to directly connect the hydraulic power source to the actuator, as this may cause the hydraulic actuator to become uncontrollable.