Various classifications and characteristics of hydraulic systems
1. Open system and closed system
Open system, the hydraulic pump of this system sucks oil from the fuel tank, and the actuator returns oil to the tank. The system requires a larger volume of fuel tank. This type of system is most commonly used.
In a closed system, in a closed system, the oil discharged from the actuator is returned to the inlet of the pump. The system is highly efficient, it needs to be replenished with a charge pump, and the oil is exchanged with a flush valve for heat exchange. Such systems are commonly used in machinery, such as vehicles, cranes, ship winches, paper and textiles.
Second, hydraulic transmission system and hydraulic control system
Hydraulic transmission system, hydraulic transmission system is generally open loop system without feedback, mainly to transmit power, with information transmission as the second, and pursue the perfect transmission characteristics. The operating characteristics of the system are determined by the characteristics of the various hydraulic components and their interactions, and the quality of their work is greatly affected by changes in operating conditions. Hydraulic final drive systems are more common. Most industrial equipment hydraulic systems fall into this category.
The hydraulic control system and the hydraulic control system are mostly closed-loop systems with feedback composed of electro-hydraulic control valves such as servo valves. The transmission of information is mainly based on the transmission of power, and the pursuit of control characteristics is perfected. Due to the addition of detection feedback, the system can be composed of general components to form an accurate control system, and its control quality is less affected by changes in working conditions. Hydraulic control systems are widely used in high-precision CNC machine tools, metallurgy, aviation, aerospace and other fields.
Third, valve control system, pump control system and actuator control system
In the valve control system, the valve control system controls the flow rate by changing the throttle opening of the valve to control the speed of the actuator. It is generally less efficient due to throttling and overflow losses. The valve control system is used in almost all kinds of mechanical equipment.
The pump control system, the pump control system controls the flow rate by changing the displacement of the variable pump for stepless speed control or by multi-quantity pump combination to provide stepwise speed control. The efficiency is higher due to no throttling and overflow losses. Mainly used in high-pressure hydraulic equipment such as pressure processing machinery and rubber plastic machinery.
Actuator control system, actuator control system controls the flow by changing the variable hydraulic motor displacement of the actuator or by combining multiple quantitative hydraulic motors or by changing the active cylinder's active area to control flow. Similar to pump control systems, such systems are more efficient due to no throttling and overflow losses. Mainly used in hydraulic equipment such as walking machinery and pressure processing machinery.
4. Medium open system and medium closed system
In the middle open system, when the main reversing valve of the middle open system is in the middle position, the reversing valve unloads the hydraulic pump and the liquid low pressure returns to the oil tank. This type of system generally uses a fixed final drive parts as the oil source; when the reversing valve is in the neutral position, the energy transfer starts from a substantially zero low value, and the energy rises after the commutation, so that the pressurized liquid enters the actuator to overcome the load; When the valve is in the middle position, the internal leakage is extremely small. The open loop energy consumption is usually lower when the same function can be satisfied. The medium open system is mostly used for types of working conditions such as intermittent movement or supporting load without the need to frequently start and stop the prime mover.
In the middle closed system, when the main reversing valve of the middle closed system is in the middle position, all the ports of the reversing valve are closed. If the dosing pump is used for oil supply, the liquid of the hydraulic pump is returned to the tank through the overflow valve. When the valve is in the neutral position, the energy transfer starts from a high value, that is, from the maximum pressure regulation value of the system. As long as the commutation, the energy can be utilized by the actuator; when the reversing valve is in the middle position, it sometimes bears the entire system. Pressure, so the amount of internal leakage is larger than that of the medium open system. Generally, in the case of meeting the same function, the energy consumption of the medium closed circuit is higher, but if the medium unloading measure is added or the pressure compensated variable pump is used for oil supply, the energy consumption of the medium closed type can be greatly reduced. The medium closed hydraulic system is used in a variety of equipment.
5. Systems for fixed equipment and systems for mobile equipment
Systems for stationary equipment, such hydraulic systems are mostly open circulation systems, including for various industrial equipment such as machine tools (workpiece clamping, table feed, reversing, spindle drive), presses (pressing, crimping) , reversing, workpiece ejection), die casting machine and injection molding machine (clamping, demoulding, pre-molding, injection mechanism) and even public facilities, such as medical equipment, garbage press and other mechanical equipment and work systems.
For mobile equipment systems, such hydraulic systems have both open and closed circulation systems, including for vehicle travel (walking drive, steering, braking and their working devices), material handling handling equipment (transmission mechanism, transfer) Institutions) and various systems in aerospace, aerospace, and marine engineering. https://www.spfinaldrives.com/