The open hydraulic system means that the hydraulic pump 1 draws oil from the oil tank 5, and supplies oil to the hydraulic cylinder 3 (or hydraulic motor) through the reversing valve 2 to drive the working mechanism, and the oil return of the hydraulic cylinder 3 (or hydraulic motor) is reversed. Valve back to the tank. Install the relief valve 4 at the pump outlet. This system structure is relatively simple.
The open hydraulic system means that the hydraulic pump 1 draws oil from the oil tank 5, and supplies oil to the hydraulic cylinder 3 (or hydraulic motor) through the reversing valve 2 to drive the working mechanism, and the oil return of the hydraulic cylinder 3 (or hydraulic motor) is reversed. Valve back to the tank. Install the relief valve 4 at the pump outlet. This system structure is relatively simple.
Since the oil that has been worked on by the system is returned to the oil tank, the heat dissipation of the oil tank and the precipitation of impurities can be exerted. However, because the oil is often in contact with the air, the air is easily infiltrated into the system, resulting in the need to provide a back pressure valve on the road, which will cause additional energy loss and increase the oil temperature.
In the open system, the hydraulic pump used is a fixed pump or a one-way variable pump. Considering the self-priming capacity of the pump and avoiding the phenomenon of suction, the hydraulic pump with poor self-priming capacity usually limits its working speed to the rated speed. Within 75% of the speed, or an auxiliary pump for infusion.
The commutation of the working mechanism is cast by means of a reversing valve. When the reversing valve is reversed, in addition to generating a hydraulic shock, the inertial energy of the moving part will be converted into thermal energy, and the temperature of the hydraulic oil will rise.
Due to the simple structure of the open system, it is still used by most cranes.
In a closed system, the inlet pipe of the hydraulic pump is directly connected to the return pipe of the actuator, and the working fluid is closed in the pipeline of the system.
The closed system has a compact structure, less chance of contact with air, and the air does not easily penetrate into the system, so the smoothness of the transmission is good.
The shifting and commutation of the working mechanism is achieved by adjusting the variable mechanism of the pump or motor, avoiding the hydraulic shock and energy loss that occurs during the commutation of the open system.
The closed system is more complicated than the open system. Since the oil that has been closed by the closed system does not return to the tank, the heat dissipation and filtration conditions of the oil are worse than those of the open system.
In order to compensate for leaks in the system, a small-capacity rehydration pump is usually required for replenishment and heat dissipation, so the system is actually a semi-closed system.
Under normal circumstances, if the actuator in the closed system adopts the double-acting single-piston rod hydraulic cylinder, the power utilization rate will decrease during the working process due to the unequal flow of the large and small chambers.
Therefore, the actuators in a closed system are generally hydraulic motors.
The closed hydraulic drive system continuously leaks oil during work (continuous high-pressure oil leakage is an inherent product of component design). In order to make up for these leaks and expenses, to keep the closed system working properly, it is necessary to make timely compensation for the closed system. liquid.
A small displacement charge pump is attached to the through shaft of the closed system main pump. Since the displacement and pressure of the charge pump are small relative to the main pump, the additional power loss is usually only 1% to 2% of the total power of the transmission. Can be ignored.
In the closed system hydraulic working device, there is a charge relief valve and a charge check valve, and the charge relief valve limits the maximum charge pressure, and the charge check valve is based on the hydraulic pressure of the pipeline on both sides, Select the direction of replenishment and replenish the oil to the low pressure side of the main oil line to compensate for the leakage caused by the loss of the volume of the pump and motor;
There are two high pressure relief valves on both sides of the main pump. The pressure peak and maximum pressure presented when the swash plate is swung rapidly are maintained by the high pressure relief valve to prevent the pump and motor from being overloaded;
The hydraulic device is further provided with a pressure shut-off valve, which is equivalent to a pressure regulation, and when the set pressure is reached, the displacement of the oil pump is adjusted back to zero.
----- Editor-in-Chief: Dalan Oil Pump Motor 02-Procurement Consultant
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