In many cases, it is necessary for the actuator to stop working for a short period of time. At this time, the hydraulic pump can be unloaded through the unloading circuit, even if the hydraulic pump is on. It is not suitable to stop and start the motor when it is running under the power (O pressure) state. The so-called “unloading” of CNC lathe means that the hydraulic pump operates with a small output power, that is, the output oil of the hydraulic pump is discharged back to the oil tank at a very low pressure; or the hydraulic pump outputs a small flow of pressure oil. This not only reduces the power consumption and the temperature rise of the system, but also prolongs the service life of the liquid pump.
The unloading circuit is adopted to avoid frequent starting and stopping of the prime mover; if unloading is performed before starting, the prime mover can be started under no load.The common unloading circuits of CNC lathes are as follows.
The Unloading Circuit Of The Reversing Valve Adopts A 3-Position Reversing Valve
The unloading circuit of the reversing valve adopts a three-position reversing valve with a neutral unloading function, which can unload the hydraulic pump. This method is simple and reliable. The neutral unloading function is M, H, K type. The unloading circuit of = 4-way reversing valve (M-type neutral function) is adopted. After the two electromagnets are powered off, the actuator stops moving, and the output oil of the hydraulic pump returns directly to the oil tank through the neutral position. A circuit in which the two-position 2-way electromagnetic reversing valve is directly unloaded is adopted. When the electromagnet is energized, the output oil of the hydraulic pump is directly discharged back to the oil tank through the reversing valve. The reversing valve is used for unloading, and its specification should be adapted to the flow rate of the hydraulic pump.
Use The Unloading Circuit Of The Pilot-Operated Relief Valve.
The CNC lathe is connected to the remote control port of the pilot relief valve 1 with a small-sized two-position 2-way solenoid valve 2. When the actuator is working, the solenoid valve is de-energized, and the pressure oil output by the hydraulic pump enters the system; when the actuator stops moving, the solenoid valve is energized, and the remote control port of the pilot relief valve is connected to the fuel tank, so that it opens at a very low pressure , the output oil of the hydraulic pump returns to the oil tank through the overflow valve to realize the unloading of the hydraulic pump. In structure, two-position 2-way solenoid valve and pilot-operated relief valve are often used in combination, which is called electromagnetic relief valve.
Use The Unloading Circuit Of The Externally Controlled Sequence Valve
In the oil supply system of the double pump, the CNC lathe uses an external control sequence 4 (or unloading valve) to make one of the pumps unload the same way. The external control sequence valve 4 limits the maximum pressure and flow rate of the two pumps together to supply oil, and the flow rate is determined by the overflow valve 3. When the system pressure is lower than the set value of the sequence valve 4, the sequence valve 4 is closed, and Shuangquan supplies oil. This is the condition of low pressure and large flow rate; when the system pressure exceeds the set value of the sequence valve 4, the sequence valve 4 is opened, The large flow pump 1 is unloaded, and the small flow pump 2 supplies oil, which is the condition of high pressure and small flow r. The set pressure of sequence valve 4 should be at least 0.5MPa lower than that of relief valve 3:
The Unloading Circuit Of The Pressure Compensation Variable Pump
Pressure-compensated variable pumps (such as pressure-limiting, constant-pressure, and constant-power variable pumps) have the characteristics of increasing pressure and decreasing flow automatically. When the reversing I resistance of the CNC lathe is 1: neutral and the actuator stops moving, the small u pressure of the pressure compensation variable pump I rises. After reaching the pressure required for the action of the compensation device, the flow of the pump is automatically reduced to the point where it only needs to be supplemented. leakage of the system. Since the output flow of the pump is very small at this time, this is also the unloading state of the flushing pump in a broad sense.
In order to prevent the failure of the pressure compensation device of the variable pump and the sluggish action of the pump, the h-force of the pump is abnormally increased, and no safety protection function is placed.
Keep Pressure And Unload The Same Way
Some hosts of CNC lathes require the hydraulic system to operate in I’. When the hydraulic pump is unloaded, the system still needs to maintain pressure. An accumulator is often used to maintain system pressure. Such as l*.1 6 8 (r), use the pressure relay to control the electromagnetic relief valve to unload the hydraulic pump, and use the accumulator to keep the pressure in the same way. The electromagnetic cycle 2 of the CNC lathe is energized, and the hydraulic pump operates normally at 1′; after the actuator stops moving, the hydraulic pump continues to supply oil to the accumulator 3.
With the increase of the allowable liquid volume of the accumulator, the pressure rises to the pressure relay 4 When the value is determined, the pressure relay will de-energize the solenoid valve, and the liquid guanidine pump will be released.
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