The speed of the hydraulic cylinder in the speed regulating circuit is slow when it returns
The speed of the hydraulic cylinder in the speed regulating circuit is slow when it returns
In the system shown in Figure 41, the hydraulic pump is a quantitative pump, the reversing valve is a two position four-way electromagnetic reversing valve, and the throttle valve is on the oil return circuit of the hydraulic cylinder, so the system is an oil return throttle speed regulation system. When the hydraulic cylinder returns, the hydraulic oil enters the rod chamber of the hydraulic cylinder through the one-way valve, and the overflow valve plays the role of constant pressure and overflow in the system.
The system fault phenomenon is that the return speed of the hydraulic cylinder is slow, and there is no maximum return speed.
Check and debug the system. It is found that the fast forward and working movements of the hydraulic cylinder are normal, but the fast backward return is abnormal. Check the one-way valve and it works normally. When the hydraulic cylinder returns, there is no working load. At this time, the system pressure is relatively low, and the outlet flow of the hydraulic pump is all input into the rod cavity of the hydraulic cylinder, which should make the hydraulic cylinder produce a higher speed. However, it is found that the return speed of the hydraulic cylinder is not only slow, but also the system pressure is still very high at this time.
After disassembling and inspecting the directional valve, it was found that the return spring of the directional valve was not only insufficient in elasticity, but also skewed, resulting in the failure of the spool of the directional valve to return to its original position after power failure, so the opening of the slide valve was too small, which throttled the oil of the channel directional valve. Most of the pressure oil output by the hydraulic pump overflows back to the oil tank by the overflow valve. At this time, the pressure in front of the reversing valve has reached the set pressure of the overflow valve, which is the reason for the pressure rise of the hydraulic cylinder when it returns.
Since most of the pressure oil overflows back to the oil tank, there must be less oil entering the rod cavity of the hydraulic cylinder through the reversing valve, so there is no maximum speed for the return of the hydraulic cylinder.
The troubleshooting method is: the failure of the slide valve to return to its original position is due to the spring, and the qualified spring should be replaced. If the radial clamping is caused by the poor accuracy of the slide valve, the slide valve should be polished or reconstituted. Generally, the allowable deviation of the roundness and taper of the valve core is 0.003 ~ 0.005mm. It is better to make the valve core have a small taper (which can be 1/4 of the minimum clearance), and make its big end on the side of the low-pressure chamber, so as to automatically reduce the eccentricity and friction, so as to reduce or avoid the radial clamping force.
The reasons for the increase of the return resistance of the spool may also be: dirt enters the gap of the spool valve, making it difficult for the spool to move; The gap between the valve core and the valve hole is too small, so that when the oil temperature rises, the valve expands and locks; The resistance at the sealing ring of the electromagnet push rod is too large, and the valve hole is deformed when installing the tight return solenoid valve. As long as we can find out the real cause of the jam, the corresponding elimination method is relatively easy.
