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Hydraulic cylinders are commonly used actuators in hydraulic systems. The stability of hydraulic cylinder operation directly affects the performance of the entire machine. Today, let’s talk about common problems in the operation of hydraulic cylinders. Why do they often drop automatically when locked? First, let’s talk about the structure and working principle of hydraulic cylinders.
1. Structure and working principle of hydraulic cylinder
A hydraulic cylinder usually consists of a rear end cover, a cylinder barrel, a piston rod, a piston assembly, a front end cover and other main parts. In order to prevent oil from leaking out of the hydraulic cylinder or from the high-pressure chamber to the low-pressure chamber, sealing devices are provided between the cylinder barrel and the end cover, the piston and the piston rod, the piston and the cylinder barrel, and the piston rod and the front end cover. A dustproof device is also installed on the outside of the front end cover. In order to prevent the piston from hitting the cylinder cover when it quickly retreats to the end of the stroke, a buffer device is also provided at the end of the hydraulic cylinder. Sometimes an exhaust device is also required.
2. General circuit of hydraulic cylinder
In a hydraulic system, when the hydraulic cylinder extends to a certain length, it does not need to continue to move, but only needs to stay in a certain position for a certain period of time. At this time, the reversing valve or hydraulic lock can be used to keep the hydraulic cylinder from moving. The general hydraulic pressure is as follows
3. Analysis of the reasons why the hydraulic cylinder descends automatically
Here, the hydraulic cylinder descent is generally understood as the hydraulic cylinder piston rod retracting under the action of external force. According to the structure and working principle of the hydraulic cylinder, we can analyze that the fundamental reason for the hydraulic cylinder retracting is that the volume of the hydraulic oil in the rodless chamber has become smaller. The possible reason for the reduction of the volume of the hydraulic oil in the rodless chamber is the reason why the hydraulic cylinder descends automatically:
Reason 1: Internal leakage of the hydraulic cylinder, the oil in the rodless chamber of the hydraulic cylinder runs into the rod chamber through the piston seal
Reason 2: The rear end cover of the hydraulic cylinder leaks, and the hydraulic oil in the rodless chamber leaks to the outside through the rear end cover. It is a leakage, which is easy to check
Reason 3: The hydraulic oil in the rodless chamber flows away through the oil port, which can be divided into several situations
- a). The oil port pipe joint or hydraulic oil pipe leaks oil, which is also a outter leakage and is easy to check
- b) In the circuit using the reversing valve to lock the middle position, the reversing valve may not be completely returned to the middle position, or the middle position seal is not good
- c) In the circuit locked by the hydraulic lock, the hydraulic lock ring may be damaged or the reversing valve middle position may be improperly selected
Reason 4: The hydraulic cylinder barrel leaks oil, which is also a outter leakage, easy to observe, and the possibility is generally small
4. Solution
1. Leakage in the hydraulic cylinder may be caused by aging of the seal ring. It is necessary to replace the seal ring or even redesign a more reasonable sealing structure.
2. The same is true for leakage at the rear end cover of the hydraulic cylinder. It is necessary to replace the seal or redesign a reasonable sealing structure.
3. When the oil pipe joint leaks oil, check whether the joint seal ring is damaged, replace the seal or replace the joint.
4. In the circuit using the reversing valve to lock the middle position, the middle seal is not good. Generally, it is caused by oil stains or other impurities that cause the valve core to not move in place, or the spring is stuck or broken, which makes it unable to return to the middle position. It needs to be repaired or replaced by a professional. If the pressure maintenance requirements are relatively high, you can consider replacing the hydraulic lock.
5. In the circuit locked by the hydraulic lock, the middle function valve with A and B ports closed cannot be used, because the closure of A and B ports may cause the hydraulic control check valve to still open in both directions and cannot play a locking role. In addition, the hydraulic lock spring breakage or impurities may also cause the hydraulic lock to be unable to be completely closed, and leakage may occur.
