Created on:2022-03-14 13:05

Fault analysis and troubleshooting of speed regulating valve

Fault analysis and troubleshooting of speed regulating valve

The speed regulating valve is composed of and pressure compensation mechanism. Therefore, in addition to the fault analysis and troubleshooting methods of the above throttle valve, there are the following points.

1. The pressure compensation mechanism (constant differential pressure reducing valve) does not act, and the speed regulating valve is like a general throttle valve

(1) Cause analysis.

1) The pressure reducing valve core is stuck by dirt, as shown in Figure 92.

2) The pressure difference between inlet and outlet is too small.

3) Hole a, hole f or hole e are blocked by dirt, as shown in Figure 92.

(2) Troubleshooting.

1) Disassemble and check the pressure reducing valve core and clean the speed regulating valve.

2) Adjust the pressure difference between inlet and outlet (the difference between P1 and P3), the medium and low pressure Q-type speed regulating valve shall be at least 0.6MPa, and the medium and high pressure shall be at least 1MPa.

3) Detachable for cleaning.

2. It is very hard to adjust the throttle castration flow regulating handle

(1) Cause analysis

1) When it is used for oil inlet throttle speed regulation, the outlet pressure of the speed regulating valve (generally load pressure) is too high.

2) The adjusting rod is stuck by dirt, or the thread of the adjusting handle does not fit well.

(2) Troubleshooting.

1) At this time, the pressure shall be relieved first, and then the handle shall be adjusted.

2) Countermeasures can be taken according to the situation.

3. Throttling failure

(1) Cause analysis.

1) If the inlet and outlet of the speed regulating valve are connected reversely, the pressure reducing valve core will tend to close, resulting in throttling failure.

2) The pressure difference between the inlet and outlet of the speed regulating valve is too small, resulting in flow regulation failure.

3) The valve core of the differential pressure reducing valve is stuck in the fully closed or small opening position, so that there is no oil in the oil outlet chamber (P2) or very little oil passes through the throttle valve.

(2) Troubleshooting.

1) - P1 (inlet) and P2 (outlet) are marked on the bottom surface of general plate speed regulating valve at each oil port, which shall be carefully identified and shall not be connected wrongly. Because the holes on the mounting surface of Q-type and QF type valves are symmetrical, they are easy to be installed incorrectly, so we must pay attention to them.

2) For Q-type speed regulating valve, the inlet pressure shall be greater than the outlet pressure by 0.5MPa, and for QF type valve, the flow can be adjusted only when the inlet pressure is greater than the outlet pressure by 1MPa.

3) It shall be disassembled, cleaned and deburred to make the pressure reducing valve core move flexibly.

4. Unstable flow

The flow instability of general throttle valve, the fault causes and troubleshooting methods are applicable to speed regulating valve. In addition, there are the following points.

(1) Cause analysis.

1) The pressure reducing valve core in the speed regulating valve is blocked with the pressure feedback hole on the valve cover, or the large and small ends of the constant pressure differential pressure reducing valve core are not concentric and do not cooperate well, so that the pressure difference △ P at the inlet and outlet of the throttle valve core changes, resulting in unstable flow.

2) The internal and external leakage of the speed regulating valve is large, resulting in unstable flow.

3) The constant differential pressure reducing valve does not move flexibly and cannot play the role of pressure feedback. It cannot stabilize the differential pressure before and after the throttle valve to a certain value, resulting in unstable flow.

4) The oil inlet and outlet are connected reversely, so that the speed regulating valve is like a general throttle valve without pressure feedback compensation.

5) The spring of the pressure reducing valve is missing, or the spring is broken and installed incorrectly.

(2) Troubleshooting.

1) If it is found that the pressure reducing valve core in the speed regulating valve and the pressure feedback hole on the valve cover are blocked, generally, a 1.0mm diameter fine steel wire can be used to connect the one-way valve sleeve and the feedback hole on the valve core, or blow through with compressed air.

2) Measures shall be taken to control the leakage.

3) The screw plug at the end of the valve shall be disassembled, and the pressure reducing valve core shall be extracted from the valve sleeve for deburring, cleaning and accuracy inspection. Special attention shall be paid to whether the large and small ends of the pressure reducing valve core are concentric, and the defective ones shall be repaired and replaced.

4) Correct and reassemble.

5) It shall be repaired or replaced.

5. The minimum stable flow is unstable

In order to realize the stability of low-speed feed of actuator such as hydraulic cylinder, the minimum stable flow limit value is specified for the flow valve, but the low-speed feed of actuator is often unstable within this limit. From the analysis of the reason of speed regulating valve, the minimum stable flow is changed. The reason affecting the minimum stable flow change is the large amount of internal leakage. The specific parts are the throttle valve core and the pressure reducing valve core.

The structure of the pressure reducing valve core is shown in Figure 93. Due to the two-stage concentricity problem of the large and small ends of the valve core, sufficient clearance is required during assembly to compensate for the processing deviation of the large and small ends (large end 0.025mm, small end 0.008 ~ 0.015mm), which increases the internal leakage and leads to the instability of the minimum stable flow.

93

In order not to make the processing of the two-stage concentric valve core too difficult, and not to cause large internal leakage due to excessive matching clearance, so that its change is large and affect the minimum stable flow, the two-stage concentric mushroom valve core of the speed regulating valve can be changed into two bodies (21 and 22), This is conducive to overcome the disadvantage of excessive assembly clearance caused by the coaxiality error of the inner and outer circle of the valve sleeve and the large and small head of the constant pressure differential pressure reducing valve core, and can significantly reduce the internal leakage, so as to effectively reduce the impact of the change of leakage on the minimum stable flow.

Home    Article    Fault analysis and troubleshooting of speed regulating valve