Troubleshooting of throttle valve
Troubleshooting of throttle valve
1. Failure of throttling regulation
This fault phenomenon is shown as:; When adjusting the regulating handle, the flow at the outlet of the throttle valve does not change with the loosening or tightening of the handle, so as to maintain the movement speed of the actuator at a certain value (depending on the opening position of the throttle valve core), whether it is fast or slow, or how to increase the flow (handle), the actuator always does not act, No matter how small the actuator is, it still can't slow down, which is the failure of throttling regulation. The causes and troubleshooting are as follows.
(1) Cause analysis.
1) The valve core is stuck or the orifice is blocked due to dirt in the oil. The oil is very dirty, the working oil is aging, and the oil has not been finely filtered. In this way, the contaminated oil passes through the throttle valve, and the contaminated particles wedge into the matching gap between the valve core and the valve body hole, resulting in the same throttling regulation failure as above.
2) Because the fit clearance between the valve core and the valve body hole is too small or too large, the valve core is stuck or the leakage is large, resulting in the failure of throttling function.
3) There are tensile scratches on the inner and outer cylindrical surfaces of the valve core and the valve hole, which makes the movement of the valve core inflexible, or stuck, or large internal leakage, resulting in throttling failure.
4) The throttle valve core is stuck due to burrs or the valve core is stuck due to burrs at the sharp edge of the countersunk groove of the valve body and the chamfer of the valve core, as shown in Figure 85. At this time, although the adjusting handle is loosened to drive the adjusting rod to move up, the clamping force of the valve core cannot be overcome due to the force of the return spring, and the valve core cannot be lifted up with the upward movement of the adjusting rod, as shown in Figure 86. When the valve core is stuck at the position of closing the valve port, there is no flow output and the actuator does not act; When the valve core is stuck at a certain opening position, there is only a small flow output and the actuator has only a certain speed.
5) The shape and position tolerance of valve core and valve hole is not good, such as out of roundness and taper, resulting in hydraulic clamping and failure of throttling regulation. At present, there is no pressure equalizing groove on the valve core of L-type throttle valve, which is easy to produce hydraulic clamping.
6) The equipment has been shut down for a long time, and the water in the oil makes the valve core rusted and stuck in the valve hole. When it is reused, the throttling regulation fails.
1) When the oil is not clean, it is necessary to take measures to change the oil and strengthen filtration. When changing the oil, it must be changed in time.
2) Check whether the fit clearance between the valve core and the valve body hole is appropriate. If not, grind the valve hole for repair or reconfigure the valve core.
If the valve hole is out of round or the fitting clearance is too small, grind the valve hole for repair or reconfigure the valve core.
2. Although the flow can be adjusted, the adjusted flow is unstable
This fault phenomenon is shown as follows: when the throttle valve is adjusted at a certain throttle opening and the adjusting screw is locked, the outlet flow is still changing, making the movement speed of the actuator fast and slow, gradually slow down or gradually increase, sudden jump and other unstable phenomena. Unstable flow will make the speed of the actuator unstable, especially when the lowest value of the flow regulation range (minimum stable flow) and the differential pressure between the inlet and outlet of the throttle valve are the lowest working pressure. The main causes of flow instability are "blockage" at the throttle, loose locking device, high oil temperature and large change of load pressure, as follows.
(1) Cause analysis.
1) Due to the blockage caused by the adsorption of polarized molecules and metal surfaces in the oil, the molecular chains in the oil will be positively charged at one end and negatively charged at the other end due to electrification and mutual attraction, and the molecular chains will become longer and larger. In addition, the potential difference on the metal surface will attract these polarized molecular chains, forming a solid boundary adsorption layer at the throttling gap and opening, with a thickness of 5 ~ 10um, which destroys the original geometry and size of the throttling gap. Moreover, for mineral oil, this adsorption layer is a gray fiber layer organization, which will be damaged periodically under pressure, Make the flow fluctuate periodically.
2) Mechanical impurities (such as dust, chip dust, paint flakes, etc.) mixed in the oil and the products of oil deterioration and aging cause accumulation when passing through the throttling gap, blocking the throttling channel and causing unstable flow.
3) The oil temperature increases with the operation time of the hydraulic system, the oil viscosity decreases accordingly, and the flow through the throttling opening increases, but it may also decrease due to the increase of internal leakage, resulting in the phenomenon of unstable flow.
4) The throttle valve core adopts clearance seal. According to the annular clearance flow formula, there must be internal leakage. When the fit clearance increases due to wear, the internal leakage will also increase. And this internal leakage changes with the changes of various factors (such as oil temperature), which affects the stability of flow, especially when the flow is small.
5) The external leakage of the throttle valve is large, resulting in unstable flow.
6) The oil is not precisely filtered, the impurities in the oil accumulate and adhere to the wall of the throttling channel, and the flow area is reduced, which slows down the speed of the actuator and completely blocks it, resulting in "cut-off"; If the dirt is washed away, it will cause "sudden jump".
7) When the pressure oil passes through the throttling gap, it will produce pressure loss, make the oil temperature rise locally, oxidize and deteriorate the oil, precipitate colloid, asphalt, carbon slag and other substances at the throttling port, and attach them to the wall of the throttling port, so as to reduce the effective flow area or even block.
8) After the throttle valve is adjusted and locked, the vertical and horizontal locking screws will be loosened due to mechanical vibration or other reasons (as shown in Figure 87), and then the adjusting rod will rotate and loosen on the support sleeve, so that the opening of the throttle valve will be changed and the flow will be changed.
9) Air is mixed into the system, which greatly increases the compressibility of the oil, sometimes compressing and sometimes releasing, and the flow is unstable.
10) The large change of system load leads to the change of hydraulic cylinder working pressure, and the throttle valve does not have a pressure feedback compensation device like the speed regulating valve, so the differential pressure flowing through the throttle valve will change and the flow will also change.
1) Some measures can be taken when designing the throttle valve, mainly using the metal with small potential difference as the throttle valve. The experiment shows that steel is better for steel than copper, and aluminum is the worst. Therefore, L-type and if type throttle valves are steel to cast iron, and the potential difference is small.
2) The oil shall be filtered at ordinary times, or an oil filter shall be installed in front of the throttle valve to keep the oil clean and pay attention to oil change.
3) Take measures to reduce the heating of the system and replace the oil with high viscosity index. If it is caused by internal leakage, targeted measures can be taken.
4) Ensure the reasonable fit clearance between the throttle valve core and the valve hole, and do not adjust the throttle valve over figure 87, and the locking screw is too large or too small.
5) Check the causes of leakage outside the throttle valve and take targeted measures.
6) To fine filter the oil, install an oil filter in front of the throttle valve to keep the oil clean. Clean the orifice and take measures to change the oil if necessary.
7) Clean the throttle, find out the oil pollution, and take measures such as oil change.
8) To eliminate the vibration source of mechanical vibration, the throttle valve with lock adjusting handle can be used.
9) Remove air from the system.
10) For the phenomenon of fast and slow due to load change, the throttle valve can be changed to speed regulating valve.
The external leakage of the throttle valve mainly occurs at the regulating handle, as well as the process screw plug, valve mounting surface, etc. The main cause of external leakage is caused by the damage of the sealing device. In actual work, corresponding measures can be taken according to the actual situation.
4. Internal leakage
The causes of large internal leakage are mainly caused by the large matching gap between the throttle valve core and the valve hole or serious wear during use, the strained groove between the valve core and the valve hole (especially the axial groove), and the high oil temperature.
The elimination method is to ensure that the fit clearance between the valve core and the valve hole is within the range of 0.007 ~ 0.015mm. If the wear is serious or there are grooves due to strain, the valve core needs to be electroplated or reprocessed for grinding and matching.
5. Repair of throttle valve
(1) Valve core
When the valve core with serious wear and tight strain groove needs to be repaired, it can be ground off by 0.05 ~ 0.10mm with through grinding method on the centerless grinder, then brush and plating a layer of hard chromium, then grind with coreless grinding, polish and repair with chromium oxide polishing paste.
(2) Valve body
Like other valves, the valve body is mainly due to the wear and roughening of the valve hole and the loss of hole accuracy. The repair part of the valve body is generally the valve hole matched with the outer circle of the valve core (geometric accuracy, dimensional accuracy and surface roughness). The valve hole can be repaired by grinding or reaming with grinding rod or adjustable diamond reamer. In case of serious wear, the inner hole can be brushed or electroplated, and then reamed, or a new valve core can be equipped.
(3) Adjusting rod
When the adjusting rod needs to be replaced, it can be processed according to the original part drawing, and all technical indexes meet the requirements.