Solenoid directional valve - electromagnet does not act and unreliable fault
Solenoid directional valve - electromagnet does not act and unreliable fault
1. Insufficient suction of electromagnet
(1) Cause analysis
1) The machining error of electromagnet itself is large. When working, the friction at the contact part of each moving part is large.
2) There is dirt or rust between the armature and the sleeve of the DC electromagnet, resulting in insufficient suction and sluggish action of the DC electromagnet.
3) Because the electromagnet is installed vertically and the electromagnet is under the valve, the electromagnet should bear the gravity of its own moving iron core and valve core, and the effective thrust is reduced.
(2) Troubleshooting
1) Replace the high-quality electromagnet.
2) Check and clean whether there is dirt or rust between DC electromagnet armature and sleeve.
3) Adjust the installation direction of electromagnet. Generally, it should be installed horizontally.
2. Electromagnet does not act
(1) Cause analysis.
1) Due to poor welding, the connection of the incoming and outgoing lines of the electromagnet is loose and the electromagnet does not act.
2) The electromagnet does not act due to circuit failure.
(2) Troubleshooting.
1) Re weld to make it well connected.
2) Check the circuit and repair it according to the actual situation.
3. The reversing of electromagnet is unreliable
(1) Cause analysis.
1) The commutation caused by the quality problem of electromagnet is unreliable.
① The electromagnet is of poor quality, or the outgoing line is broken due to vibration, or falls off due to loose welding, or the circuit is blocked due to circuit failure, resulting in the non commutation of the change-over valve.
② The movable iron core of the AC electromagnet is stuck by the guide plate (refer to Fig. 26), and there is dirt stuck or rusted between the armature of the DC electromagnet and the sleeve. Both of these conditions make the electromagnet unable to pull in well, the valve core cannot move or cannot move in place, and the oil circuit does not switch, that is, there is no commutation.
③ Insufficient electromagnet suction due to insufficient coil turns.
④ The small hole on the fixed iron core of the electromagnet is facing the axis line of the valve body push rod spool, as shown in Figure 27, resulting in the deflection of the push rod during the suction process and increasing the friction force of the moving pair of the spool. In addition, there is a great difference in the density of the magnetic force lines between gap a and gap B, which will produce a unilateral force, which will move the push rod to a, resulting in the deflection of the push rod, which is more exciting.
⑤ The electromagnet voltage is wrong and is not controlled within the allowable range. If the voltage is too low, a slight change in voltage will have a great impact on the attraction, resulting in the failure that the electromagnet can not be engaged, resulting in the valve can not be reversed.
⑥ The power frequency is incorrect. According to the suction formula, the frequency has an effect on the magnitude of suction.
2) Poor reversing caused by poor machining and assembly quality of the valve itself.
① The screws for installing the valve are over tightened. The fit clearance between the valve body and the valve core of the electromagnetic directional valve is very small, generally 0.007 ~ 0.02mm. If the mounting screw is tightened too tightly, the inner hole of the valve will be deformed, and the valve core will be stuck and cannot be reversed. The tightening torque of the screw should be tightened with a torque wrench according to the recommended value of the manufacturer. Generally, the tightening torque of M5 mounting screw is recommended to be 6 ~ 9N · m, M6 is L2 ~ 15N · m, M8 is 20 ~ 25N · m and ML2 is 75 ~ 105N · M.
② The burrs at the sharp edges of the valve core shoulder and the balance groove of the valve core, and the burrs at the sharp edges of the undercut groove of the valve body are not cleaned or not removed at all. In particular, the burr in the valve body hole often turns into the countersunk groove, which is difficult to remove and does great harm.
③ Poor geometric accuracy (such as roundness and cylindricity) of valve core and valve hole will produce hydraulic clamping force. Especially after staying for a few minutes (6min in bench test), plus the high pressure, the valve core often generates hydraulic clamping force, and the directional valve does not reverse. It is worth mentioning that: the hydraulic clamping appears in the working condition. When it is not working and shutdown, the valve core may be flexible in the valve hole, but this is an illusion.
④ The oil drain hole (L oil hole) or oil return hole is blocked (it is occasionally found that there are undrilled holes). Especially in the processing, the crossing area of the intersection between the oil drain hole (L oil hole) and the valve hole is very small due to the deflection. In addition, the process plug is too long or the pressure is too deep, and the oil drain hole (L oil hole) is blocked, which makes the oil drain channel blocked, resulting in oil trapped at both ends of the valve core and unable to push the valve core, as shown in Figure 28.
⑤ The valve hole is not perpendicular to the end face of the valve body. After the electromagnet is installed, the push rod will be skewed and the movement resistance of the valve core will increase.
⑥ The processing of pressure equalizing (balancing) groove on the valve core is unilateral eccentric, which produces hydraulic clamping force after assembly and use, resulting in poor commutation, as shown in Figure 29.
⑦ The fit clearance between valve core and valve body is too large or too small. Too large is easy to produce hydraulic clamping; Too small is easy to cause increased friction resistance and clamping.
③ The size of the shoulder of the valve core and the undercut groove of the valve body is incorrect, resulting in inconsistent reversing speed at both ends.
⑨ The material of the casting (valve body) is not good. After the installation screw is tightened, the valve hole becomes oval, which blocks the valve core or causes inflexible movement.
3) Unreliable commutation caused by dirt.
① The fine iron powder in the oil is magnetized by the magnetic field formed by the energization of electromagnetic iron and adsorbed on the outer surface of the valve core or the inner surface of the valve hole, causing clamping.
② When the valve is assembled, the cleaning is poor or the cleaning oil is not clean, and the dirt accumulates in the matching gap between the valve core and the valve body, jamming the valve core.
③ There are no dust-proof measures for the oil tank and no filtering measures during refueling. The poor filtration of the system itself causes oil dirt to enter the system.
④ During operation, the dust and dirt in the air enter the hydraulic system and are brought into the electromagnetic enclosure.
⑤ Packaging, transportation, repair and assembly do not pay attention to cleaning, so that dirt enters the valve and rust is caused by moisture.
⑥ Aging and deterioration of hydraulic oil, resulting in oil sludge and other dirt.
4) Unreliable commutation caused by other reasons.
① The back pressure is too large, exceeding the rated back pressure of the solenoid valve.
② Due to spring fatigue, wrong installation of soft spring after disassembly, or broken return spring, the force of return spring is not enough, resulting in failure or poor reversal of valve core without return.
③ When designing the hydraulic mounting plate, the user does not design the l-hole oil drain channel, or although the l-hole oil drain channel is designed, it is connected with the oil return hole. The former has no place to drain the oil, and the latter may have high pressure in the l-hole communication chamber due to the high back pressure of the oil return, so that the electromagnet cannot be reversed. The L chamber (port) shall be independent of the oil return tank and cannot be shared with the oil return chamber.
④ There is a problem with the quality of the O-ring seal at the push rod.
(2) Troubleshooting.
1) Check the quality of electromagnet and take targeted measures.
① If the electromagnet is not energized, the reversing valve will not reverse. At this time, the meter can be used to check the cause and location of power failure, and take countermeasures.
② Check the reason why the movable iron core of AC electromagnet is stuck by the guide plate and take measures to repair it; Check whether there is dirt stuck or rusted between DC electromagnet armature and sleeve, and take measures in time.
③ Rewind the coil and increase the number of turns of the coil.
④ The size of the fixed iron core perforation can be increased, as shown in the figure Ф Replace 6 with Ф 8。
⑤ Check the voltage of the electromagnet, adjust and ensure that the voltage of the electromagnet is within the specified range. The allowable range of domestic specified voltage is 85% ~ 105% of the rated voltage, and most of them are 90% ~ 110% abroad. As the domestic power grid fluctuates greatly, it is best to use voltage regulator.
⑥ Check whether the frequency of power supply is wrong, especially for imported hydraulic equipment. If it is wrong, correct it. The domestic power frequency is 50Hz, while some imported equipment is 60Hz, such as AC electromagnet in Japan.
2) Check the machining quality of directional valve and take targeted measures.
① Refit the screws that install the valve. The tightening torque of the screw should be tightened with a torque wrench according to the recommended value of the manufacturer. Generally, the tightening torque of M5 mounting screw is recommended to be 6 ~ 9N · m, M6 is L2 ~ 15N · m, M8 is 20 ~ 25N · m and ML2 is 75 ~ 105N · M.
② At present, the manufacturer of hydraulic components has used nylon brush to deburr the valve hole and vibration method to deburr the valve core, which may not be cleaned up. It can be carefully checked and further cleaned according to the situation.
③ Check the geometric accuracy of the valve core and valve hole, and regrind the valve core and valve hole to make the geometric accuracy (such as roundness and cylindricity) meet the requirements. Generally, it shall be controlled within 0.003 ~ 0.005mm.
④ Check the condition of oil drain hole (L oil hole) or oil return hole, and take corresponding measures to keep the oil drain hole (L oil hole) or oil return hole unblocked.
⑤ Check and adjust the valve hole and the end face of the valve body to keep it vertical.
⑥ Try to make them concentric to prevent eccentricity.
⑦ Repair the valve core and valve body to make the matching clearance meet the requirements.
⑧ Check the dimensions of the valve core shoulder and the valve body undercut. If they are inconsistent, repair the valve core shoulder and the valve body undercut in time to make them meet the requirements.
⑨ Directional valve with good performance.
3) Take measures to minimize the entry of dirt.
① The hydraulic system shall be equipped with magnetic filtering device in appropriate position.
② The valve shall be carefully cleaned before assembly and assembled after cleaning.
③ Dust proof measures shall be taken during refueling. Generally, hydraulic oil shall be added in a relatively clean environment.
④ The oil tank shall be added at the oil filling hole, and attention shall be paid to inspection and cleaning.
⑤ Strengthen packaging and transportation, pay attention to repair and assembly, and carefully clean before assembly.
⑥ Replace the hydraulic oil regularly according to the actual situation.
4) Exclude according to different situations.
① Find out the cause and properly reduce the pressure.
② Suitable springs should be replaced.
③ Reasonably design a separate l-hole oil drain channel.
④ Check whether the O-ring at the push rod has flash, whether the wire diameter is too large, whether the size is correct, and whether it is soaked and swollen by oil due to poor material. If any of the above conditions is found, replace the O-ring in time.
