Created on:2022-03-07 10:01

Fault analysis and troubleshooting of electro-hydraulic proportional valve

Fault analysis and troubleshooting of electro-hydraulic proportional valve

1. Proportional electromagnet failure

(1) Due to the aging of the wiring socket (base) of the plug assembly, poor contact and the desoldering of the electromagnet lead, the proportional electromagnet cannot work (cannot be connected with current). At this time, the electricity meter can be used to detect. If the resistance is infinite, the lead can be welded firmly again, the socket can be repaired and plugged firmly.

(2) The faults of coil components include coil aging, coil burning, internal disconnection of coil and excessive temperature rise of coil. Excessive coil temperature rise will cause insufficient output force of the proportional electromagnet, and the rest will make the proportional electromagnet unable to work.

For excessive coil temperature rise, check whether the incoming current is too large, whether the coil enameled wire is poorly insulated, whether the valve core is stuck due to dirt, etc., find out the causes one by one and eliminate them; The coil shall be replaced in case of disconnection and burning out.

(3) The failure of armature assembly is mainly due to the wear of the friction pair composed of armature and magnetic guide sleeve, resulting in the increase of force hysteresis of the valve. In addition, the non concentricity between the push rod guide rod and the armature will also cause the increase of force hysteresis, which must be eliminated.

(4) The proportional electromagnet loses its function because the welding is not firm, or the welding part of the magnetic guide sleeve is broken under the action of the pulse pressure of the proportional valve in use.

(5) The deformation of the magnetic sleeve under the impact pressure and the wear of the friction pair composed of the magnetic sleeve and the armature during use lead to the increase of the force hysteresis of the proportional valve.

(6) The proportional amplifier is faulty, causing the proportional electromagnet to not work. At this time, check various components of the amplifier circuit to eliminate the fault of the proportional amplifier circuit.

(7) The wiring between the proportional amplifier and the electromagnet is broken or the wiring of the amplifier terminal is disconnected, so that the proportional electromagnet does not work. At this time, replace the broken wire and reconnect it firmly.

2. Fault analysis and troubleshooting of proportional pressure valve

Because the proportional pressure valve is only replacing the pressure regulating handle with proportional electromagnet on the basis of ordinary pressure valve, it will also produce various faults caused by ordinary pressure valve. The fault causes and troubleshooting methods of ordinary pressure valves are also fully applicable to the corresponding proportional pressure valves (such as the proportional overflow valve corresponding to the overflow valve), which can be handled by reference. In addition, there are several faults as follows.

(1) The proportional electromagnet has no current, which makes the voltage regulation failure. At this time, it can be analyzed according to the above "1 proportional electromagnet fault". In case of voltage regulation failure, check the current value with an ammeter to determine whether there is a problem with the control circuit of the electromagnet, the proportional electromagnet, or the valve part, and then deal with the symptoms.

(2) Although the current flowing through the proportional electromagnet is rated, the pressure can not go up at all, or the required pressure can not be obtained. Figure 166 shows the proportional overflow valve. Between the proportional pilot pressure regulating valve 1 (overflow valve) and the main overflow valve 5, the ordinary pilot manual pressure regulating valve 4 is still retained, which acts as a safety valve.

When the regulating pressure of valve 4 is too low, although the passing current of proportional electromagnet 3 is the rated value, the pressure cannot go up. If the set pressure of valve 4 is too low, the pilot flow flows back from valve 4 to the tank, so that the pressure does not increase. At this time, the set pressure of valve 4 should be about 1MPa higher than the maximum working pressure of valve 1.

(3) The current flowing through the proportional electromagnet has been too large, but the pressure still can not go up, or the required pressure can not be obtained. At this time, the coil resistance of the proportional electromagnet can be checked. If it is far less than the specified value, the internal circuit of the electromagnet coil is open; If the resistance of the electromagnet coil is normal, the wiring connecting the proportional amplifier is short circuited. At this time, replace the proportional electromagnet, connect the wiring, or rewind the coil.

(4) When the pressure step changes, the pressure with small amplitude fluctuates continuously, and the set pressure is unstable. The main reason is that there is dirt attached between the iron core and the guide part (guide sleeve) of the proportional electromagnet, which hinders the movement of the iron core. In addition, the sliding part of the main valve core is adhered with dirt, which hinders the movement of the main valve core. Due to the influence of these pollutants, the hysteresis loop increases. In the range of hysteresis, the pressure is unstable and fluctuates constantly. Another reason is the wear of the matching pair between the iron core and the magnetic sleeve, the increase of the gap, and the instability of the regulated pressure (through a certain current value).

At this time, the valve and proportional electromagnet can be disassembled for cleaning, and the pollution degree of hydraulic oil can be checked. Change the oil if it exceeds the regulations; For the excessive gap caused by core wear, resulting in the increase of force hysteresis and unstable voltage regulation, the outer diameter of the core shall be increased to maintain a good fit with the guide sleeve.

(5) The pressure response is sluggish and changes slowly. The reason is that the air in the proportional electromagnet is not discharged completely; The fixed orifice for damping and the orifice (or bypass orifice) of the main valve core arranged on the electromagnet iron core are blocked by dirt, and the movement of the proportional electromagnet iron core and the main valve core is unnecessarily hindered; In addition, air is introduced into the system, which usually occurs when the equipment starts running just after installation or when there is air mixing after long-term shutdown.

The solution is to loosen the vent screw of the proportional pressure valve just before use, and drain the air until there is oil flow m. In case of dirt blocking the damping hole, disassemble the proportional electromagnet and the main valve for cleaning, and at the highest position of the system oil circuit where the air is easy to concentrate, it is best to set a vent valve or loosen the pipe joint for venting.

(6) Two faults of CGE electro-hydraulic proportional overflow valve.

1) When the coil inputs the rated current (50mA), the inlet pressure cannot reach the rated working pressure (21MPa), but is 2 ~ 6Mpa lower than the rated pressure. The causes are; After long-term use, due to the loosening of the fastening screw of the magnetic gap adjusting gasket, the magnetic gap increases, and the magnetic resistance of the magnetic gap (air gap) in the magnetic circuit is very large. From the suction formula of the electromagnet

F=k(iN/Rm)2S

Where k is a constant; I is the coil input current; N is the number of coil turns; RM is magnetoresistance; S is the cross-sectional area of the magnetic circuit.

It can be seen that as long as the magnetic gap increases slightly, the magnetoresistance R_ It increases significantly and the electromagnetic force F decreases in a square relationship. As the hydraulic clearance increases, the pressure upstream of the nozzle decreases, so the pressure in the upper chamber of the main valve core decreases. The force added by the reduced pressure and the weak spring in the upper chamber of the main valve decreases, which reduces the opening pressure of the main valve core, that is, the inlet pressure, but cannot reach the maximum pressure (21MPa).

terms of settlement; Appropriately increase or decrease the thickness of the magnetic gap adjusting gasket, tighten the fastening screw of the magnetic gap adjusting gasket, and reduce the magnetic gap to increase the inlet pressure. The initially set magnetic gap shall be 0.89 ~ 0.94mm.

2) When the input current of the coil is zero, the initial pressure of the valve is too high (4 ~ 7MPa). Under normal conditions, the initial pressure should be about 1MPa. The minimum set pressure mainly depends on the initial clearance 8 of the nozzle baffle (see Figure 167). The normal clearance is 0.1 ~ 0.13MM. If it is too small, the initial pressure is too high.

3. Fault analysis and troubleshooting of proportional flow valve

(1) The flow cannot be adjusted, and the throttling regulation function fails. In addition to the fault analysis and troubleshooting methods of speed regulating valve, there are the following two points.

1) Proportional electromagnet failed to energize. The causes are: aging of proportional electromagnet socket and poor contact; Supporting welding of electromagnet lead; Refer to the above method of "1. Proportional electromagnet fault" for troubleshooting of short wires inside the coil.

2) Proportional amplifier failure. The same as (1), (5) and (6) in "2. Fault analysis and troubleshooting of proportional pressure valve" above.

(2) The adjusted flow is unstable. The regulation of proportional flow valve is realized by changing the current through its proportional electromagnet. When the input current value remains unchanged, the adjusted current should remain unchanged. However, the actual adjusted flow (when the same signal value is input) often changes in the working process, which is caused by the increase of force hysteresis. Hysteresis refers to the maximum change of output flow (or pressure) when passing through the same current signal value due to different input directions (positive and negative directions) when the same signal value is input.

The main factors affecting the hysteresis are the radial unbalanced force and mechanical friction. Measures such as reducing the radial unbalanced force and reducing the friction factor can reduce the influence of mechanical friction on the hysteresis. The hysteresis loop is reduced, and the adjusted flow has little change. Specific measures are as follows.

1)       Minimize the wear of armature and magnetic sleeve.

2)       Push rod guide rod and armature shall be concentric.

3)       Pay attention to the cleaning of the oil to prevent dirt from entering the gap between the armature and the magnetic guide sleeve and jamming the armature, so that the armature can move evenly in proportion with the input current value without sudden jump. Once the sudden jump occurs, the output flow of the proportional flow valve will also jump with the sudden jump, making the regulated flow unstable.

4)       After the armature of the magnetic guide sleeve is damaged, pay attention to repair to keep the gap between them within an appropriate range. These measures are very beneficial and effective to maintain the stability of the flow regulated by the proportional flow valve.

In addition, generally, the hysteresis of proportional valve driven by proportional electromagnet is 3% ~ 7%, that of proportional valve driven by torque motor is 15% ~ 3%, and that of proportional valve driven by servo motor is about 1.5%, that is, the change of flow is relatively small when driven by servo motor.

 

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