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What are the common errors of proportional valves? What is the reason of these errors? How to avoid them?
1. Proportional electromagnet error
① Due to the aging of wiring socket (base) of plug assembly, poor contact, and de-soldering of electromagnet lead, the proportional electromagnet cannot work (cannot pass current). At this time, the meter can be used for testing. If the resistance is found to be infinite, the lead wire can be re-soldered, the socket can be repaired and the socket can be inserted firmly.
② The errors of coil components include coil aging, coil burnout, internal disconnection of the coil, and excessive temperature rise of the coil. If the temperature of coil is too high, the output force of proportional electromagnet will be insufficient, and the rest will make the proportional electromagnet unable to work.
If the temperature of coil rises too high, you can check whether the passing current is too large, whether the insulation of enameled wire of coil is poor, whether the valve core is stuck due to dirt to find out the reasons and eliminate them one by one. For disconnection, burnout, the coil must be replaced.
③ The error of armature assembly is mainly due to the wear of the friction pair formed by the armature and the magnetic guide sleeve during use, which leads to an increase in the force hysteresis of the valve. There is also a misalignment between the push rod guide and the armature, which will also cause an increase in the force hysteresis, which must be ruled out.
④ The welding part of the magnetic guide sleeve is broken due to the weak welding or the pulse pressure of the proportional valve during use, so that the proportional electromagnet loses its function.
⑤ The magnetic guide sleeve is deformed under the impact pressure, and the friction pair formed by the magnetic guide sleeve and the armature is worn during use, resulting in an increase in the force hysteresis of the proportional valve.
⑥ The proportional amplifier is shut down, causing the proportional electromagnet not working. At this time, various components of amplifier circuit should be checked to eliminate the error of proportional amplifier circuit.
⑦ The connection between proportional amplifier and the electromagnet is broken or the connection of amplifier terminal is disconnected, so that the proportional electromagnet does not work. At this time, the broken wire should be replaced and reconnected firmly.
2. Error analysis and elimination of proportional pressure regulator
Since the proportional pressure regulator is just based on the ordinary pressurevalve, the pressure regulating handle is replaced by a proportional electromagnet. Therefore, the various errors caused by ordinary pressure valves will also cause error and troubleshooting methods of ordinary pressure valves, which are also completely applicable to the corresponding proportional pressure valves (such as the relief valve corresponding to proportional relief valve), and can be handled with reference.
Beside this there is:
① When the voltage regulation fails, you can first check the current value with electric meter to determine whether there is a problem with the control circuit of electromagnet, proportional electromagnet, or valve part, which can be treated symptomatically.
②Although the current flowing through proportional electromagnet is the rated value, but the pressure cannot go up at all, or the required pressure cannot be obtained, between proportional pilot pressure regulating valve (relief valve) and the main relief valve. The pilot-operated manual pressure-regulating valve of common pilot-operated relief valve is still retained, which acts as a safety valve here. When the regulating pressure of valve is too low, although the passing current of proportional electromagnet is the rated value, the pressure cannot rise. If the set pressure of valve is too low, the pilot flow will flow back to the tank from valve, so that the pressure cannot rise. At this time, the set pressure of valve should be adjusted to be about 1MPa higher than the maximum working pressure of valve.
③ The current flowing through proportional electromagnet has been too large, but the pressure still cannot go up, or the required pressure cannot be obtained. At this time, the coil resistance of proportional electromagnet can be checked. If it is far less than the specified value, then the coil of electromagnet is internally open circuited. If the solenoid coil resistance is normal, then the connection line connected to proportional amplifier is short-circuited. At this time, the proportional electromagnet should be replaced, the wiring should be connected, or the coil should be rewound
and installed.
④ When the pressure is changed stepwise, the pressure fluctuation of small amplitude is continuous, and the reason for the instability of the set pressure is mainly due to the adhesion of dirt between the iron core of the proportional electromagnet and the guide part (guide sleeve), which hinders the movement of the iron core. In addition, the sliding part of the main spool is stuck with dirt, which hinders the movement of the main spool. Due to the influence of these contaminants, the hysteresis is increased. In the range of hysteresis, the pressure is unstable and the pressure fluctuates continuously. Another reason is the wear of the iron core and the magnetic guide sleeve, the gap increases, and the adjusted pressure (through a certain current value) is unstable.
⑤ The pressure response is delayed and the pressure changes slowly because the air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the movement of proportional electromagnet core and the main valve core is unnecessarily hindered. In addition, air enters the system, which usually occurs when the equipment starts to run after being installed or after an occasion of long-term shutdown.
The solution is to loosen the bleed screw before the proportional pressure regulator starts to use, and let out clean air until the oil flows out. In the case of dirt blocking the damping hole, the proportional solenoid and the main valve should be disassembled for cleaning, and at the highest position of the system oil circuit where the air is easy to concentrate, it is best to set the air release valve to release air or loosen the pipe joint to release air.
⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.
⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.
⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.
⑥Two faults of electro-hydraulic proportional relief valve
a. When the rated current (50mA) is input to the coil, the inlet pressure cannot reach the rated working pressure (21MPa), but is 2-6MPa lower than the rated pressure. The reason is: after long-term use, due to the loosening of the fastening screws of the magnetic gap adjustment gasket, the magnetic gap increases, and the magnetic resistance of the magnetic gap (air gap) in the magnetic circuit is very large.
F=k(iN/Rm)2S
where k-constant;
i——the coil input current;
N - the number of turns of the coil;
Rm - magnetoresistance;
S - the cross-sectional area of the magnetic circuit.
It can be seen that as long as the magnetic gap is slightly increased, the reluctance Rm increases significantly, and the electromagnetic force F decreases in a square relationship. The hydraulic clearance increases, the pressure upstream of the nozzle decreases, so the pressure in the upper chamber of the main spool decreases. The force added by reduced pressure and weak spring in the upper chamber of the main valve decreases, so that the opening pressure of the main spool decreases, that is, the inlet pressure decreased, and the maximum pressure (21MPa) could not be reached.
Solution: Appropriately increase or decrease the thickness of the magnetic gap adjustment gasket, tighten the fastening screws of the magnetic gap adjustment gasket, and reduce the magnetic gap, which can increase the inlet pressure. The initial setting of the magnetic gap should be 0.89 ~ 0.94mm.
b. When the input current of the coil is zero, the initial pressure of the valve is too high (4-7MPa). Normally, the initial pressure should be about 1MPa. The minimum set pressure mainly depends on the initial gap 8 of the nozzle baffle. The normal gap is 0.1 to 0.13 mm. If it is too small, the initial pressure will be too high.
3. Error analysis and elimination of proportional flow valve
①The flow cannot be adjusted, and the throttling adjustment function is invalid. In addition to the error analysis and troubleshooting method of speed control valve, there are the following two points: a. Proportional electromagnet failed to energize.
The reasons are: aging of the proportional electromagnet socket and poor contact; unsoldering of the electromagnet lead; wire breakage inside the coil, you can refer to the above "(1) Proportional electromagnet error" method for troubleshooting.
b. Proportional amplifier error. Same as ①, ⑤, ⑥ in the above (2).
②The adjusted flow is unstable. The flow adjustment of the proportional flow valve is reached by changing the current flowing into its proportional electromagnet. When the input current value remains unchanged, the adjusted flow rate should remain unchanged. But in fact, the adjusted flow rate (when the same signal value is input) often changes in the working process, which is caused by the increase of the force hysteresis. Hysteresis means that when the same signal (current) value is input, the maximum change value of the output flow (or pressure) is caused when the same current signal value is passed due to different input directions (forward and reverse directions).
The factors affecting the force hysteresis are mainly caused by the existence of radial unbalanced force and mechanical friction. Then 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 is reduced, and the natural change of the adjusted flow is small. The following measures can be taken specifically:
a. Minimize the wear of the armature and the magnetic guide sleeve.
b. The push rod guide rod and the armature should be same.
c. Pay attention to the cleaning of the oil to prevent the dirt from entering the gap between the armature and the magnetic guide sleeve and jam the armature, so that the armature can move evenly in proportion to the input current value without sudden jumping. Once the sudden jump phenomenon occurs, the output flow of the proportional flow valve will also follow the sudden jump and make the adjusted flow unstable.
d. After the magnetizing sleeve armature is worn, noticing repair, so that the gap between the two is kept within an appropriate range. These measures are quite beneficial and effective to maintain the stability of the flow rate adjusted by the proportional flow valve.
In addition, the hysteresis of proportional valve driven by the general proportional electromagnet is 3% to 7%, the hysteresis of proportional valve driven by the torque motor is 1.5% to 3%, and the proportional valve driven by the servo motor is about 1.5%. The proportional flow valve driven by the servo motor has a relatively small change in flow.
For further information about electro-pneumatic pressure regulator, please visit https://www.genndih.com/proportional-pressure-regulator.htm
1. Proportional electromagnet error
① Due to the aging of wiring socket (base) of plug assembly, poor contact, and de-soldering of electromagnet lead, the proportional electromagnet cannot work (cannot pass current). At this time, the meter can be used for testing. If the resistance is found to be infinite, the lead wire can be re-soldered, the socket can be repaired and the socket can be inserted firmly.
② The errors of coil components include coil aging, coil burnout, internal disconnection of the coil, and excessive temperature rise of the coil. If the temperature of coil is too high, the output force of proportional electromagnet will be insufficient, and the rest will make the proportional electromagnet unable to work.
If the temperature of coil rises too high, you can check whether the passing current is too large, whether the insulation of enameled wire of coil is poor, whether the valve core is stuck due to dirt to find out the reasons and eliminate them one by one. For disconnection, burnout, the coil must be replaced.
③ The error of armature assembly is mainly due to the wear of the friction pair formed by the armature and the magnetic guide sleeve during use, which leads to an increase in the force hysteresis of the valve. There is also a misalignment between the push rod guide and the armature, which will also cause an increase in the force hysteresis, which must be ruled out.
④ The welding part of the magnetic guide sleeve is broken due to the weak welding or the pulse pressure of the proportional valve during use, so that the proportional electromagnet loses its function.
⑤ The magnetic guide sleeve is deformed under the impact pressure, and the friction pair formed by the magnetic guide sleeve and the armature is worn during use, resulting in an increase in the force hysteresis of the proportional valve.
⑥ The proportional amplifier is shut down, causing the proportional electromagnet not working. At this time, various components of amplifier circuit should be checked to eliminate the error of proportional amplifier circuit.
⑦ The connection between proportional amplifier and the electromagnet is broken or the connection of amplifier terminal is disconnected, so that the proportional electromagnet does not work. At this time, the broken wire should be replaced and reconnected firmly.
2. Error analysis and elimination of proportional pressure regulator
Since the proportional pressure regulator is just based on the ordinary pressurevalve, the pressure regulating handle is replaced by a proportional electromagnet. Therefore, the various errors caused by ordinary pressure valves will also cause error and troubleshooting methods of ordinary pressure valves, which are also completely applicable to the corresponding proportional pressure valves (such as the relief valve corresponding to proportional relief valve), and can be handled with reference.
Beside this there is:
① When the voltage regulation fails, you can first check the current value with electric meter to determine whether there is a problem with the control circuit of electromagnet, proportional electromagnet, or valve part, which can be treated symptomatically.
②Although the current flowing through proportional electromagnet is the rated value, but the pressure cannot go up at all, or the required pressure cannot be obtained, between proportional pilot pressure regulating valve (relief valve) and the main relief valve. The pilot-operated manual pressure-regulating valve of common pilot-operated relief valve is still retained, which acts as a safety valve here. When the regulating pressure of valve is too low, although the passing current of proportional electromagnet is the rated value, the pressure cannot rise. If the set pressure of valve is too low, the pilot flow will flow back to the tank from valve, so that the pressure cannot rise. At this time, the set pressure of valve should be adjusted to be about 1MPa higher than the maximum working pressure of valve.
③ The current flowing through proportional electromagnet has been too large, but the pressure still cannot go up, or the required pressure cannot be obtained. At this time, the coil resistance of proportional electromagnet can be checked. If it is far less than the specified value, then the coil of electromagnet is internally open circuited. If the solenoid coil resistance is normal, then the connection line connected to proportional amplifier is short-circuited. At this time, the proportional electromagnet should be replaced, the wiring should be connected, or the coil should be rewound
and installed.
④ When the pressure is changed stepwise, the pressure fluctuation of small amplitude is continuous, and the reason for the instability of the set pressure is mainly due to the adhesion of dirt between the iron core of the proportional electromagnet and the guide part (guide sleeve), which hinders the movement of the iron core. In addition, the sliding part of the main spool is stuck with dirt, which hinders the movement of the main spool. Due to the influence of these contaminants, the hysteresis is increased. In the range of hysteresis, the pressure is unstable and the pressure fluctuates continuously. Another reason is the wear of the iron core and the magnetic guide sleeve, the gap increases, and the adjusted pressure (through a certain current value) is unstable.
⑤ The pressure response is delayed and the pressure changes slowly because the air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the movement of proportional electromagnet core and the main valve core is unnecessarily hindered. In addition, air enters the system, which usually occurs when the equipment starts to run after being installed or after an occasion of long-term shutdown.
The solution is to loosen the bleed screw before the proportional pressure regulator starts to use, and let out clean air until the oil flows out. In the case of dirt blocking the damping hole, the proportional solenoid and the main valve should be disassembled for cleaning, and at the highest position of the system oil circuit where the air is easy to concentrate, it is best to set the air release valve to release air or loosen the pipe joint to release air.
⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.
⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.
⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.
⑥Two faults of electro-hydraulic proportional relief valve
a. When the rated current (50mA) is input to the coil, the inlet pressure cannot reach the rated working pressure (21MPa), but is 2-6MPa lower than the rated pressure. The reason is: after long-term use, due to the loosening of the fastening screws of the magnetic gap adjustment gasket, the magnetic gap increases, and the magnetic resistance of the magnetic gap (air gap) in the magnetic circuit is very large.
F=k(iN/Rm)2S
where k-constant;
i——the coil input current;
N - the number of turns of the coil;
Rm - magnetoresistance;
S - the cross-sectional area of the magnetic circuit.
It can be seen that as long as the magnetic gap is slightly increased, the reluctance Rm increases significantly, and the electromagnetic force F decreases in a square relationship. The hydraulic clearance increases, the pressure upstream of the nozzle decreases, so the pressure in the upper chamber of the main spool decreases. The force added by reduced pressure and weak spring in the upper chamber of the main valve decreases, so that the opening pressure of the main spool decreases, that is, the inlet pressure decreased, and the maximum pressure (21MPa) could not be reached.
Solution: Appropriately increase or decrease the thickness of the magnetic gap adjustment gasket, tighten the fastening screws of the magnetic gap adjustment gasket, and reduce the magnetic gap, which can increase the inlet pressure. The initial setting of the magnetic gap should be 0.89 ~ 0.94mm.
b. When the input current of the coil is zero, the initial pressure of the valve is too high (4-7MPa). Normally, the initial pressure should be about 1MPa. The minimum set pressure mainly depends on the initial gap 8 of the nozzle baffle. The normal gap is 0.1 to 0.13 mm. If it is too small, the initial pressure will be too high.
3. Error analysis and elimination of proportional flow valve
①The flow cannot be adjusted, and the throttling adjustment function is invalid. In addition to the error analysis and troubleshooting method of speed control valve, there are the following two points: a. Proportional electromagnet failed to energize.
The reasons are: aging of the proportional electromagnet socket and poor contact; unsoldering of the electromagnet lead; wire breakage inside the coil, you can refer to the above "(1) Proportional electromagnet error" method for troubleshooting.
b. Proportional amplifier error. Same as ①, ⑤, ⑥ in the above (2).
②The adjusted flow is unstable. The flow adjustment of the proportional flow valve is reached by changing the current flowing into its proportional electromagnet. When the input current value remains unchanged, the adjusted flow rate should remain unchanged. But in fact, the adjusted flow rate (when the same signal value is input) often changes in the working process, which is caused by the increase of the force hysteresis. Hysteresis means that when the same signal (current) value is input, the maximum change value of the output flow (or pressure) is caused when the same current signal value is passed due to different input directions (forward and reverse directions).
The factors affecting the force hysteresis are mainly caused by the existence of radial unbalanced force and mechanical friction. Then 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 is reduced, and the natural change of the adjusted flow is small. The following measures can be taken specifically:
a. Minimize the wear of the armature and the magnetic guide sleeve.
b. The push rod guide rod and the armature should be same.
c. Pay attention to the cleaning of the oil to prevent the dirt from entering the gap between the armature and the magnetic guide sleeve and jam the armature, so that the armature can move evenly in proportion to the input current value without sudden jumping. Once the sudden jump phenomenon occurs, the output flow of the proportional flow valve will also follow the sudden jump and make the adjusted flow unstable.
d. After the magnetizing sleeve armature is worn, noticing repair, so that the gap between the two is kept within an appropriate range. These measures are quite beneficial and effective to maintain the stability of the flow rate adjusted by the proportional flow valve.
In addition, the hysteresis of proportional valve driven by the general proportional electromagnet is 3% to 7%, the hysteresis of proportional valve driven by the torque motor is 1.5% to 3%, and the proportional valve driven by the servo motor is about 1.5%. The proportional flow valve driven by the servo motor has a relatively small change in flow.
For further information about electro-pneumatic pressure regulator, please visit https://www.genndih.com/proportional-pressure-regulator.htm