A question about shielded pumps

The principle behind the TRG gauge for shielded pumps is as follows: A coil is installed above and below the stator coils of the shielded pump (which can be thought of as being at the top and bottom of a horizontally placed cylinder). These two coils are connected to each other but have opposite phases. When the rotor rotates, if the “center line of the rotor” coincides with the “geometric midpoint of the two coils, which is also the midpoint of the pump bearings”, then the upper and lower coils generate voltages of equal magnitude but opposite phases; these voltages cancel each other out, resulting in no current flow, and the TRG gauge indicates a value of 0, i.e., it is at the lowest point in the green zone. When the bearings wear out, the center line of the rotor shifts, and the induced currents in the upper and lower coils are no longer of equal magnitude. After certain processing, a current is generated, and the TRG pointer changes accordingly based on the magnitude of this current. As long as the value remains within the green zone, the wear caused by the bearings is acceptable; the rotating rotor will not damage the shielding sleeve, and the pump can continue to operate. However, when the pointer moves into the yellow zone, it indicates that the wear is worsening, and maintenance is necessary, including the replacement of the bearings. Once the pointer reaches the red zone, it means that the rotor has damaged the shielding sleeve, and it is necessary to disassemble the pump to check whether the shielding sleeve is still intact. If it is damaged, it must be sent back to the factory for repair. This gauge plays a vital role in the routine maintenance of shielded pumps. As can be seen from the above, the TRG gauge only detects radial wear of the bearings, as it is only after radial wear occurs that a deviation in the rotor’s centerline is created; the gauge is unable to detect axial displacement of the rotor. However, if the axial displacement is excessive, it can cause wear in certain parts of the pump (not detailed here), leading to an increased current level. If there is a current protection device in place, it will trigger a shutdown, but this will not cause damage to the pump. Generally, replacing the thrust disc and bearings resolves the issue. In summary: The TRG gauge and ammeter serve as two means to determine whether a shielded pump is operating properly. Based on the readings from the TRG gauge, it can be determined that: A. If the gauge indicates a value in the yellow or red zone (with all other parameters normal), this indicates that the bearings are worn out and need to be replaced. B. The gauge indicates a green area, but there is vibration at the motor side bearing; upon disassembly, it was found that the bearing was excessively worn, indicating that the module is faulty and cannot provide accurate readings, so it needs to be replaced. C. When the pump is started for the first time or after the power cable is reconnected (that is, when there is no wear on the bearings), if the gauge indicates the red zone, it means the pump is running in reverse; the phase sequence of the power cable needs to be adjusted. D. If there is no reaction on the gauge after starting the pump and the motor emits only a faint humming sound, it indicates that one phase is missing in the pump’s power supply; the electrical wiring needs to be checked. E. If there is no response from the gauge after the pump is started, but the outlet pressure, current, and everything else are normal, it indicates that the gauge is damaged and needs to be replaced with a new one. F. If the gauge reading is high and not at zero after the pump is started (assuming there is no bearing wear), disconnect the U, V, and W wires connected to the module from the terminals; once the pump’s pointer is at zero, it indicates that the voltage is too high, there is a magnetic field, or some frequency conversion device is interfering with the gauge. This issue can be resolved by replacing the frequency conversion module.

When a shielded pump runs in reverse, the hydraulic effects of its impeller are completely mismatched with those of the pump casing; both axial and radial forces become unbalanced, which results in significant vibration.

When a shielded pump runs in reverse, the axial force and the radial force are unbalanced, and the axial movement occurs in the opposite direction; as a result, vibration becomes very severe.