The drive of ordinary centrifugal pump is to connect the impeller shaft with the electric shaft through the coupling, so that the impeller and the motor rotate together, and the shield pump is a kind of unsealed pump. Both the pump and the drive motor are sealed in a pressure vessel filled with pumped medium. This pressure vessel has only static seal, and a wire group provides the rotating magnetic field and drives the rotor. This structure cancels the rotary shaft sealing device of the traditional centrifugal pump, so it can be completely leak free.
The shield pump connects the pump and the motor. The rotor of the motor and the impeller of the pump are fixed on the same shaft. The shield sleeve is used to separate the rotor and the stator of the motor. The rotor operates in the medium being transported, and its power is transmitted to the rotor through the stator magnetic field.
In addition, the manufacture of canned motor pump is not complicated, and its hydraulic end can be designed and manufactured according to the commonly used structure and relevant standards and specifications of centrifugal pump. So in the daily use of the shield pump failure, how should we repair it? Let’s follow the EVP vacuum pump manufacturer to learn about the maintenance experience.
1. Analyze and judge the wear condition of the parts when disassembling the pump:
A. The pump body ring and impeller ring are worn, indicating that the inner diameter of the bearing is excessively worn, and the bearing needs to be replaced.
B. The front cover plate of impeller and pump body are worn, indicating that the front bearing end face is excessively worn, and the bearing needs to be replaced.
C. The inner diameter of the bearing is worn, the shaft sleeve and thrust disk are worn and the color turns black, which indicates that the air in the motor cavity is not discharged completely, there is no liquid or idling, so it is necessary to replace the spare parts.
D. The front bearing end face and thrust disk surface are worn, and the rear bearing and thrust disk are not worn, indicating that the shaft thrust is forward and the pump is in the state of liquid shortage. Check whether the inlet filter is blocked, whether the system has insufficient liquid supply, and whether the pump has cavitation.
E. The end face of the rear bearing and the surface of the thrust disk are worn, and the front bearing and the thrust disk are not worn, indicating that the shaft thrust is backward, the flow may be too large, and check whether the outlet valve is opened too large.
F. The shield sleeve of stator and rotor is worn, but the inner diameter of bearing does not exceed the limit value, indicating that there is foreign matter entering the motor cavity, and check whether the inlet filter is damaged.
2. According to the vibration and noise analysis of the pump:
A. There is vibration in the pump. The vibration source comes from the two bearings of the motor. It means that the bearings are worn. It is necessary to check the wear condition of the bearings.
B. The pump has vibration. The vibration source comes from the pump body. The outlet valve closes and the pump pressure is normal, but the indication of the pressure gauge drops suddenly when the valve is opened, and the operating current is lower than the normal value, indicating the pump cavitation state. The height of the inlet liquid level needs to be increased to meet the following requirements: NPSH of the device = 1.3 × NPSH of the pump.
C. Pump vibration, noise, TRG indicator in the red area, low pressure on the pump outlet pressure gauge, pump not up to indicate pump reversal, need to adjust the power line phase sequence.
3. According to the indication analysis of TRG (bearing monitor) table:
A. The indicator in the yellow area or red area (other conditions are normal) indicates that the bearing is worn and needs to be replaced.
B. After the pump is turned on, the meter has no reaction, but the outlet pressure and current are all normal, indicating that the meter is damaged and needs to be replaced.
Standard for routine maintenance of canned motor pump:
(1) check whether the electric pump has abnormal vibration.
(2) check whether the indication of TRG table of canned motor pump is within the allowable range.
(3) check whether the liquid circulation pipeline and cooling system pipeline are smooth and meet the design requirements.
(4) check whether the pressure, flow and temperature of each part are normal on time, and make records.
(5) regularly check whether the bolts at the fastening parts are loose and the vibration after loosening.
(6) check the sealing parts for running, emitting, dripping and leaking.
(7) make sure the equipment label is clear, the surrounding environment is clean, and the equipment surface is free of dust, oil dirt and sundries.