1. The higher the working pressure of the multistage centrifugal pump, the greater the axial force of the pump rotor, and the water pump rotor will move to the low pressure side severely.
If the axial force is not balanced by the balancing device and directly acts on the impeller rotating at high speed, it will generate a great resistance, which is easy to overload or burn the motor.
Therefore, when overhauling, you must master the principle of pump balance.
During the operation of the multi-stage centrifugal pump, the balance disc is in direct contact with the balance ring and friction occurs. The limited gap between them is about 0.10-0.20mm, and this gap is constantly changing. A balance chamber is formed between the balance disc and the balance ring, and the pressure is generated in the balance chamber during high-speed rotation, and the direction is opposite to the axial force, so as to achieve the purpose of balance.
Pay attention to whether there is any deflection of the balance plate and the balance ring. If the deflection occurs, a large amount of leakage will occur in the balance chamber during operation. The balance chamber cannot form the axial force required by the balance rotor. If it is greater than 0.03mm, it should be carefully scraped and ground until the surface is in precise contact, and the larger the contact surface, the better.
2. The balancing holes on the multi-stage centrifugal pump and the balancing holes on the impeller are also very important, and serve to reduce the pressure on the balancing disk.
If the balance pipe and the balance hole are blocked, the pressure on the balance plate increases, and the load also increases, which may overload or burn the motor. Therefore, the balance pipe and the scale and debris in the hole must be unblocked during maintenance.
3. Installation should pay attention to problems
(1) When the pump is disassembled, it is required to mark the tie rod bolts, pump casing, impeller, guide vane and other accessories, and measure the original length of the tie rod.
After assembly, the sequence and position of the impeller, pump casing, guide vanes, etc. should be corresponding to the original position, the position is basically the same as the original, and the length of the tie rod is equal. If it is a new shaft, install it according to the requirements on the drawing.
(2) When the rotor is installed, the rotor needs to be measured for radial runout. The most radial runout should not exceed 0.06mm. The radial runout at the outer seal ring of the impeller should not exceed 0.06mm. Many, can also be processed by the above method.
If it exceeds a lot, you must remove the impeller and shaft sleeve, measure the pump shaft bending and bending direction, you can straighten, or replace the new shaft.
4. Pump packing too tight, packing gland tilt and packing selection should also be paid attention to.
Loosen the packing gland, adjust the packing gland, and tighten the bolts symmetrically, not too tightly.
Graphite asbestos packing is recommended for boiler feed water pump, which has good strength, water resistance and self-lubrication.
Other chemical materials can meet the requirements by selecting appropriate fillers in terms of corrosion resistance and strength. The cooling water pipe of the packing water cooling chamber cannot be mistakenly connected to the balance pipe or the water seal pipe, so as not to cause the short life of the packing, and may also cause the pump to be overloaded.
5. The switching sequence and power supply of the outlet valve of the multistage centrifugal pump will also cause the motor to be overloaded.
The outlet valve of the centrifugal pump is fully open, the resistance of the outlet pipeline is too small, and the flow rate is too large, thereby causing overload. The outlet valve should be closed.
