Overloads in multi-stage pump operation and solutions

1, the higher the working pressure of the multi-stage centrifugal pump, the greater the axial force of the pump rotor, the pump rotor will be to the low-pressure side of the faltering. Axial force if there is no balancing device to balance, acting directly on the high-speed rotation of the impeller, will generate a lot of resistance, easy to make the motor overload or burn out.

Therefore, when overhauling, it is necessary to master the principle of pump balancing. Multi-stage centrifugal pump in operation, the balance plate in direct contact with the balance ring and friction, which has a small gap, in 0.10-0.20 or so, and this gap is constantly changing, automatically balance the axial force of the rotor, in the balance plate and balance ring between the formation of a balance chamber, in the high-speed rotation of the balance chamber pressure, the direction of the opposite of the axial force, so as to achieve the purpose of balance. This creates a pressure in the balancing chamber during high speed rotation in the opposite direction to the axial force, thus achieving the purpose of balance. So how to play the role of the balancing disk?

(1) Adjust the gap between the balancing rings within the range of 0.10-0.20mm during maintenance.

(2) pay attention to the balance plate and balance ring each other flat and no skew phenomenon, if skewed, the balance chamber in operation will produce a lot of leakage, the balance chamber can not form the axial force required to balance the rotor, therefore, in the assembly of the maximum skew not more than 0.03mm, should also be carefully scraped, grinding, until the surface precision contact, the larger the contact surface the better.

2, multi-stage centrifugal pump on the balance tube and impeller balance of the small hole is also very important, as the role of reducing the pressure of the balance plate. If the balancing tube and balancing hole are blocked, the pressure on the balancing disk increases, the load also increases, and it may overload or burn the motor, therefore, the balancing tube and hole must be cleared of scale and debris when overhauling, so that it is unobstructed.

3, installation in the overhaul should pay attention to the problem

(1) When the pump is disassembled, it is required that the tie bolt, pump casing, impeller, guide vane and other accessories be marked with a good number, and the original length of the tie bar is measured at the same time. After assembly so that the order and position of the impeller, pump casing, guide vane, etc. corresponds to the original position, the position is basically the same as the original, and the tie rod length is equal. If the shaft is new, it is installed according to the requirements on the drawing.

(2) At the time of rotor installation, the rotor needs to be measured for radial runout, the most radial runout should not exceed 0.06mm, if it is within 0.10mm, the rotor can be turned to 0.06-0.10mm, so that it meets the requirements. Impeller outer circle main seal at the radial runout also shall not exceed 0.06mm, if more than not too much, also can be used to deal with the above method. If more than a lot, the impeller and sleeve must be removed, measuring the pump shaft curvature and bending direction, you can straighten, or replace the new shaft.

4, the pump packing pressure is too tight, packing gland tilt and the selection of packing should also pay attention to. Loosen the packing gland, set the packing gland right, and tighten the bolts symmetrically, not too tight. Boiler feed pumps are recommended to use graphite asbestos packing, which has better strength, water resistance and self-lubricating properties. Other chemical materials choose suitable packing in terms of corrosion resistance and strength to meet the requirements. The cooling water pipe of the water-cooling chamber of the packing cannot be mistakenly connected to the balance pipe or water seal pipe, which may cause short packing life and may also cause overloading of the pump.

5, multi-stage centrifugal pump outlet valve switching sequence and power supply can also cause motor overload. Centrifugal pump export valve fully open, the export pipe resistance is too small, the flow is too large, thus leading to overload, the export valve should be closed, multi-stage centrifugal pump start according to the current size slowly open the export valve. Three-phase power supply is also caused by the lack of phase tripping, should check the three-phase power supply, and newly connected to the three-phase power supply.