Causes of water pump vibration and results of transformation

Vibration causes and transformation results of water pumps

A water pump is a machine that transports liquids or pressurizes liquids. It transfers the mechanical energy of the prime mover or other external energy to the liquid to increase the energy of the liquid. It is mainly used to transport liquids including water, oil, acid and alkali liquids, emulsions, suspensions and liquid metals, etc. It can also transport liquids, gas mixtures and liquids containing suspended solids. The technical parameters for measuring the performance of water pumps include flow, suction, head, shaft power, water power, efficiency, etc.; according to different working principles, it can be divided into positive displacement water pumps, vane pumps and other types. Positive displacement pumps use the change in the volume of their working chambers to transfer energy; vane pumps use the interaction between the rotating blades and water to transfer energy, and there are centrifugal pumps, axial flow pumps and mixed flow pumps.

I. Analysis of the causes of water pump vibration

1. For example: The Chinese-made vertical water pump 28SLA-10 is directly modified from a horizontal pump. The vertical height between the motor base and the water pump base is 4.3m, and the transmission shaft system weighs 3t. Compared with the horizontal pump, it adds an intermediate transmission shaft with a length of 3752mm and a diameter of 140mm. In terms of structure, except for installing a bearing on the intermediate transmission shaft, no modification has been made. The operating pressure of these four water pumps has been 0.7-0.85MPa for a long time. Under the working conditions of high head and large flow, such a system with a high center of gravity and large mass rotates at high speed, and the centrifugal force generated is very large, which will cause greater vibration of the unit. In addition, the connection rigidity between the bracket and the water inlet and outlet directions of the water pump is not enough, resulting in a large displacement of the water pump and various connecting parts. The displacement of the water pump during operation causes the stress condition of the upper bearing to change, the vibration increases, and it is easy to heat up. If the displacement of the water pump is corrected and the stress condition of the bearing is improved, the vibration intensity of the system can be reduced.

2. The water pump and the transmission shaft are rigidly connected. Due to manufacturing and installation reasons, the pump shaft and the transmission shaft are concentric during operation, causing the water pump to vibrate; the vibration generated by other sources such as the motor and the transmission shaft is also directly transmitted to the water pump, forming a superposition of vibration, further increasing the vibration of the water pump. In addition, this rigid connection increases the external force on the bearing of the water pump, causing the bearing to heat up easily and affecting the pump shaft.

2. Renovation

For the above reasons, we took the following two steps to transform.

1. Strengthen the rigidity of the pipeline. Considering that it is difficult to reinforce the water pump, the method of welding reinforcement ribs on the steel pipe at the outlet of the water pump is adopted. Along the inlet and outlet direction, the flanges at both ends of the connecting steel pipe between the outlet expansion pipe of the water pump and the outlet valve are welded with 8 steel plates with a thickness of 32mm and a width of 100mm. Increase the rigidity of the steel pipe, reduce the deformation, and resist the displacement of the water pump. After measurement, after reinforcement, the displacement of point A of the water pump is reduced to 0.35mm.

2. Transform the transmission system. In order to reduce the transmission of vibration of the motor and transmission shaft to the water pump, the rigid connection between the water pump and the transmission shaft is changed to an elastic connection. Using GB4323-84 elastic sleeve pin coupling, the maximum compensation displacement of the centrifugal pump is 0.6mm, and the compensation angle is 130?. In this way, the vibration of the motor and the transmission shaft can be compensated by the elastic coupling and will not be directly transmitted to the water pump.

3. Renovation results

After the renovation, it was measured that the vibration of the water pump was reduced from 4.3cm/s before the renovation to 1.48cm/s. According to the vibration intensity standard ISO2372, it can be determined that the water pump is in the excellent zone. At the same time, the water pump runs smoothly, the upper bearing only needs normal maintenance, and the pump shaft is no longer worn, indicating that the renovation is successful.

Brief description of hydraulic ejector

Structure and advantages:

The hydraulic ejector consists of a body, a cover, a nozzle, a nozzle seat plate, a guide plate, a diffuser and a one-way valve. The nozzle adopts a multi-nozzle structure to obtain a larger water vapor contact area, which is conducive to heat exchange and obtains a better vacuum effect. The nozzle seat plate is precisely processed with high precision to prevent the spray water flow from deflecting and reduce the pumping efficiency. The whole device has a compact and precise structure and high strength. It is used in vacuum evaporation systems. Since the condensation function of the condenser and the exhaust function of the vacuum pump can be combined in one device and completed at the same time, the process flow is greatly simplified. Compared with the original device using a vacuum pump and an old condenser, it can save equipment such as vacuum pumps, condensers, and water distributors. It also has the following advantages:

(1) The hydraulic ejector is small in size, light in weight, and compact in structure. It has relatively high efficiency and consumes less power than the vacuum pump system, saving investment.

(2) It is easy to operate and maintain, and does not require full-time personnel to manage it. Since there is no mechanical transmission part, it has low noise and does not consume lubricating oil.

(3) It can be installed outdoors at the bottom, occupying a small area, saving factory building area and installation costs.

The hydraulic ejector is a mechanical device with three effective functions: vacuuming, condensing, and drainage. It uses a certain pressure of water to flow symmetrically and evenly into a nozzle with a certain inclination and spray out, converging at a focus. Since the speed of the jet water is very high, negative pressure is formed around to generate vacuum in the chamber. In addition, since the secondary steam is in direct contact with the jet water flow, heat exchange is carried out, and most of the steam condenses into water. A small amount of uncondensed steam and non-condensable gas are also mixed and squeezed by the high-speed jet water flow, and are discharged through the diffuser, so that a higher vacuum is formed in the chamber. The hydraulic ejector is widely used, mainly used in vacuum and evaporation systems, for vacuum pumping, vacuum evaporation, vacuum filtration, vacuum crystallization, drying, deodorization and other processes. It is a widely needed equipment in sugar making, pharmaceutical, chemical, food, salt making, monosodium glutamate, milk, fermentation, and some light industry and defense departments. However, the current manufacturers of hydraulic ejectors are small and the varieties are not complete. For this reason, after continuous improvement of design in recent years, the multi-jet resistance and steam ring (guide plate) structures are adopted, and the water is fed by a multi-stage pump. The low-position installation only requires an installation height of 4.5 meters, which improves and improves its working performance. It has certain advancement and is an innovation of vacuum condensation equipment.