Water Pump Vibration and Its Vibration Mitigation Measures

     In the big flood, due to severe vibration of the pump unit was forced to shut down caused by "close flooded" situation is more common. Some pumping station during abnormal vibration violent vibration of the pump room glass.

According to the different disturbance, the vibration of pump unit can be divided into three categories: hydraulic vibration, mechanical vibration and electromagnetic vibration. The vibration in production is inevitable. The vibration of different types of pump units are always generated at the same time. Separately. The direct cause of these vibrations is also different. During the flood, the main source of disturbance to the abnormally severe vibration of the pump unit is the hydraulic imbalance. The reasons should be correctly analyzed according to the actual situation at that time, and the main contradiction should be grasped to take effective measures to reduce vibration.

1. The flood level is extremely high in the river and the pumping station needs to be lifted. The pump works in a saddle-shaped unstable area near the inflection point. The main features of this vibration are instability and periodic repetitions within moments. If the frequency of this cycle and the system's oscillation frequency of the time, it is possible to induce resonance and cause more serious damage, the damping measures are:

(1) clear the local blockage, clear the diversion channel such as water diversion, inflow and outflow, on the one hand, improve the flow regime, on the other hand, reduce the pumping head as much as possible.

(2) For the fully adjustable pump can change the blade angle, reduce or increase the blade angle may make the pump work to avoid the inflection point. Adjust the angle of small leaves can also improve the pump Q ~ H performance curve, reduce the unstable work area.

(3) Use variable speed adjustment method under the possible conditions to change the working point of the pump to stable working area.

(4) small and medium-sized pump can be set bypass or bypass valve, control the pump outlet flow is not less than the unstable working flow.

2. The flood level is extremely high in the outer river, and some are even 2 to 3 meters high. In this case, the pump is started and the air in the water outlet channel is difficult to be discharged and the water holding capacity is also greatly reduced. Repeated compression of the air expansion, causing pressure pulsation, induced vibration of the unit, the crew will not be able to start serious. According to the actual project situation, to divert, improve or increase the outlet of the effluent facilities to improve exhaust speed and ability to seize gas, as far as possible to shorten the start-up process.

3. Front pool water level is too low, changing the water flow pattern, the formation of water entrainment surface vortex and Coanda vortex into the impeller studio after being cut by the blade caused by vibration, the frequency is proportional to the number of blades, and often accompanied Have a lot of noise. Usually diversion, set the partition and other emergency measures to effectively reduce vibration.

4. Fluctuations in the flood outside the river are large, the flow pattern is disorderly, wave pressure waves are reflected into the water runner and lead to unit vibration. Active and effective outlet anti-wave and wave-stabilizing measures should be actively taken.

5 waterlogging water (may diffuse through the trash rack) impulse foreign matter, into the runner and impeller studio, resulting in partial blockage, the formation of asymmetric flow field in the triggering of hydraulic vibrations may also aggravate arcuate gyratory mechanical vibration . Timely discovery of thorough decontamination, you can effectively vibration.

6. Because the working point of the pump is far away from the normal working range, the pump itself has an excessively large required Naphthic residual Δhr, or cavitation occurs due to the deterioration of the influent flow condition, causing the vibration of the pump unit. Cavitation vibration frequency higher, up to tens of thousands of times per second, accompanied by strong noise, the vibration reduction measures are as follows:

(1) The use of variable angle, variable speed or bypass method to adjust the pump conditions, reduce the pump required NPSH Δhr, to avoid cavitation operating conditions.

(2) to take practical measures to diversion, water diversion and other measures to improve the flow pattern.

(3) consider the pump outlet pipe (or flow) in the water into the inlet pipe (or flow), but also set up another pressure pump device, the nozzle with a ring mixer to improve the pump inlet Pressure, to eliminate or reduce cavitation and its vibration, the nozzle can be used for a small nozzle, the pump can consider the use of multiple nozzles. The length of the mixing section, the position of the nozzle and the flow rate injected shall be reasonably determined according to the pilot pressure, the head of the booster, the flow velocity at the nozzle mouth, the main velocity and the number of nozzles.

(4) Replenishment (0.4 ~ 1%) of the gas at the pump inlet (calculated as the volume flow rate) can greatly reduce the cavitation strength of the pump and significantly reduce the erosion, noise and vibration. Specific qi mode and location, should be based on cavitation phenomenon and the relevant engineering experience to determine. 5. If possible, consider the main impeller in the axial flow pump set before the guide wheel, on the one hand can be rectified, on the other hand to provide energy for the import of the main impeller to improve its cavitation performance, eliminate or reduce cavitation vibration.

7. Foreign material entrained in the waterlogging water is clogged and adsorbed on the rotating impeller. In addition to the aforementioned asymmetric hydraulic vibrations of the flow field, it will also destroy the static and dynamic balance of the rotor and lead to mechanical imbalance disturbance Vibration phenomenon. Stop pumping part of the water after the backwash back to boot, the vibration will be greatly reduced.

8. Under the effect of long-term flooding and waterlogging, if the pump house is unevenly subsided, its inclination may cause asymmetric hydraulic flow in the flow field due to the unevenness of the impeller clearance. Due to the uneven bearing clearance, Dry friction and vibration and other mechanical vibration, and due to uneven air gap generated electromagnetic tension imbalance vibration. The corresponding damping measures are:

(1) rectification of the main plant pumping station.

(2) For large vertical axial-flow pump units, the vertical concentricity, horizontalness, rotor verticality, swing, center, and motor of the fixed components of the unit can be re-measured based on the inflow passage within the allowable adjustment range The magnetic field center and bearing clearance, blade clearance and air gap.

9. At present, most pumping station projects have serious aging problems. Under these circumstances, long-term floods may cause unbalanced electromagnetic tension due to faults such as short circuit of rotor windings caused by insulation damage. After confirmation can take the appropriate repair measures.

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