Vertical centrifugal pump vibration and vibration reduction

Large vertical centrifugal pumps in the process of operation often have a large vibration, and the the up and

down bearings often fever and damaged, sometimes the connection parts between pump shaft and

bearingea is easy to wear and tear. Unstable operation will affect the normal water supply, so we need to

make some control to the vibration.

 

I,  the analysis of water pump vibration cause

1, 28 SLA - 10 Chinese domestic vertical water pump for an example, is transformed from horizontal pump

directly. There is 4.3m vertical height between motor base and pump base, the drive shaft bears 3 tons

weight.Compared with the horizontal pump, the vertical pump is added a middle transmission shaft with

lenght 3752mm and diameter 140mm. On the structure, except added a bearing on the middle shaft, no

other modification. The operational pressure of those 4 pcs pump is  0.7 ~ 0.85 MPa for a long time. Under

high head and large capacity conditions, as a system like this with high central of gravity and big quality, in

the high-speed rotation, the centrifugal force is big and will cause the big vibration to the pump set. In the

case of the connection stiffness of the support frame and inlet & outlet direction of water pump is insufficient,

it is easy to lead to the pump and the fittings have larger displacement, in the running of pump, which will

cause the force condition of up bearing change and vibration increase, so easy to fever. If we  correct pump

displacement and improve bearing force condition, we can reduce the pump system's vibration intensity.

II, the rigid connection between pump and the shaft. In manufacture, installation and operation, the pump

shaft and the drive shaft must be concentric, which cause water pump vibration; The vibration from motor,

drive shaft and other source are also passed directly to the pump, thus make vibration

superposition,furtherly strengthen the pump vibration. In addition, such a rigid connection increases the

external force the water pump bearing can bear, as a result the bearing is easy to fever and make bad

affection to the pump shaft.

2, the water pump reform situation

For these reasons, we adopted the following two steps.

1, strengthen rigidity of pipeline.Considering it is difficult to reinforce the pump, we adopt the way through

welding the "reinforcement" in the steel pipe of pump outlet. Along inlet and outlet direction of water,

welding  8 pcs steel plates with thickness 32mm, width 100mm each piece in the both flanges of connection

steel pipes from the water pump divergent tube and the water valve. Increase the stiffness of the steel pipe,

reduce the deformation and resistance to water pump displacement. By measured, after "reinforcement"

way, the pump displacement of point A dropped to 0.35 mm.

2, to modify the transmission system.In order to reduce the vibration of the motor and drive shaft to the

water pump, changing the rigid connection between the pump and the drive shaft to elastic connection.Use

GB4323-84 column elastic sleeve pin couplings, centrifugal pump maximum compensation displacement is

0.6 mm, the compensation Angle of 1 ° 30.In this way, the vibration from the motor and drive shaft can be

obtained compensation by elastic coupling , not directly transfer to the pump.

3, modification results

After modification, by measured, the pump vibrating velocity of original  4.3 cm/s lowers for 1.48 cm/s.

According to the vibration intensity ISO2372-1974 standard, the pumps are running in a good area and in

smooth operation. Up bearing only need normal maintenace, shaft shaft wear never happens, which of all

are proved the transformation was a success.