Vibration is an important index to evaluate the operational reliability of water pump units. This article will explain the hazards, causes and elimination measures of the vibration of the pump unit.

The harm of excessive vibration of pump

The main hazards of excessive vibration are:

Vibration causes the pump unit to not operate normally;

Cause vibration of the motor and pipeline, causing damage to the machine;

Cause damage to bearings and other parts;

Cause loose connection parts, foundation cracks or motor damage;

Cause loosening or damage to the pipes or valves connected to the water pump;

There are many reasons for pump vibration, such as vibration and noise.

Causes of pump vibration

There are many reasons for pump vibration:

The shaft of the pump is generally directly connected to the drive motor shaft

The dynamic performance of the pump and the dynamic performance of the motor interfere with each other;

There are many high-speed rotating parts, and the dynamic and static balance cannot meet the requirements;

The parts that interact with the fluid are greatly affected by the water flow;

The complexity of fluid movement itself is also a factor that limits the dynamic stability of pump dynamic performance.

Self-examination of machine pump vibration troubleshooting

1.Mechanical aspect

First determine whether the foundation is fixed, whether the housing bolts and impeller lock nut are loose; then whether the coupling is well aligned and whether the main shaft is bent; whether the pump and motor bearings run out of the outer ring, that is, whether the bearing seat hole is worn and the clearance is too large ; Look at whether there are foreign objects in the impeller and whether the support is not firm and cause the pipeline to vibrate; in addition, look at the condition of the material and whether the viscosity is too high; determine whether the suction pipe or filter is blocked and whether it extends too shallowly into the liquid.

2.Hydraulic

Uneven flow rate and pressure distribution at the inlet and outlet of the pump, pressure pulsation of the working fluid at the inlet and outlet of the pump, liquid bypass, drift and de-flow, non-rated working conditions and pump cavitation caused by various reasons, are common causes of pump unit vibration s reason. The rapid changes in pressure in the water pipeline and the effect of water hammer caused by dynamic transition processes such as pump startup and shutdown, valve opening and closing, changes in working conditions, and emergency shutdown of accidents, etc., also often cause vibrations in the pump room and unit.

3.Electrical aspect

The motor is the main equipment of the unit. The internal magnetic force of the motor and the imbalance of other electrical systems often cause vibration and noise. For example, in the operation of an asynchronous motor, the radial alternating magnetic pull between the stator and the rotor generated by the interaction of the stator and rotor tooth harmonic magnetic flux, the large synchronous motor is inconsistent in the stator and rotor magnetic center or the air gap difference in all directions exceeds the allowable Deviations, etc., may cause periodic vibration and noise of the motor. Check whether the three phases are balanced when the motor is running, and check whether the power frequency is stable.

4.Hydraulics

The unreasonable design of the unit inlet flow passage or the unmatched unit, improper submerged depth of the pump, and unreasonable start and shutdown sequence of the unit will deteriorate the water inlet conditions, generate vortexes, induce cavitation or aggravate the vibration of the unit and pump room. When the unit that uses the vacuum interrupter to break the siphon is started, if the air entrainment in the hump section is difficult, the siphon time is too long; the design of the shutter door of the shutter door is unreasonable, and it opens and closes constantly, constantly hitting the door seat; Uneven subsidence of the foundation of the pump and motor or poor rigidity of the foundation will also cause the unit to vibrate.

5.Process

Check whether the pump is running under the design department: head, flow, water temperature, vacuum suction height, etc. (existing in cavitation conditions); check whether the pump inlet and outlet valves are intact; whether the water is entrained with air or other gases, and the pump outlet pipeline Whether there is a phenomenon that the air is not exhausted and whether the pump inlet is leaking.

Ways to eliminate pump vibration

1.Eliminate vibration from design and manufacturing

(1) Points to note in mechanical structure design

Shaft design

Increase the number of support bearings of the drive shaft, reduce the support spacing, reduce the shaft length within an appropriate range, appropriately increase the diameter of the shaft, and increase the rigidity of the shaft;

When the speed of the pump shaft gradually increases and is close to or an integer multiple of the natural vibration frequency of the pump rotor, the pump will vibrate violently. Therefore, the natural frequency of the drive shaft should be designed to avoid the angular frequency of the motor rotor;

Improve the quality of shaft manufacturing and prevent quality eccentricity and excessive geometric tolerances.

Selection of sliding bearings

In chemical pumps such as liquid hydrocarbons, the sliding bearing materials should be materials with good self-lubricating properties, such as polytetrafluoroethylene;

In the deep well hot water pump, the diversion bushing is filled with polytetrafluoroethylene, graphite and copper powder, and its structure is reasonably designed to make the sliding bearing fixed and reliable;

The impeller seal ring and the pump body seal ring adopt a friction pair with a small friction factor, such as M20lK graphite material and steel;

Limit the maximum speed and improve the bearing capacity of the bearing and the stiffness of the bearing seat.

Use a stress relief system

For pumps that deliver hot water, the structural stress between the connecting parts caused by the deformation of the pump body should be released during the design, such as adding bolt sleeves on the pump body anchor bolts to avoid the direct pump body and the rigid foundation contact.

(2) Precautions for hydraulic design of water pump

Reasonable design of pump impeller and flow channel

Reasonably design the impeller and flow channel of the water pump to reduce the occurrence of cavitation and leakage in the impeller. Reasonably choose the number of blades, blade exit angle, and blade width

The parameters such as the squeezing coefficient of the blade outlet and the blade outlet can eliminate the hump of the head curve. The distance between the outlet of the pump impeller and the tongue of the volute. According to some data, when the value is one-tenth of the outer diameter of the impeller, the pulsating pressure is the smallest. The outlet edge of the blade is inclined (such as about 20°) to reduce Little shock. Ensure the clearance between the impeller and the volute and improve the working efficiency of the pump. At the same time, optimize the design of related flow channels such as the water outlet channel of the pump to reduce vibration caused by hydraulic loss. Reasonably design the suction chamber at the inlet section of various pumps and the mechanical structure of the compression stage to reduce pressure pulses, ensure the stability of the flow field, improve the working efficiency of the pump, reduce energy loss, and increase pump vibration Stability of dynamic performance.

Cavitation vibration

This is a very important part of pump vibration. In order to ensure that there is no air accumulation in the suction pipe or pressurized water pipe, no part of the suction pipe should be higher than the inlet of the pump. In order to reduce the pressure pulsation at the water inlet, the diameter of the suction pipe should be an order of magnitude larger than the diameter of the pump inlet, so that the water flow has a certain contraction at the pump inlet, so that the flow rate distribution is more uniform, and there should be a section before the pump inlet. Straight pipe, the length of the straight pipe is not less than 10 times the pipe diameter. And pay attention to creating good water inlet conditions, and the water flow in the inlet pool should be stable and even to eliminate the vibration accompanying the Carmen vortex.

Basic design

The weight of the foundation should be more than three times the combined weight of the pump and motor. The foundation of the water tank should have considerable strength. The motor support and the foundation should preferably be integrated or surface contacted, and set between the pump and the support. Vibration isolation pads or vibration isolators. In addition, the damping material is used to connect the pipelines to reduce pipeline layout and eliminate vibration caused by elastic contact and hydraulic loss.

2.Eliminate vibration from installation and maintenance

(1) Shaft and shaft system

Before installation, check whether the water pump shaft, motor shaft, and transmission shaft are bent, deformed, or eccentric in quality. If so, it must be corrected or further processed. Check whether the drive shaft in contact with the guide bearing is energized by bending and rubbing against the bearing bush or bushing. If the monitoring shows that the shaft has actually been bent, correct the pump shaft. At the same time, check the end clearance value of the shaft. If the value is too large, it indicates that the bearing is worn and needs to be replaced.

(2) Impeller

Check whether the dynamic and static balance is qualified.

(3) Coupling

Check whether the bolt spacing is good, and the combination of elastic pin and elastic ring cannot be too tight. Whether the fit between the inner hole of the coupling and the shaft is too loose, if it is too loose, you can use methods such as spraying to reduce the inner diameter of the coupling until it reaches the size required by the transition fit, and then fix the coupling on the shaft.

(4) Sliding bearing

Determine whether the gap value meets the standard and whether the lubrication is good. Improve the pump's bearing bush inspection and repair process level, strictly follow the cycle procedure of scraping the bushes first, grinding later, and scraping the bushes again to ensure that the contact area between the bushing and the journal meets the prescribed standards:

The clearance value between the pump journal and the bearing is qualified by means of replacing the front and rear bearings, grinding, scraping, and adjusting;

The clearance value between the pump bearing body and the spherical top of the bearing box is qualified;

The contact point and contact angle of the pump shaft bearing lower bush and the pump shaft journal. The standard stipulates that the contact area between the lower shoe back and the bearing seat should be more than 60%, the contact point density on the sliding contact surface at the journal is maintained at 2 to 4 points per square centimeter, and the contact angle is maintained at 60°-90°.

(5) Bracket and bottom plate

Find the fatigue of the vibrating support in time to prevent the natural frequency from falling due to the decrease in strength and stiffness.

(6) Clearance and wearing parts

Ensure that the motor bearing clearance is appropriate, and adjust the clearance between the impeller and the volute appropriately. Regularly check and replace the easily worn parts such as the impeller mouth ring, pump body mouth ring, interstage bushing, and partition bushing.

3.Vibration caused by improper pump selection and operation

Parallel connection of two pumps should ensure that the pump performance is the same, and the pump performance curve should be a slow-down type, and there should be no hump. Pay attention when using: eliminate the factors that cause the pump to overload, such as blockage of the flow channel.

Properly extend the starting time of the pump, reduce the disturbance to the drive shaft, reduce the collision and friction between the rotating parts and the stationary parts, and the thermal deformation caused by this. For water-lubricated sliding bearings, sufficient pre-lubricated water should be added during the starting process to avoid dry starting, and stop filling water until the water pump is discharged.