Causes and solutions for abnormal vibration in double-suction split-case pumps

As a core component of fluid transport systems, the vibration of double-suction split-case pumps is a key technical challenge in engineering management. Vibration not only directly weakens the pump's operational stability and reduces transport efficiency, but also accelerates the wear and aging of critical components such as bearings and seals. Long-term accumulation can lead to structural damage to the pump body and even cause pipeline leaks, equipment downtime, and other safety risks. Therefore, accurately identifying the causes of vibration, mastering scientific judgment methods, and implementing targeted prevention and control measures are crucial for extending equipment lifespan and ensuring continuous production.

• The core cause of abnormal vibration in a double-suction split-case pump

Vibration in dual-suction pumps is mostly caused by a combination of factors, including equipment installation, component condition, pipeline design, and operating parameters. These factors can be summarized into the following categories:

Cavitation

Cause: This is one of the main causes of pump vibration. Local pressure within the pump is lower than the saturated vapor pressure of the pumped liquid, generating bubbles. These bubbles collapse in the high-pressure area, causing strong impacts and vibrations.

Symptoms: Vibration accompanied by popping sounds, violent swinging of the outlet pressure gauge pointer, and decreased performance (reduced flow rate and head).

Specific Causes:

Insufficient inlet pressure (e.g., inlet valve opening too small, filter blockage, improper inlet piping design with air pockets).

Excessively high medium temperature, leading to increased saturated vapor pressure.

Pump operating point deviates too far from the design point (operating in high or low flow rate ranges).

Hydraulic pulsation / surge

Cause: When the pump operates under off-design conditions (especially at low flow rates), flow separation and vortices occur within the impeller, leading to periodic and severe fluctuations in outlet pressure.

Symptoms: Low-frequency, high-amplitude periodic and severe vibrations and noise occur in the pump and pipeline, resembling "breathing."

Water hammer

Cause: Rapid start-up and shutdown of pumps or valves causes a drastic change in fluid momentum, generating pressure waves in the pipeline.

Symptoms: Sudden, loud noises and impact vibrations, which can cause serious damage to pumps and pipelines.

Unstable flow rate / Intake vortex

Cause: Inadequate inlet tank design (e.g., insufficient submersion depth, proximity to tank walls or bottom), creating vortices that draw air into the pump.

Symptoms: Irregular vibration, accompanied by noise, and fluctuating performance.

Rotor Imbalance

Causes: Uneven mass distribution in the pump rotor (impeller, bushing, etc.) due to wear, corrosion, scaling, or manufacturing defects.

Symptoms: Vibration frequency is primarily at 1 times the rotational speed, with amplitude increasing with speed. This is the most common cause of mechanical vibration in rotating machinery.

Poor alignment

Cause: The alignment accuracy of the pump and motor coupling is out of tolerance. For double-suction split-case pumps, the pump and motor are usually aligned as a whole.

Symptoms: Vibration frequencies are mainly at 1 and 2 times the rotational speed, with potentially significant axial vibration. After hot operation, temperature changes may alter the alignment.

Bearing Failure

Causes: Wear, pitting, or cage damage in rolling bearings; excessive clearance or oil film oscillation in sliding bearings.

Symptoms: High vibration frequency, possibly accompanied by a characteristic impact sound. Spectral analysis is required for diagnosis.

Shaft bending or wear

Causes: Long-term operation, thermal deformation, or uneven wear can cause the pump shaft to bend.

Symptoms: Similar to imbalance, but axial vibration is usually also more pronounced.

• Scientific methods for judging the vibration of double-suction split-case pumps

Accurate diagnosis of vibration problems requires a combination of visual observation and professional testing. In practice, the following three methods can be used:

1. Visual Observation Method: By listening to the pump unit's operating sound (normally a uniform and stable sound; abnormal sounds and noises appear), observing the vibration amplitude (significantly increased amplitude on the pump body surface, pipe vibration), and checking for leaks in the seals, a preliminary judgment can be made regarding the presence and severity of vibration.
2. Professional Instrument Monitoring Method: Using a vibration analyzer, data on vibration acceleration, velocity, and displacement of key components such as the pump body bearing end and pump shaft are collected. This data is then compared with the standard values ​​in the national standard GB/T6075.3-2019 "Mechanical Vibration - Determination of Vibration Intensity of Machines - Part 3: Industrial Machines with Rated Power Greater Than 15kW and Rated Speed ​​Between 120r/min and 15000r/min" to pinpoint the type of vibration exceeding the standard (e.g., unbalanced vibration, misalignment vibration).
3. Component disassembly and inspection method: Periodically stop the pump and disassemble the pump body to check the bearing clearance (replace if it exceeds the standard), impeller wear and dynamic balance (can be tested by a dynamic balancer), shaft deflection and seal integrity, and investigate potential vibration hazards caused by component wear.

• Targeted solutions for vibration in double-suction split-case pumps

Combined with the causes of vibration, the following engineering solutions are formulated from the entire process of equipment manufacturing, installation, operation and maintenance, which can effectively reduce vibration risks:

1. Strict pump body inspection standards: Before leaving the factory, dynamic balance tests and stiffness tests are required to ensure that core components such as impellers and pump shafts comply with the "GB/T13008-2018 General Technical Conditions for Centrifugal Pumps, Mixed Flow Pumps, Axial Flow Pumps and Vortex Pumps"; the processing accuracy of the pump body is reviewed before installation to avoid vibration caused by manufacturing defects.
2. Optimize the impeller structural design: Based on the actual transmission medium (such as clean water, fluids containing a small amount of impurities) and working condition parameters, use fluid mechanics simulation to optimize the impeller blade radian and inlet and outlet angles, improve the hydraulic efficiency of the impeller, and reduce vibration caused by fluid impact; regularly check the impeller wear and repair or replace it in a timely manner if cavitation and corrosion are found.
3. Strengthen media pretreatment: Install a filter (filter pore size ≤ 0.1mm) at the inlet end of the pump unit to reduce the content of impurities such as sediment and particulate matter in the water, reduce the grinding wear of the impeller and bearings, and avoid vibration caused by media contamination from the source.
4. Optimize the configuration of the pipeline system: adjust the layout of the inlet and outlet pipelines to ensure that the distance between the pump port and the elbow is not less than 3 times the pipe diameter to reduce fluid eddy currents; increase pipeline brackets to enhance stiffness and avoid pipeline resonance; install slow-closing valves and mufflers to alleviate the impact of water hammer on the pump body.
5. Standardize the installation and construction process: the foundation of the pump unit must be poured with concrete with a strength grade of not less than C30, and the anchor bolts must be installed with anti-loosening washers and tightened according to the specified torque; during installation, use a dial indicator to correct the coaxiality of the pump shaft and the motor shaft (radial runout ≤ 0.05mm), ensure that the horizontality deviation of the pump body is ≤ 0.2mm/m, and ensure balanced stress during operation.
6. Optimize the operating environment and parameters: Control the operating environment temperature of the pump set at 5-40°C to avoid accelerated aging of bearings and seals due to high temperatures; reasonably adjust operating parameters according to production needs to ensure that the speed and flow rate are within the rated range of the pump set (it is recommended that the operating efficiency be maintained in the high-efficiency zone 75%-100%) to avoid overload operation.

Vibration control of double-suction split-case pumps should adhere to the principle of "prevention first, precise management": enterprises should establish regular operation and maintenance logs and conduct vibration data monitoring and component inspections every 3-6 months; for older pump sets (operating for more than 5 years), the frequency of dynamic balance verification and coaxiality check can be increased; if excessive vibration is found, the cause should be located first through instrument monitoring, and then targeted measures such as replacing components, adjusting pipelines or optimizing parameters should be taken to avoid blind repairs.