Technical measures to eliminate the hazards caused by pump vibration

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Technical measures to eliminate the hazards of pump vibration: In rotating equipment and flowing media, low-intensity mechanical vibration is inevitable. Therefore, during the manufacturing and installation of the unit, interference caused by vibration should be avoided as much as possible in terms of its design, operation, and management, in order to minimize the hazards associated with vibration. When vibration occurs in the pump house or the machine unit, it is necessary to analyze the possible causes of the vibration on a case-by-case basis. Once the root cause of the problem is identified, effective technical measures should be taken to eliminate it. Some measures are relatively simple, while some are quite complex. If a large amount of funding is required, a technical and economic comparison of the available options should be conducted, taking into account the technical upgrades of the units. The following outlines the common causes of vibration in motors, water pumps, and pump houses, as well as the measures to eliminate it. 1. Common causes of motor vibration and mitigation measures 1) Uneven bearing wear: Misalignment of the unit or worn bearings. Remedial measures: Realign the concentricity of the unit, and adjust or replace the bearings. 2) Stator-rotor friction: uneven air gap or bearing wear. Remedial measures: Readjust the air gap, adjust or replace the bearings. 3) The rotor cannot stop at any position or there is power imbalance. Remedial action: Rebalance the rotor statically and dynamically. 4) Axial looseness: Loose screws or improper installation. Remedial action: Tighten the screws and check the installation quality. 5) Foundation vibrating: Poor foundation stiffness or loose corner screws. Remedial measures: Reinforce the foundation or tighten the bottom corner screws. 6) Unstable three-phase current: reduced torque, fault in the rotor bars or end rings. Remedial action: Inspect and repair the rotor bar slots or end rings. 2. Common causes of pump vibration and countermeasures 1) Difficulty in manual shaft turning: bent pump shaft, worn bearings, misalignment of the unit, impeller hitting the pump casing. Remedial measures: Straighten the pump shaft, adjust or replace the bearings, realign the concentricity of the unit, and readjust the clearance. 2) Excessive pump shaft runout: Wear of bearings and journal or excessive clearance. Remedial measures: Repair the shaft journal, adjust or replace the bearings. 3) Hydraulic imbalance: Imbalance of the impeller, or blockage or damage in certain vanes of the centrifugal pump. Remedial measures: Re-check the static and dynamic balance of the impeller, remove blockages, and repair or replace the impeller. 4) Excessive shaft power of the axial flow pump: The water level in the inlet tank is too low, the immersion depth of the impeller is insufficient, debris gets entangled around the impeller, the degree of cavitation damage to the pump varies, and the impeller is damaged. Remedial measures: Raise the water level in the inlet tank, lower the installation height of the pump to remove debris, install trash racks, and repair or replace the impeller. 5) Foundation vibration: poor foundation stiffness, loose corner screws, or resonance. Remedial measures: Reinforce the foundation, tighten the foot screws. 6) The efficiency of the centrifugal pump unit drops sharply, or the efficiency of the axial flow pump unit decreases slightly, accompanied by cavitation noise. Remedial measures: Change the pump speed to avoid the resonance range, identify the cause of cavitation, and take actions to eliminate it. 3. Vibration of the unit caused by other reasons and countermeasures 1) Blockage of the trash rack, resulting in a decrease in the water level in the inlet tank. Remedial measures: Clean the trash racks, and install devices for cleaning the trash racks. 2) The design of the front pool and the water intake pool is unreasonable, and the mismatch between the water intake channel and the pump deteriorates the water intake conditions. Remedial measures: Clean the trash racks, install devices for cleaning these trash racks, and design them properly, in addition to optimizing the design of the inlet forebay, inlet tank, and inlet channels. 3) The time required to form a siphon is too long, causing the unit to operate under conditions other than those designed for an extended period. Remedial measures: Install a vacuum extraction device, and design and improve the siphonic water outlet channel appropriately. 4) The water inlet pipe is not securely fixed, causing resonance. Remedial measures: Add pipeline piers and supports, reinforce pipe supports, and change operating parameters to avoid the resonance zone. 5) Repeated knocking on the door, impacting the door frame, or excessive force when closing the door. Remedial measures: Install exhaust vents before the outlet of the flow channel (or pipeline), and design the check valves appropriately to take control measures and reduce the impact force when the check valves close. 6) Sudden pressure changes in the outlet pipeline and water hammer effect. Remedial measures: check valves and pressure regulation chambers, as well as other measures to prevent water hammer. 7) The sequence of unit startup and shutdown is unreasonable, resulting in deteriorated water intake conditions for the water pump. Remedial measure: Optimize the startup and shutdown sequence.