Diagnosing Fluoroplastic Centrifugal Pump Malfunctions by Sound

In petrochemical plants, fluoroplastic centrifugal pumps are widely used to transfer highly corrosive media. Thanks to their unique lined structure, any slight abnormal noise may be a precursor to catastrophic equipment failure.

As a technical expert at Omron Tech Pumps, I will guide you to accurately identify the sub-healthy state of pump units by understanding the "language" of sound.

I. Abnormal Rolling Bearing Noises: From Whistling to Cracking

Bearings are the "heart" of a pump, and changes in their operating noise best reflect lubrication conditions and mechanical integrity. Based on a review of numerous on-site cases, we have categorized bearing abnormal noises into the following four types:

1. Continuous Whistling → Insufficient Lubricant

Diagnosis: A continuous, uniform high-frequency whistle typically indicates dried-up grease or insufficient lubricant in the bearing housing.

Risks: Friction-induced heating will cause a sharp rise in bearing temperature and accelerate cage aging.

Solutions: Immediately check the lubricant level and replenish with special grease in accordance with the manufacturer’s specifications. Do not overfill, to avoid heat generation from grease churning.

2. Dull Humming → Excessive Interference in Assembly

Diagnosis: A dull hum accompanied by temperature rise from a newly replaced bearing is mostly caused by excessive radial interference during assembly, leading to stiff rotation of rolling elements.

Risks: Long-term operation will result in early fatigue spalling of the raceways.

Solutions: Shut down the pump to recheck bearing clearance and fit tolerances; replace the bearing if necessary.

3. Intermittent Impact and Rattling → Surface Spalling

Diagnosis: Pitting or spalling on the raceways of the inner/outer bearing rings or the surface of rolling elements will cause intermittent impact noise during operation, with noticeable vibration felt by hand.

Risks: The spalled area will expand rapidly, leading to bearing seizure.

Solutions: Immediately shut down the pump and replace the bearing; inspect the journal and bearing housing for wear.

4. Severe Crackling or Swishing → Severe Damage

Diagnosis:

• Crackling: Disordered cracking noise occurs when the cage breaks, rolling elements shatter, or inner/outer rings crack.
• Swishing: A loud airflow-like swishing noise is produced when the clearance between rolling elements and the cage is excessively large.

Risks: The bearing may disintegrate at any time, causing rotor rubbing against the pump casing.

Solutions: Perform an emergency shutdown! Operation is strictly prohibited; the entire bearing assembly must be disassembled and replaced.

II. Cavitation Noises: Dangerous Cracking and Popping

Sound Characteristics

The most typical cavitation noise in a pump is a crackling and popping sound similar to frying bacon. This noise stems from micro-jet impact generated by the instantaneous collapse of bubbles in the high-pressure zone.

Unique Risks for Fluoroplastic Pumps

Although the sound characteristics are similar to those of metal pumps, the consequences are far more severe. Fluoroplastics have a much lower resistance to physical impact than metals. Prolonged cavitation erosion will form honeycomb pitting on the inner lining surfaces of the impeller and pump cover, rapidly thinning the lining and eventually causing the housing to be penetrated by highly corrosive media.

Solutions

• Check NPSHa: Ensure the net positive suction head available is greater than the net positive suction head required (NPSHr).
• Adjust operating conditions: Avoid long-term operation of the pump at excessively low or high flow rates; operate as close to the best efficiency point (BEP) as possible.
• Vent and temperature control: Inspect the suction pipeline for air leakage and appropriately reduce the medium temperature.

III. Low-Flow Noises: The Misdiagnosed "Gravel Impact Sound"

Sound Characteristics

Under low-flow conditions, some fluoroplastic centrifugal pumps (especially volute-type designs) produce louder noise similar to cavitation, sounding like gravel hitting the pump casing.

In-Depth Analysis

This is not true cavitation but is caused by recirculation vortices. When the flow rate is far below the design value, intense recirculation and vortices form at the impeller outlet, impacting the volute tongue.

• Design Shortcoming: This impact noise is particularly noticeable if the pump tongue is improperly positioned.
• Hazards: Long-term operation under such conditions not only causes a nuisance from noise but also leads to severe vibration of the pump body, resulting in mechanical seal failure and premature bearing damage.

Solutions

Activate the minimum flow recirculation loop: Install an automatic recirculation valve to ensure the pump’s minimum flow rate is no less than 30% of the design value.

Adjust the discharge valve: Open the discharge valve appropriately to increase the system flow rate.

IV. Looseness Noises: Fracture Risks Behind Periodic Clunking

This is the most dangerous type of fault and requires the highest vigilance!

Sound Characteristics

A distinct periodic clunking impact noise is produced, and the noise frequency is usually synchronous with or a multiple of the rotational speed.

Fatal Mechanism

This is caused by the loosening of rotor components (impeller, shaft sleeve) on the shaft.

1.Gravitational Effect: As the shaft rotates, the loose impeller/shaft sleeve sags due to gravity, creating a clearance (even up to 1-3mm) with the shaft.

2.Periodic Impact:

• When the convex side of the bent pump shaft rotates downward, it strikes the impeller, causing it to move down.
• When the convex side rotates upward, it strikes the impeller again, causing it to move up.
• If the shaft is bent, the impact amplitude is larger and the noise is more intense.

3.Chain Reaction: In addition to air leakage, the more severe consequence is that alternating stress will cause cracks in the impeller, or even direct fracture of the pump shaft at the edge of the fitting area.

4.Spacer Sleeve Issue: If the spacer sleeve of the rolling bearing is not fully compressed, it will also rattle up and down in the axial clearance, producing a slight impact noise.

Solutions

• Immediate Shutdown: This type of fault develops extremely rapidly; continued operation will most likely lead to shaft breakage and leakage accidents.
• Disassembly and Inspection: Check the fit clearance between the impeller, shaft sleeve and the shaft; inspect the shaft for bending deformation.
• Repair or Replacement: Perform spray repair on loose components or replace them with new ones; realign the pump shaft and tighten the lock nut in strict accordance with the torque requirements.

Conclusion

Sound is the most intuitive "language" of fluoroplastic centrifugal pumps, and understanding it means understanding the safety bottom line of the equipment. Accurate noise-based diagnosis not only enables you to significantly reduce maintenance costs but also builds a solid safety barrier for chemical production.

👉 Contact the Omron Tech Pumps expert team now to obtain a free pump unit health diagnosis plan, or a tailor-made solution for a new generation of low-noise, high-reliability fluoroplastic centrifugal pumps. Let Omron Tech Pumps be your trusted fluid handling partner!