What Are Common Liquid Ring Vacuum Pump Issues in Papermaking Dewatering?

Liquid ring vacuum pumps are core supporting equipment for papermaking vacuum dewatering systems, responsible for negative pressure forming and web dewatering in paper production. Running in 24/7 high-load, fiber and chemical-rich environments, these vacuum pumps are prone to various scenario-specific faults, which directly affect paper quality, dewatering efficiency and continuous production stability.

Most paper mill equipment failures are not caused by product quality defects, but by poor adaptation to papermaking’s unique working conditions, including fine fiber pollution, complex circulating water quality and long-term uninterrupted operation. Stable vacuum pump operation is the key to reducing downtime and defective paper products.

This article comprehensively sorts out the most common faults of liquid ring vacuum pumps in papermaking vacuum dewatering, analyzes hazard manifestations and root causes, and provides professional reference for paper mill operation, maintenance and system optimization.

1. Vacuum Instability & Reduced Dewatering Efficiency

Vacuum degree fluctuation and continuous efficiency decline are the most intuitive and high-frequency problems of liquid ring vacuum pumps in papermaking vacuum dewatering. Stable negative pressure is the core guarantee of uniform paper sheet dewatering and high-speed production. Once the vacuum degree fluctuates or decreases, it will directly trigger a series of production quality problems and restrict overall line capacity.

1.1 Fluctuating Vacuum Degree Causing Uneven Paper Dewatering

In actual papermaking production, many vacuum pumps exhibit obvious vacuum surge problems, with unstable negative pressure output during high-speed operation. This phenomenon leads to inconsistent dewatering effect on the paper web, resulting in uneven paper thickness, local wet spots and reduced paper flatness. For high-grade cultural paper and packaging paper production, unstable vacuum is the main cause of defective products and increased scrap rate.

Key Causes:

• Fiber & impurity intermittent clogging: Fine paper fibers and pulp residues intermittently block pump cavities and pipeline inner walls, breaking the stable negative pressure balance and causing real-time vacuum fluctuation.

• Inconsistent working fluid flow: Unstable circulating water supply leads to irregular liquid ring forming, resulting in fluctuating vacuum output of liquid ring vacuum pumps.

1.2 Continuous Vacuum Drop Leading to Low Production Capacity

Long-term operation in impurity-rich papermaking environments will cause gradual vacuum attenuation of liquid ring pumps. Although the equipment can still run normally, the effective negative pressure cannot reach the rated standard, resulting in insufficient dewatering capacity. To ensure paper quality, paper mills have to reduce production speed, which seriously restricts overall production efficiency and economic benefits.

Key Causes:

• Severely contaminated working fluid: Sizing agents, fillers and chemical residues in circulating water accumulate continuously, reducing the sealing and compression performance of liquid ring vacuum pumps and lowering ultimate vacuum degree.

• Long-term pipeline air leakage:Long-term unit vibration loosens pipeline connections and aging sealing gaskets. External air infiltration destroys vacuum tightness and causes continuous vacuum loss.

2. Severe Cavitation Erosion & Permanent Structural Damage

Papermaking vacuum dewatering requires long-term high-vacuum and high-load operation, making cavitation the most destructive hidden danger for liquid ring vacuum pumps. Different from temporary operational faults, cavitation will cause irreversible structural wear to internal components, permanently reducing equipment performance and greatly shortening service life.

2.1 Bubble Erosion Causing Impeller & Pump Wall Pitting

When the liquid ring pump runs under ultra-high negative pressure for a long time, the internal circulating water is prone to instantaneous vaporization to form a large number of tiny bubbles. These bubbles burst rapidly near the impeller and pump wall, generating strong impact force. Long-term repeated impact will form dense pitting and peeling on the metal surface, damaging the precision structure of the pump body.

Key Causes:

• Long-term ultra-high vacuum operation: Pursuing excessive dewatering effect makes the pump run beyond the optimal vacuum range for a long time, accelerating liquid vaporization and bubble generation.

• Overheated circulating water: Poor workshop heat dissipation leads to rising water temperature, further reducing the vaporization threshold of working liquid and aggravating cavitation erosion.

2.2 Pipeline Resistance Abnormity Aggravating Cavitation Degree

Unreasonable pipeline layout and blocked filter equipment in papermaking vacuum systems will increase inlet resistance, reduce pump inlet pressure, and induce severe cavitation. Many paper mills ignore pipeline maintenance, resulting in continuous accumulation of fiber impurities in pipelines, which changes airflow stability and forms a vicious cycle of cavitation and component wear.

Key Causes:

• Excessively bent and long pipelines: Unstandardized pipeline design increases transmission resistance and pressure loss.

• Blocked pre-filter screens: Uncleaned filter screens cause inlet pressure attenuation, further worsening cavitation of liquid ring vacuum pumps.

3. Fiber Scaling & Recurring Internal Blockage Faults

Fiber adhesion and chemical scaling are unique faults exclusive to papermaking working conditions. Unlike general industrial scenarios with clean working media, papermaking circulating water contains a large amount of suspended fine fibers and chemical residues. Long-term uninterrupted operation will lead to continuous deposition and scaling inside the pump body, triggering repeated blockage faults.

3.1 Fine Fiber Adhesion Weakening Vacuum Efficiency

Micro paper fibers suspended in circulating water will continuously adhere to impellers, liquid ring channels and pump body inner walls during negative pressure operation. The accumulated fiber layer changes the internal flow channel structure, destroys the stability of the liquid ring, and reduces the pumping speed and vacuuming efficiency of the equipment. In the early stage of adhesion, the fault is not obvious, but long-term accumulation will lead to obvious performance attenuation.

Key Causes:

• Lack of effective pre-filtration: The inlet lacks high-precision filtering equipment, resulting in a large number of fine fibers entering the pump body with the airflow.

• Long-term continuous operation: 24-hour non-stop production makes fibers unable to be discharged in time and gradually deposit and adhere.

• Complex water quality components: Diversified papermaking chemicals provide conditions for scaling and precipitation.

• Insufficient regular cleaning maintenance: Routine maintenance only focuses on external inspection, ignoring internal scale and fiber cleaning of liquid ring vacuum pumps.

4. Abnormal Vibration, Noise & Accelerated Mechanical Wear

Under the combined action of fiber pollution, cavitation impact and long-term high-load operation, liquid ring vacuum pumps in papermaking dewatering systems are prone to abnormal vibration and harsh noise. These phenomena are not only environmental problems but also early warning signals of accelerated mechanical wear, which will lead to component failure and equipment scrap if not handled in time.

4.1 Unbalanced Operation Inducing Mechanical Vibration

Uneven fiber scaling and internal dirt accumulation lead to asymmetric mass distribution of the impeller. During high-speed operation, the unbalanced rotor will generate strong mechanical vibration, causing overall jitter of the pump body, loose foundation bolts and aggravated pipeline vibration. Long-term vibration will further damage sealing components and fixed structures.

4.2 Cavitation & Wear Causing Abnormal Harsh Noise

Severe cavitation produces continuous bubble explosion impact noise inside the pump body, forming harsh irregular noise different from normal operating sound. At the same time, wear of bearings and mechanical seals will cause friction noise. Excessive noise indicates that the equipment has entered a sub-health operating state, with greatly increased failure risk.

Key Causes:

• Serious impeller scaling and dirt accumulation: Destroying rotor dynamic balance and causing vibration noise.

• Aging and wear of bearings and seals: Impurity water lubrication aggravates component friction and produces abnormal noise.

• Continuous cavitation impact: Bubble explosion forms persistent impact noise and structural damage.

5. Water Quality Defects & System Mismatch Sub-health Operation

Most long-term sub-health operation of papermaking liquid ring vacuum pumps stems from unqualified circulating water quality and unreasonable vacuum system matching, rather than equipment quality defects. Mismatched system parameters and unoptimized water quality keep the pump in low-efficiency and high-loss operation for a long time.

5.1 Unqualified Circulating Water Intensifying Internal Wear

Papermaking circulating water contains a large number of suspended solids, fiber residues and chemical corrosives. Long-term use of unqualified water as working fluid will continuously wear internal precision components, accelerate seal aging and cause internal corrosion of the pump body, greatly reducing equipment stability and service life.

5.2 Unreasonable System Matching Leading to Low Efficiency

Many paper mills have problems such as mismatched pump model, unreasonable water circulation mode and missing purification equipment. The traditional open circulation mode causes unstable water temperature and pressure, and the lack of pre-filtration devices forms a closed loop of pollution and wear, making the vacuum pump unable to exert optimal dewatering performance.

Key Causes:

• Lack of inlet pre-filtration and purification devices: Impurities enter the pump body continuously to form cyclic pollution.

• Unstable open water circulation system: Water temperature and pressure fluctuate greatly, affecting liquid ring forming stability.

• Model parameter mismatch: Excessive or insufficient vacuum parameters lead to long-term sub-health operation.

Summary

In papermaking vacuum dewatering scenarios, liquid ring vacuum pumps mainly suffer from five typical categories of faults: vacuum fluctuation and dewatering efficiency decline, cavitation-induced permanent structural damage, fiber scaling and repeated blockage, abnormal vibration and noise wear, and sub-health operation caused by water quality and system mismatch. All these faults are highly consistent with the unique characteristics of papermaking production, including fiber pollution, complex chemical water quality and 24-hour long-term high-load operation. Paper mill operation and maintenance teams can effectively eliminate hidden operational dangers, stabilize vacuum dewatering performance, reduce equipment failure rate and production downtime loss, and maximize the long-term operational value of liquid ring vacuum pumps by adopting targeted pre-filtration optimization, circulating water quality improvement, scientific anti-cavitation measures and standardized refined maintenance mechanisms.