Types of Mechanical Bar Screens
A mechanical bar screen is a robust filtration barrier composed of parallel metal bars spaced at specific intervals, designed to intercept and remove debris from flowing water in treatment systems. Installed typically at the intake points of wastewater treatment plants, pump stations, hydropower facilities, and industrial water systems, these screens play a vital role in protecting downstream equipment—such as pumps, pipelines, and clarifiers—from clogging, mechanical damage, and operational inefficiencies.
By filtering out solid waste early in the process, mechanical bar screens ensure smooth operation, reduce maintenance costs, and enhance the overall efficiency of water and wastewater management systems. They are available in various configurations based on bar spacing, orientation, construction, and cleaning mechanism to suit different environmental and operational requirements.
Classification by Bar Spacing
The spacing between the bars determines the size of debris that can be captured and is one of the most critical design factors. Screens are categorized into three main types based on this criterion:
Tight Bar Spacing Screens
Also known as fine screens, these feature bar gaps of less than 1 inch (typically 6–25 mm), enabling capture of small debris such as gravel, plastic fragments, small fish, and organic matter like tetezo (a type of aquatic vegetation).
Advantages
- High level of protection for sensitive downstream equipment
- Effective removal of fine particulates and small solids
- Ideal for urban wastewater with high debris load
- Reduces risk of pump clogging
Limitations
- Higher headloss due to restricted flow
- Requires frequent cleaning
- More prone to clogging in high-debris environments
Best for: Municipal wastewater plants, industrial facilities, and locations with high concentrations of fine debris
Normal Bar Spacing Screens
These medium screens have bar spacing between 2–3 inches (50–75 mm) and are designed to capture larger floating and suspended solids such as branches, leaves, weeds, and rags.
Advantages
- Balanced efficiency between flow and filtration
- Lower maintenance frequency than fine screens
- Cost-effective for general debris removal
- Widely used and standardized in design
Limitations
- May allow passage of smaller damaging debris
- Less effective in highly polluted inflows
- Still requires regular monitoring
Best for: Wastewater treatment plants, hydropower intakes, and stormwater systems
Wide Bar Spacing Screens
Also referred to as coarse screens or trash racks, these have bar gaps exceeding 3 inches (75+ mm) and are intended to stop only the largest debris such as logs, large vegetation, and stranded animals.
Advantages
- Minimal headloss and high flow capacity
- Durable and low-maintenance in open water
- Ideal for natural water sources with large debris
- Often used as primary protection upstream
Limitations
- Does not protect against smaller debris
- Requires secondary screening downstream
- Manual cleaning often needed in remote areas
Best for: River intakes, reservoirs, hydropower stations, and confluences of natural water bodies
Classification by Bar Orientation
The orientation of the bars affects cleaning efficiency, structural strength, and ease of installation:
- Vertical Bar Screens: Most common configuration. Provide uniform flow distribution and are easily integrated with automatic cleaning rakes. Ideal for most treatment plant applications.
- Inclined (Angled) Bar Screens: Set at angles between 30°–60° from vertical. Facilitate easier debris removal and are often used with mechanical rakes. Improve access for maintenance.
- Horizontal Bar Screens: Less common due to flow restriction and cleaning challenges. Used in specialized applications where space or flow dynamics require horizontal alignment.
Classification by Construction Type
- Solid Bar Screens: Constructed with continuous metal bars, offering maximum strength and durability. Block debris effectively but may cause higher headloss. Often used in high-flow or high-debris environments.
- Perforated Screens: Feature punched or laser-cut holes in metal plates instead of bars. Allow more uniform water passage while filtering out solids. Suitable for applications requiring finer filtration without using fine bar spacing.
Classification by Cleaning Mechanism
The method of debris removal significantly impacts efficiency, labor requirements, and system reliability:
| Type | Cleaning Method | Efficiency | Labor Required | Best Applications |
|---|---|---|---|---|
| Manual Bar Screens | Hand removal by operators | Low | High | Small plants, remote locations, low-flow systems |
| Semi-Automatic Screens | Mechanical rake operated manually or on-demand | Moderate | Medium | Medium-sized facilities, periodic high debris |
| Fully Automatic Screens | Motor-driven rake with timer or sensor activation | High | Low | Large treatment plants, critical infrastructure, 24/7 operations |
Expert Tip: For optimal performance, pair automatic cleaning systems with level sensors or differential pressure monitors to trigger cleaning only when necessary—this reduces energy use and wear while maintaining screen efficiency.
In summary, selecting the right mechanical bar screen involves evaluating debris type, flow rate, maintenance capabilities, and downstream process sensitivity. A well-chosen screen not only protects infrastructure but also contributes to the long-term reliability and cost-effectiveness of water treatment operations.
Specifications and Maintenance of Mechanical Bar Screens
Mechanical bar screens are essential components in wastewater treatment systems, designed to remove large solids and debris from influent water before it enters downstream processes. These automated screening devices come in a variety of sizes, flow capacities, and design configurations to suit different treatment requirements—from municipal sewage plants to industrial effluent facilities. Proper selection and consistent maintenance ensure reliable performance, reduced downtime, and extended equipment life.
Key Design Specifications
Bar Spacing and Screen Configuration
The spacing between the inclined bars of a mechanical bar screen is a critical design parameter that determines the size of solids captured. Standard spacing ranges from 6 mm to 100 mm, with finer spacing used in plants requiring higher levels of pretreatment. Customizable bar gaps allow engineers to target specific contaminants such as rags, plastics, or organic matter.
Inclined screens (typically at 30°–60° angles) enhance gravity-assisted cleaning and facilitate self-cleaning mechanisms, while vertical installations are preferred for space-constrained environments. The choice of configuration depends on flow rate, debris load, and available footprint.
Material Selection and Corrosion Resistance
The durability and longevity of a mechanical bar screen are largely determined by its construction material. Stainless steel (especially grades 304 and 316) is the most widely used due to its excellent corrosion resistance, structural strength, and compatibility with harsh wastewater environments. Grade 316 stainless steel is recommended for saline or chemically aggressive wastewater with high chloride content.
Alternative materials include polyvinyl chloride (PVC) for lightweight, non-corrosive applications in low-load settings, and carbon steel with protective epoxy or paint coatings for cost-sensitive projects. However, coated carbon steel requires vigilant inspection to prevent coating degradation and subsequent rusting.
Screen Capacity and Flow Rate
The hydraulic capacity of a mechanical bar screen must match the peak flow rates of the treatment plant to prevent overflow or clogging. Screens are rated based on maximum flow velocity (typically 0.6–1.0 m/s) and solids loading capacity. Undersized units can lead to frequent blockages, while oversized systems may reduce screening efficiency due to lower water velocity.
Engineers should consider both average and peak flow conditions when selecting a screen, along with surge events or stormwater inflows that could temporarily increase load. Computational fluid dynamics (CFD) modeling can help optimize screen placement and orientation for uniform flow distribution.
Automation and Cleaning Mechanisms
Modern mechanical bar screens are equipped with automated raking systems that continuously or intermittently remove trapped debris, minimizing manual intervention. Common types include chain-driven scrapers, wire rope systems, and step screens with integrated combing mechanisms.
Automatic operation is often controlled by time-based cycles or level sensors that detect rising water levels behind the screen, indicating blockage. Advanced models feature variable frequency drives (VFDs) for energy-efficient motor control and remote monitoring via SCADA integration, enhancing operational responsiveness.
| Specification | Typical Range | Selection Guidelines |
|---|---|---|
| Bar Spacing | 6 – 100 mm | Use 6–20 mm for fine screening; 50–100 mm for coarse screening in combined sewers |
| Screen Angle | 30° – 90° | Inclined (30°–60°) improves self-cleaning; vertical saves space |
| Material Options | Stainless steel, PVC, coated carbon steel | Choose 316 SS for corrosive environments; PVC for light-duty use |
| Flow Velocity | 0.6 – 1.0 m/s | Maintain optimal velocity to prevent settling or erosion |
| Automation Type | Time-based, level-sensor, or demand-driven | Use sensor-based control in variable flow conditions |
Essential Maintenance Practices
Important: Always follow the manufacturer’s maintenance manual and safety protocols when servicing mechanical bar screens. Neglecting routine upkeep can lead to mechanical failure, increased energy consumption, and compromised treatment efficiency. Implementing a preventive maintenance program not only extends equipment lifespan but also supports uninterrupted plant operation and regulatory compliance.
Uses of Mechanical Bar Screens in Industrial and Municipal Applications
Mechanical bar screens are essential components in a wide range of water and wastewater management systems. By removing large debris and solid materials early in the process, these screens protect downstream equipment, enhance treatment efficiency, and ensure regulatory compliance. Their robust design and automated operation make them ideal for continuous use in demanding environments.
Municipal Wastewater Treatment Plants
In municipal wastewater facilities, mechanical bar screens serve as the first line of defense, intercepting large solids such as rags, plastics, sticks, and sanitary products before they enter the treatment process.
- Prevents clogging of pumps, pipes, and valves, reducing maintenance costs and downtime
- Improves the efficiency of downstream processes like sedimentation and biological treatment
- Enhances overall effluent quality by minimizing the load of floating and suspended solids
- Commonly used with coarse screens (1–3 inch gaps) or medium screens (0.5–1 inch gaps)
Key benefit: Reduces risk of system blockages and protects critical infrastructure
Pulp and Paper Mills
These industrial facilities generate wastewater containing high concentrations of fiber clumps, bark, and process debris, making mechanical bar screens vital for operational continuity.
- Removes fiber aggregates that could jam pumps or foul treatment basins
- Protects chemical dosing systems and clarifiers from solid interference
- Helps maintain consistent flow rates and treatment performance
- Often integrated with screening conveyors for automatic waste removal
Operational advantage: Minimizes unplanned shutdowns due to mechanical obstructions
Food Processing Plants
Food manufacturing operations produce organic-laden wastewater containing food scraps, peels, bones, and packaging fragments. Mechanical bar screens are used to pre-treat this effluent before discharge.
- Separates solid food waste from process water, reducing BOD and TSS levels
- Protects municipal sewer systems from grease and solid buildup
- Helps food processors comply with local pretreatment regulations
- Reduces odor generation by removing decomposable organic matter early
Environmental impact: Supports sustainable wastewater management and prevents sewer overloads
Industrial Cooling Water Intakes
Facilities drawing cooling water from natural sources like rivers, lakes, or estuaries use mechanical bar screens to protect intake systems from aquatic and environmental debris.
- Prevents fish, leaves, algae mats, and floating debris from entering cooling circuits
- Reduces risk of biofouling and heat exchange inefficiencies
- Minimizes damage to pumps and heat exchangers, lowering maintenance costs
- Complies with environmental regulations (e.g., EPA 316(b)) regarding aquatic organism protection
Critical function: Ensures uninterrupted cooling operations and reduces ecological impact
Power Generation Facilities
Thermal and nuclear power plants rely on large volumes of cooling water, making mechanical bar screens a critical component of their intake systems.
- Utilizes drum-type or basket-type screens for high-flow, continuous operation
- Protects condensers and circulating water pumps from debris damage
- Often equipped with self-cleaning mechanisms to maintain flow efficiency
- Designed to handle high debris loads during storm events or seasonal changes
Design flexibility: Can be customized for tidal variations, flow rates, and site-specific conditions
Construction and Stormwater Management
Construction sites and urban runoff systems use mechanical bar screens as gross pollutant traps (GPTs) to capture debris before it enters storm drains or public sewers.
- Removes sediments, plastic, leaves, and construction waste from stormwater
- Prevents blockages in drainage systems and reduces pollution in waterways
- Supports compliance with stormwater discharge permits (e.g., NPDES)
- Can be combined with oil-water separators and sediment traps for enhanced treatment
Regulatory benefit: Helps meet environmental protection standards and avoid fines
Drinking Water Treatment Facilities
Before raw water undergoes purification, mechanical bar screens remove large particulates that could damage pumps or interfere with treatment processes.
- Serves as primary screening to protect pumps, valves, and filtration systems
- Often used in conjunction with fine screens (e.g., band screens) or microscreens
- Improves the performance of coagulation, flocculation, and disinfection stages
- Reduces turbidity and particulate load entering the treatment train
System protection: Extends equipment lifespan and ensures consistent water quality
Industrial Pretreatment Systems
Many industrial sectors use mechanical bar screens as part of their on-site pretreatment to meet discharge standards and protect internal infrastructure.
- Used in chemical plants, textile mills, and metal fabrication facilities
- Removes process-generated solids before biological or chemical treatment
- Reduces sludge volume and disposal costs
- Improves the reliability of automated systems and sensors downstream
Cost-saving insight: Early solids removal reduces long-term operational expenses
Best Practice Tip: When selecting a mechanical bar screen, consider factors such as flow rate, debris type, screen aperture size, cleaning mechanism (manual vs. automatic), and material of construction (e.g., stainless steel for corrosion resistance). Proper sizing and maintenance are key to ensuring optimal performance and longevity.
| Application Sector | Primary Function | Typical Debris Removed | Screen Type |
|---|---|---|---|
| Municipal Wastewater | Primary solids removal | Rags, plastics, sticks, wipes | Coarse/Medium rake or chain-driven |
| Pulp & Paper | Fiber and bark separation | Fiber clumps, bark, process waste | Band or drum screens |
| Food Processing | Organic solids separation | Food scraps, peels, bones | Step or rotary screens |
| Power & Cooling Plants | Intake protection | Fish, leaves, algae, debris | Drum, basket, or traveling screens |
| Stormwater/Construction | Gross pollutant trapping | Sediments, plastic, leaves | Gross pollutant traps (GPTs) |
| Drinking Water | Raw water protection | Leaves, twigs, aquatic vegetation | Fixed or automatic bar screens |
Additional Considerations
- Maintenance Requirements: Regular inspection and cleaning are essential to prevent screen clogging and ensure continuous operation
- Automation Features: Modern systems include sensors, automatic raking, and remote monitoring for improved efficiency
- Material Durability: Stainless steel or corrosion-resistant coatings extend lifespan in harsh environments
- Environmental Compliance: Proper screening helps facilities meet local, state, and federal discharge regulations
- System Integration: Bar screens can be paired with conveyors, grinders, and compaction units for complete debris management
How to Choose Mechanical Bar Screens for Wastewater Treatment Plants
Selecting the right mechanical bar screen is a critical decision in the design and operation of a wastewater treatment plant. A well-chosen screen ensures efficient removal of debris, protects downstream equipment, and contributes to the overall reliability and longevity of the treatment process. This comprehensive guide outlines the key parameters buyers should evaluate when choosing mechanical bar screens, including capacity, construction materials, installation, and maintenance requirements. Each factor plays a vital role in ensuring optimal performance, cost-efficiency, and regulatory compliance.
Important Note: Always consult with engineering professionals and equipment manufacturers during the selection process. Site-specific conditions such as flow variability, debris composition, and local environmental regulations can significantly influence the ideal screen choice.
Key Selection Criteria for Mechanical Bar Screens
- Capacity
The capacity of a mechanical bar screen refers to its ability to handle the volume or flow rate of wastewater effectively within a given time frame—typically measured in gallons per minute (GPM) or cubic meters per hour (m³/h). Selecting a screen with appropriate capacity is essential to prevent overloading, clogging, or bypassing of untreated water during peak flow periods.
To accurately assess capacity needs, buyers should:
- Analyze historical and projected peak flow rates at the treatment facility
- Account for seasonal variations and wet-weather events (e.g., storm surges)
- Estimate the volume and type of screenings (e.g., rags, plastics, organic matter) commonly encountered
- Ensure the screen can handle hydraulic surges without compromising performance
- Consider future plant expansions or increased service demands
A screen operating beyond its rated capacity may suffer from frequent jams, increased wear, and higher energy consumption, ultimately leading to unplanned downtime and costly repairs.
- Construction Materials
The durability, corrosion resistance, and lifespan of a mechanical bar screen are directly influenced by the materials used in its construction. Wastewater environments are inherently corrosive due to the presence of hydrogen sulfide, chlorides, and fluctuating pH levels, making material selection crucial for long-term reliability.
The most common construction materials include:
- Stainless Steel (Grade 304 or 316): Offers excellent corrosion resistance and strength; ideal for most municipal and industrial applications. Grade 316 is preferred in high-chloride environments (e.g., coastal plants).
- Carbon Steel: More economical but requires protective coatings (e.g., epoxy or galvanization) to resist corrosion. Best suited for indoor or less aggressive environments.
- Fiberglass-Reinforced Plastic (FRP): Lightweight and highly resistant to chemical corrosion. Suitable for corrosive industrial effluents and areas where metal contamination must be avoided.
When evaluating materials, consider not only initial cost but also lifecycle expenses, maintenance frequency, and compatibility with the specific wastewater composition at your site.
- Installation Requirements
Proper installation is critical to the performance and integration of mechanical bar screens within the treatment process. Installation requirements vary significantly based on screen type (e.g., front-clean, rear-clean, step, or band screens), channel dimensions, and plant layout.
Key installation considerations include:
- Spatial Constraints: Ensure adequate clearance for screen operation, maintenance access, and debris removal equipment.
- Anchoring and Support: Secure the screen to a stable foundation or channel structure to prevent vibration and misalignment.
- Hydraulic Alignment: Position the screen perpendicular to flow to ensure even distribution and prevent bypassing of solids.
- Power and Control Connections: Plan for electrical supply, control panels, and integration with SCADA or automation systems.
- Site-Specific Adaptations: Account for existing infrastructure, retrofitting needs, and environmental conditions (e.g., underground vaults, outdoor exposure).
Improper installation can lead to inefficient screening, accelerated wear, and safety hazards. Always follow manufacturer specifications and involve qualified engineers during the planning phase.
- Maintenance Requirements
The long-term effectiveness and operational efficiency of a wastewater treatment facility depend heavily on the maintenance needs of its mechanical bar screens. Regular maintenance prevents clogs, reduces wear, and extends equipment life, minimizing costly downtime and repairs.
Maintenance requirements vary by screen design and include:
- Lubrication: Regular greasing of bearings, chains, and moving parts to ensure smooth operation.
- Inspection: Routine checks for wear on耙s, chains, guides, and seals; look for signs of corrosion or misalignment.
- Cleaning: Removal of accumulated debris and biofilm to maintain hydraulic efficiency.
- Component Replacement: Scheduled replacement of wear-prone parts such as scrapers, pins, and bushings.
- Automation Calibration: Verification of sensor accuracy and control system responsiveness.
Some modern screens feature self-cleaning mechanisms, remote monitoring, and predictive maintenance alerts, which can significantly reduce manual labor and improve reliability. When selecting a screen, evaluate the availability of spare parts, technical support, and ease of servicing to ensure sustainable operation.
| Selection Parameter | Key Evaluation Factors | Common Mistakes to Avoid | Recommended Actions |
|---|---|---|---|
| Capacity | Peak flow rates, debris load, future scalability | Undersizing for peak flows, ignoring surge events | Conduct hydraulic modeling; include safety margin (e.g., 1.5x peak flow) |
| Construction Materials | Corrosion resistance, wastewater chemistry, lifecycle cost | Choosing low-cost materials without long-term analysis | Use 316 stainless steel or FRP in aggressive environments |
| Installation | Channel alignment, structural support, electrical access | Poor alignment causing uneven wear or bypass | Engage engineers; follow manufacturer’s installation manual |
| Maintenance | Accessibility, spare parts availability, automation features | Overlooking ongoing labor and parts costs | Select screens with modular design and remote diagnostics |
Expert Tip: Consider conducting a pilot test or site visit to observe similar screens in operation at comparable facilities. Real-world performance data and operator feedback can provide invaluable insights that specifications alone cannot convey.
Additional Selection Recommendations
- Evaluate energy efficiency ratings and motor specifications to minimize operating costs
- Choose screens with adjustable rake speeds or variable frequency drives (VFDs) for adaptive operation
- Incorporate redundancy or bypass systems for critical applications to maintain uptime during maintenance
- Verify compliance with environmental and safety standards (e.g., EPA, OSHA, ISO)
- Request performance guarantees and warranties from suppliers
- Train operations staff on proper use, troubleshooting, and preventive maintenance procedures
Ultimately, selecting the right mechanical bar screen involves balancing upfront costs with long-term performance, reliability, and maintenance demands. By carefully evaluating capacity, materials, installation, and service requirements, wastewater treatment plant operators can make informed decisions that enhance system efficiency, reduce lifecycle costs, and ensure consistent regulatory compliance. When in doubt, consult with experienced engineers or equipment specialists to validate your selection and optimize system integration.
Mechanical Bar Screens: Frequently Asked Questions
The design and deployment of mechanical bar screens are evolving in response to the growing demands of modern wastewater treatment facilities. Municipalities, especially in large urban areas, are increasingly adopting larger and more robust systems capable of handling high flow rates and peak hydraulic loads.
- Size Trends: There is a clear industry shift toward wider and taller bar screens to accommodate increased water volume and improve screening efficiency. Modern installations often feature widths exceeding 3 meters and depths designed for deep channel integration.
- Capacity Growth: Systems are being engineered for higher flow-to-peak ratios, allowing consistent performance even during storm events or periods of high inflow.
- Comprehensive Design: "Far-down" or deep-channel screens are becoming more common, integrating seamlessly into underground or submerged infrastructure for space efficiency and improved solids capture.
Overall, the trend is toward scalable, durable, and high-capacity mechanical bar screens that support the operational needs of expanding urban wastewater networks.
Mechanical bar screens play a critical first-line role in wastewater treatment by removing large solid contaminants—such as rags, plastics, wood, and debris—early in the process at the influent stage. This initial screening significantly enhances the quality of the wastewater stream.
- Protection of Downstream Equipment: By eliminating bulky materials, bar screens prevent clogging and damage to pumps, mixers, and pipelines in subsequent treatment stages.
- Improved Process Efficiency: Cleaner influent allows biological and chemical treatment processes to operate more effectively, reducing the risk of process upsets and enhancing overall treatment performance.
- Environmental Compliance: Effective screening contributes to producing a final effluent that meets regulatory standards for safe discharge or reuse in irrigation, industrial processes, or even groundwater recharge.
In essence, mechanical bar screens are foundational to ensuring the reliability, efficiency, and environmental safety of wastewater treatment operations.
While highly effective, mechanical bar screens do have certain operational and design limitations that must be considered:
- Waste Handling Challenges: The screenings collected (rags, plastics, organic matter) require proper removal, compaction, and disposal. This can involve additional equipment like conveyor systems, wash presses, and waste containers, increasing both cost and maintenance needs.
- Size Limitations: Bar screens are primarily designed to capture larger solids. They are less effective at removing fine particles, oils, or dissolved contaminants, which may require secondary screening (e.g., fine screens, drum screens) or filtration systems.
- Clogging Risk: In systems with high organic load or fibrous materials (e.g., wipes, hair), screens can become clogged, requiring frequent cleaning or manual intervention.
- Need for Complementary Systems: Due to these limitations, mechanical bar screens are often used in conjunction with other screening technologies or pretreatment methods to achieve comprehensive solids removal.
Proper system design, regular maintenance, and integration with downstream processes are essential to overcoming these limitations.
Mechanical bar screens are not limited to municipal wastewater treatment—they serve vital functions in a variety of industrial and environmental applications:
- Municipal Wastewater Plants: Protect pumps and equipment, reduce organic loading, and improve treatment efficiency by removing large debris from raw sewage.
- Power Generation: Used in cooling water intake systems to prevent debris from entering condensers and heat exchangers, ensuring uninterrupted operation and reducing maintenance downtime.
- Pulp and Paper Industry: Prevent wood scraps and process debris from damaging pumps and affecting water recirculation systems.
- Food and Beverage Processing: Remove solid waste from process water, protecting equipment and supporting sustainable water reuse practices.
- Marine and Desalination Plants: Serve as primary intake protection against seaweed, shells, and marine debris in seawater treatment systems.
In all these settings, the core function remains the same: safeguarding critical infrastructure by filtering out damaging solids before they enter sensitive processes.
The future of mechanical bar screens is focused on enhancing performance, sustainability, and integration with smart infrastructure. Key development areas include:
- Increased Automation: Advanced sensors and programmable logic controllers (PLCs) enable real-time monitoring of screen performance, automatic cleaning cycles, and remote diagnostics, reducing labor costs and improving reliability.
- Energy Efficiency: New drive systems, optimized rake designs, and variable frequency drives (VFDs) are being implemented to reduce power consumption.
- Improved Materials: Use of corrosion-resistant alloys and engineered polymers extends service life, especially in harsh environments like seawater or chemically aggressive wastewater.
- Modular and Scalable Designs: Prefabricated, modular units allow for easier installation, expansion, and retrofitting in existing facilities.
- Integration with IoT: Smart bar screens with data connectivity can feed performance metrics into central control systems, enabling predictive maintenance and better operational decision-making.
As urbanization and environmental regulations intensify, mechanical bar screens will continue to evolve into smarter, more efficient, and more resilient components of water and wastewater infrastructure.
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