Climber-type Bar Screens

Climber-type bar screens remove large debris and solids from raw wastewater using vertically mounted bars with a mechanical rake that travels up the screen face. The rake mechanism climbs from bottom to top, collecting accumulated debris and depositing it into a collection trough or conveyor system. These screens typically handle flows from 0.5 to 50 MGD with bar spacings ranging from 0.5 to 3 inches, achieving 85-95% removal efficiency for debris larger than the bar spacing. The primary trade-off is higher maintenance requirements compared to traveling water screens, as the climbing mechanism involves more moving parts exposed to the harsh wastewater environment.

• Primary Headworks (0.5-50 MGD): Climber screens serve as the first mechanical screening stage after grit removal, handling 6-25 mm bar spacing. Selected for their ability to continuously remove large debris while maintaining consistent head loss. Positioned upstream of primary clarifiers, downstream of screening channels.
• Bypass/Emergency Screening: Installed in emergency overflow channels or plant bypass lines where intermittent operation is required. Chosen for reliability during storm events and ability to handle variable flows from 2-15 MGD without operator intervention.
• Pump Station Protection: Positioned upstream of raw sewage lift stations to protect pumps from rags and debris. Typically 10-20 mm spacing, selected for automated operation and minimal maintenance requirements in remote locations.
• Secondary Screening: Used after primary treatment for facilities requiring enhanced solids removal before biological processes, particularly in plants with strict effluent limits or membrane bioreactor applications.

Daily Operations: Operators monitor cleaning cycles (typically 15-30 minute intervals), verify proper rake travel, and check screenings discharge quality. Visual inspection for unusual debris accumulation or head loss increases. Most systems operate automatically with minimal daily intervention, requiring only screenings container management and basic performance verification.

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Maintenance: Monthly lubrication of drive chains and bearings using marine-grade grease. Quarterly inspection of rake teeth alignment and bar rack condition. Annual drive motor service and torque sensor calibration. Requires confined space training for channel access and lockout/tagout procedures. Most maintenance performed by plant electricians with basic mechanical skills.

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Troubleshooting: Common failures include chain stretch (replace every 3-5 years), rake tooth damage from large objects, and drive motor overload from excessive debris. Warning signs include irregular cleaning cycles, increased head loss, and unusual motor current draw. Typical service life: 15-20 years for mechanical components, 8-12 years for electrical systems.

• Climbing Mechanism: Chain-driven carriage system with rake assembly that travels vertically along fixed bar rack. Stainless steel construction (316SS minimum), with gear reducers sized for 0.5-2 HP motors. Selection based on screen height (8-25 feet typical) and cleaning frequency requirements.
• Bar Rack Assembly: Fixed stainless steel bars with 6-25 mm spacing, mounted at 70-85° angle. Depth ranges 4-12 feet for municipal applications. Bar profile (rectangular vs. teardrop) selected based on head loss requirements and debris characteristics.
• Drive System: Variable frequency drives with torque monitoring for automatic operation. Includes emergency manual override and position feedback systems.
• Screenings Handling: Integrated conveyor or container systems for debris discharge, with wash water spray systems (10-15 PSI) for cleaning. Compaction units reduce screenings volume by 50-70%.

• Flow Velocity Through Bars: 2-4 fps (0.6-1.2 m/s) for peak flow conditions. Velocities below 2 fps allow debris settling; above 4 fps cause excessive head loss and potential debris forcing through bars.
• Bar Spacing: 0.75-2.0 inches (19-51 mm) clear spacing. Fine screens (0.75-1.0") for combined sewer systems; coarse screens (1.5-2.0") for separate sanitary systems. Spacing determines debris capture efficiency and cleaning frequency.
• Approach Velocity: 1.5-3.0 fps (0.46-0.91 m/s) in approach channel. Higher velocities prevent grit settling; lower velocities reduce turbulence and improve flow distribution.
• Head Loss (Clean): 0.1-0.3 feet (30-90 mm) at design flow. Increases exponentially with debris accumulation; automated cleaning maintains 0.5-1.0 feet maximum operating head loss.
• Rake Speed: 15-30 fpm (4.6-9.1 m/min) during cleaning cycle. Slower speeds for heavy debris loading; faster for light loading to minimize cleaning duration.
• Channel Width: 2-12 feet (0.6-3.7 m) for municipal applications. Wider channels require multiple rake assemblies or specialized wide-span designs from manufacturers like Huber or Parkson.
• Installation Angle: 75-85 degrees from horizontal. Steeper angles improve debris discharge; shallower angles reduce power requirements but may cause debris hangup.

• Question 1: What bar spacing is required based on downstream equipment protection and debris characteristics? Fine screening (0.75-1.0") protects pumps and UV systems but increases cleaning frequency and power consumption. Coarse screening (1.5-2.0") reduces maintenance but may allow damaging debris through. Decision requires analysis of typical debris size distribution and downstream equipment tolerances.
• Question 2: Should the system include automatic or manual cleaning activation? Automatic systems using differential level sensors cost $15,000-25,000 more but prevent operator oversight failures that can cause flooding. Manual systems work for smaller plants (<2 MGD) with 24/7 staffing. Decision depends on staffing levels, redundancy requirements, and consequence of cleaning failure.
• Question 3: What level of redundancy is required for the installation? Single units acceptable for plants <5 MGD with bypass capability and 4-hour response time. Dual units required for larger plants or those without adequate bypass. Redundant systems double equipment costs but prevent treatment disruption during maintenance or failure.
• Question 4: How will screenings be handled and disposed? Integral washing/compaction reduces disposal volume by 50-70% but adds $20,000-40,000 to system cost. Simple discharge to containers adequate for <1 MGD plants. Decision affects long-term operating costs and disposal logistics.

• Primary: Division 46 - Water and Wastewater Equipment, Section 46 05 33 - Mechanical Bar Screens
• Secondary: Division

• Material/Equipment Verification: Stainless steel grade verification (316SS minimum), Motor enclosure ratings for wet well environment, Rake material compatibility with local debris
• Installation Requirements: Crane access for equipment placement, Electrical rough-in coordination with control panels, Concrete anchor bolt templates critical for alignment
• Field Challenges: Channel width tolerance ±1/4 inch maximum, Screening discharge conveyor coordination, Bypass pumping during installation
• Coordination Issues: SCADA integration with existing plant systems, Lead times: 16-20 weeks typical, 24+ weeks for custom sizing

• Huber Technology - ROTAMAT Ro1 (0.5-25 MGD typical)
• Lakeside Equipment - Raptor Complete Plant (municipal packages)
• JWC Environmental - Monster Industrial (heavy-duty applications)
• Headworks International - BioMag systems (integrated screening/grit)

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All maintain strong municipal references with installations at major utilities including Orange County, Denver Water, and Toronto Water.

• Perforated Plate Screens - Lower maintenance, 15-20% less expensive, suitable for smaller plants (<2 MGD) with consistent debris loading.
• Rotating Drum Screens - Better solids capture (1mm), 25-30% higher capital cost, preferred for plants with downstream membrane systems requiring fine screening.
• Static Wedge Wire Screens - No moving parts, 40-50% lower O&M costs, limited to low-debris applications with good upstream screening.

Establish direct technical contact with manufacturer's field service engineer early - they often catch design issues missed in standard submittals. Consider factory acceptance testing for critical installations over 10 MGD. Standardize on one manufacturer across multiple plants for parts inventory and operator training efficiency. Negotiate service contracts during equipment purchase for better pricing on future maintenance agreements.