Traveling Water Screens

Traveling Water Screens protect municipal water treatment intake pumps by continuously removing debris, leaves, and aquatic life from raw water sources. The system uses a rotating chain-driven screen that carries captured debris above the water surface for automatic cleaning via spray wash or mechanical rakes. These screens typically achieve 85-95% debris removal efficiency for particles larger than the screen opening size (commonly 3/8" to 1" bar spacing). The primary trade-off is higher capital and maintenance costs compared to static screens, but this investment provides essential pump protection and reduces downstream fouling in plants processing 2-50 MGD from surface water intakes.

• Raw Water Intake Screening: Traveling water screens serve as the primary coarse screening at surface water intakes, removing leaves, debris, and fish from raw water flows of 2-50 MGD. They're selected over static screens because continuous cleaning prevents blinding and maintains consistent head loss. Screens typically connect upstream to intake channels and downstream to raw water pumping stations.
• Plant Influent Screening: At wastewater plants handling 1-25 MGD, traveling screens provide preliminary treatment ahead of primary clarifiers. They remove rags, plastics, and large organics that would otherwise clog downstream processes. Selection over bar screens occurs when debris loading exceeds 2-3 cubic feet per day or when automated cleaning is essential for staffing constraints.
• Combined Sewer Overflow (CSO) Facilities: Traveling screens treat high-flow CSO events (10-100 MGD peak), removing gross solids before discharge or storage. They're chosen for their ability to handle variable flows and heavy debris loads during storm events, connecting upstream to diversion structures and downstream to disinfection systems.

Daily Operations: Operators monitor screen differential pressure (typically 6-12 inches maximum), debris accumulation rates, and spray wash effectiveness. VFD settings require adjustment based on debris loading - continuous operation during high debris periods, intermittent during normal conditions. Flow meters and level sensors provide automated start/stop control, but manual override capability remains essential for unusual debris events.

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Maintenance: Monthly lubrication of drive chains and bearings, quarterly spray nozzle cleaning, and semi-annual chain tension adjustment. Safety requires lockout/tagout procedures and fall protection for elevated screens. Maintenance staff need basic mechanical skills for chain adjustment and nozzle replacement. Annual bearing replacement and chain inspection prevent catastrophic failures.

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Troubleshooting: Chain binding indicates debris buildup or worn sprockets, typically resolved by increased wash frequency or manual cleaning. Excessive differential pressure suggests blinded screen sections or inadequate wash pressure. Screen life averages 8-12 years with proper maintenance, with chain replacement every 5-7 years. Warning signs include unusual noise, irregular movement, or increasing power consumption indicating bearing wear or debris jamming.

• Screen Panels: Perforated stainless steel or polyurethane panels with 6mm to 25mm openings, mounted on continuous chain assemblies. Panel selection depends on debris characteristics and required capture efficiency. Municipal installations typically use 316SS for corrosion resistance.
• Drive System: Variable frequency drives (0.5-5 HP) provide continuous or intermittent screen rotation at 2-10 feet per minute. Gear reducers ensure adequate torque for debris-loaded conditions. Sizing based on screen dimensions and expected debris loading.
• Spray Wash System: High-pressure water jets (60-100 PSI) remove captured debris from screen panels. Nozzle spacing and pressure selected based on debris type - organic matter requires higher pressure than leaves or plastic films.
• Debris Collection: Hoppers or conveyors collect washed debris for disposal. Sizing typically 2-8 cubic yards for municipal applications, with consideration for weekend storage capacity and truck access for removal.

• Flow Velocity Through Screen: 0.5-2.0 fps (typical 1.0-1.5 fps) - critical for debris removal efficiency and head loss minimization
• Screen Opening Size: 1/4" to 1" clear spacing (6-25mm) - municipal applications typically use 3/8" to 3/4" openings based on downstream equipment protection requirements
• Approach Velocity: 1.0-3.0 fps maximum to prevent debris impingement and screen blinding
• Head Loss: 6-24 inches clean, maximum 36 inches with debris loading before cleaning cycle initiates
• Screen Width: 4-20 feet standard widths, with multiple units for larger flows (>10 MGD typically requires parallel screens)
• Rake Speed: 8-25 fpm during cleaning cycle, variable speed preferred for debris load optimization
• Channel Depth: 8-25 feet typical, minimum 6 feet submergence below low water level
• Debris Handling Capacity: 0.1-2.0 cubic yards per million gallons treated, varies significantly with seasonal conditions
• Power Requirements: 3-15 HP per screen unit depending on size and debris loading
• Screen Angle: 70-85 degrees from horizontal (75 degrees most common) for optimal debris removal and structural efficiency

• What is the design debris loading and seasonal variation? Requires 2-year minimum operating data from similar watersheds. Underestimating by >50% leads to frequent maintenance shutdowns and potential bypass events. Need upstream watershed analysis, storm frequency data, and seasonal vegetation patterns.
• Should screens operate continuously or intermittently based on differential pressure? Continuous operation (8-12 hours/day) suits heavy debris loads >1 cy/MG, while differential-based operation (2-6 inch head loss trigger) works for lighter loads. Wrong choice increases power costs by 30-60% or causes screen blinding emergencies.
• What opening size balances downstream equipment protection versus maintenance frequency? 1/4" openings protect fine screens and UV systems but require 2-3x more cleaning cycles. 3/4" openings reduce maintenance but may damage downstream pumps. Critical threshold: if >20% of debris passes through, downstream damage risk increases exponentially.
• How many parallel units are required for redundancy during maintenance? N+1 redundancy essential for plants >5 MGD. Single screen failure during storm events can force plant bypass, violating discharge permits.

• Division 40-48: Process Integration
• Primary: 46 13 13 - Traveling Water Screens
• Secondary sections: 46 05 00 (Common Work Results for Water and Wastewater Equipment) for installation requirements, and 46 73 00 (Packaged Water and Wastewater Treatment Equipment) if supplied as integrated headworks package

• Material/Equipment Verification: Verify 316SS construction for all wetted parts, Confirm NEMA 4X electrical ratings for outdoor installations, Check drive motor sizing against actual head conditions
• Installation Requirements: Crane access for 8,000-15,000 lb assemblies, Precise channel dimensions (±1/4" tolerance typical), Electrical rough-in coordination with PLC integration
• Field Challenges: Channel concrete finishing critical for seal performance, Debris discharge chute alignment affects operation
• Coordination Issues: 16-20 week lead times typical; order early in design phase

• Evoqua (ENEXIO brand) - Rotamat RoK4 series for 1-50 MGD applications
• Huber Technology - ROTAMAT Ro1 screens, popular in 0.5-20 MGD plants
• Xylem (Sanitaire) - Brackett Green traveling screens for larger facilities
• WesTech Engineering - Conventional traveling water screens for 5-100 MGD applications

• Static bar screens - 40-60% lower capital cost, suitable for smaller plants (<2 MGD) with lower debris loads
• Drum screens - Better fine screening capability, 20-30% higher cost but reduced maintenance
• Step screens - Compact footprint for space-constrained sites, similar capital cost

Establish direct relationships with manufacturer field service teams - they provide invaluable troubleshooting support and spare parts guidance. Budget 3-5% of capital cost annually for preventive maintenance contracts. Consider standardizing on single manufacturer across multiple plants for parts inventory efficiency. Specify stainless steel hardware throughout; carbon steel components fail prematurely in wastewater environments. Request factory acceptance testing for critical installations.