Tipping Trough Skimmer

Tipping trough skimmers remove floating scum and debris from clarifier surfaces in municipal water and wastewater treatment plants. The system consists of a pivoting collection trough that automatically tips when filled, discharging collected material into a scum box or hopper. Typical units handle surface loading rates of 2-4 gallons per minute per linear foot of skimmer length. The primary trade-off is mechanical complexity versus reliability - while effective at continuous scum removal, the pivoting mechanism requires regular maintenance and can jam with heavy debris loads or freezing conditions.

• Primary Clarifier Scum Removal (5-25 MGD plants): Tipping troughs collect floating scum across the clarifier surface, typically positioned 6-12 inches below normal water level. Selected for continuous removal without mechanical scrapers that can break up scum mats. Connects upstream from scum pumps to waste handling.

• Secondary Clarifier Foam Control (1-15 MGD plants): Handles biological foam and surfactant accumulation in activated sludge systems. Positioned along effluent weirs where foam concentrates. Chosen over fixed skimmers when foam production varies seasonally or with industrial discharge patterns.

• DAF Unit Concentrate Collection (0.5-8 MGD plants): Collects concentrated float from dissolved air flotation systems treating high-strength waste or phosphorus removal applications. Integrates with DAF sweep mechanisms for continuous float removal to thickening processes.

• Equalization Basin Oil/Grease Removal (2-20 MGD plants): Removes petroleum products and fats/oils/grease in facilities with significant industrial pretreatment. Selected when surface loading varies significantly with industrial discharge schedules.

Daily Operations: Operators monitor tipping frequency (should cycle every 15-30 minutes under normal conditions) and observe scum consistency in discharge. Adjust counterweight position if tipping becomes irregular. Check water levels to ensure proper skimmer positioning 6-12 inches below surface. Document cycles per hour and scum volume collected for process optimization.

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Maintenance: Weekly lubrication of pivot bearings using marine-grade grease. Monthly inspection of counterweight cables and pivot mechanism for wear. Quarterly cleaning of discharge chutes and water spray nozzles. Annual bearing replacement typically required. Requires confined space entry training for clarifier access. Standard PPE includes fall protection, gas monitoring, and slip-resistant footwear.

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Troubleshooting: Irregular tipping indicates counterweight adjustment needed or bearing wear. Scum carryover suggests insufficient tipping frequency or worn pivot mechanism. Typical service life 8-12 years for mechanical components, 15-20 years for stainless steel construction.

• Tipping Trough Assembly: Stainless steel 316L construction, typically 4-8 feet long, 12-18 inches wide. Pivots on corrosion-resistant bearings rated for continuous outdoor service. Sizing based on surface loading rates of 200-800 gpd/sf and expected scum production rates.

• Counterweight System: Cast iron or concrete counterweights, 50-200 lbs capacity depending on trough size. Adjustable positioning allows fine-tuning of tipping frequency (typically 2-6 cycles per hour). Critical for consistent operation across varying scum consistency.

• Pivot Mechanism: Heavy-duty stainless steel or bronze bearings with grease fittings. Must handle 500-2000 lb total loads including trough, scum, and counterweight. Selection based on expected cycle frequency and environmental exposure.

• Discharge Chute: Stainless steel or HDPE construction, 6-12 inch width, connects trough to collection sump or conveyor. Slope minimum 1:12 for gravity drainage. Sized for peak discharge volumes during tipping cycles.

• Water Supply System: Low-pressure wash water connections (20-40 psi) with manual or automatic valves for trough cleaning between cycles.

• Surface Loading Rate: 800-1,500 gpd/sf (typical municipal range), with 1,000 gpd/sf standard for new installations. Higher rates (up to 2,000 gpd/sf) acceptable for retrofit applications with space constraints.

• Trough Capacity: 0.5-5.0 gallons per linear foot, sized for 15-30 second retention at design flow. Larger capacities needed for plants with significant flow variations or high oil/grease loading.

• Skimmed Material Flow Rate: 0.1-0.5% of influent flow for typical municipal applications. Design for 2-5 gpm per 1 MGD plant capacity, with higher rates for industrial discharge areas.

• Tipping Frequency: 2-8 tips per hour at design conditions. More frequent tipping (every 7-15 minutes) improves removal efficiency but increases wear on mechanical components.

• Weir Loading Rate: 10,000-20,000 gpd/linear foot maximum. Standard municipal practice uses 15,000 gpd/lf for rectangular clarifiers, 12,000 gpd/lf for circular units.

• Minimum Water Depth: 8-12 feet required for proper hydraulics and scum accumulation. Shallower basins require modified trough positioning and may reduce efficiency.

• Operating Temperature Range: 32-120°F for standard materials. Extended range units available for extreme climates with special seals and materials.

• What surface loading rate should drive the sizing? Municipal plants typically operate at 1,000-1,200 gpd/sf average, with peak rates up to 1,500 gpd/sf. Exceeding 1,800 gpd/sf compromises settling and increases carryover. Decision requires accurate flow projections and consideration of future capacity needs. Wrong sizing leads to poor clarification or oversized, expensive basins.

• How should trough capacity be matched to actual skimming loads? Standard 2-gallon capacity per linear foot works for typical municipal loads (0.2-0.4% of flow). Plants with significant industrial discharge or high FOG loading need 3-5 gallon capacity. Undersized troughs cause frequent overflow and poor removal; oversized units increase costs and maintenance complexity.

• What tipping mechanism reliability is required? Pneumatic systems offer 95%+ uptime but require compressed air infrastructure. Mechanical linkage systems are simpler but need more frequent adjustment. Electric actuators provide precise control but are vulnerable to power issues. Decision depends on plant staffing, maintenance capabilities, and redundancy requirements.

• Should multiple units be specified for redundancy? Plants above 5 MGD typically install 2+ independent skimmer systems. Single-unit failure can compromise entire clarifier performance. Multiple smaller units cost 15-25% more but provide operational flexibility and maintenance access.

• Division 40-48: Process Integration

• Primary: 40 31 33 - Clarification Equipment

• Secondary: 40 20 00 - Water Treatment Equipment (for integrated clarifier systems)

• Material/Equipment Verification: Verify 316SS construction for all wetted parts, Confirm pivot bearing materials and lubrication access, Check counterweight material (typically concrete-filled steel)

• Installation Requirements: Precise elevation control (±1/8") for proper tipping action, Adequate crane access for installation, Electrical coordination for optional position indicators

• Field Challenges: Basin wall anchor embedment verification, Scum trough alignment and slope verification, Access platform integration

• Coordination Issues: 12-16 week typical lead times, Early electrical rough-in coordination required

• Lakeside Equipment - Raptor Tipping Trough Skimmers (municipal installations at 15+ MGD plants)

• WesTech Engineering - TipSkimmer series (proven in 5-50 MGD applications)

• Evoqua Water Technologies - Envirex Tipping Bucket Skimmers (legacy Eimco designs)

• Hydro International - HydroTip systems (newer market entry, focus on smaller plants)

• Chain and flight skimmers - Lower cost ($15-25K vs $30-45K), better for heavy scum loads, higher maintenance

• Rotating tube skimmers - Preferred for deep basins (>16'), continuous operation, moderate cost premium

• Beach-type skimmers - Best for variable flow plants, minimal maintenance, limited to shallow applications (<12')

Establish direct relationships with manufacturer field service teams early - they provide invaluable startup support and troubleshooting expertise. Consider specifying spare pivot bushings and seals during initial procurement to avoid future sourcing delays. Many plants achieve 15-20% cost savings by bundling tipping trough orders with other clarifier equipment from the same manufacturer. Request factory acceptance testing for critical installations over 25 MGD.