A multi rake bar screen is a coarse screening device installed at the inlet of a wastewater treatment plant to capture and remove large solid material from the incoming flow. A multi rake bar screen in wastewater treatment uses several rake arms working in sequence along a bar rack, allowing it to handle higher solids loads and wider channels than a single-rake design. As the first mechanical barrier wastewater encounters, the multi rake bar screen protects pumps, pipework, and downstream treatment processes from rags, debris, and large solid waste.
The defining advantage of the multi rake configuration is its capacity to capture and remove larger volumes of solid material continuously, making it well suited to plants with high flow rates or significant coarse solids loading.
What Is a Multi Rake Bar Screen?
A multi rake bar screen consists of a fixed bar rack installed across the width of an inlet channel, combined with multiple rake arms that travel along the rack to remove captured solids. As wastewater flows through the bars, solid material larger than the bar spacing is retained on the screen surface while the liquid passes through.
As a multi rake bar screen manufacturer and worldwide supplier, Vortex Engineering offers a wide range of dimension and stainless steel grade options to suit different channel widths, bar spacings, and flow conditions.
Unlike a single-rake bar screen, where one rake arm must travel the full height of the screen to clean it, a multi rake design distributes the cleaning workload across several rake arms operating in a coordinated sequence. This allows continuous cleaning coverage along the screen face, even under high solids loading conditions.
How Does a Multi Rake Bar Screen Work?
Solid Capture
Wastewater enters the inlet channel and flows through the bar rack. The spacing between bars — typically ranging from 6 mm to 50 mm depending on the application — determines the minimum size of solid material captured. As flow passes through, rags, plastics, wood, and other coarse debris are retained on the upstream face of the bars.
Rake Cleaning Cycle
Multiple rake arms, mounted on a chain or cable drive system, travel up the bar rack in sequence. Each rake arm engages with the bars near the bottom of the screen, collects the accumulated solids as it travels upward, and carries the captured material to the top of the screen. Because several rakes operate in this continuous, staggered sequence, the screen face is cleaned more frequently than a single-rake system could achieve — important for managing high or variable solids loads without allowing head loss across the screen to build up excessively.
Discharge
At the top of the screen, each rake arm releases its load of captured solids into a discharge chute, conveyor, or container. The rake arm then returns to the bottom of the rack to begin another collection cycle. This continuous cycle of capture, lift, and discharge keeps the bar rack clear and maintains consistent hydraulic performance through the screen.
Why Multiple Rakes?
The decision to use multiple rake arms rather than a single rake is driven primarily by flow rate and solids loading.
Higher flow capacity. Wider channels and higher flow rates generate more frequent solids accumulation across the bar rack. A single rake travelling the full screen height cannot keep pace with this accumulation rate without allowing head loss to build up between cleaning cycles.
Taller screen installations. In deep channels or pump station applications where the bar rack extends to significant depth, a single rake arm would require a long travel cycle to clean the full screen height. Multiple rakes working in sequence reduce the time between cleaning passes at any given point on the screen.
Continuous solids removal. With several rake arms staggered along the cleaning cycle, solids are removed from the screen face more frequently and more evenly, reducing the risk of excessive head loss or screen blinding during peak flow or high debris loading events.
Multi Rake Bar Screen vs Other Bar Screens
| Multi Rake Bar Screen | Single Rake Bar Screen | Perforated Bar Screen | |
|---|---|---|---|
| Cleaning mechanism | Multiple rake arms in sequence | Single rake arm | Perforated plate, mechanical cleaning |
| Best for | High flow, wide or deep channels | Lower flow, smaller channels | Fine solids capture |
| Solids captured | Coarse | Coarse | Finer than bar screens |
| Maintenance complexity | Moderate — multiple drive components | Lower — single drive mechanism | Moderate |
| Throughput capacity | High | Lower | Application-dependent |
The multi rake bar screen is the preferred choice for larger municipal plants and high-flow industrial applications where solids loading exceeds what a single-rake system can reliably manage. Smaller plants or lower-flow channels are often adequately served by a single-rake configuration at lower equipment cost.
Applications
Municipal wastewater treatment plants. Multi rake bar screens are standard equipment at the headworks of medium to large municipal plants, providing the first line of coarse solids removal before grit chambers and finer screening equipment.
Pumping stations. Wastewater pumping stations handling significant flow volumes use multi rake bar screens to protect pumps from large debris and rags that could cause blockages or mechanical damage.
Industrial wastewater treatment. Industrial facilities with high coarse solids content in their effluent — food processing, paper, and similar industries — use multi rake bar screens as a robust first-stage screening solution.
Combined sewer systems. Plants receiving combined sewer flow, which carries higher and more variable debris loads than separate sanitary sewer systems, particularly benefit from the continuous cleaning capacity of a multi rake design.
Materials and Construction
Vortex Engineering multi rake bar screens are manufactured from stainless steel throughout, selected for durability in the abrasive, corrosive headworks environment.
Bar rack and frame: Stainless steel AISI 304 standard; AISI 316 available for more aggressive environments, including coastal or industrial applications.
Rake arms and chain/cable drive: Wear-resistant stainless steel components, designed for continuous cyclic operation under load.
Drive system: Motorised gearmotor drive with overload protection to prevent damage in the event of jamming from oversized debris.
Fasteners: Stainless steel A2 or A4 depending on the installation environment.
Frequently Asked Questions
How many rake arms does a multi rake bar screen typically have?
The number of rake arms depends on the screen height, flow rate, and solids loading. Vortex Engineering sizes the rake configuration for each project based on these specific parameters — there is no fixed standard number across all applications.
What bar spacing is used for a multi rake bar screen?
Bar spacing typically ranges from 6 mm to 50 mm depending on the application. Finer spacing captures smaller debris but increases head loss and cleaning frequency requirements; coarser spacing reduces head loss but allows smaller solids to pass through.
Can a multi rake bar screen handle combined sewer flows?
Yes. The continuous, staggered cleaning cycle of a multi rake design is well suited to the higher and more variable debris loads typical of combined sewer systems, where flow and solids content can change rapidly during storm events.
What happens if oversized debris jams the screen?
Vortex Engineering multi rake bar screens are equipped with overload protection on the drive system, which stops the rake mechanism if excessive resistance is detected, preventing damage. Manual clearing of the obstruction is then required before resuming operation.
Is a multi rake bar screen suitable for smaller treatment plants?
Smaller plants with lower flow rates and modest solids loading are often better served by a single-rake bar screen, which offers lower equipment cost and mechanical complexity. Multi rake configurations are generally justified where flow rate, channel size, or solids loading exceed what a single rake can reliably handle.
Vortex Engineering designs and manufactures Multi Rake Bar Screens as part of its complete Screening Equipment range and the full Wastewater Treatment Equipment lineup.
