Bar Screens

Clarifiers and screens are used to remove solids from liquids through gravity settling or mechanical screening processes. Wastewater clarifiers are also used for clarification of bio-solids prior to discharge to the fields. Clarifiers and screens perform primary functions in wastewater treatment systems.

Treatment equipment such as clarifiers and screens, comminutors, and grit chambers are used as wastewater first enters the treatment plant. API (American Petroleum Institute) separators are used in the treatment of refinery wastewater that has been contaminated by oil and oil-bearing sludge. In an API separator, wastewater is collected in a pretreatment section that allows sludge removal, and then further treatment processes are used to more completely remove entrained oil in all forms.

Water clarifiers, similar to clarifiers and screens, assist in optimizing a treating system by improving efficiency and helping to purify produced water to meet effluent water specifications. A water clarifier consists of special blends of polymers, coagulants, surfactants, and metal salts which work in conjunction with process systems to remove oil and water soluble organics (WSOs) from the water. These types of clarifiers and screens reduce the turbidity or cloudiness of the water and remove particulate matter that could plug up down-hole production or disposal formations.

Oil/water separators (OWS) are specialty tanks designed to separate free oil, grease and settleable solids from water. After separation, clean water is discharged to a storm sewer, while the separated oil is retained in the tank for proper disposal at a later time. Oil/water separator applications are generally for rainwater runoff and equipment wash downs.

The Copa Mechanical Raked Bar Screen is suitable for almost all CSO applications. The Mechanical Raked Bar screen's modular design makes it easy to retrofit, through 600mm diameter manholes, into existing overflow chambers.

  •  4, 6, 8, 10 and 12 mm bar spacings
  • Continuously mechanically raked
  • Can retrofit through 600mm diameter manhole
  • Stainless steel
  • Retains screenings in the flow
  • Hydraulic Drive


The Mechanical Raked Bar Screen applications include storm tank discharges, emergency overflows on pumping stations, storm weirs on sewage treatment works and overflows within the sewage system. The screen is ideal for both retro-fit and new Storm overflow chambers.

Operating Principle

The Copa Mechanical Raked Bar Screen allows water to pass through to overflow whilst retaining the screenings in the flow. The screen is continually raked by a hydraulically driven cleaning mechanism. Flow rates from 50 -2400 l/s can be catered for with a single screen module, although multiple units may be used to increase flow capacity.

With over 250 screen installations ranging from 50 l/s to in excess of 20,000 l/s the Copa Mechanical Raked Bar Screen has a proven track record for efficient, reliable and cost-effective sewer overflow screening.


Eimco Water Technologies, following extensive testing into vertical CSO screens concluded that they are far less efficient than screens which are installed horizontally. The Copa Mechanical Raked Bar Screen utilizes fixed stainless steel bars which can be retrofitted through a 600mm diameter manhole.

The bars are continually raked by a hydraulically driven cleaning mechanism. Water is allowed to pass through to overflow whilst screenings are retained in the continuation flow.

Research Lays Vertical Screen to Rest

Use of the horizontally configured screens ensures that all flows, whether high or low, are screened with velocities kept to a minimum. The entire flow is in contact with the screen whilst the perpendicular flow path screens more efficiently.

Because the bars of the horizontal screen are actually oriented vertically, they are far stronger than horizontal bars which tend to sag, especially on longer screens and the vertical bars can be walked on for more convenient access to the installation.


The normal maintenance of the Mechanical Raked Bar Screen is to inspect the screen periodically to ensure the surface area of the screen is free from any obstruction. It is also recommended that a dry run test is carried out. Both procedures are easy to carry out.

All maintenance may be carried out from the top/clean water side of the screen with the guide rods, combs, and drive unit being easily removed for replacement/inspection. The main framework and screening bars should not be required to be removed; however should this be necessary, each module may be split from its partners and removed. Should this be a slave unit from the end of the screen assembly, then it is possible to re-establish the operation of the screen without this module at a reduced flow capacity.

Other required maintenance includes replacing the hydraulic fluid within the hydraulic pump which may be carried out at its location within the control kiosk. These oil changes/checks should be carried out on an annual basis.