FILTRATION & SEPARATION
ENHANCING STRAINER EFFICIENCY
Targeted modifications can enhance the performance of automatic self- cleaning scraper strainers, says Robert Presser, President of Acme Engineering Products
or industrial plant managers, automatic scraper strainers are among the closest solutions to a true “set-and-forget” system, effectively removing both large and fine suspended solids from industrial water, cooling tower water, liquids, and slurries. The basic design represents an efficient and cost-effective industrial self-cleaning strainer. The motorised unit is engineered for minimal maintenance and operator involvement and can remove solids as small as 75 microns. These strainers allow for continuous, uninterrupted flow, including during blowdown cycles.
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Cleaning is performed by a spring-loaded blade and brush system controlled by a fully automatic control unit. The two blades and two brushes rotate at 8rpm, producing an effective cleaning rate of 32 passes per minute. The scraper brushes penetrate the wedge-wire slots to dislodge stubborn particulates and adhered solids.
This design enables the scraper strainers to resist clogging and fouling even in applications with large debris and high solids concentrations. It also ensures complete cleaning and is effective against biofouling. However, incorporating minor customisations or application-specific modifications can further optimise the automatic scraper strainer’s performance and suitability for a given application, says Robert Presser. He recommends the following design refinements that can improve overall effectiveness and operational results of scraper strainers for specific applications: Scraper strainers are available in various screen constructions, each engineered to address different process requirements and operating conditions.
Reverse-formed wedge wire screens are the standard configuration and are widely used due to their mechanical strength, long service life, and resistance to deformation under high differential pressures. Their smooth,
14 MARCH 2026 | PROCESS & CONTROL
continuous slot profile minimises particle wedging and allows effective use of automatic brush cleaning mechanisms, making them well suited for continuous-duty and demanding industrial applications. For processes that require finer filtration or more precise particle retention, multilayer sintered metal mesh screens are the preferred option. These screens consist of multiple layers of woven wire mesh bonded together to form a rigid, porous structure. This construction provides consistent and accurate filtration ratings while maintaining good permeability and structural stability, making them suitable for applications involving fine solids or strict product quality requirements. In applications handling fibrous or stringy materials, perforated screens with round holes offer superior performance. The round-hole geometry reduces the tendency of fibres to lodge in the openings, promoting easier self- cleaning and more reliable operation. As a result, these screens help maintain stable flow conditions and reduce the risk of blinding in fibre-laden process streams. Scraper strainers allow the solids to accumulate at the bottom of the vessel, where the blowdown valve will open periodically to clear them out. Blowdown occurs only at the end of the intermittent scraping cycle. Liquid loss is minimal, accounting for less than one percent of the total system flow.
If additional pressure is required to clean the screen, however, an inexpensive trash pump can be added to the blowdown line to assist in removing the solids, debris, and sediment that collect in the strainer sump.
Alternatively, the sump can be replaced by a cylinder bracketed by two gate valves that open and close as needed to remove the solids waste.
For applications with high solids loading that are prone to clogging, a macerator can be installed upstream of the automated scraper strainer. This solution accommodates heavy
solids loading while ensuring uninterrupted flow and dependable, clog-free performance. When the chemical properties and temperature of the process fluid raise concerns about material compatibility, automated scraper strainers are available in other materials such as Monel, D2205, SD2507, and even Fibre-Reinforced Plastic (FRP). The internal mechanism and wetted components can be manufactured from super duplex or similar high-performance steels. Although standard carbon steel construction is adequate for typical use, corrosive environments such as those involving seawater, erosive slurries, or aggressive chemicals can quickly corrode conventional equipment. This can lead to potential issues in safety, quality, and compliance as well as production downtime, requiring premature strainer component replacement.
In many industries, duplex or super duplex stainless-steel construction is used to resist corrosion, but at considerable cost. Today, a much more cost-effective option is to utilise Fibre-Reinforced Plastic (FRP) strainers that are specifically designed to be resistant to corrosive environments at a fraction of the cost of duplex or super duplex stainless steels. Presser points out that FRP can be used for external strainer construction, including for pressure vessel applications up to 300 PSI. The internal mechanism is still manufactured with super duplex or similar steels. With this approach, manufacturers can reduce costs by approximately 50 percent or more while maintaining required performance standards. Typical uses include desalination systems, wastewater treatment, irrigation infrastructure, power generation facilities, and equipment used in the manufacture of food, pharmaceuticals, and both consumer and industrial products.
Most manufacturers of automatic filtration systems commit to either backwash or
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