Double Girder Perimeter Traction Overhead Crane

Usage Function

The double girder overhead crane falls under the category of perimeter traction cranes, designed for the removal of biological sludge and suspended substances in circular settling tanks of the primary and secondary sedimentation section in municipal and industrial wastewater treatment plants. Its primary uses include: downstream of the sand removal process to further capture sedimentable solids to lighten subsequent treatments; after the biological phase to allow the separation of the sludge-liquid mixture; in any chemical-physical treatment to separate flocculated reactants from the treated liquid. The double girder crane is specifically sized for heavy loads and large bridge spans.

Surface Scraper


Gear motor

Construction Features

Within the tank, solids deposited by gravity on the bottom are removed and sent to the central part of the cone for extraction using a dedicated bottom scraper. The bottom scraper is connected via tubular elements to the mobile girder, which also serves as a walkway. This girder is supported on one side by a central base bearing in the tank while the other end is fixed to the traction trolley that moves along the tank’s edge. The water separated at the top of the decanter overflows through a special profile (Thomson). In addition to its primary function (separation of heavy solids), the scraper bridge is also equipped for the collection of surface substances. To this end, it is supplied with a surface scraper mounted on the mobile girder and placed inside the foam blade, which removes any un-sedimented floating substances and sends them to a collection and evacuation tray (scum-box). This system, known as a double girder, consists of two translation trolleys with a double axis, complete with wheel supports and a rubber blade for cleaning the trolley’s running tracks. Each trolley is individually powered by a gearbox of a leading brand, sized to ensure the necessary peripheral speed of the crane. The translation of each trolley is achieved with two rubber-wheeled wheels, one driving and the other idling. The drive wheel is directly mounted on the gearbox shaft through a special flange, while the driven wheel is mounted on a carbon steel shaft. Additionally, it features two bottom scrapers, two surface scrapers supported by adjustable supports fixed under the bridge beam, two scum-boxes for collecting floating substances, a Thomson profile, and a foam blade, complete with fastening brackets typically made of AISI 304 stainless steel.


  • Enables more stable operations
  • Uniform operation with motor control
  • High removal capacity of biological sludge and suspended substances
  • Easy application to existing basins
  • Available for tanks of various diameters according to the client’s needs.


  • Materials: stainless steel AISI 304 L / 316 L / paint coating:
  • Immersed parts in AISI 304 – Emerged parts in hot-dip galvanized carbon steel


  • Foam scraper blade
  • Thomson profile
  • Scum collection hopper Scumbox
  • Paraschiuma edge
  • Bottom scraper blade
  • Central deflector
  • Mobile girder with a walkway function
  • Side traction trolley
  • Central pin

Purchase request

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Purchase request