22 September 2017

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Weaverbrook Circular Tank Scrapers : Machine Types

The Weaverbrook range of circular tank scrapers can be categorised into the following Machine Types :

Rotating ½ Bridge Scraper
The ½ bridge is pivoted at the tank centre and driven on the tank wall. Rakes suspended from the bridge present an echelon scraper blade on the sloping floor of the tank to convey thickened settled sludge towards the sludge hopper. The tank floor receives one pass of the blades for each rotation of the ½ bridge.
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Rotating Full Bridge Scraper
The rotating full bridge scraper is used for large diameter tanks in excess of 30m diameter. The bridge is again pivoted at the tank centre and driven on the tank wall at either end of the bridge. An additional series of rakes and echelon scraper blades are added to the extra ½ length of the bridge thus creating two passes of blades on the tank floor for each rotation of the bridge. This reduces the time that the sludge is on the tank floor, essential for large diameter tanks where sludge settlement is greater.
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Rotating 2/3 Bridge Scraper
The rotating 2/3 bridge scraper is typically used in the tank diameter range 20~25m where there is a need to put additional rakes/echelon blades over centre at the point where the sludge volume is greatest. The bridge is again pivoted at the tank centre and driven on the tank wall.
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Rotating ¾ Bridge Scraper
The rotating ¾ bridge scraper is typically used in tank diameter range 25~30m where there is a need to put additional rakes/echelon blades over centre at the point where the sludge volume is greatest. The bridge is again pivoted at the tank centre and driven on the tank wall.
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Fixed Full Bridge Scraper (Centre Driven)
The fixed full bridge scraper is a stationary bridge spanning the full width of the tank. A top centre mounted drive system directly drives a centre rotating shaft which in turn transmits rotation to the diametral rake boom arms which are equipped with echelon scraper blades. The fixed full bridge scraper is an alternative to the ½ bridge scraper on smaller diameter tanks typically <10m.
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Fixed ½ Bridge Scraper (Centre Driven)
The fixed ½ bridge scraper is a stationary bridge with a centre supported top mounted drive system to directly drive and transmit rotation through a torque cage to the diametral rake boom arms which are equipped with echelon scraper blades. The bridge centre is supported above an influent feedwell. The fixed ½ bridge is an alternative to the rotating bridge scraper on larger diameters >10m.
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Suction Clarifier (Syphon Type)
The Syphon Suction Clarifier is a design which is suitable for rotating ½ bridges. Attached to the bridge are a series of rakes from which is suspended a series of vee-shaped ploughs which are designed to collect settled sludge from the floor of the tank. The sludge is lifted from the vee-ploughs by hydrostatic pressure to transfer it into a partly submerged trough at TWL which is fixed to the underside of the rotating bridge. A separate pipe connects each vee-plough to the partly submerged trough and a regulating device is used to set the flow from each pipe. Once delivered to the trough the sludge is then transferred by a siphon device to a central annular static tank ready for subsequent transfer to the external pipework. Suction type mechanisms are used extensively to remove relatively lightweight solids of activated sludge secondary clarifiers. The advantage is that the sludge is removed from the tank quickly keeping them as aerobic as possible.
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Suction Clarifier (Hood Type)
The Suction Hood Clarifier is a design suitable for both fixed bridges or rotating bridges. In each case the rake system consists of a series of vee-shaped ploughs from which outlet pipes go to a central suction hood rotating at tank floor level with the rakes. An external line with an adjustable TWL valve generates a hydrostatic pressure which induces the sludge to flow out of the tank. Suction type mechanisms are used extensively to remove relatively lightweight solids of activated sludge secondary clarifiers. The advantage is that the sludge is removed from the tank quickly keeping them as aerobic as possible.
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Picket Fence Thickener
The Picket Fence Thickener is normally used in sewage sludge consolidation tanks but occasionally specified in potable water treatment. Essentially a fixed full bridge centre-drive scraper with a series of vertical “picket-fence” blades attached to and rotating with the rakes.
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T.P. Aspinall & Sons Limited is a customer focused, innovative, solutions-driven, engineering company which designs, manufactures and installs specialised, be-spoke fabrications, providing both products and services that fully conform to the requirements of our customers and appropriate national and/or international standards.

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