Filtec :: Rapid Gravity Filters
Rapid Gravity Filters - Theory of Operation
Introduction
The Rapid Gravity Filter (RGF) forms the backbone of the water treatment industry as it offers excellent performance whilst having low operating and maintenance costs ( in comparison to faster, specialised filter techniques ) and it is precisely because of these advantages that the RGF is the water treatment method most favoured by the major water utilities.
The RGF has been used in increasing numbers since the late 19th century where it replaced the slow sand filter as the technique most used since the slow sand filter requires more real estate to produce the same throughput as the equivalent RGF whilst producing, in the main, a much purer end result.
We have tried to outline the major operations in the RGF i.e. the normal operating mode and the backwash cycle in an attempt to help explain how the RGF is constructed and its simplicity of operation.
| Normal Operating Mode |
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| 1. When the RGF media is placed and water to be filtered is added the RGF system reaches a point of equilibrium where the head ( weight ) of water is not sufficient to penetrate the filter media layers although some percolation does occur. |
| 2. When the inlet valve is opened to allow more water to be filtered to enter the system the head of water increases to a point where the water is 'forced' through the filter media. The particulates in the water are trapped in both the pores of the anthracite and in the gaps between the sand grains. |
3. The water travels through the filter media layers leaving particulates trapped in the filter media. It finally emerges through the fine filter nozzles and is collected and drawn off for distribution.
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Backwash Cycle |
| 1. The outlet valve is closed and clean storage water is pumped into the plenum chamber. Air is then pumped into the plenum chamber which flows through the filter media layers releasing trapped particulates due to abrasion. |
| 2. The water is then pumped which forces water up through the media layers causing them to expand. |
3. The action of the air and the water being pumped into the system causes the particulates to be released from both filter media types. These particulates are then forced up and into the surface of the head of water.
4. The head of water increases until it finally overflows with water rich in particulates. This overflow into the backwash channel is drawn off into settlement tanks for disposal.
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