Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Patent
1998-02-19
2000-10-17
Lithgow, Thomas M.
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
210744, 210108, 210125, 210128, 210129, 210791, 210793, 210411, 210162, B01D 2962, B01D 3502
Patent
active
061326267
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to filter means incorporating solid/Liquid filtering screens such as those used in the filtration of sewage, and in particular to units incorporating a self-cleaning action to the filtering screens.
BACKGROUND OF THE INVENTION
In general, existing methods of screening liquids which carry solids in suspension attempt to remove some or all of those solids using fixed or reciprocating, perforated or bars screens situated within the liquid flow. These screens must be routinely cleared to remove the build-up of solid material or screenings from the face of the screen in order to maintain adequate flow of liquid through the screen.
Typically, this clearing operation is carried out by one or more of a number of known mechanical methods, such as the action of rakes, scrapers or brushes on the screen. These methods necessarily require expensive equipment such as motors, gearing and drive systems as well as brushes or scrapers which require regular servicing and/or replacement, with consequent implications for the cost and reliability of the operation of such systems.
Such equipment also invariably consumes substantial quantities of electrical power. Not only is this expensive, but the times when frequent blockage of sewerage systems is most likely, e.g. during storms, can also be the times when the electricity supplies are most vulnerable to interruption. In any event, there are particular problems associated with screening to remove solids and floatables from systems which handle both rainwater and sewage. During heavy rainfall, the collected rainwater flow can easily be one or two orders of magnitude greater than the sewage flow which can result in the system exceeding its capacity and overflowing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid/solid filter unit which incorporates a self-cleaning screen. It is a further object of the present invention to provide such a filter unit which requires little or no electrical power to perform the self cleaning action. It is yet another object of the present invention to provide a filtration unit for a rainwater and sewage system which filters additional fluid in the system resulting from heavy rainfall.
To achieve these and other objects, the filter unit of the present invention uses the hydraulic power of the liquid being screened in order to remove screenings from the face of a screening element.
In accordance with a first aspect of the present invention there is provided filter means comprising an inlet, an outlet, and a filter disposed between the inlet and the outlet to filter fluid flowing from the inlet to the outlet, characterised by means for accumulating a head of filtered fluid between the filter and the outlet and means for reversing fluid flow to pass the head of filtered fluid through the filter.
Initially, the pressure of fluid on the inlet and outlet sides of the filter will be substantially equal. However, as the inlet side of the filter becomes blocked with filtrate, a pressure differential will develop as a back pressure on the inlet side builds up. By temporarily reversing the direction of fluid flow the head of filtered fluid passes through the filter dislodging filtrate which has accumulated on the inlet side of the filter without giving rise to any build up of solid on the outlet side. Once the filtrate has been dislodged, the filtering operation may be resumed.
Preferably, the means for reversing fluid flow comprises an additional outlet, disposed on the same side of the filter as the inlet and having means such as a valve for regulating fluid flow through the additional outlet. In one embodiment, the fluid flow through the additional outlet is increased by the valve when the pressure of fluid between the inlet and the filter exceeds a predetermined level. In another embodiment, the valve prevents fluid flowing through the additional outlet when the pressure of fluid between the inlet and filter is at or below the predetermined level.
In a preferred
REFERENCES:
patent: 3298523 (1967-01-01), Johnson
patent: 3534855 (1970-10-01), Guillerd
patent: 3820658 (1974-06-01), Cruze, Jr.
patent: 3841485 (1974-10-01), Malkin
patent: 3948773 (1976-04-01), Tucker
patent: 4055500 (1977-10-01), Parker
Boss Maguire
Lithgow Thomas M.
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