Abstract: A backwash distribution apparatus for a filter having a filter tank and a plurality of underdrain laterals includes a first and second separator device positioned in a common main conduit to define first and second auxiliary flumes. The first and second auxiliary flumes are in fluid communication with the common main conduit and the underdrain laterals. The first separator device has at least one flume liquid metering orifice preferably located near the bottom of the first separator device so that it may be below a gas liquid interface in the first auxiliary flume. The second separator device has either a weir edge or a plurality of metering orifices (or both) for passing backwash liquid from the common main conduit into the second auxiliary flume.

Abstract: A concurrent backwash distribution apparatus for a filter having a filter tank and a plurality of underdrain laterals includes a baffle positioned in a common main conduit to define an auxiliary flume between the baffle and the underdrain laterals. The auxiliary flume is in fluid communication with the common main conduit and the underdrain laterals. The baffle has at least one flume liquid metering orifice preferably located near the bottom of the baffle so that it may be below a gas/liquid interface in the auxiliary flume during concurrent gas/liquid backwash operations. A flow distribution plate may be positioned between the auxiliary flume and the underdrain laterals, the flow distribution plate having at least one liquid metering orifice and at least one gas metering orifice. The baffle may take one of many forms. The baffle creates an adequate liquid pool in the common main conduit for low velocity flow of backwash liquid while at the same time providing uninhibited flow of backwash gas.

Abstract: A cap for filter underdrain blocks is provided, wherein the cap has a porous body with a top surface, a bottom surface and downwardly extending flanges. The cap is installed on a filter block having a plurality of orifices in a top wall of the filter block for channelling fluids to and from an overlying filter media. The bottom surface of the cap along with the flanges define a distribution chamber above the orifices, and the cap has a porosity such that a fine grain filter media may be placed directly on the top surface of the cap without media penetrating therethrough and clogging the underdrain blocks. The distribution chamber enhances distribution of backwash fluids throughout the filter media, and the cap eliminates the need for a separate gravel support layer to be installed between the fine grain filter media and the underdrain blocks.

Abstract: An air duct block for air/water underdrain systems in gravity filters comprising a row of interconnected air duct blocks positioned below the filtering media and extending transversely to the underdrain laterals. Each air duct block is in communication with at least one adjacent individual underdrain filter block to supply backwash gas thereto during backwashing operations, thereby supplying backwash gas to its associated lateral. Each air duct block is in further communication with at least one adjacent air duct block such that backwash gas flows between the interconnected air duct blocks and along the row of air duct blocks. This system supplies backwash gas to the entire underdrain system through a single pipe from a source of supply.

Abstract: A cap for filter underdrain blocks is provided, wherein the cap has a porous body with a top surface, a bottom surface and downwardly extending flanges. The cap is installed on a filter block having a plurality of orifices in a top wall of the filter block for channelling fluids to and from an overyling filter media. The bottom surface of the cap along with the flanges define a distribution chamber above the orifices, and the cap has a porosity such that a fine grain filter media may be placed directly on the top surface of the cap without media penetrating therethrough and clogging the underdrain blocks. The distribution chamber enhances distribution of backwash fluids throughout the filter media, and the cap eliminates the need for a separate gravel support layer to be installed between the fine grain filter media and the underdrain blocks.

Abstract: A filter block having a plurality of exterior and interior walls defining a plurality of interior chambers, said chambers including at least a first and second conduits parallel to the longitudinal axis of said block, one disposed above the other, with a third conduit provided to supply gas under pressure to the upper conduit; a top exterior wall of the block having a plurality of apertures distributed thereover. The interior chambers comprise separate conduits for both gas and liquid backwash flows. The interior walls defining the conduits are disposed to provide even distribution of the backwashing gas and to provide bearing support for the top wall of the block.

Abstract: A flume distribution system includes a distributor having a stationary lower portion and a removable upper portion. The lower portion defines a duct which is in fluid communication with a flume and at least one underdrain lateral. The lower portion also includes an apertured end wall which abuts one of the underdrain laterals at a lateral inlet, and a stop is disposed within the duct and spaced from the end wall. The duct receives a removable orifice plate which is adapted to pivot between a slant inactive position abutting the stop and an upright active position restricting the aperture in the end wall. During backwash operations, water is introduced to the flume and enters each duct in the lower portion of the distributor, and the pressure of the incoming water causes the orifice plate to pivot from the slant position to the upright position, reducing the cross-sectional area of the aperture in the end wall and thereby regulating the velocity of backwash flow from the flume into the lateral inlet.