Lateral member assembly for underdrain lateral system

Abstract

Lateral member assembly for use in an underdrain lateral distribution system is made of plastics but is as capable as much heavier and more costly prior art metallic assemblies in supporting a bed of filter media which must be periodically backwashed with liquid and gas. Complementary elements, including a rigid extruded floor plate member having longitudinally extending side edge channels, and an overlying screen member having flange portions adapted to be retained by undercut recesses in the side edge channels, are adapted to be assembled to each other to form hollow lateral assemblies. In a preferred embodiment, the screen member is telescopically assembled to the floor plate member to cause the screen flange portions to interlock with the recesses in the side edge channels. The resulting assembly is sealed against leakage where the members are interlocked by a pair of flexible, integral plastic sealing strips which are co-extruded with the rigid floor plate member. In an alternative arrangement, the flange portions of the screen members engage a cam surface on the floor plate member which forces them away from each other as the screen member is pressed down against the floor plate member, thus causing them to snap into the undercut recesses in the side edge channels. The flange portions are then retained in a locked relationship with the floorplate member and sealed by flexible rod members forced into the space between the outside surfaces of the screen member and the outer walls of the side edge channels.