Abstract: A method for back-washing a submerged-type ceramic membrane separation apparatus is provided in which filtrate once removed from the apparatus and a chemical agent are forcibly supplied to filtrate passages in ceramic membrane filters to wash the ceramic membrane filters with the filtrate and with the chemical agent, wherein the water washing and chemical washing are carried out at a predetermined frequency ratio and for a predetermined time period, or wherein the frequency and time period of the chemical washing are determined on the basis of a transmembrane pressure difference, suction pressure or filtrate flux observed during a filtering operation performed by the membrane separation apparatus. This method makes it possible to avoid an excessive chemical washing, and to reduce the amounts of water and chemical agent and the time required for the chemical washing.

Abstract: Two plastic tubelike members on which an annular protrusion or an annular groove are respectively provided to be used as two constructive block members for assembling valve or joint devices are directly coupled to assemble such devices. Critical dimensional relationships on the coupling end having the annular groove are established wherein a deformation process can be controlled to engage the annular groove with the annular protrusion by a radially widening motion and an axially spring motion in elastic dynamics, while the coupling end having the annular groove is softened by heating to become elastic. High coupling accuracy can be secured with high coupling strength and durability.