The Experimental Research On The Maximum Allowable Fullness Ratio (α) Of UPVC Plastic Drainage Stack

Application Enforcement of the plastic drainage pipes had to stablish the theory for estimating of the maximum discharge capacity of the plastic drainage stack in building and the core issue of the theory was to determining of the maximum allowable fullness ratio of the plastic stack.A seven-story experimental system using UPVC drainage pipes was employed in the study, three major aspects about the study were as follows:( 1) The maximum allowable fullness ratio of UPVC plastic stack( 110-mm) was determined after its discharge capacity and terminal velocity were measured in different ventilated conditions. The results indicated that the maximum discharge capacity, the terminal velocity and the largest permissible fullness ratio of 110mm plastic stack were 6.255L/s, 4.201m/s,and 0.18 respectively when there was only stack vent. It also was measured that they were 11.516L/s, 5.597m/s, and 0.25 respectively when there was specific vent stack.(2) The reference value of the largest permissible fullness ratio of plastic stack was obtained after theoretical analyses, Inference of the terminal velocity and the largest rate of flow in plastic stack were also made. It was recommended that the α value could adopt from 0.15 to 0.18 in single stack venting system and 0.24 to 0.26 in specific stack venting system.(3 ) The measurement of the maximum negative pressure of UPVC plastic stack( 110-mm) and the study of the pressure variation in stack were made. It was obtained that the maximum negative pressure which led to trap-seal breakage was about -10mmH2O instead of the generally recognized value—-40 mmH2O. It was also observed that the pressure in plastic stack was varied with different rate of flow.