A study of the transport of solids in hospital above ground drainage systems

Abstract

The transport of solids in "horizontal" above ground drainage pipes was the subject of an investigation aimed at establishing a method for the design of deposit free drainage systems. Tests were based on the measurement of solid velocity in a discharge pipe of variable gradient, the solid being a maternity pad either with or without three paper towels. A test rig capable of supporting discharge pipes of various materials, enabling the incorporation of bends and junctions, was employed and an instrumentation method for measuring solid velocity, depth of flow and rate of flow was developed. Results showed that solid velocity in straight discharge pipes can be characterized by three separate zones of flow, the second zone being the most fundamental, with solid velocity defined by an equation of the form V = (C1-C2)*Sqrt(L/G), where C1 and C2 are empirical coefficients, L is the distance travelled from the w.c. discharge and G is the pipe gradient. The limits of the flow zones can be defined by values of Sqrt(L/G), the larger limit defining the maximum length of deposit free discharge pipe at any gradient. The effect of pipe fittings on the velocity of the solid can be represented by a sharp velocity reduction followed by a gradual velocity regain and may be ignored as long as the pipe fitting is positioned approximately 5 metres before the end of the second flow zone conditions, as defined by a value of Sqrt(L/G), thus allowing sufficient length for the velocity to regain its straight pipe characteristic value. A design method is presented, based on the experimental data collected, which in its present form can be applied to check for the possible deposition of Solids within the "horizontal" discharge pipe system, either due to traversing excessive lengths of horizontal pipework or as a result of bend or junction positioning.