A simple analytical model for estimating air leakage through rotary valves

Abstract

Abstract

This paper presents an analytical model from which to estimate the air leakage through rotary valves feeding positive-pressure pneumatic conveying systems. Estimating air leakage through rotary valves is an important part of the design of certain pneumatic conveying systems. Accounting for leakage assists in estimating blower and bin vent requirements and reduces maintenance costs and downtime. An overestimate of the leakage can contribute to inefficiencies, excessive pipeline wear and particle attrition, while an underestimate can lead to blocked pipelines and severely reduced solid flowrates through the valve.

The formulation of the analytical model presented in this paper is based on the principle of air flow through multiple orifice plates in series. The leakage rate across a pressure differential is determined by treating each constriction between rotor blade and casing as an orifice plate. The validity of the model is confirmed by comparing its results to previously recorded empirical data.

Note that, while this paper addresses rotary valves feeding positive-pressure pneumatic conveying systems, the same principles can be used for the design of vacuum pneumatic conveying systems. For vacuum systems the air density and differential pressure must be accounted for in order to estimate the air leakage rate in the opposite direction through the valve. Accounting for this type of leakage is especially important for vacuum systems with (a) multiple feed points, in order to ensure that adequate upstream transport velocities are reached, and (b) inert gas as the transport medium, where air leakage into the system can dilute the conveying gas.