The Characteristics of Flow in the Vacuum Siphon System

Abstract

At the site, when the vacuum sewer system crosses a river or irrigation canals, a apparatus needs to be installed in the system to reduce vacuum loss. In this paper, a new type of vacuum siphon apparatus is investigated using a full scale test model.
Water and air are separated at the upstream end of the apparatus ; that is, water flows with a so-called gravity siphon pipe across the river and the separated air flows in an adjacent pipe. Then water and air are mixed at the downstream end of the apparatus and flow into vacuum sewer system again.
The flow characteristics of the vacuum siphon apparatus are examined under various conditions of inflow rate and negative pressure levels in the system. The results are 1) the new vacuum siphon apparatus worked smoothly without unexpected difficulties, such as air entrapment in the siphon pipe. 2) The flow characteristics of the siphon pipe are not affected by the conditions of negative pressure levels in the vacuum sewer system. 3) The time interval of inflow to the apparatus and the surge period occurring in the siphon pipe are important time scale for the flow conditions in this apparatus. 4) The simulation model for conditions of the siphon pipe was set up and this model makes it possible to define the design factors for an actual vacuum siphon apparatus in the vacuum sewer system.