Gate required to divert sewage

Lower Murray Water (LMW) in Mildura required a gate to divert sewage flows to catchment ponds. Darren Bennett from LMW was concerned with the traditional square bottom penstocks that had previously been used to control water flows. The square profile had caused entrapment issues on the round channel benching due to the solids lodging in the grooves required to install the square profile in the round benching. This prevented a good long-term seal.

Sewers have a semi-circle profile (benching) to facilitate smooth transition of raw sewage. It is important that all junction and control points are also smooth to prevent material catching and blocking the sewer trunks. Penstocks are often used to divert flow to ponds and treatment plants or facilitate a system shutdown. Placing a square-based penstock in this application has, before now, proved a 'difficult situation'.

Darren contacted AWMA to design a penstock that would provide a solution for his application.

The AWMA design team has developed a 'round bottom' stainless steel penstock. The base of the penstock is custom designed and manufactured to seat exactly within the original profile of the benching. The gate can be made to be cast in-situ for new installations or made to retrofit existing sites. The penstock can be raised manually with a hand wheel, which can be contained level with pits, or motorised using AC or DC actuators.

The round bottom penstock for LMW was designed to fit the same profile as the 525 mm sewer. A second round bottom penstock was retrofitted to an existing manhole pit. This unit was custom made by AWMA to slide inside an original pipe and match the profile of the existing benching.

Darren stated that the stainless steel round bottom penstock was quick and efficient to install and provides greater security than the conventional square-based penstock traditionally used. The custom manufacturing resulted in fast and efficient installation, reducing civil works and decreasing the shutdown time required to install, which is an important consideration on sewer systems.

Barwon Water in Geelong has also used the AWMA round bottom penstock. It is used to control a storage system used in peak demand overflow situations. When the system reaches a peak flow, any excess is diverted into the storage system via a weir and when the peak flow has reduced, the penstock is opened to introduce the overflow back into the system.

Neville Smith from Barwon Water said: "We decided on the AWMA round bottom penstock to reduce the civil works and the time taken for installation. The design suited the limited space in the pit and there was no need to cut the benching."