The structure contains four venturi meters that were used to measure water flow on the O-K pipeline.
The decommissioned O-K Pipe Venturi Meter House, a small concrete hut mostly underground, was built to measure the flow in the Orongorongo Karori main, usually called the O-K main. The pipeline was a high pressure pipeline carrying water from the Orongorongo Water Catchment, through Wainuiomata, over the Wainuiomata Hill, and ultimately toward Karori for Wellington’s supply. The O-K Main was built as a major new water source for Wellington, entering service on 23 December 1926 and remaining in operation until its decommissioning in the early 1990s.
The building was under construction at the same time as the Wainuiomata Chlorine Plant in 1964 so may have been operational in 1965. It replaced an earlier structure that had housed the original Venturi meter for the O-K main. The main, and consequently the venturi meters were decommissioned in 1993 when the Wainuiomata Water Treatment Plant came online.
The four Venturi meters inside the building operated by taking four separate pressure readings from different points along the pipe. In many installations, the pressure tappings were positioned at the top and bottom of the pipe, and sometimes on the sides as seems to be the case with this setup. This arrangement allowed engineers to account for variations in flow caused by air pockets, sediment, or turbulence. By averaging the readings from these four points, they could obtain a precise and reliable measurement of the water’s flow rate through the pipeline. This multi-point approach ensured consistent accuracy in monitoring the performance of the water-supply system.
Today, O-K Pipe Venturi Meter House lies hidden on Maintenance Road, its outside concrete walls now carpeted with moss and surrounded by thick ground vegetation.
Credits
Special thanks to Tony Weir for some information in this article.
