Harmonizing Nature and Innovation: The Larner-Johnson® Valve's Pivotal Role in Central Otago's Legacy

A World of Difference

Situated within New Zealand’s South Island you’ll find an area known as Central Otago. It is a place that spreads out under the southern sun, supporting an array of alpine herbs and coarse savannah grasses, undulating and ancient. In the 1860s it offered the prospect of wealth via conquest and gold – you can still pan for it along the miners' old trails where you’ll be greeted by their decaying stone cottages and the relics of mining machinery.

And yet it is not a mournful place that seeks succour from its past. Today, it is the grape and its rich, extracted bounty, in the form of wine, that provides much of the wealth that nourishes and sustains this vibrant and spirited community. Unsurprisingly, and no doubt born out of the optimism of those early pioneers, the abiding motto of the region is ‘A World of Difference’. A fitting maxim and one that resonates with the story I am about to relate about Blackhall valve application.

An act of rejuvenation

Commanded by mountain ranges the Central Otago boasts a plentiful palette of rivers and tributaries that decant into the green and brown valley floors below. Within such a milieu it would be uncommon not to find man’s imprint and influence in relation to these naturally occurring phenomena. One such is the magnificent Poolburn Dam. Built during the Great Depression to provide water to the Ida Valley farmers as a means of alleviating the need for rationing, and as an employment initiative; it is somewhat akin in this sense to the construction of the Hoover Dam in America.

It is about 100 feet (30 m) high and 480 feet (150 m) long at its crest. And as with all structures that serve to benefit mankind it is an awe-inspiring piece of architecture. Simple in its form and yet mind boggling in its purpose, it sits resolute and alone at the edge of a blue oasis in a vast barren landscape; a place on this planet that one only comes to appreciate after the journey through it is over. It is remote and yet rewarding – a spot such beauty that it was immortalised when depicting Rohan in The Lord of the Rings film trilogy. Decades of service have seen this man-made construction fulfil its task.

Holding back the waters and controlling the supply to the local population. However, it was around 2018 that negative issues were starting to surface – literally; not with the dam, but the type of water control system employed. It was noticeable that the cam-centric valve was beginning to fail in its operation, causing turbulence and inefficiencies that were both vexing and potentially dangerous. Having delt with decades of slurries, grit and various solids passing through the apparatus it was time to scout around for a worthy replacement.

Solving the problem

As world renowned experts in valve technology, with over 50 years’ experience, it was our proven track record and company ethos that made Blackhall Engineering the perfect choice to be called in to assess and provide a solution to the ongoing problem confronting the Ida Valley Irrigation Company. It had to be found fast and had to be the right one first time. There are no second or third attempts to be had in an environment such as this. A dam’s release system has to be functioning properly if it is to meet the needs of the communities it was built to serve. This was a true double-edged sword situation.

It presented our dam engineers with a unique and exciting opportunity on the one hand, tempered with the pressure of finding the appropriate valve to sort out the issue of cavitation, to ensure a smooth flow of water. It also had to achieve a high degree of longevity into the bargain. In the end there was only one answer – the right one!

The choice of experts

To meet the expectations of all parties concerned and the ongoing issues at the site it was decided overwhelmingly to opt for a Larner-Johnson® Flow Control Valve. A tried and tested high-quality product, incorporating a streamlined needle flow control and integral air belt, it would be ideal for this environment. Made from ductile iron, cast steel and aluminium bronze the Larner-Johnson® valve is extremely well suited for in-line pressure or flow control applications, offering a full range adjustment settings.

The valve can also be used for free discharge control at pressures above that of the fixed cone valve. Due to the nature of its design the flow through the valve (in all positions of the plunger) is smooth and free from eddies or disturbance. Just the issue that the old valve was failing to solve. So, all in all it was the perfect valve solution, leading to a very positive impact on the dam's performance. Ultimately it demonstrates the importance of choosing the right control system for dams and reservoirs and the benefits of Blackhall's Larner-Johnson® Valve in achieving long-term reliability and safety.