Bladder holds for Scottish Water

A bladder surge vessel to prevent pipe and pump damage has been installed at a new water treatment plant. Heather Freeman of distributor Olaer Fawcett Christie explains

A Charlatte Surge Vessel from distributor Olaer Fawcett Christie has been installed at Scottish Water's new Blackpark water treatment works (WTW) in Aviemore. The vessels protect pipelines from damage caused by the transient induced by a pump trip or sudden valve closure. Such incidents result in decompression and overpressure effects within the pipeline and can cause collapsed and burst pipes, leakage or pump damage.

The Blackpark WTW will serve more than 12,000 residents in the Aviemore area is expected to go into supply in October. Construction is being carried out by engineering consultancy Black & Veatch (B&V).

As part of the brief, B&V were tasked with designing, sourcing and delivering the most efficient equipment life cycle cost for Scottish Water. It was key to find a solution which required minimum operation, installation and servicing resources in terms of power and cost. Niall Darrant, B&V's mechanical engineer for the Aviemore Project says: "This is the first time I have worked with a bladder surge vessel and we are extremely pleased to find a system which supports our client's key goals of minimising power consumption and reducing CO2 emissions. There was a tight power restraint for the new works, so it was advantageous to utilise the Charlatte vessel."

The hydraulic analysis service offered by Charlatte was seen as a huge benefit by B&V.

The additional simulation and modelling undertaken was a key assurance to B&V that the vessel capacity design developed by B&V for this application was verified by the supplier.

Darrant adds: "The overall service level we received was extremely positive in terms of the support to B&V during the specification phase, where details such as vessel orientation requirements, dimensional constraints and additional features were all incorporated into the design, as we requested, and right through to vessel delivery. "

B&V considered both the capex and opex costs associated with a surge suppression application. The preferred bladder solution in this case has a capital cost benefit compared to a similar sized compressor vessel of 30-40%.

The Blackpark vessel incorporated an nonreturn valve (NRV), which helped Charlatte optimised the volume of the vessel. The NRV is equipped with a shunt to create head losses, removing the need for an additional external nozzle check valve on the pipework, thus giving further savings. The bladder vessel's electrical independence helped B&V overcome one of the project's biggest challenges. Since the 1,500l surge vessel requires no electrical supply, power consumption during operation is nil.

The vessel also requires very little maintenance. This means that typically only three to four checks per year are needed to monitor the pre-charge. The checks can be done at the control desk, thanks to a low voltage signal sent by the magnetic level gauge, meaning that B&V could meet their client's brief.

Installation was very straight forward, taking less than two days, compared with a compressor type system which can typically take several weeks to install. Overall, the bladder surge vessel is an un-complicated solution to the surge suppression application for the new Aviemore WTW.

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