Pressure Management Scheme: PRV Install on Live Main

The brief

Affinity Water engaged us to install a pressure reducing valve (PRV) on a live water main as part of a pressure management scheme. Pressure management is how a water utility holds network pressure at a target setpoint rather than letting it run at whatever the upstream pressure happens to be. Properly managed, it cuts leakage rates, reduces burst frequency on ageing pipework, and extends the operating life of the assets downstream. Installing the PRV on a live main, without taking customers off supply, is the bit that needs the technique stack to all line up.

The challenge

A PRV can’t be cut into a pressurised main while the main is still flowing. Something has to isolate the working section. Two options exist: shut the main upstream (which takes customers off supply), or install line stops on either side of the working section (which keeps the main live and customers in supply). The second option is standard on pressure management schemes because the whole point of the scheme is network reliability, and pulling customers off supply to install the asset that’s going to protect them would be self-defeating.

Line stops on their own aren’t enough either. While the PRV is being installed, the water still has to get past the working section to downstream customers. That’s where the bypass pipework comes in. A temporary parallel run is built round the working section so flow is diverted through the bypass while the main run is worked on. When the PRV is in and commissioned, flow switches back through the main run and the bypass comes out.

Our approach

Mark and Ciaran carried out the works. The sequence ran as follows.

Full excavation first, exposing the live main down to working depth and giving the crew room for the installation to follow. Under-pressure drilling next, tapping the main at two points to mount the line stops. Line stops set, isolating the working section of main while leaving the rest of the network under pressure.

Bypass pipework installed to route flow around the isolated section. With the working section dry and the network still live, the PRV was cut in, jointed up, and commissioned with its downstream pressure setpoint configured to Affinity’s requirements. Once the PRV was proved under pressure and passing, the bypass was dismantled, the line stops removed, and the main returned to full service with the new PRV active.

Site reinstatement followed, bringing the carriageway and surroundings back to their original condition.

Outcome

PRV commissioned on a live main with no service interruption throughout the works. This is the full pressure management install sequence delivered in-house: the excavation, the tapping, the isolation, the temporary flow management, the valve install, and the reinstatement, all running as one sequenced job. It’s the shape of work we do when a water companies needs a PRV scheme delivered end to end on a live distribution main.

For the individual technique pages see our under pressure drilling and line stopping capability pages. The service context sits under water mains repair and maintenance for water companies.