The biggest nozzle check-valve yet made by Aveng Manufacturing DFC has been delivered to a neighbouring state for incorporation in a pipeline project as a key part of pipeline pressure management.

The giant 1200mm nominal bore Vent-O-Mat NCV model B weighs almost 5 tons and has a flow range of 800 to 4500 l/s.  DFC shipped the completed valve in February.

The design engineers for the pipeline project elected to use a nozzle check-valve in the pressure management system because of its suitability for systems using water flow rather than air to protect against damage by surge and water hammer.

Pipeline surge and water hammer are caused by separation of the water column when a pump trips or is switched off.  The column separates, and potentially damaging volumes of water begin to surge back and forth within the pipeline.

Damage is usually prevented by the use of air valves that allow air to be drawn into or ejected from the pipeline to compensate for pressure build-up and vacuum caused by movement of the water column, but in the case of the neighbouring state’s pipeline, the time needed to refill the pipeline against the pressure of indrawn air was viewed as undesirable.

Instead, an alternative solution was designed to use the vacuum created by water column separation to draw additional water into the pipeline from a feeder tank at the top of the pipeline profile.

The nozzle check valve (NCV) is the ideal product to aid this process, because it is designed to open readily for forward flow under normal conditions, to backseat firmly at low flow, and to close fully and rapidly on reverse flow without any of the shock associated with standard check-valves as they slam shut.

Seat leakage in the closed position is minimal.

In the case of the DFC NCV, an annular ring design is used to minimise disc weight, allowing the valve to switch from fully open to fully closed in a fraction of a second.  Dynamic and head loss performance is outstanding because of the low disc mass and superior pressure recovery capabilities of this annulus configuration.  The annular ring design also prevents jamming under conditions of unevenly distributed flow, for example after a bend.

DFC won the neighbouring state contract because of the Vent-O-Mat NCV’s ability to meet project application parameters.  These are that the valve has to be in the closed position at the minimum system static head of 7 metres, and re-open under a differential head of between 2,5 and 5 metres.

The NCVs of other manufacturers require much larger differential heads to open, and competitors declined to submit tenders.

Manufacture presented challenges because of the very large size of the 5-ton valve, and the need to find a machining centre capable of managing the weight and dimensions of the casting.  DFC contracted out for this process, supplying the necessary software models for programming the outsourced CNC machining centre.

The completed nozzle check-valve passed all performance tests after manufacture was complete.  Leakage in the closed position was well within the specification of BS EN 12334 section 4.2.3.

DFC has delivered the valve to site for installation and commissioning in March.