Ventomat Series ‘RBX’ Air Release and Vacuum Break Valve situated on the levee bank at Nyngan.

Nyngan is located between Narromine and Bourke, 583 km north-west of Sydney.  Most people will remember Nyngan for the 1990 floods, when the entire town had to be evacuated by helicopter.  This was despite the efforts of the townspeople building a levee out of more than 200 000 sand bags, to no avail.  The entire town was flooded after the Bogan River rose to 5.2 metres which was 1 metre higher than the previous record.

After the event a levee bank was built around the town to prevent future occurrences.

Unfortunately the first time it was tested large sections of pipe collapsed and completely flattened. This was due to the negative pressure induced into the system as the water rose and then flowed away from the high points along the levee bank.  No air valves were included in the system.

The sections of steel pipe that collapsed were replaced and Ventomat Air Release and Vacuum Break Valves with an Integral Surge Alleviation mechanism were introduced along the levee.

The Ventomat range of air valves are unique for the following reasons:

1)      Every valve in the Ventomat range of air valves includes a surge alleviation mechanism for protection against water hammer and surge in pipelines.

2)      Full flow capacity of the valve range i.e. a 150mm valve as shown in the picture has a 150mm flow area allowing the valve to ‘suck’ in air at maximum capacity therefore preventing a vacuum occurring in the pipe and protecting it from collapse and structural damage from fatigue.

This is an important fact as a lot of air valves sold in the market place do not have a full flow capacity meaning in similar circumstances damage to the pipeline could still occur if this is not taken into account when the valves are sized.

An Important design feature of Ventomat is a cylindrical float.  All air valves “suck” air as a vacuum occurs.  Air valves with ball or spherical floats react differently to the Ventomat valve.  As air rushes over the top and around a ball float it will create low pressure on the top of the ball, causing the ball to lift up to the outlet and greatly reduce the air intake volume. This is known as the ‘Venturi Effect’ and can be demonstrated by placing a ping pong ball in a small funnel and blowing into the funnel. You would think the ball would fall out but it is held there by the negative pressure formed on the top of the ball.  This is prevented by Ventomat valves.

See the Venturi Effect:  http://www.youtube.com/watch?v=13eoSasj4hw

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