Specifying modern air valves
When Vent-O-Mat air valves first came on the market in South Africa, more than 20 years ago, they were a significant improvement on the old ‘double ball’ air valves.
A combination of great marketing, and what was, at the time, the most reliable design, meant that these valves were quickly adopted. Engineers became comfortable specifying them, and thousands have since been installed on potable water pipelines from Poffadder to Piet Retief.
In a perfect world, these air valves would continue protecting pipelines from slam and water hammer, forever. But in the African context, where maintenance doesn’t always happen as well as it should, those older design air valves can leave a pipe network vulnerable to water hammer.
The seal on the older air valves is not submerged all the time – it sits in an air gap. When the harsh African sun beats down on a valve full of chlorinated water, the chlorine gas is released. Over time this causes the seals to break down and leak. At best, replacing these seals is a skilled operation, which involves tightening long bolts to exact torques. At worst, the operator simply shuts the isolating valve, and removes the air valve from the circuit. No more leaks, but no more protection either.
The valve body is stainless steel which, of course, has great resistance to corrosion. What’s often overlooked though, is that the flanges are epoxy coated mild steel. In practice, that epoxy coating is easily damaged on installation, and rapid corrosion between the dissimilar materials can happen.
When A.R.I., who are the largest manufacturers of air valves worldwide, decided to enter the South African market several years ago, they knew that they’d have to overcome these problems. A.R.I. invested heavily in research and development, with the desired solution being an air valve that would be suitable for use in areas where maintenance might not be done well.
Their target was to be able to guarantee against seal leakages, caused by faulty components, for 10 years. The air valve also had to keep working even if the water was dirty.
They started by ensuring the large seal is always submerged, so that it doesn’t get exposed to repeated wetting and drying in chlorinated air. That means longer, more reliable seal life. All A.R.I air valves are subsequently guaranteed against seal leakages, caused by faulty components, for 10 years.
The small orifice was then redesigned. Most of the older designs have had to settle for a very small small orifice. In practice, they get blocked, and the air valve stops being able to continually vent the tiny entrained air bubbles. The A.R.I. valve uses a rolling seal mechanism for the small orifice. This means that they could make it much bigger – about 14 times the size of older designs. If you stand next to one of these valves, you’ll hear it hissing as it allows tiny bubbles to discharge almost continuously.
If your upcoming tender specifies air valves, please get in touch, and I’ll send you specifications for modern air valves that you can use in your documentation.