We have a professional responsibility to consider the total cost of ownership of equipment we specify. Sometimes the lowest up-front price ends up being the most expensive. This is especially true for air valves.
Air valves make up a tiny part of the capital cost of a pipeline but they’re often the cause of significant ongoing repair and maintenance expense.
Most air valves are designed in a way that makes high maintenance costs inevitable:-
- The flexible seals are under high load – as much as 5 tons for a 200mm valve in a 16bar line.
- The seals are not submerged. They’re exposed to high temperatures. And, if the water is treated, they’re exposed to the chlorine / air mix. This causes the seals to perish.
- The float deforms after sitting in the closed position for long periods under this high force.
As a result many air valves start leaking soon after installation. And, they incur high repair and maintenance costs forever after. I’ve worked with pipeline operators who have had to replace every seal every year or risk flooded valve chambers, corrosion and even catastrophic pipeline failure.
Some years ago ARI, the largest air valve manufacturer in the world, set out to design an air valve that wouldn’t leak. It would keep working even in dirty water and any maintenance would be quick and cheap.
The resulting air valve is the only one on the market that offers a 10-year warranty against seal leakages.
The key to its success is the design of the main seal. It has a bronze ring to resist the load from water pressure. This ensures that the rubber part of the seal doesn’t distort over time. And, the rubber part of the seal is always submerged. It isn’t exposed to high temperatures or corrosive chlorine gas so it lasts for many years.
Air valves have two orifices (holes) that let air out: –
- During filling or a sudden stop in pumping causing fast reverse flow, the air valve switches to allow less air to escape through the large orifice. This slows down reverser flow and prevents water hammer.
- During normal operation the small orifice lets out tiny air bubbles trapped in the liquid. This prevents air pockets forming which reduce pumping efficiency.
Most air valves have a tiny small orifice (0.5mm – 2mm diameter). It gets clogged. Once it’s clogged the air valve doesn’t allow air out during normal operation. You can test this by opening the bleed valve at the bottom of the air valve. If air comes out, the air valve isn’t working.
The rolling seal design allows ARI air valves to have much bigger small orifices (about 12 times the size of competing air valves). There is much less chance of it getting clogged and it’s big enough to be self-cleaning. And, if something as large as say, a twig, got caught between the orifice and the seal it can be cleared in 2 minutes without shutting the pipeline down.
If you’re currently planning a pipeline project or thinking of replacing air valves please contact me. I’ll help you calculate the total cost of ownership of various makes of air valves.