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What the heck are 'air stacks' and why are they all over Vancouver?

What do these metal mushrooms do?
air valve stack vent
Vancouverites want to know what this thing is. The City of Vancouver explains.

If you've ever walked along a Vancouver street you may have noticed a metal pole sticking out of the ground with a yellow cap.

They're not the mailboxes of the mole people or some elaborate urban art piece.

They're ventilation points for underground water or liquid waste infrastructure known as air stacks.

The short poles function as air release valves for the City of Vancouver and Metro Vancouver water systems.

According to a spokesperson from the City of Vancouver, "they are typically located at high points in the system or local high points for a water main. They release any trapped air from the water system to prevent it from building up and creating air pockets."

What happens if an air pocket forms? Well, the pocket can restrict water flow through the mains and so these poles are an important part of maintaining the system.

"We have about 325 located throughout the City. We inspect and maintain all of these valves annually so you may notice City crews working around these air stacks on occasion," the spokesperson tells V.I.A in an emailed statement.

The coloured caps indicate to workers what the vents service. For instance, the Water Services vents have yellow painted caps and Liquid Waste Services have orange ones.

Some conscientious Vancouverites have asked on social media if they can park in front of the vents, wondering if perhaps a similar rule to that of fire hydrants apply but the city and Metro Vancouver assure that, unlike fire hydrants, there aren't any parking restrictions associated with air valves. "So as long as the local parking restrictions allow for street parking residents are welcome to park in front of these air stacks," says the City.

Metro Vancouver adds that "crews will install temporary 'no parking' signs in advance of any work so that people don’t inadvertently park on the maintenance covers."

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