I am on a tour of Cranbrook’s water system with Director of Public Works Joe McGowan. So far, we’ve seen where our water is stored at Phillips Reservoir, and learnt why Cranbrook is blessed to have lots of pressure in our water distribution system.
In this second article in the “Under Pressure” series, we are looking at how the city reduces the pressure in our water, and why that excess pressure causes problems with leaking pipes.
Because Cranbrook’s water reservoir sits at a higher elevation to the city itself, our water is high pressure. Water gains pressure based on the amount of elevation it loses getting to the tap.
But the elevation difference is big enough that the city has to work to reduce the pressure in our water to make it safe to turn on the tap. The safe zone for water pressure is 42 to 65 psi. Without pressure reducing valves, at Cranbrook’s lowest the pressure would be 260 psi.
To reduce water pressure, Cranbrook is divided into five pressure zones. Every time a trunk water main crosses one of those zones, the city has built a pressure reducing station – there are 13 in total.
Joe has brought me to one of the 13 pressure-reducing stations. We are standing in a small concrete building, filled with blue-painted 24-inch pipes and the technology used to control the water inside.
“We are in the lucky position where we have to lose energy, as opposed to other folks who have to spend it,” says Joe. “The way we do that is with a pressure reducing valve. It takes the energy and converts it so that less energy comes out than goes in.”
The valves look very complex, but the concept is simple. The water comes through the pipe to a special valve that holds a circular rubber disc, or diaphragm. On the top of the diaphragm, the valve uses a combination of hydraulic pressure and a spring to exert force on the water passing through the valve.
Water coming into the valve is forced to push up the rubber diaphragm in order to pass and continue on its burbling way. Pushing against the rubber diaphragm uses energy, thus causing the pressure to drop.
Utilities staff can control the amount of energy, or pressure that the rubber diaphragm takes away from the water passing through.
“We can control the amount of water going through the valve. If we turn it down, there will be less pressure in the water. If we turn it up, there will be more pressure coming in, less pressure coming out,” Joe explains.
For instance, at one pressure reducing station in the highest elevation zone, the water comes in at 120 psi. The valve drops it down to 50 psi.
The fanciest piece of technology involved in the process is the remote monitoring system. The pressure can be watched remotely using specialty software and a radio linked communication network called SCADA, which stands for Supervisory Control And Data Acquisition.
Sitting in his truck, Joe pulls out his cell phone and opens an app that connects to the city’s SCADA system, showing how he can see water pressure and water quality throughout the city with the touch of a button.
The SCADA system also gives the city accurate data about when the most water is being drawn from the system, and where. This helps the city with diagnostics when there is a problem with the pipes.
Cranbrook’s pipes leak surprisingly often, especially in the oldest parts of town on Baker Hill.
“The older pipes get, the less capable they are,” Joe says.
But the age of the pipe is not the only thing that causes it to burst.
If the pipe is not installed properly, it will fail sooner.
The more water the pipe carries and the faster that water travels, the sooner it will fail because the tiny minerals in the water are abrasive in large quantities.
The type of soil surrounding the pipe also plays a role, since moving water creates electricity, and electrons will leave the pipe at a weak point if the soil surrounding the pipe seems more appealing to the electron.
These factors, as well as nicks in the pipes created by rocks or rough treatment when the pipe was installed, all create weakness in the pipe. And water is mean: it will spot a weakness and prey on it.
“What causes the pipes to fail? It’s very much like a person with high blood pressure. What will happen is if you have a weakened vein, that’s where the pressure will want to escape,” Joe says. “If there is a weakened portion of the main, that’s where it is going to rupture.”
Plus, Cranbrook’s pipes are getting on in years. On average, our pipes are 30 to 60 years through a 60 to 80-year lifespan.
Since our water gathers so much pressure from the elevation change, in some areas of the community the pipes are more likely to fail sooner.
“In Cranbrook, we’ve got old pipes that are falling apart, and we’ve got pressure issues,” Joe says.
“After World War 2, a lot of communities grew. We changed from a rural country to an urban country. In order to accommodate that influx, communities built a lot of water and sewer mains. Those mains are getting old, like the people who put them in.”
Like Cranbrook’s roads, the water system needs quite a bit of money spent on it, money the city doesn’t have.
According to a 2012 Infrastructure Report Card, if the city had the money, Cranbrook’s water system would need $8.3 million spent on it immediately just to get it up to scratch before the city can begin to replace pipes.
What’s more, water, sewer, storm water and road systems usually need to be fixed at the same time, so the cost of repairs is cumulative.
In Cranbrook, on top of the $8.3 million initial cost the water system needs spent on it, our wastewater system needs $10 million spent on it, storm water $6.3 million, and roads $58 million.
“These staggering dollar values are required prior to the start of any asset replacement program,” explains Joe.
Mayor Wayne Stetski has previously said that every $200,000 in new money that the City of Cranbrook adds to its budget is a one per cent increase in property taxes.
In 2012, Cranbrook made 24 repairs to water services, 44 repairs to the water mains under the streets, and one repair to a hydrant.
In older parts of town, each repair costs around $5,000. In newer areas, the figure is closer to $10,000.
Joe drives me through the parts of Cranbrook where the pipes are the weakest.
“I liken it to a popcorn popper,” he says, because the ruptures are coming fast.
We drive down one block on Baker Hill where Joe estimates that every lot has had a break in the past two years.
“In this area, we are digging out water mains once a week,” he says.
The situation may seem dire, but the City of Cranbrook is taking steps to reduce the amount of breaks in the pipe, while it waits for money to replace the pipes.
See Wednesday’s Townsman to learn about those ingenuous measures in the third part of the feature series, “Under Pressure”.