Valve operation prevents damage to system
The District of Central Saanich is a member municipality of the Capital Regional District (CRD) of Greater Victoria in British Columbia, Canada. The district has a medium-size, widely dispersed sewerage collection system that sends its sewage to a regional wastewater treatment plant. There is minimal storage capacity within the municipal collection system; multiple lift stations pump sewage through force mains into the regional trunk sewer system and from there to treatment.
One of these facilities pumps sewage through a 12-in. (300-mm) asbestos cement force main to a sewer siphon several kilometers away. When fluids travel such long distances, there is the potential that a surge may be created by even the slightest change in velocity.
When a sewer main ruptures under these circumstances, it can have a significant negative impact on the environment and present headaches involving repair and associated costs for the municipality, in addition to being disruptive to the residents. This is exactly what was happening in Central Saanich due to aging infrastructure and surges created by pumps breaking down and power failures.
The district—in conjunction with the CRD and its consultants Stantec—reviewed its options for upgrading the existing facility to address the ongoing operating conditions. Officials decided the solution was to add an anticipating surge relief valve that was designed to reduce stress on the pipes, thus preventing bursts and adding longevity to the lives of the pipes.
Central Saanich has three 75-hp pumps that each cycle from 30 to 50 times a day. “As the valve operates on every shutdown, it is crucial that the valve operation is precise and occurs at the right times to prevent surges,” said Mark Gimson, Singer Valve’s account sales manager for the project. “Otherwise you can literally blow lines out of the ground.”
The Singer Valve Pneumatic Dynamic Lifter is a very responsive compact sewage relief valve that can handle high pressures (200 psi/13.8 bar or higher) and uses a standard plant air supply to hold the valve closed. It is fitted with a relief pilot that is closed as long as the line pressure is lower than the set point. If pressure rises above the set point, the relief pilot opens, causing the air in the cylinder to vent, which opens the valve.
Central Saanich also needed to address surges caused by power interruptions. When this happened, all the pumps suddenly stopped, resulting in severe surges.
The Pneumatic Dynamic Lifter also solved this problem with its surge-anticipating function. The surge-anticipating application has two three-way solenoid valves—one to put air into the cylinder under the piston and the other to vent air above the piston, driving the valve open during power failures. This way, when the surge returns, it is not coming back to a closed system where it can cause damage—it comes back to an open valve through which it can be discharged safely back into the storage well underneath the pump. The main valve needs to be open long enough to handle the initial surge, but not longer; otherwise it will continue to drain the line. To prevent this, the solenoid is on a timer, which the field crew set at startup. After the timer has elapsed, the solenoid valve allows air to recharge the cylinder, thus closing the main valve.
“The installation and set-up was a relatively simple process,” said Rob Nelson, an electrician with the district who was part of the works crew that assisted in the actual installation. “This unit has worked very well in this application, and we’ve also had great technical support from Singer Valve.”