Pipe Down the Chatter
Imagine yourself on a crowded bus, squeezed into the last available seat with people towering all around you. The person seated on your right starts up a conversation, talking about how his day went, what he had for breakfast that morning, the amazing talents of his grandchildren, the state of the economy, the fleas his dog Max just can’t get rid of—he goes on and on and on.
The incessant chattering grates on your nerves until you feel like your head is going to explode. When you finally collapse through your front door, you fall into your favorite chair in a stupor, unable to function. You are completely worn out.
Now, imagine a valve. Your brand-new check valve is doing its part to help regulate the flow of water through a system.
With a relatively low-flow centrifugal pumping system, the flow rate may be insufficient to get the check valve to fully open. After the pump is started, it develops pressure to open the check valve. But as the pump flow increases, the pressure decreases, and the check valve disc closes against the seat, setting up a repetitive banging cycle. This process continues until full flow velocity develops. This rapid opening and closing creates an unacceptable “chattering” noise and causes damage to the seat over time, reducing its effectiveness and the valve life.
Utilities spend significant amounts of money repairing and replacing equipment from normal wear and tear or age, but damage caused by preventable conditions, such as chatter, adds unnecessary expense to the bottom line. Many times, the damage, especially to valves, could have been prevented.
An easy solution exists to prevent check valve chatter. Val-Matic Valve & Mfg. Corp. manufactures a valve called the Tilted Disc check valve, which has a low cracking pressure (less than 0.25 psi), and because of its aerodynamic design, tends to open rapidly and fully to prevent chatter.
The Tilted Disc has optional top- and bottom-mounted oil dashpots that allow an operator to adjust the timing of the last 10% of disc closure to best meet the needs of the system. These valves were installed in a pumping station near Toronto, Ontario with great results.
Located in the Regional Municipality of Peel, one of five administrative regions that are part of the greater Toronto area, the public works department operates and maintains two water treatment plants, two wastewater treatment plants and 80 pumping stations that provide over one million Peel residents with clean water every day. The Hanlan Pumping Station consists of two 800-hp pumps and two 1,000-hp pumps. The station is located near the airport, which makes it central to the system, and able to carry the water 15.5 miles to the reservoir
Anthony Parente, manager of capital works for the region of Peel, explained how the chatter was affecting the system. “Before we added the Tilted Disc check valves with top-mounted dashpots, we were experiencing what I will refer to as check valve chatter.”
Running at elevated pressure
Essentially, the pump was running at an elevated pressure for a short duration of time—it ran close to the pump’s shutoff head. The higher pressure would cause the check valve to open. Once it was open, however, the flow from the pump would increase. Any pump’s discharge head will decrease once the flow increases; therefore, when the flow increased and head decreased, the check valve would close. This chatter didn’t cause any specific concerns in the transmission system, but it is completely inefficient for the pump in operation.
“That and the constant slamming of the check valve would cause some pressure spikes,” Parente said.
A number of considerations went into choosing Tilted Disc check valve with a top-mounted oil dashpot. Roland Barbazza, vice president of Syntec Process Equipment just outside of Toronto, was the manufacturer’s representative who worked with the municipality and design engineer on the project.
“Due to the insufficient space between the location of the check valve in proximity to the pump, the selection of a top-mounted dashpot with its full disc control capabilities and energy-saving design made it the way to go,” Barbazza said.
Besides causing premature deterioration of line components, chatter and other system inefficiencies combine to increase energy consumption and the costs of running the system. The initial costs involved with building or upgrading a system are always on the mind of design engineers, but the consideration of energy costs is a key component in the system planning process. The estimated energy consumption and associated costs are controllable and can be calculated during the system design.
“One of the benefits of the Val-Matic Tilted Disc is the amount of energy savings realized over the life of the valve. It has a very low rate of head loss, which means a system can recover the cost of the valve within a short time span of operation,” said John Ballun, vice president of engineering at Val-Matic.
Taking this into consideration, Parente worked with KMK Consultants, a design-engineering firm, and installed the valve on the troubled pump.
It did the trick, but it wasn’t the complete solution they were looking for.
“The problem had been intermittent for a long period of time at the station. Once we changed the check on Pump 8, we found that the problem moved to Pump 6,” Parente said. As a result, they retrofitted all of the pump lines to contain a Tilted Disc valve with top-mounted oil dashpot.
Because of the success of the Tilted Disc check valves at the Hanlan Pumping Station, all applications within the region of Peel that require a pump check valve are specified with the Tilted Disc with top- or bottom-mounted oil dashpot. It virtually eliminated chatter from the system and significantly increased the energy efficiency of the system.
The problem is solved; the chatter is gone; and it is quiet once again in the region of Peel.