Multifunctional control valves help provide potable water from two different sources in South Carolina
Mount Pleasant is a charming, historic town just across the Cooper River from Charleston, S.C. The Charleston harbor, rivers and creeks infuse a coastal spirit so distinctive that it lures people to visit and live in its wonder. The area boasts a variety of water-based recreational activities, restaurants with great views, and inspired golf courses. English settlers arrived in 1680, sparking a wave of patriotic activity during the Revolutionary War as well as the Civil War. Significant military landmarks and museums pay tribute to the CSS H.L. Hunley and USS Yorktown, located at Patriots Point Naval and Maritime Museum. The region’s historic landmarks and natural beauty, coupled with the friendly people, attract many visitors each year, as evidenced by Mount Pleasant being designated “America’s Most Friendly City” and “World’s Best City” by Travel & Leisure.
Mount Pleasant’s growth is unmatched in South Carolina—it is the largest town in the state with a population of 87,710. Nestled in this booming coastal region is Mount Pleasant Waterworks (MPW), a public utility that serves the town by providing potable water from two sources: groundwater from the Middendorf Aquifer that is pumped from six deep wells and treated at four reverse osmosis treatment plants, and surface-treated water from Charleston Water System. Water is stored in six ground storage tanks and one elevated tank. Two active aquifer storage and recovery wells also provide water during high demand periods.
The water department at MPW was experiencing some control issues with two booster pump stations: Wando Park and Highway 41. Filling the reservoir at a desired rate had to be done manually. This made it difficult to peg the exact flow necessary to manage water moving to storage and what was needed in the distribution system. At this point, MPW staff—including Chris Martin, SCADA and electrical supervisor, and Tony Hill, operations foreman—decided to improve control capabilities involving these assets. The utility already had a state-of-the-art SCADA system utilizing cellular technology, so the ability to control a valve remotely seemed like a good solution. The valve would need the capability to control flow based on an operator setpoint while ensuring that system pressure is maintained above a critical operating point. A method to prevent cavitation also was necessary due to the high pressure differential from filling a low-pressure tank from a high-pressure water distribution system.
After doing some research, MPW determined that an existing valve could be retrofitted to suit the new requirements. However, the utility had to decide between two options for the controlling pilot system: mechanical or electronic. A mechanical system would require a motorized rate-of-flow control pilot with an orifice plate and sensing element to achieve adjustable flow control, and a pressure-sustaining pilot to maintain system back pressure.
The electronic system was a much simpler option, requiring only two electronic solenoids and an electronic controller to achieve the desired flow control and back pressure sustainability. The less-complex electronic system would make future valve maintenance easier when compared to the mechanical system. The electronic pilot system was the clear choice and was installed with an anti-cavitation trim.
The burden of installing a supporting flowmeter and a pressure instrument also was avoided by utilizing the electronic control system. Inlet and outlet pressure transmitters along with a valve position transmitter were retrofitted to the existing ports on the valve. The transmitters were wired into the supplied electronic controller, which allowed the controller to see upstream distribution pressure for sustainability and to determine flow rate through valve for adjustable flow control. This all-in-one solution bypassed the need to reconfigure existing piping for additional instruments.
The electronic controller came preloaded with a variety of typical valve control applications, including valve characteristic flow calculations, adjustable flow control and pressure sustaining control—all desired control features for MPW’s application.
The controller was wired back into MPW’s SCADA system through a local programmable logic controller, giving full remote valve control and feedback. The commissioning of the tank fill system was simplified by the controller’s full color graphical display and preloaded applications, which alleviated the need for custom programming and loop tuning.
Martin was pleased with the fact that the new controller was easy to set up, with loop tunings being performed right on the unit. This saves his department valuable time. In fact, the controller can be tuned remotely with factory support which was a real benefit during the learning curve. He also is pleased with the multifunctionality of the new generation of control valves using dual solenoid control that can be controlled remotely and can perform multiple duties, all electronically.
This initial installation proved so successful that the water department has added three more valves with the same configuration, also supplied with valve controllers. Hill stated that he is “very happy with the new valves. They get great control and are very easy to maintain.”