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Modesto maintains water control with custom-designed solutions
The City of Modesto, Calif., is located 90 miles (145 km) east of San Francisco. Modesto’s 200,000 residents use 55 million gal of potable water per day. In 2006, the city decided to upgrade three of its eight water storage tanks. The plan was to modernize the booster pumps and automatic valve controls at these locations. The project would provide an immediate improvement in water pressure to customers in South Modesto.
The butterfly effect
After years of using motor-operated butterfly valves and electric actuators for filling these tanks, the city came to terms with the problems associated with using this technology.
First, the valves experienced stem-seal problems after just a few years of operation. The root cause of this problem was turbulence in the flow stream that would cause the butterfly valve to rock back and forth. The result was stem-seal leakage and premature bearing failure.
Second, mainline pressures would fluctuate when opening electric actuators too quickly, as well as pressure-surge and water-hammer when closing them. These issues were direct results of poor speed control. Newer electronic actuators provide better speed control features, but a butterfly-style valve still offers limited flow control.
“For our application, motor-operated butterfly valves were not the right choice,” said Steve Fassio, an instrument technician for the City of Modesto. “It was time to look for alternative solutions.”
In order to improve the water distribution system for residential and industrial customers, the city needed automatic control valves with adjustable flow control, adjustable opening and closing speeds (to minimize mainline pressure fluctuations), manual override for emergency operation and an interface to the city’s SCADA system for remote operation.
The solution was Singer Valve’s 2SC-MV valve with MV1-TP electronic flow control and metering. The MV1-TP provides touch-screen functionality for local control. Remote operation was easy to implement: Singer’s documentation made it simple to connect and integrate the control panel into the City’s SCADA system. The PLC-based touch-screen controller offers on-screen calibration of process signals, graphic trending displays for valve PID tuning and manual mode selection for testing and maintenance. “This flexible package of controls was just what they needed for their system,” said Dave Burrell of Southwest Valve, the exclusive representative for Singer Valve in California.
Eugene Bahia, instrumentation technologist for Singer Valve, was on-site for the start-up to ensure that the valves and panels were installed and wired correctly. Bahia spent time observing valve and panel operations, then simulated failures to insure that the system was performing to City of Modesto’s specifications. The city requested a modification to the touch panel in order to make it easier for its water system operators to use. These changes were programmed on site before the valve was placed in full automatic control. “Eugene understood our needs,” said Fassio. “He was invaluable in commissioning our valves and training our maintenance staff.”
“Our three original valves have been in operation for five years without one mechanical or electrical failure,” said Fassio. “We have been very pleased with our Singer valves. The product quality and service support have been outstanding. We continue to purchase Singer flow-control and pressure-reducing valves for many applications.”
The most notable of these purchases was in 2010, with the installation of a fill-control valve on a new 4-million-gal (15,141,647-liter) storage tank. In this case, another storage tank is in close proximity and connected to the same distribution pipeline. It was crucial that the pipeline maintain normal pressure during filling cycles. Pressure can drop substantially if both tanks attempt to fill at the same time.
Singer Valve’s solution was to add an influent pressure transmitter to a MCP-TP multi-process control panel. This meant that if inlet pressure drops below an adjustable set point during filling, the PLC controller would send an override signal to reduce the flow until inlet pressure returns to normal. This enhanced control program includes all the functions of the original flow-control valves plus this essential customized feature. This results in stable mainline pressures. It also means that during peak summer demand, the City of Modesto is confident it can fill both tanks simultaneously.
This new valve also incorporates an additional safety feature: It includes an optional dual-diaphragm valve chamber and a tank-level-sensing altitude pilot control, which provides a positive mechanical override for valve shutdown in the event of a control system failure. If the tank level continues to rise above its normal level set point, the valve will close regardless of panel command, primary diaphragm integrity, primary pilot system failure, solenoid failure or even a plugged strainer.
“Based on our five-year history of outstanding performance from our previous Singer valves and control panels, I believe I may never need this feature,” said Fassio. “It still provides the City of Modesto with additional peace of mind.”