Digital Flow and Pressure Control With a Motorized Quarter-Turn Valve

In the rural and municipal water industries, valve control of pressure and flow has often been accomplished using diaphragm-type valves.  These types of valves can be tuned to provide altitude control at water towers, pumping stations, and custody-transfer valve stations.  The valves offer a no-slam open/close actuation and can be tuned to sustain a desired back-pressure.  However, these valves also present the owner with challenges.  First, they tend to require a large amount of maintenance to both the diaphragm and the pilot tubes.  Also, due to their reliance on narrow-gauge needle valves for tuning, they can become stuck in the open or closed position when those needle valves become clogged.

Because of these issues, many of our customers have challenged us to provide a more effective solution.  Our approach, which was initially rolled out in 2002, is the digitally-controlled, motorized butterfly valve.  Our initial solution consisted of a Jamesbury High-Performance Butterfly Valve driven by a Limitorque LY-series motorized actuator.  In later applications, the newer Limitorque QX-series motorized actuator was used.

 

To meet the same flow-control and back-pressure-sustaining goals, the Telemetry RTU controlled the position of the valve by utilizing feedback control theory methods.  As an example, such an installation could be used to open/close a valve that fills a GST (ground storage tank).  When the tank drops to a low level, the valve is opened to fill the tank.  When the tank is full, the valve is closed to prevent the tank from overflowing.  While filling the tank, the customer may wish to limit the flow (eg do not exceed 800 GPM), sustain backpressure (eg do not allow the backpressure to fall below 35 PSI), or both simultaneously.  In laymen’s terms, if the flow begins to exceed the example setpoint 800 GPM, the Telemetry RTU slowly closes the valve until the flow rate drops back to 800  GPM.  Or, if the backpressure falls below 35 PSI, the Telemetry RTU slowly closes the valve until the backpressure climbs back to 35 PSI.  Much like the cruise control adjusting the throttle on an automobile, the Telemetry RTU continuously monitors and adjusts the valve position in order to maintain a constant flow or backpressure.

 

 

 

The advantages of this method over those based on diaphragm valves are profound.  First, the operational setpoints are fully integrated into the Telemetry system.  Therefore, the Operator may adjust the settings remotely through the Telemetry software without having to be on-site.  Secondly, the open/close speed of the valve can be greatly reduced using a motorized actuator.  For example, a valve can be tuned for a 20 minute time-to-open and a 20 minute time-to-close.  A diaphragm valve could not be tuned for such a slow operation without soon experiencing a stuck operation.

One particular Water Utility that takes full advantage of throttled quarter-turn valve technology is Jersey County Rural Water (Jerseyville, IL).  Jersey County Rural Water, located within Jersey, Macoupin, Madison, and Greene Counties, is one of the largest rural water districts in the State of Illinois; and it serves over 5000 households, farms, and businesses.  A sampling of Jersey County’s 24-hour SCADA historical charts below tell a complete story of a digitally-controlled, high-performance butterfly valve utilized to control the fill of a GST (ground storage tank) at its Beatty Mound Pumping Station.  The position of the valve (0-100%) is controlled so as to maintain the desired level in the tank, as well as to maintain 55 PSIG back-pressure during fill cycles:

The motorized valve will behave differently during a power outage, though, and it is always important for the Operator to understand this distinction.  When a motorized valve loses line power, it will remain in the current position, since its motor requires power in order to turn.  Therefore, during a power outage, the Operator would need to manually open or close the valve using the hand-crank.  A solenoid-operated diaphragm valve, on the other hand, will generally seek a fully-closed or fully-open position upon loss of power, depending upon the specified configuration of the solenoid valve.  For the diaphragm valve, the Operator would need to manually actuate a pilot valve in order to actuate the valve during a power outage.

Recently, in an effort to improve the performance of our digitally-controlled valve technology, we have investigated the use of a Quarter-Turn, V-Port/Baffled Segmented Ball Valve as a replacement to the High-Performance Butterfly Valve.  Due to the unique shape of its internal v-notched segmented ball and baffles, this valve offers increased Cv Flow Coefficient linearity throughout the 90 degree turn.  And because it presents less obstruction when fully-open, its Cv Flow Coefficient is generally higher than the Butterfly Valve for a given diameter.  On 04 September 2014, we hosted a lunch-and-learn in Saint Louis (MO) where these valve and actuator technologies were demonstrated live.

Would this technology help solve a control challenge in your potable water treatment or distribution system?  Give us a call.  Our Telemetry/Controls Systems are designed to leverage this exciting technology; and we’ll be glad to discuss in further detail.

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