SPECIAL FOCUS: OPERATORS’ FORUM
Anti-cavitation trim should be an engineered product created for the application to ensure the destructive nature of cavitation is controlled. There are many operational issues faced when dealing with control valves. Here are some common ones: Q: WHAT ARE THE LOCATIONS AND FUNCTIONS OF EACH CONTROL VALVE IN THE SYSTEM?
This Singer valve can control upstream pressure, downstream pressure, level of water flow or open position of the valve, depending on the sensors installed.
How to diagnose and repair automatic control valves By Ryan Carroll
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utomatic control valves are often viewed as simple pieces of equipment. They open, close, or modulate to control water pressure, flow, level, or pumps. Automatic control valves are found all over the world in varying areas such as irrigation, fire protection, aviation, building trades and waterworks distribution systems. As control valves are often unseen or in remote locations, how do crews know when something is wrong before it causes a bigger problem? What can they do to prevent or reduce the risk? The answers lie in the capabilities of the control valve. Many are located in areas where access to power is unavailable. In these locations, hydraulic pilots are utilized to control valves based on flow, pressure, or level sensed by the pilot system. Operators responsible for these valves should look into creating and/or utilizing a preventative maintenance and valve exercising program. This ensures correct 36 | December 2021
operation and that the valves are able to perform as required when hydraulically called into service. If there is access to power, then electronically actuated controls utilizing solenoids, motor operators, and panels will help integrate the control valve to a SCADA system. This enhances the monitoring and control of the system or zone it controls. When choosing a control valve for a specific application, consider conditions that will exist where they do not perform well. They need at least 10 psi of differential pressure to work effectively in most cases. If there is not this amount of differential in the application, a control valve manufacturer can help provide a solution. Issues like cavitation will occur whenever there is a pressure drop of greater than 65% through the valve. This condition is unavoidable at times and can be mitigated by utilizing orifice plates or anti-cavitation trim to provide additional pressure drop areas before the water flows downstream of the valve.
A: If you are responsible for a system with multiple automatic control valves, you should utilize a spreadsheet or database to enter the important data about them. Enter the manufacturer, model, serial number and any other pertinent information available. Take a picture of the valve when it is installed when possible. Then, use a map to show the location of the valve with a corresponding number that can be cross-referenced with the spreadsheet or database. Make a reference sheet of customer service numbers for manufacturers responsible for items within the system and who is responsible for service and supply for those valves. The database can be used to keep track of valve servicing and additional parts that may be added to the valve and changes made to its operating conditions. Q: WHAT ARE THE MOST IMPORTANT MAINTENANCE TASKS FOR VALVE OPERATORS TO PERFORM AND HOW CAN WE STREAMLINE TASKS? A: As mentioned earlier, there are many valves that perform control tasks for different applications in different areas. For example, valve 1 may perform the same tasks as valve 2, but valve 1 operates in a distant area with more particulates, increased pressures, and a higher possibility for tuberculation. As these are identified, valve 1 is at a much higher risk for problems that can lead to reduced performance. If maintenance is not performed at an appropriate rate (i.e., quarterly) it may lead to a failure due to a blocked strainer. If electrical options are present, utilizing local panels or integration to SCADA controls can alert an operator to a possible failure in some applications. Many manufacturers have products that can help with reactionary mainte-
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