A guide to introducing electronic instrumentation & automation in water distribution systems
Adding electronic instrumentation and automation to a water management system can provide a number of benefits, but it can seem daunting when users first move from a purely hydraulic system. While there are many instrumentation and automation options available, an electronic control system does not have to be overly complicated. Control valves are a natural place to start since they already perform much of the control in water management. For those who are considering instrumentation and automation for their valves but are unsure of where to start, here are some simple suggestions that can have a large impact.
Where to Start Without Electronics
A good first step into the world of electronics is on the instrumentation side: Add sensors to monitor pressures, flow rates, tank levels, valve positions and other parameters throughout the system. Sensors provide valuable feedback that enables operators and engineers to monitor sites and gain a deeper understanding of their systems’ performance. Even when control is accomplished by hydraulic and mechanical means, having sensor feedback is critical to setting up that control effectively. For example, a flowmeter can provide data that are valuable for setting up a pressure-reducing valve chamber and ensuring equal flow across multiple lines. Electronic instrumentation has become increasingly common in many parts of the industry as a fundamental piece of water systems, and it is worth incorporating.
Avoiding Abandoning Mechanical Methods
When first adding electronic automation, it can be easier to use products that work with existing mechanical components than to replace them completely. There are a number of products that enhance valve control by adding the ability to change set points or actuate valves electronically. These methods retain the original mechanical control mechanism but remove the need to send personnel into the field to adjust a pilot screw when pressure needs to be adjusted.
Battery-operated latching solenoids that can be paired with a programmable timer do not need constant power to hold a position but instead switch position when they receive a pulse of power. They are ideal for low-power applications in remote locations that need pressure modulation set point changes.
In water distribution systems, latching solenoids commonly are used to address the need for pressure regulation to two set points at varying times throughout the day. Lowering system pressure during off-peak hours reduces pipe wear and breakage and lowers maintenance and water loss costs. A latching solenoid on a control valve can switch between high and low pressure pilots at preset times, removing the need for manual set point adjustment but retaining mechanical pilot control.
Pilot actuators fit over a pilot and turn the set point-adjusting screw in response to a control signal. They are not limited to a few predetermined set points, but instead can adjust the pilot to any set point in its range. This makes them a good addition to control valves in applications that need multiple set points.
Pilot actuators are suitable for adding electronic automation to an existing valve because they are easy to retrofit and control. Because the mechanical pilot is doing the actual modulation, the actuator does not require a complicated control algorithm. Instead, operators send the desired 4-20mA set point signal from a control panel, SCADA system or signal generator. The actuator then adjusts the pilot set point and the pilot continues to control the valve as usual.
Valve actuators are used for butterfly valves, ball valves and other direct acting valves. They work similarly to pilot actuators, except that they are mounted on the main valve rather than on a pilot. These actuators typically can be controlled with a 4-20mA signal. However, valve actuators require a control algorithm and can have complex behavior in modulating applications, making them a bit more difficult to control. These actuators can be retrofitted onto existing valves and are suitable for adding electronic automation to butterfly and ball valves.
Control & Flexibility
To get the full potential of electronic automation, consider full electronic control. For diaphragm valves, that means solenoid pilot systems. The main valve is still operated hydraulically via the diaphragm; however, the mechanical pilots are replaced with electronic solenoid pilots. For modulating control, a two-solenoid pilot system is used. A two-solenoid control valve, sometimes called a “double clicker,” works by having the solenoids pulse on and off at varying lengths to control the flow of water entering or leaving the valve bonnet, similar to how a mechanical pilot throttles the bonnet flow to modulate the valve. The pulse lengths are determined by a control algorithm to smoothly and accurately bring the valve to its set point.
Dealing with control algorithms can be one of the most daunting aspects of adding electronic automation. However, manufacturers who offer electronic control valves often also offer control panels pre-programmed with algorithms tailored to control their valves. These kinds of ready-made, plug-and-play options simplify the switch to electronic automation and make it easy for operators and engineers to adapt. A panel like the SCP-TP allows both local and remote set points, data logging, signal retransmission, alarm notifications, and SCADA communication. It also allows valve control speed and accuracy to be adjusted through the panel. These panels can be connected to SCADA for remote control or act as standalone units. For applications with multiple processes or custom requirements, custom panels like the MCP-TP are good options. Custom panels require more communication to design to each user’s needs, but ultimately they are only as complicated as the system’s requirements.
When in doubt, ask questions. Valve manufacturers and their local representatives are usually happy to help determine the best fit for a given application. Talking to others who have already implemented electronic automation in their systems also can be helpful for seeing what is possible. Also, be sure to know what you want your valve to do and what benefits you want to see from adding electronics. Knowing what you want, seeing what others have done and talking to the experts will get you on the right track to bringing electronic automation to your valves.