Move to Automated Water-Processing Operations
Jane Alexander | November 13, 2017
Regardless of application, the right initial decisions are crucial to the successful operation and maintenance of automated-valve systems.
When considering whether a water-processing operation is a candidate for automation, it’s important to understand why. Automation can reduce labor costs, control devices in remote areas, engage a sequence of operations, or increase the safety measures. One of the best ways to add automation to an existing system is to use an actuator instead of a hand-wheel and operate the valve through a control cabinet (Fig. 1).
According to automation experts with Festo (festo.com, Hauppauge, NY), choosing the right level of technology and implementing a control cabinet for water applications begins with an audit of the current system. Making a detailed list of valves and equipment that control the process is essential when planning to upgrade a system. Consider common equipment such as pumps, valves, sensors, and the presence of a compressor.
Other important considerations are whether the installation is indoors or outdoors and if hazardous systems or environments exist. Planning for automation must also consider the type of media that flows through the pipes (media other than water may dictate the type of components and control panels to be specified).
Additional considerations include sensors and valve assemblies. Selecting the right types is key when automating a water-processing operation. Festo’s experts offered the following advice. Consider the types of sensors that the automated controls will rely on for system feedback. Temperature, turbidity, flow, and pressure are common measurements in a water facility. Once a sensor inventory is completed, note which are critical for operation, those that are required for safe operation, and which may be luxuries. With this list, a minimum and maximum requirement for the inputs and outputs (I/O) can be determined. Different types of systems can be configured to allow expansion.
Sensors can be used as triggers to initiate a sequence of events or a single operation in an automated system. For example, a sensor may indicate to the controller—typically a programmable logic controller (PLC)—that the pressure is too low and that a filter may be clogged. This can cause the system to pause the operation until the filter is replaced. When the sensor indicates an acceptable pressure level, the PLC can notify an operator or automatically turn on the flow.
In addition to pressure measurements, other operations can include a sequence of automated valves opening and closing based on time, level, temperature, and water condition. A likely scenario begins with a large butterfly valve providing the water to the system. This valve may be operated manually as it is opened at the beginning of the day and closed at the end, or that same valve may be automatically opened and closed. The water passing through the butterfly valve is then transported to a filtration skid or preparation equipment before it’s diverted to another area of the plant.
Depending on the required filtration, multiple valve-actuator assemblies are likely to be installed, and they can be controlled by a PLC in a control cabinet. These valves will divert the water through multiple filtration assemblies. Such systems are often configured to remove large particles first and smaller particles afterwards.
With many automated-valve configurations, including pneumatic and electrical signals, a short run of wires to the control cabinet can save costly installation and difficult, time-consuming troubleshooting time if an open circuit becomes an issue (Fig. 2). Using a cabinet for local control, an Ethernet wire is all that is needed to ensure communication throughout the facility.
Information from Festo points to four valve assemblies and the combinations of inputs and outputs that can be used for pneumatically actuated control (Fig. 3):
Configuration 1 uses a Namur valve connected to the compressed-air line, which will direct the air to either the “open” port or “close” port of the actuator. This setup requires an electrical signal to be wired to the Namur valve, a sensor box, and a pneumatic connection to the compressed-air line. The sensor box detects which position the valve is in and sends the feedback to the controller. The inventory for Configuration 1 includes two electrical wires and one pneumatic line. This configuration is best suited for a local control panel, especially if multiple valves will have a similar configuration. This one input and one output setup does not require a valve terminal to be installed in the control cabinet.
Configuration 2 uses a valve terminal in a cabinet and two pneumatic lines running to the actuator. One of the lines will be pressurized, depending on the desired valve state. This setup also includes one electrical wire to communicate the state of the valve. Inventory: one electrical wire and two controlled pneumatic lines. This system benefits from short runs of electric and pneumatic lines to a local control panel.
Configuration 3 uses only a Namur valve and does not provide feedback to the controller. This setup requires one electrical line for control and one connection to the supply air. The advantage of this system is that it does not require a local controller in a panel. It does however, require a potentially long run of electrical wire to communicate with the PLC. Inventory: one electrical wire and one pneumatic connection to the compressed-air line.
Configuration 4 uses a valve terminal to control an actuator and two controlled pneumatic lines from a cabinet. This design requires only two pneumatic lines and may be ideal for a hazardous location or in an area where there are concerns that electrical devices may be exposed to excessive water. Potential disadvantages include the run of long pneumatic lines if a local controller is not included. Inventory: two controlled pneumatic lines.
Determining where the control cabinet will be mounted is critical in each of the four configuration scenarios, i.e., will it be at risk of overheating or require positive ventilation?
Different types of enclosures offer different levels of protection. The cabinet manufacturer will provide a rating for environmental resistance based on National Electrical Manufacturers Association (NEMA) standards.
Understanding the basics of automating valves puts plant personnel in a better position to operate and maintain these systems. This knowledge takes some of the mystery out of automation and ultimately leads to higher water quality and consistency. EP
For more details on automating water processing operations and other applications, standardized control panels, and information on a variety of related support services, visit festo.com.