Unless your plant or production facilities was recently built, chances are that your process has a mix of automatic and manual control. A common area for manual control are on-off valves used in many general purpose applications such as tank filling and emptying, filter backwash and blowback, and sequencing operations to name a few.In a Control Engineering Asia article, Intelligent On-Off Valves, Emerson’s Jonas Berge describes:
…how intelligent on-off valves, in conjunction with asset management software, can help reduce unnecessary valve inspection, speed up valve overhaul, and enable shorter turnarounds to be planned in plants.
Traditionally, the automation of manual on-off valves required a bit of wiring:
…with a separate solenoid valve and two feedback limit switches for open and closed positions. However, the feedback limit switches can be challenging to align for correct position indication.
Technology advancements have simplified the wiring requirements with:
…an integrated on-off valve controller mounted on the on-off valve. A low-power piezo pilot valve with spool valve and limit switches are built into the self-contained on-off valve controller protective housing. The single integrated unit simplifies engineering, procurement, and construction which makes it easy to mount on the valve actuator and connect the wiring.
These on-off valve controllers are powered with a single pair of wires powered by the automation system discrete outputs. These valve controllers can be used on a wide variety of on-off valve actuator/valve types including:
…rotary or linear motion valves, most commonly with rack and pinion, scotch-yoke, or vane actuators, but also linear type of actuators with direct or reverse action.
Jonas notes the reason many of these on-off valves are not automated is because of the expense and/or difficulty in getting them wired. The tradeoff is:
Manual valves require operators to go to the field to manually open and close the valve, or simply check if it is open or closed. Such tasks are time-consuming and inefficient, particularly considering how huge and expansive plant complexes can be.
Wireless on-off valve controllers have helped to overcome these hurdles:
The WirelessHART digital communication technology enables on-off valves to be automated without running any wires or using up I/O card channels on the control system. Only compressed air has to be provided.
He describes how these intelligent on-off valves connect with the control system:
A WirelessHART gateway is installed at the edge of the plant unit and integrates with the existing control system. Control system uses Modbus/RTU, Modbus/TCP, or OPC communication to send “open” and “close” commands to the valve via the wireless gateway and to read the feedback, while other software uses HART-IP communication to write configuration settings and read the diagnostics. The same wireless gateway is also the access point for various wireless transmitters around the plant used for asset monitoring to improve reliability and maintenance, submetering for energy efficiency, and monitoring various other points for reduced HS&E risk.
Diagnostics play an important role in the life of the automated on-off valve and may include:
…open and close travel time, which can be trended to detect deteriorating valve performance, as well as reversal counters used to estimate wear and tear. Diagnostics also include high and low temperature monitoring to detect exceeded operating conditions. It is possible to distinguish between an internal on-off valve controller problem and a valve problem in where the valve is not moving. The on-off valve diagnostics makes it possible to more accurately predict need for maintenance and schedule maintenance and turnaround activities based on how hard the valve is actually working and how it performs.
These diagnostics are available to the operators and maintenance personnel and:
…managed centrally from a computer in an office accessing configuration and diagnostics without going to the field. The software also provides around-the-clock automatic device diagnostics monitoring, alerting personnel to any problems.
An on-off valve controller is an integral unit that includes position feedback. A built-in microprocessor and digital communication capabilities enable valve diagnostics from a central location to allow for greater maintenance efficiency. Wired on-off valve controllers can be designed into new plants and wireless on-off valve controller can easily be deployed into existing plants to automate manual valves.
You can connect and interact with other final control and wireless specialists in the Valves, Valve Controllers & Positioners, Valve Actuators, and Wireless groups in the Emerson Exchange 365 community.