It’s 3:00 am, and you are fast asleep when you get an alert that the power is out at your plant due to a severe storm. Complicating matters there appears to be numerous faulty air actuated ball valves which are apparently “stuck open” causing material to drain from multiple storage vessels.
The automated ball valves which are supposed to be “Fail Safe” upon loss of power have not moved at all. You immediately arrange to have a crew remove the pneumatic actuators and manually shut the valves minimizing the already extensive damage.
You say to yourself “What happened? I know my valves were specified as fail closed. In fact, we just tested them recently, and everything functioned properly when we simulated a power failure on the system. What possibly did I miss?”
The answer is not too difficult to figure out when you look at the installed equipment and factor in one important thing that happened before the power went out…Your air compressor went down! Here is the setup, let’s run through the scenario and see what happened.
To receive a PDF copy of the full article by Brian Booth and Jeff Rinker of Assured Automation, please contact Sarah Bradley (s.bradley@kci-world.com).