Improving Local Control around Safety Shutdown Valves

You have to admire the way a team of engineers when presented with a challenge, come up with a better, less costly approach. Such is the case with a local control panel for a safety valve that Emerson Fisher division’s Riyaz Ali showed me. You may recall Riyaz from earlier posts on the topic of safety.

Local Control Panel 10 IO

The challenge is that safety shutdown valves with conventional local control panels have typically required ten input/output connections between the safety system’s logic solver, local control panel, solenoid and digital valve controller as the picture indicates. These panels get hard wired signals from the safety instrumented system’s logic solver for light indication of valve Open, Close, and Ready to Reset. Also, if the logic solver needs to open the valve after “Ready to Reset” light indicator, “Valve Open” signal needs to be sent to local controller for field technician to open the valve on separate pair of wire. It will also require an additional I/O for shutting the valve from local controller in case of an emergency.

Now, many plants keep metrics on what it costs to install each I/O point, but a ballpark figure of $2,000 USD per I/O point is typical.

Local Control Panel 5 IO

The approach Riyaz describes is based on the Fisher LCP100 local control panel which requires 5 I/O. This means roughly $10,000 savings per installed smart local control panel. If your facility is a refinery, petrochemical, or chemical plant, this could add up, based on your number of safety valves with local control panels. This panel digitally communicates directly with Emerson’s Fisher DVC6000 digital valve controller to eliminate the need for separate wiring for Valve Open and Close indication, Ready to Reset indication, and pushbuttons for manual Valve Open and Close. These digital communications also provide diagnostics to reduce the ongoing costs of maintenance typical with hard-wired solutions.

Riyaz also points out the digital valve controller can provide on-line diagnostics and partial-stroke testing to assist the process manufacturer in checking the safety instrumented function which includes these shutdown valves.

As with most digital communications, the long term benefits in diagnostic coverage with this integrated approach are usually greater than the initial benefits in installation cost savings.

Posted Wednesday, February 7th, 2007 under Safety.

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