Manufacturers and producers must think through their process safety on ways to mitigate risks against failure conditions in the components within a basic process control system (BPCS) or safety instrumented system (SIS). For instance, failures can occur on air filter regulators (AFRs) on valve actuators. I mention this because I connected with Emerson’s Riyaz Ali, who had a discussion with a major international oil company. Engineers at this company wanted to eliminate any relief valve or the need for a higher pressure-rated actuator should the AFR fail.
Riyaz shared that the general practice in case of an AFR failure is to protect the valve actuator with an additional relief valve in the pneumatic path. This relief valve relieves the pressure on the actuator to avoid damage. Another approach is to size the actuator for a higher-pressure rating. If the AFR fails, the actuator could see the full line pressure at the positioner (output pressure equal to supply pressure at saturation) but be sized for a higher pressure rating to avoid damage.
For the relief valve approach, the challenge is that it adds an extra component for cost, complexity, and ongoing maintenance. A higher pressure-rated actuator increases the cost of the valve package.
He explained to the staff engineers that the DVC6200 with firmware 7 (FW7) avoids these challenges. An overpressure alert and output pressure limit can be set on this digital valve controller. The alert will be active if the output pressure from Port A of the DVC6200 exceeds the configured pressure limit setting for a single-acting direct application.
This new actuator overpressure protection capability in FW7 is helpful in this AFR failure scenario. This capability means that the DVC6200 can be configured to put the valve in a failsafe position with zero pressure in the actuator, thus avoiding mechanical damage and a potential safety incident.
At the October 24-28 Emerson Exchange conference, you can find the DVC6200 and discuss its full range of capabilities with experts. You can also catch Riyaz’s presentation, Can Control valve of BPCS, used as “Final Element’’ for SIF loop?
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