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Proximity Switches for Manual Switch Valve and Drum Isolation Valves

Home Forums Coking Safety Safety Interlocks, Automation, Fire Suppression Safety Interlocks Proximity Switches for Manual Switch Valve and Drum Isolation Valves

This topic contains 5 replies, has 3 voices, and was last updated by  Richard Perk 12 years ago.

  • Author
  • #4326

    Darren Hudema

    I am looking for some information from refiners who have installed proximity switches on their switch valves and drum isolation valves. Our Delayed Coker currently has a manually operated Wilson Snyder switch valve and manually operated wedge plug valves for drum isolation.
    We would like to install a safety system to minimize the potential of swinging into a blocked in valve without automating our switch valve and wedge plug valves at this time.

    How does one go about setting up these proximity switches? What type of switch is typically used?

    Thanks in advance.

  • #7758

    Richard Perk

    We used to have proximity switches on our wedge plug valves. They were activated while the valve was seated in either the open or closed positions by switch and shaft collar “contact”. During operation of the valves, once unseated, the valve indication on the TDC would go from either open or closed to moving. As for the Wilson Synder we’ve never had an in house proximity switch. Now that we use the MEA Operator it has a local switch for seat/unseat. I do not see any reason though why the shaft couldn’t be tapped for bolt installations that will “contact” proximity switches located at the Drum 1, Drum 2 and Bypass positions. As for showing seated/unseated some sort of collar “contacting” a proximity switch as we have with our MEA appears to be an easy installation. One thing to keep in mind is that the Coke Dust will sometimes keep the switches from working, so occasional cleaning of the switches may be needed.

  • #7757


    Our experience at ExxonMobil says that the use of retrofit limit switches on wedge plug valves is not reliable over time. They get damaged and fouled. Unfortunately the only realistic way to reliably address the problem is install valves with a factory-installed, self-contained postion switch design. Another option is to have a mechanic clean and calibrate the devices on a daily basis.

    Use of field-installed retrofit limit switches on Wilson-Snyder valves is even more problematic. We do not recommend such an operation, since reliability is essential in this safety application. The alternatives are, of course, an expensive MOV ball valve, or strict application of procedures, involving the use of two field technicians to check each other, plus review with the console supervisor.

    Mitch Moloney 703-846-5095

  • #7746


    We tried prox switches at our Coker, and had disappointing results. The service is too hot / severe to expect reliable operation from these devices. We have had much better luck using pressure indications located between the switch valve and drum isolation valves. The pressure indication is purged using 150 psig steam, and 150 psig purge steam is piped into the system there as well.

  • #5346


    Trust and Train your Operators!

  • #5339


    The Coker I worked at evolved from the old Wilson/Snyder valves to the ball valve with proximity switches. Back in 67 the blowdown valves and warm up valves also had proximity switches which were later discontinued when the vibration and heat and crusty environment caused wiring to fail and valves would open or close causing some major upsets. We went to Operator Training and physical use of chains and padlocks with a well written set of procedures with keys left in the control room and only the correct keys for the operation at hand was allowed to accompany the operator to the structure during that particular procedure. Over time, operators would carry all keys to the structure and being human and tired (as we never convinced management that naps on the midnight shift might me beneficial to fewer mistakes being made by tired humans) mistakes were being made. The joining of companies, new engineers, new money of the nineties brought back the proximity switches and ball valves to avoid operator error mistakes. We’re talking about 30 to 35 years later than the original stuff, so over those years better wiring, better switches, smarter operators came into play. The ball valves, proximity switches of today work well and avoid many mistakes. That having been said, we still had the locks and chains on the blowdown and warmup valves and upstairs on the vent valves, only the switching valves were upgraded to the proximity switches. They were combined with software that the TDC or rather GUS operator had to “OK” the outside structure operators moves in order that the outside man could move the valves needed to make the switches. Me coming out of the old era of nothing locked and not many, but some, mistakes made to using the new stuff with not many but some mistakes being made, well IMHO it was a waste of a lot of hard earned cash. But engineers are paid to think and think they will. Refiners of the future will need to rely on everybodies input in the design and planning stages if they want to avoid mistakes totally and design a fool proof system that works. Will there be money for this? Hopefully so.

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