Foxboro/Eckart SRD991 Positioners Overheating

[jlr899]

Replacing old Bailey control valve positioners with Foxboro-Eckardt SRD991 intelligent positioners on our waste heat boilers. Worked fantastic until the warmer ambient temps reach into the 90'S at which time they started to overheat and fail until they cool down. Foxboro stated temp rating at 80c (175f). Units are controling feedwater drum level and boilers are heated from waste heat off of Coke ovens. Normal temps in the area range around 110f to 130f deg. Has anybody else out there had the same problem, and how did you correct it. Not getting alot of ideas from Foxboro. As of right now we've tubed plant air into the housing to keep them operational, don't want to continue this due to the least bit of moisture will fry the electronics. Our options are, find a solution or rip them off and send them back. Any ideas will be greatly appreciated
Thanks

 

[KiwiMace]

Ask Foxboro to come on over and sort it out. Until then, use low dewpoint instrument air for the casing purge, and if you reduce the pressure abruptly into the casing with a restrictor the air will adiabatically cool. Make sure you add a nice sintered vent!