Welcome to the forum. I agree with Mr. Moloney that you should competitively bid both valves. You can read more deltavalve user’s experience in the: All Forums>>[Cokedrums]>>Top&Bottom Unheading section in this forum.
The 4 drum delayed coker I worked in a few years ago had the Hahn & Clay hydraulic unheading cart that was replaced with Delta Valves bottom unheading devices. The only problem with this installation was not with the valves but the transition spool was bolted to the coke drums and started leaking a few months after put in service. An upgraded gasket has been put in place with good results. I would recommend you weld the transition spool to the coke drum.
Regards,
CG
