Thunder Horse ballast problems "revealed"

TX Designer over at Big Cat Chronicles has some additional information as to the mechanics of the problem that Thunder Horse experienced. It would appear the issue was trapped pressure in the Hydraulic system that bled backwards through the HPU that controlled the valves in the Ballast system. These valves were configured such that if Hydraulic pressure that opened them was lost, the valves would close automatically. However because a blowdown valve in the HPU bypass circuit was left closed, the trapped pressure seeped back into the hydraulic lines that went to the vales, the valves opened slowly after the rig was abandoned. Apparently BP has duplicated the behavior and has taken steps to prevent it's occurrence. This sort of thing is why I HATE working with hydraulics....