If it was sudden loss, I would look at what was happen in you hydraulic system… e.g. was there proper level resivour or was it low enough to suck a pocket of air? Also has there been any issue with water in the hydraulic oil reservoir? it is incredible how a little water or air pocket will make the cylinder react. Also check for a blown line some where or maybe it was cold and cause the oil to get too viscuos before the pump? was there any other valve reactions (even minor ones)? has there been any issue of the valve hydrualics leaking (operators needing to ‘bump check’)? Also how did you double check how quickly it closed? expander inlet temps, pressure of your seperate/ regenerator?
I realize that there always needs to be a reason when the train trips but if the valve is working fine now…. You might need to get more information from your operators about what happend then the actual valve company.
Great lakes region, US
PS hydrualic cylinder failure would not become normal on its own