Appreciate the response, not sure what you mean by Boeings initial findings.
I know it took them years, through several different investigations until they found the unit could jam or reverse. Off the top of my head I can't remember which incident it was, but I know if the primary slide jamed and the valve was subjected to thermal shock the secondary slide could jam or reverse. Is this the point you're referring to or have I missed something?
I've tried to get hold of a valve from Parker, refered me to one of their offices in Michegan but no response.
Cheers for the response