Ballvalves in double bl & bl service are no difference from the normal ballvalves with built-in lenghts acc. to Ansi B16.5 B16.10 API602 BS5351 and DIN2501.
Maybe you should also look at the DBB plug valves? They come as an integrated unit with the same build emasures as a standard ball valve.
I've never seen a true double block and bleed ball valve.  Some models have a body blow down port and it looks and acts a lot like a gate valve that has two distict and powered (powered by cam or taped action)seals. Most balvalves will have a perfered pressurized end.  Even the orbit valve is a specialized ball valve that uses a cam action to force a seal isn't a true DBB.
Som tunnion mounted ball valves has a bleed between the seats, that enables testing of the seat tightness. Some vendors may use the term DBB for this feature - BUT ITS NOT! In a trunnion mounted valves the seats are only tight if there is a pressure difference - both upstream and downstream!

MORE NEWS