IMO, it is the design feature for the triple offset valve. So, the valve can be used for the bi-directional flows. You may confirm with the vendor for the correct model number for your valve.
good day dear
in many designs of the triple offset valves i have seen bi directional seals are used but regarding the reason i cant see that it is due to bi- dirrectional flow . due to that the seat arrangement won't be symmetric to allow the offset seating snd movement of the valve disc ,so i think that it is used to prevent erosion on the rear of the valve seat which is partially a part of the valve body and sometimes welded..
the reasons why i cant see the reason of bi- directional flow :
1- it is not a good practice to have the flow being resisted against the valve stem .
2- these valves are only used for on-off systems or flow reatriction , and bi directional flow system won't be applied through using these valves.
