Valve Disc & Gasket Changes
Valve Disc and Gaskets are sometimes changed/substituted for better performance with a given fluid. The change is represented by the insertion of a leter representing the substituted Disc/Gasket material (see examples below).
Valve Type Disc / Gasket Changes:

V ----- Vition Disc (i.e. Type 18A44 with Vition Seals becomes 18AV44)
T ----- Teflon Disc (i.e. Type 18A44 with Teflon Seals becomes 18AT44)
B ----- Buna-N Disc (i.e. Type 16L44 with Buna-N Seals becomes 16LB44)