The Viking Model D-2 Accelerator is a quick-opening device, with an integral anti-flood assembly, used to increase the operating speed of a differential type dry pipe valve.  The Viking Model D-2 Accelerator is a direct replacement for the Model D-1 Accelerator. Video Model D-2 Accelerator (Part 1 of 2) - Product Repair Video Model D-2 Accelerator (Part 2 of 2) - Product Repair Video