O-rings play an important part in serving as a key, wetted sealing point at elbows and manifold seat areas, as well as at dry connection points between block and air valve, pilot sleeve, and shaft bushing. The rings can be procured in the same materials as the ball seats and diaphragms and are sold separately or in kits. PTFE rings are available in solid form or PTFE encapsulated Viton for more “squeeze” and forgiveness when used in wetted areas.