These manage (reduce) the amount of air feeding your drone reeds. They also ensure clean cut-offs.
True story. I was playing with Niagara Police in 1999. The Vic Police had won the World Championships playing the first generation of the Ross Canister, so of course, everyone flocked to Ross bags. We found clean cutoffs very challenging. PM Al Ash got hold of some regulators and said “Hey. I can make that.” I came up with the name and the marketing words. Al sold a ton of these and they did their job!
In line valves for Ross System – $45
Highland Reeds valves – $30
K-Valves – $20
Ash Plugs – $15 (I have several sets)
