The External Valve Plate (EVP) was developed about a year after the BMH-30 comb. Valves enable you to control the air flow to specific reeds. Because the SUB-30 has three reeds in each chamber as compared to two in a standard diatonic harmonica, valves are necessary to prevent specific reeds from playing when you don't want them to. The stock SUB-30 has 10 valves. The Blue Moon EVP enables you to add 10 more valves via a single component. It requires no special tools or screws to install. Simply unscrew the reed plates, place the EVP on the top reed plate and using the same screws, re-attach the reed plates to the comb. It's that simple. The EVP is precision CNC Milled from a solid block of 6061 Aircraft Grade Aluminum.  After installing the EVP, the SUB-30 has two valves in every chamber. Regardless of whether you breathe in or out, one valve in the chamber will open and the other will close. This enables you to isolate two of the three reeds in each chamber and employ standard draw bend or blow bend techniques to play 10 additional notes on the SUB-30. These notes enable you to play chromatically on a diatonic harmonica. It eliminates the need to play over-blows or over-draws.

Installation is easy.  To install the External Valve Plate, simply disassemble your SUB-30 harmonica, lay the External Valve Plate on the top reed plate and re-assemble the harmonica with the stock screws.  It is that easy.