Operation of current valves is dufficult and they allow sand and dirt to enter resulting in damage to the valve. The rotary valve design eliminates this problem. The location of the breathing gas over pressure relief valve. Most systems have located the valve on the counter lung.
Water pressure makes the valve position sensitive.
Locating the valve on the mouth piece eliminates this problem. The over pressure relief valve is a double valve body, one spring loaded and one free moving to insure the valve always seals. The mouth piece is easy to disassemble to allow easy cleaning. The mouthpiece is the part of the rebreather with which the user has the most contact.