Still seeking information on this one. It has a never before seen front valve, which actually does not act as a smoke control valve, just a removable end cap to facilitate cleaning.
The unusual bowl attachment has not been seen before, by me anyway
The size of the shank is that of the early 'L' model and the early 'L' model valve and stem fit it. 'O' rings litted to both 'valve' and stem and the push rod is a one piece
The stamping underneath is just PATS & PATS PEND MADE IN USA, there is no model letter.
Dave Whitney points out that the stamping and 'O' rings does suggest the 1955-58 era when he believes, from Lynne Kirsten, the firm made up some pipes from 'bits and pieces' around the works. That being so there are unlikely to many of this type around