1.  Field of the Invention
The invention pertains to diving snorkels of the "dry" type utilizing separate passages for inlet air and exhaust air. 
2.  Description of the Related Art
Originally, diving snorkels consisted only of a shaped tube whereby the diver could breathe through the tube while the face was submerged.  Over the years, more sophisticated snorkel constructions have utilized valves to close the snorkel to the entrance of water when the snorkel is entirely submerged, for instance when the diver dives. " Dry" snorkels have been developed wherein valves are utilized to minimize the entrance of water into the valve body during snorkel submersion, however, as the usual snorkel construction uses a single passage for both inlet and exhaust air, the clearing of the exhaust air from the snorkel prior to drawing clean air therein requires greater difficulty than involved in normal breathing, and the majority of snorkel constructions do not separate inlet or inhaled air from expired air. 
Attempts have been made to devise snorkels having a plurality of air passages, and devices of this type are shown in U.S. Pat.  Nos.  46,902; 2,362,775; 3,721,236; 5,117,817; and 5,664,558.  However, the snorkels disclosed in the aforementioned patents are either unduly burdensome, heavy or expensive, and are not capable of readily maintaining separation of air inlet and exhaust air control, and such devices are of such complexity as to substantially raise the cost of the snorkel.  In U.S. Pat.  No.  5,664,558, separate passages for air inlet and exhaust air are shown, but the valving therefor is not so located and positioned with respect to the snorkel construction as to provide optimum advantages such as those achieved by the invention.