Apparatus for limiting back pressure in an exhaust-type engine suppressor

Claim 1

Apparatus for limiting back pressure in an exahust-type suppressor comprising a butterfly-type throttle valve pivotally mounted about a valve pivot in an engine exhaust pipe of circular cross-section, such that the throttle valve can be moved from an open position to a closed position, the throttle valve having a rim and assuming an oblique attitude when in the closed position, a valve bore communicating with the exhaust pipe at a location which is circumferentially spaced and longitudinally offset from the valve pivot so as to correspond with a location occupied by an end face portion of the throttle valve rim remote from the pivot when the valve is in closed position, a valve poppet slidable in the bore, and a spring disposed outwardly of the exhaust pipe with respect to the poppet for urging the poppet inwardly toward the throttle valve and permitting movement of the poppet outwardly in response to a back pressure of predetermined value being created in the exhaust pipe so as to provide a bypass around the throttle valve, the poppet valve having a concave end face which conforms in curvature to the curvature of the exhaust pipe.