A hydraulically actuated nozzle unit, including
- (a) a housing having
- (i) first and second open ends,
- (ii) a cylindrical inner wall,
- (iii) first shoulder means attached to and inwardly extending from said inner wall, and
- (iv) second shoulder means spaced apart from said first shoulder means and inwardly extending from said inner wall;
- (b) annular means interposed in said housing between said first and second shoulder means for captive slidable displacement therebetween;
- (c) cylindrical conduit means connected to and extending away from said annular means toward said second end of said housing and having
- (i) an upper end having an outer cylindrical wall spaced apart from said inner wall of said housing and said second shoulder means, and
- (ii) a lower end contacting said annular means,
- said annular means and conduit means being displaced in said housing between at least two operative positions,
- (iii) a first operative position with said annular means contacting said first shoulder means and without fluid flowing under pressure into said first end of said housing and against said annular means, and
- (iv) a second operative position with
- fluid flowing under pressure into said first end of said housing and against said annular means,
- said upper end of said conduit means extending through said second open end of said housing, and
- said annular means contacting said second shoulder means,
- said fluid flow against said annular means producing a displacement force causing said annular means to move in a direction of travel from said first to said second operative position and to impact said second shoulder means,
- said annular means and inner wall being shaped and dimensioned to permit fluid flow intermediate
- said annular means and inner wall, and
- said outer wall of said conduit means and said inner wall of said housing
- (d) at least one elongate groove formed in said cylindrical inner wall of said housing intermediate said first and second shoulder means,
- said groove having
- (i) a lower end through which a portion of said fluid flowing under pressure into said housing enters said groove, and
- (ii) an upper end from which fluid flowing through said groove toward said second shoulder means exits said groove,
- said groove being shaped and dimensioned such that when said annular means and conduit means are intermediate said first and second operative positions, said portion of said fluid flowing into said groove
- (iii) initially flows away from said outer cylindrical wall of said cylindrical conduit means, and
- (iv) flows through said upper end beneath said second shoulder means toward said outer cylindrical wall and generally perpendicular to the direction of travel of said annular means and conduit means from said first to said second operative position,
- said flow of fluid from said upper end of said groove
- (v) causing fluid flow intermediate said annular means and said second shoudler means to generate buffer pressure resisting movement of said annular means from said first to said second operative position, and
- (vi) reducing said impact force of said annular means against said second shoulder means.