Hammer

In an impactor apparatus including an axially reciprocable free piston and motive fluid supply means for reciprocating said piston through alternate work strokes and return strokes, the improvement comprising:

• a working chamber defined within said apparatus in conjunction with said free piston and adapted to receive therein motive fluid from said motive fluid supply means for propelling said piston through a return stroke;
• at least one exhaust port for communicating in fluid flow relation with said working chamber to selectively release motive fluid from said working chamber to permit said free piston to be propelled through a work stroke;
• exhaust valve means cooperable with said exhaust port to selectively open and close said exhaust port;
• moveable means cooperable with said exhaust valve means and with other portions of said apparatus to define a pair of variable volume chambers;
• one of said variable volume chambers being maintained in selective fluid flow communication with said working chamber to receive motive fluid from said working chamber when said exhaust port is open;
• and vent means at least partially carried by said moveable means and communicating in fluid flow relation between said one variable volume chamber and the ambient atmosphere through the other of said variable volume chambers and cooperable with said moveable means in a manner to ventilate said one variable volume chamber by fluid flow from said other of said variable volume chambers during opening of said exhaust port by said exhaust valve means while precluding discharge of motive fluid through said vent means to the ambient atmosphere and precluding fluid flow between said variable volume chambers during closing of said exhaust port by said exhaust valve means while providing fluid flow from the ambient atmosphere to said other of said variable volume chambers.