HYDRAULIC HAMMER
A piston cylinder is formed inside a ram and is fitted with a piston attached to a stationary hollow piston rod, creating an upper piston chamber for receiving pressurized hydraulic fluid, which causes the ram to rise as the volume of the upper piston chamber is expanded due to the hydraulic pressure and increasing volume of hydraulic fluid. When the ram reaches a predetermined desired height, hydraulic pressure is released by opening a directional valve, allowing the ram to drop. A lower piston chamber is sealed and filled with gas. A moveable shuttle member reciprocates up and down inside a hollow piston rod in response to the changing volume of the lower piston cylinder, facilitating the evacuation of hydraulic fluid from the upper piston chamber. An alternative embodiment uses a single fluid and has no shuttle member.