Patent ID: 8496072

Claim:
A drop hammer for driving a pile comprising: a ram member supported within a housing chamber for movement relative to the housing member between the lower position and the upper position; a lifting system for moving the ram member from the lower position to the upper position; and a helmet member; whereby when the lifting system raises the ram member above a preload position, ambient air substantially freely flows into the housing chamber through a vent port; when the lifting system releases the ram member from the upper position, the ram member moves from the upper position towards the preload position, and the ram member forces a first portion of ambient air within the housing chamber out of the housing chamber through the vent port; when the ram member falls below the preload position, the ram member compresses a second portion of the ambient air within a preload chamber portion of the housing chamber, where compression of the second portion of the ambient air within the preload chamber creates a preload force on the helmet member that is transmitted to the pile; when the ram member falls into the lower position, the ram member strikes the helmet member to generate an impact force that is transmitted through the helmet member to the pile; and seal system for sealing the preload chamber portion of the housing chamber when the ram member is below the preload position.