Patent ID: 8763719

Claim:
A drop hammer for driving a pile comprising: a housing assembly defining a drive axis, a main chamber, and a plurality of vent openings that allow fluid to flow into and out of the main chamber, where at least one vent opening is arranged at a first vent location along the drive axis, and at least one vent opening is arranged at a second vent location along the drive axis, where the second vent location is spaced along the drive axis from the first vent location; a hammer supported within the main chamber for movement relative to the housing assembly between an upper position and a lower position, where the first and second vent locations are located between the upper and lower positions; a helmet member supported by the housing assembly for movement relative to the housing assembly between a first position and a second position; a lifting system capable of being operatively connected to and detached from the hammer, where the lifting system positively acts on the hammer to displace the hammer from the lower position to the upper position during each cycle, and is released from the hammer to allow gravity to displace the hammer from the upper position to the lower position during each cycle; and at least one plug; whereby when the hammer drops and is above the first vent location, ambient air flows from the main chamber through the vent openings formed at the first and second vent locations; when the hammer drops and is below the first vent location and above the second vent location, ambient air flows from the main chamber through the vent openings formed at the second vent location; when the hammer drops and is below the second vent location, air within the main chamber is compressed to preload the helmet member prior to contact between the hammer and helmet member; and the pile driving system operates in a first mode in which the vent openings at the first and second locations are open, and a second mode in which the at least one plug is configured to prevent fluid flow through the at least one vent opening at the second location.