US Patent 7575051 Downhole vibratory tool

A vibratory tool for downhole use is capable of letting a wireline or other tools pass a passage therethrough that can be subsequently closed by landing a plug on a seat. The dump valve is disposed annularly about the central passage so that cycling the tool does not cause it to be slammed against a seat. Since only a plug is delivered to a passage the functioning parts already in the housing are made stronger to improve reliability. Additional power is delivered per stroke from modular stacked piston units. The tool can be run in a manner where the high amplitude low frequency oscillating forces are delivered to the stuck fish without impacts of the pistons on the housing.