DOWNHOLE HAMMER (VARIANTS) Russian patent published in 2006 - IPC E21B4/14 

FIELD: mining, particularly rotary-percussion drilling.

SUBSTANCE: downhole hammer comprises body with discharge channels, striker, which divides body interior into working stroke chamber and return stroke chamber, distribution system having seat with orifices, shell with discharge channels and stepped valve installed between the seat and the shell. Inner valve surface and shell define back chamber located downstream of valve and communicated with atmosphere through discharge channels of the shell and the body from one side thereof. The valve back chamber is also communicated with working stroke chamber through longitudinal channel, radial channel and orifices of seat from another back chamber side. The longitudinal channel is located near lesser valve step. The radial channel is created between seat and stepped valve end. The seat has three steps. Longitudinal channel is made as slots located in lesser valve step or in medium valve step so that centering bridges are created between the slots.

EFFECT: increased impact energy due to increased striker stroke, which is provided by reduction of back pressure in working stroke chamber as striker travels in reverse direction.

2 cl, 3 dwg