1900: Hydraulic Ram Drill by Wacław Wolski
In 1900, Wacław Wolski improved cable drilling by using a hydraulically driven chisel at the end of the drill string. This was the first hydraulic down-the-hole percussion mechanism, also called the “Ram of Volsky”.
The mechanism works like a hydraulic ram: If the velocity of the drilling fluid is high enough, it will close the valve and the pressure built up will shoot out the chisel. To dampen the water hammer effect, a small gas-filled cavity is placed before the mechanism. For greater depths, this was then replaced by a spring-loaded piston due to the increasing hydrostatic pressure.
1908: Invention of the roller cone drill bit by Howard R. Hughes
Howard Robard Hughes invented the roller cone bit om 1908, this was the breakthrough for rotary drilling and made the later invention of the tricone carbide insert drill bit possible. Percussion drilling now needs to have significant advantages over this technology to reach a breakthrough. This is the main reason why hydraulic DTH percussion drilling still has not evolved over rotary drilling.
1927: Hydraulic percussion drill of Harry Pennington
Harry Pennington patented his hydraulic percussion drive in 1927. The drilling fluid is lifting the hammer piston, it is accelerated towards the anvil by a spring and its gravity. Button Bits were not invented at this time so the drill bit was a flat chisel.
As the hammer piston hits the anvil, it will close the valve placed inside the anvil. This will lift the piston as the hydraulic pressure builds up inside the tool until the hammer piston will lift up the valve. The valve will be held open by a spring after it was lifted a bit, the lifting of the valve will cause a pressure drop. As the pressure dropped, the hammer piston will be accelerated towards the anvil by the spring and by gravity, hitting the anvil and closing the valve again.
