This Foremost floating cushion sub is designed to be installed on rotary drilling rigs below the gear box and into the drive spindle by means of a threaded connection. The cushion sub will reduce vertical shock transmitted by the bit while drilling using either DTH hammer or rotary drilling methods. The two and one half inches (2 1/2”) of free floating travel of the piston allows the drill operator to make-up and break-out threaded connections with minimal flank loading on the threads of the drill pipe or casing. This float within the housing enables the drill operators to make-up casing threads with little or no thread damage when stabbing the connections together or taking them apart. The sub can be used in vertical and or slant drilling applications.

The foremost floating cushion sub is available with all popular thread configurations up to a pin or box shoulder diameter of 7” at the top end and a 6” shoulder diameter pin or box on the lower end. Customised extended lengths between 20” to 32.5” shoulder to shoulder and housing diameter of 10” do not interfere with drilling or pipe handling operations.​

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FUNCTION AND OPERATION

The pin / box connection on the upper cap assembly is made up directly to the drive spindle, while the box / pin connection on the piston is free to move axially within the body cavity. A stationary wash pipe and seal arrangement isolate drilling fluids / air from the inner components of the body. The piston will either extend or retract within the cushion sub body if the drill string is held stationary and the drive spindle rotated to breakout or makeup the threads in the drill string.

Raising or lowering of the rotary drive is not necessary until full engagement or disengagement of the threads is complete. In tension or compression, the shock transmitted by the bit is minimised by cushions within the body cavity. The configuration of the cushion sub allows for pullback of 200,000 lbs. With a three to one safety margin and working torque capacity of 20,000 ft/lbs.