Flow-Activated Hydraulic Knuckle Joint

The flow-activated knuckle joint gives a torque-through capability via its ball-and-socket knuckle with a key.


The coiled tubing flow-activated hydraulic knuckle joint, when incorporated within the coiled tubing, has the flexibility of being a straight semi-rigid tool string. When pressure is applied to the tool string, the flow-activated elbow bends and becomes inclined.

An additional flow-activated knuckle joint extension is also available to add greater reconfiguration options to the flow-activated knuckle joint. With an elbow extension, the flow-activated knuckle joint can be reconfigured into a double-acting knuckle joint end form to aid side-wall fishing operations.

The flow-activated knuckle joint has a ball-and-socket knuckle with a key that gives a torque-through capability.

The knuckle joint is flow activated and will allow normal through-circulation without activating the bending mechanism.

By increasing the flow rate above the normal circulating flow rate, a pressure differential is achieved at the tool, typically in the range of 1,000 psi. This causes the elbow, if unrestrained, to bend and become rigid, creating a pressure drop indication of full inclination. Under normal circumstances, to achieve the necessary operating pressure differentials, a choke will be installed at a point below the elbow.

To repeat the cycle, the flow rate should be reduced back to normal circulation, causing the tool to straighten. This will cause the piston to automatically return to its start position so that the tool is reset. The pressure cycle can then be repeated as before to make the elbow joint bend.

When adding a knuckle joint extension to a single elbow, there are six positions of possible alignment. This allows the operator to control the orientation selection of the extension elbow.


  • Full flow-through bore
  • Internal pressure seal
  • 15 or 30° inclusive angular deviation
  • Torque-through capability
  • Lifting ability: 200 lb at 12 in.
  • May be reconfigured to give a double-acting elbow arrangement
  • Pressure bleed-off at full inclination
  • TerraTECH Coiled Tubing Tools Brochure

  • TerraLINK Coiled Tubing Connectors Data Summary