# De-Tensioning Procedure

1. Remove the most accessible blanking plugs from every hydraulic nut to be de-tensioned and replace them with the required male and female couplers.

   Hydraulic couplers of either type should be tightened into the tool from the adaptor piece only. Required tightening torque is 25 Nm.

   Do not overtighten the connection, it can damage the male sealing cone in the fitting.

   Bolting calculations should only be carried out by trained and qualified engineers who have been appropriately trained or have suitable experience in bolting technology.

   If simultaneous tensioning of more than one bolt is to be carried out, fit one male and one female quick connect coupling to each hydraulic nut, and by using link hoses, link each nut together. The end nut on the application should have either an unconnected female coupling (to a link hose) or a blanking plug.

2. Make sure that the pump pressure release valve is fully open and the pump is switched off. Connect the link hoses to the hydraulic nuts. See section Hydraulic Nut System Configuration for different tensioning procedure configurations and illustrations.

   Make sure that the pressure rating for the Atlas Copco link hose matches the maximum working pressure of the tool. Refer to the hard stamped details on the hydraulic nut.

   The system must be at zero pressure before starting any investigation, maintenance or leak repair work.

   During the de-tensioning procedure NEVER exceed the maximum working pressure of the hydraulic nut.

   Definition: Break Loose Pressure (BLP) is the pressure at which the user can rotate the load retaining collar on the hydraulic nuts by hand with a tommy bar.

3. Once the pressure is holding steady, continue to slowly increase the pressure. Apply a light force to a tommy bar inserted into the collar. As soon as the collar rotates, BLP is reached. Once the BLP is found, stop the pump to hold the pressure and make a note of the pressure.

4. Make sure the pressure is holding steady. By using a tommy bar inserted into the locking collars, unscrew every hydraulic nut locking collar until there is 1mm gap between the collar and joint face. Make sure that the collars do not make contact with the joint face.

   If locking collars are difficult to rotate at this BLP, slightly increase the pressure until the locking collars become loose.

   Never exceed the maximum working pressure of the hydraulic nuts.

   Make sure that the bolt material and joint material can withstand the load you are applying.

   Never stand in line with the bolt axis while seating the collar. Unexpected bolt failure can result in serious personal injury or death.

5. Open the pump pressure release valve and make sure the pressure falls to zero.

6. Use a tommy bar inserted into the holes in the hydraulic nut body. Rotate them down onto the stud to close the hydraulic nut piston to zero stroke.

   Repeat on all hydraulic nuts until all of the pistons are fully closed.

7. Remove all link hoses from the hydraulic nuts.

   Only attempt to uncouple high pressure hydraulics while the system is not holding any pressure.

8. Remove the hydraulic coupler(s) and replace the blanking plugs removed during installation. Blanking Plugs have a required tightening torque of 25Nm.

   Never attempt to remove fittings from a high pressure hydraulic tool when the system is pressurized. Escaping high-pressure oil can penetrate the skin and is extremely dangerous. Seek urgent medical attention if oil penetrates skin.

   The tensioning procedure is now complete.

9. Disassemble the hydraulic nuts from the application. If the hydraulic nut cannot be disassembled from the stud, it means the collar was not backed off enough in step 4 and the de-tensioning sequence must be repeated.

The de-tensioning procedure is complete.

Relevant Information

- Hydraulic Nut System Configuration