Operating Instructions Continued
© SPX FLOW, Inc.
12
Form No. 1000996
Rev. 0 Oct. 3, 2016
Use of Backing Wrenches
Backing wrenches are often used to prevent the non-tightening nut on the opposite side of the
joint assembly from turning during the torquing operation. Verify that the backing wrench is the
correct size and securely fastened in position (using straps, ropes, etc.). As the torquing
operation begins, it is normal for the backing wrench to move/rotate in conjunction with the
torqued nut, until the backing wrench contacts an adjacent reaction point. It is important that the
operator stand clear of the moving backing wrench to prevent accidental entrapment. The
operator must also verify that the reaction point is secure and sufficiently rigid to prevent damage
to the structure.
Torque Wrench Selection
To choose the correct capacity Torque Wrench for the application, the estimated break-out torque
should be considered, not the tightening torque. Loosening bolts usually requires a higher torque,
and if a wrench has been selected on tightening criteria only, it will seldom perform in a break-out
situation.
Break-out Considerations
Nuts / Bolts which have been correctly lubricated at the make-up / tightening stage will require
approximately 1.5 x tightening torque to loosen following a period of service, PROVIDED THEY
HAVE NOT BEEN SUBJECTED TO HEAT.
Corroded / rusted bolts, and bolts without lubrication applied at make-up, will require
approximately 2 x tightening torque to loosen. PROVIDED THEY HAVE NOT BEEN
SUBJECTED TO HEAT.
Nuts / bolts subjected to heat, seawater corrosion, chemical corrosion, can require 3 to 4 x
tightening torque.
Before selecting a torque wrench for the application, ensure that the above has been considered.
Tightening Bolts
1. Apply the torque wrench to the nut to be tightened and verify that the reaction pad is braced
firmly and squarely against the selected reaction point.
2. Start the pump and advance the hydraulic torque wrench. As the wrench strokes forward, the
reaction pad will press against the reaction point and the nut will rotate. When the hydraulic
torque wrench reaches the end of its stroke, the pump pressure will build rapidly. Fully retract
the hydraulic torque wrench (the wrench ratchet mechanism will be heard clicking as it
retracts), and apply another forward stroke.
3. Several forward strokes are made until the nut ceases to rotate during the stroke (known as
stalling), but bear in mind that nut rotation will always cease at the end of the wrench stroke and
must not be confused with the wrench stalling. When the wrench stalls, apply another forward
stroke and observe the pump pressure gauge. The pump pressure gauge should read the
desired preset pressure.
4. Retract the hydraulic torque wrench, stop the pump unit, and remove the wrench from the nut.
Tightening a Flanged Joint
This procedure outlines the basic steps to torque-tighten a flanged joint with a TWSL hydraulic
torque wrench. It is important that personal protective equipment (gloves, footwear, safety
helmet, eye protection, etc.) is worn at all times by the operator and any other personnel in the
work area. The torquing procedure uses a single hydraulic torque wrench to accurately achieve
a predetermined residual bolt stress.