Farr HD8625, Technical Manual

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T
echnical
M
anual
hD8625 8-
5
/
8
” 35K T
ong
6.1
T
orque
M
easureMenT
A. BASIC TORQUE MEASUREMENT
Basic torque measurements are performed using a simple hydraulic measurement system. A hydraulic load cell connects to a calibrated
torque gauge through a reinforced flexible hydraulic hose. The torque gauge is factory-calibrated to display accurate torque measurements
for a tong or tong and backup assembly with a particular arm length. The arm length is a measurement from the centre of the pipe or cas-
ing to the centre of the force being applied to the load cell.
Two load cell options are available. A tension load cell is typically used with a suspended stand-alone tong. This application requires that
the load cell be attached to the rear of the tong as part of the restraint line that opposes the force generated when the tong makes up
or breaks out a joint. A compression load cell is used in a tong and backup assembly, and is typically located on the rear of the backup
between the backup and a stationary frame. The load cell must be located in the centre of the compression force vector generated between
the backup and the frame.
Hydraulic force generated by a load cell is transmitted to the torque gauge via a reinforced flexible hydraulic line. The hydraulic force is
displayed as torque in units of Ft.-Lbs. The torque gauge has a red “peak torque” indicator that tracks with the torque gauge needle to
the point of highest torque, and remains at the point of highest torque until manually reset. Note that every model of tong and tong and
backup assembly has a unique arm length, and the torque gauge must be calibrated for that arm length. Torque gauges that are not
calibrated for the arm length of the tool in service will not display correct torque. To ensure correct torque measurement, ensure the arm
length or “handle” as displayed on your torque gauge matches the arm length of the tool in service as listed on the specifications page of
the technical manual.
The images on this page are for illustration purposes only and may not accurately represent the torque gauge and load cell that have been
supplied with your equipment.
I
llustratIon
6.a.1: t
orque
g
auge
(f
or
I
llustratIon
P
urPoses
o
nly
)
I
llustratIon
6.a.2: t
ensIon
l
oaD
C
ell
I
llustratIon
6.a.3: C
omPressIon
l
oaD
C
ell
THE IMAGES DISPLAYED ARE SUPPLIED FOR ILLUSTRATION PURPOSES ONLY
TORQUE GAUGES AND LOAD CELLS ARE FACTORY-SUPPLIED SUPPLIED AS MATCHED CALI-
BRATED PAIRS. IF REPLACING EITHER COMPONENT THE LOAD CELL AND TORQUE GAUGE
MUST BE RETURNED TO THE FACTORY FOR RE-CALIBRATION BEFORE PLACED INTO SERVICE.
Torque gauges and load cells are supplied as a matched calibrated pair. Substituting one or the other will render the calibration inaccurate
even if the actual model numbers appear to be identical. The serial numbers of matching load cell and torque gauges are clearly identified
on the calibration certificate. Should you suspect the accuracy of your torque measurements, or wish to replace either component the pair
should be returned to the factory for re-calibration before placing into service.