To provide an adequate speed to evacuate cuttings from a hole, drilled with a DTH hammer, an uphole velocity of 900-1800 Metres/Minute (3000-6000 Ft/Min) is required.

The formula for calculating up hole velocity is as follows –

METRIC                                          IMPERIAL

VM = X(M3) x 1,305,096                VF = Y(CFM) x 183.40
DM2 – dm2                                         DI2 – di2

Where –

VM = Velocity in metres per minute.
X(M3 ) = M3 /Min. of air volume passed by the hammer at the selected air pressure.

DM2 = Diameter of hole – squared (in millimetres).
dm2 = Diameter of drill tube squared (in millimetres).

VF = Velocity in feet per minute.
Y(CFM) = Volume of CFM of air passed by the hammer at the selected air pressure.

DI2 = Diameter of hole – squared (in inches).
di2 = Diameter of drill tube – squared (in inches).

AN ALTERNATIVE METHOD OF CALCULATING UP HOLE VELOCITY WITH
HAMMER IS AS FOLLOWS:

1. Establish the volume of air in M3 /Min. being passed through the hammer.
2. Establish the velocity per M3 of air , from chart across, with relevant tube and
and hole diameter.
3. Multiply A x B = answer in Metres/Minute.
4. If Feet per minute required – Multiply Metres/Minute x 3.28.

*While every effort has been made to insure the accuracy of the formulas herein, this material is presented as a reference guide only. The technical information contained herein should not be construed as a recommendation. Wilson Drill Tools cannot assume responsibility for the results obtained through the use of this material. No expressed or implied warranty is intended.