Page 620 - Air and Gas Drilling Manual

11-58 Air and Gas Drilling Manual
.
Torque
The stall torque of the drive shaft (drill bit), Torque , is
38
5
. ) (112
(35
Torque sr 35 38 ft lb . ) sb
sb
,
Torque sb 3 980 ft lb
30˚

Figure 11-15: Cutaway of the a typical compressible flow stator nozzle and rotor bucket
configuration.

The periphery speed of the turbine rotor is determined by the gas velocity at the exit
of each nozzle. When there is no load on the drill bit, the tip speed of the turbine
rotor will approach the velocity of the gas exiting each nozzle. Thus, the theoretical
runaway speed of the rotor, N , is
rr
V (60 )
s
N rr
D cl
2
2
(,206 ) (60 )
1
N
rr . 0 414
2
2
N rr 55 642 rpm
,
The runaway speed of the motor drive shaft (drill bit), N , is
rb
N rr
N rb (11-3)
G r