chamber is relatively small, and the influence of dV=dt on dp=dt. is equal to that of
dM=dt. dp=dt is positive and negative under the action of these two factors, so the
pressure will fluctuate. When the piston speed increases, the value of dV=dt also
increases. At this time, dV=dt plays a decisive role in dp=dt, so the pressure of the
intake chamber changes in one direction, and there will be no fluctuation.
The pressure fluctuation of the front chamber lasts for a very short time and has a
small fluctuation range, so its influence can be neglected. The pressure fluctuation
of the rear chamber lasts for a long time and has a large fluctuation amplitude,
which may cause hidden danger to the construction of DTH hammer. It is found
that the pressure fluctuation can be greatly reduced by increasing the inlet flow area
of rear chamber. As shown in Fig. 11.24, the inlet passage of the rear chamber of
the prototype is composed of four slots on the inner wall of the inner cylinder of the
Time t/s
Pressure p/Pa
Fig. 11.22 Pressure–time
curve of front chamber at the
beginning of return journey
Time t/s
Pressure p/Pa
Fig. 11.23 Rear chamber
pressure fluctuation at return
end stroke initial stage
238
11 Pneumatic Down-the-Hole Hammer