(4) According to the central through hole of DTH hammer, it can be divided into
ordinary DTH hammer and through DTH hammer. For example, FGC-150 is a
through DTH hammer, the rest are ordinary DTH hammers. The through DTH
hammer can drill in hard rock and sandy pebble with large diameter, and carry
out continuous reverse circulation sampling. It has high drilling efficiency, low
requirements for matching equipment (compressor air volume and air volume),
and improves drilling depth.
11.2.2 Principle of Valve-Type Pneumatic DTH Hammer
Figure 11.3 shows that when the valve-type pneumatic DTH hammer is working,
high-pressure gas enters the cylinder body from the upper connector 1 and opens
the check valve 2. A part of the gas enters the bottom of the hole through the central
hole passage of valve seat 5, piston 6 and the exhaust hole of drilling bit 12, and
directly blows and washes the bottom of the hole. Other compressed air enters the
valve train with valve plate 4, and relies on piston 6 and valve rod (integrated with
seat 5), bore on inner cylinder 8 and groove on bushing 9 to cooperate, so that the
valve plate rises and falls, realizes the conversion of inlet and exhaust of front and
rear air chambers, and promotes reciprocating motion of piston. Pneumatic DTH
hammer with valve consumes a lot of air and the valve is easy to be damaged.
11.2.3 Valveless Pneumatic DTH Hammer
Figure 11.4 shows the schematic structure of valveless pneumatic DTH hammer.
The working principle is that the compressor discharges compressed air, enters the
DTH hammer upper joint 1 through the pipeline system, pushes open the check
valve 2, and reaches the annular space at the upper end of the valve seat 3. At this
time, compressed air is divided into two ways: one way from the radial hole on the
check valve to the central passage between the check valve and the valve seat; the
other way into the space between the outer cylinder 6 and the inner cylinder 4.
When one of the compressed air enters the valve seat, it is continuously discharged through the central small hole of the valve seat, and through the piston 5
central hole, the central hole and the exhaust hole of the drill bit to the outside of the
bit, cooling the bit, carrying bottom hole cuttings, and returning to the surface
through the annular hole between the drill string and the borehole wall. The airflow
in this way is strong jet flow. It does not enter the DTH hammer chamber and does
not participate in the work. It only plays the role of strong blow hole bottom,
cooling drill bit and removing cuttings. The adjusting gaskets in the valve seat are
designed as a group. The central holes of different sizes are designed on the gaskets
to adjust the velocity of strong jet flow. According to the requirement of air source
200
11 Pneumatic Down-the-Hole Hammer
ordinary DTH hammer and through DTH hammer. For example, FGC-150 is a
through DTH hammer, the rest are ordinary DTH hammers. The through DTH
hammer can drill in hard rock and sandy pebble with large diameter, and carry
out continuous reverse circulation sampling. It has high drilling efficiency, low
requirements for matching equipment (compressor air volume and air volume),
and improves drilling depth.
11.2.2 Principle of Valve-Type Pneumatic DTH Hammer
Figure 11.3 shows that when the valve-type pneumatic DTH hammer is working,
high-pressure gas enters the cylinder body from the upper connector 1 and opens
the check valve 2. A part of the gas enters the bottom of the hole through the central
hole passage of valve seat 5, piston 6 and the exhaust hole of drilling bit 12, and
directly blows and washes the bottom of the hole. Other compressed air enters the
valve train with valve plate 4, and relies on piston 6 and valve rod (integrated with
seat 5), bore on inner cylinder 8 and groove on bushing 9 to cooperate, so that the
valve plate rises and falls, realizes the conversion of inlet and exhaust of front and
rear air chambers, and promotes reciprocating motion of piston. Pneumatic DTH
hammer with valve consumes a lot of air and the valve is easy to be damaged.
11.2.3 Valveless Pneumatic DTH Hammer
Figure 11.4 shows the schematic structure of valveless pneumatic DTH hammer.
The working principle is that the compressor discharges compressed air, enters the
DTH hammer upper joint 1 through the pipeline system, pushes open the check
valve 2, and reaches the annular space at the upper end of the valve seat 3. At this
time, compressed air is divided into two ways: one way from the radial hole on the
check valve to the central passage between the check valve and the valve seat; the
other way into the space between the outer cylinder 6 and the inner cylinder 4.
When one of the compressed air enters the valve seat, it is continuously discharged through the central small hole of the valve seat, and through the piston 5
central hole, the central hole and the exhaust hole of the drill bit to the outside of the
bit, cooling the bit, carrying bottom hole cuttings, and returning to the surface
through the annular hole between the drill string and the borehole wall. The airflow
in this way is strong jet flow. It does not enter the DTH hammer chamber and does
not participate in the work. It only plays the role of strong blow hole bottom,
cooling drill bit and removing cuttings. The adjusting gaskets in the valve seat are
designed as a group. The central holes of different sizes are designed on the gaskets
to adjust the velocity of strong jet flow. According to the requirement of air source
200
11 Pneumatic Down-the-Hole Hammer