Note: Descriptions are shown in the official language in which they were submitted.
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Pressurized fluid flow system for a reverse circulation down-the-hole
hammer and hammer thereof
FIELD OF APPLICATION OF THE INVENTION
The present invention generally relates to a pressurized fluid flow system for
a percussive mechanism operating with said fluid, particularly for a DTH (Down-
The-Hole) hammer and more particularly for a reverse circulation DTH hammer,
and to a DTH hammer with said system.
STATE OF THE ART
DTH hammers that operate with pressurized fluid are characterized by
comprising a cylindrical outer casing, a rear sub for connecting the hammer to
the
source of pressurized fluid, a drill bit at its foremost end to perform the
drilling
function and a piston that effects a reciprocating movement due to the change
in
pressure of the pressurized fluid contained in two main work chambers, a front
chamber and a rear chamber, formed inside the hammer and located at opposite
ends of the piston, said reciprocating movement of the piston allowing to
transfer
the energy from the pressurized fluid to the rock with each impact of the
piston on
the drill bit.
The hammer's thermodynamic cycle develops in accordance with the
piston's reciprocating movement from the point of its stroke in which the
piston is in
contact with the drill bit (known as impact position) up to the rearmost point
of its
stroke, the latter dependent on the hammer's operation. Accordingly, as the
piston
moves, the front and rear chambers are alternatively and cyclically supplied
with
pressurized fluid, discharged of the same, or subject to an expansion or
compression process, the latter depending on the direction of the piston's
movement and the chamber being tightly sealed, thus causing the volume
enclosed within the chamber to respectively increase or decrease.The
transition
from one state to the other is independent for each chamber and is controlled
by
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the position of the piston with respect to other parts of the hammer in such a
way
that the piston acts in itself as a valve, as well as an impact element.
In reverse circulation drilling a double walled rod is used, that is formed by
two concentric pipes, an inner pipe or sampling tube and an outer pipe. An
extension of said sampling tube is provided along the center of the hammer,
from
the drill bit to the rear sub, forming a continuous central passage along the
center
of the hammer for enabling to recover the rock cuttings and soil samples and
convey these to the ground surface through the center of the drill string.
The hammer may be operated in two modes. In the first one, or drilling
mode, pressurized fluid is supplied to the hammer producing the reciprocating
movement of the piston which at the end of each cycle impacts the drill bit,
the
front end of the drill bit thereby peforming the function of drilling the rock
and rock
cuttings being exhausted to the ground surface by the pressurized fluid
discharged
to the bottom of the hole. In the second one, or flushing mode, the drill
string and
the hammer are lifted by the drill rig in such a way that the drill bit loses
contact
with the rock, and all the pressurized fluid is discharged through the hammer
directly to the bottom of the hole for cleaning purposes, without passing
through
the hammer cycle, thus ceasing the reciprocating movement of the piston.
There are many different types of reverse circulation DTH hammers
available for drilling and sample recovering. Three methods are commonly used
for
controlling the supply of pressurized fluid to the front and rear chambers: 1)
use of
a fluid passageway formed between the outer surface of a cylinder and inner
surface of the outer casing, the cylinder being mounted inside the outer
casing
coaxial with the piston; 2) use of a supply chamber formed within the outer
casing
that interacts with recesses in the outer sliding surfaces of the piston and
passages
in the outer casing as the piston reciprocates; and 3) use of a feed tube to
create a
supply chamber inside the piston, wherein this feed tube interacts with
recesses in
the inner or central bore-side surfaces of the piston as the piston
reciprocates. On
the other hand, the discharge of pressurized fluid from the front chamber is
commonly controlled by either a foot valve mounted in the drill bit or a front
portion
of the piston of smaller diameter interacting with a piston guide. Similarly,
the
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discharge of pressurized fluid from the rear chamber is commonly controlled by
either an air guide placed on the rear part of the rear chamber or by the
front end
of the feed tube.
Generally to convey the pressurized fluid from the rear end of the drill bit
to
the front end of the same some channels are created in the outer surface of
the
drill bit that cooperatively work with splines on the inner surface of the
driver sub
and with a ring or sleeve acting as sealing element so as to form enclosed
passages in such a manner as to discharge the pressurized fluid to the
periphery
of the front end of the drill bit. The pressurized fluid may also be deviated
from an
intermediate point in the drill bit through bores in the driver sub to a
passage
formed between the outer surface of the driver sub and the inner surface of
the
sealing ring. Alternatively, the pressurized fluid may be deviated from said
intermediate point through longitudinal bores created on the head of the drill
bit.
One type of reverse circulation DTH hammer that offers a new way of
controlling the supply of pressurized fluid to the front and rear chambers and
of
discharging the pressurized fluid from them is disclosed in U.S. Patent No.
7.921.941 (B2). Specifically, a cylinder is coaxially disposed in between the
outer
casing and the piston, and a supply chamber is disposed longitudinally in
series
with a discharge chamber, wherein both chambers are defined by respective
recesses in the inner surface of the outer casing and internally delimited by
the
outer surface of the cylinder, and are separated by a dividing wall. The
supply
chamber is permanently connected to the source of pressurized fluid for
supplying
said fluid to the front chamber and rear chambers of the hammer, while the
discharge chamber is permanently communicated with the bottom of the hole for
discharging the pressurized fluid from the front and rear chambers. A set of
fluid
conducting means is provided in the piston for channeling the flow of
pressurized
fluid from the supply chamber to the front and rear chambers and out of said
chambers. In a second embodiment of the '941 patent an internal chamber is
provided in between the piston and the sampling tube for a more efficient
filling of
the chambers. The internal chamber is defined by a recess in the inner
surfaces of
the piston and is permanently connected to the supply chamber.
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In said same patent, to discharge the pressurized fluid from the discharge
chamber and convey it to the peripheral region of the front end of the drill
bit, end
discharge ports are provided in the front end portion of the outer casing.
These end
discharge ports are aligned with respective longitudinal channels formed along
the
outer surface of the outer casing. Further, both the end discharge ports and
longitudinal channels are covered by a shroud or outer sealing sleeve.
The control of the flow of pressurized fluid in and out of the front and rear
chambers is thus simplified and thanks to the use of "blind" passages in the
piston
the thrust areas in the piston are maximized for better transfer of energy to
the
rock, hence improving the deep drilling capacity of the hammer. Also, a
simpler
and sturdier bit design is provided as opposed to other known reverse
circulation
DTH hammers where discharge of pressurized fluid to the bottom of the hole is
achieved by more centrally located fluid-conducting means.
In spite of the above-mentioned advantages of the '941 patent, it would be
desirable to combine them with the following improvements:
= providing a structurally simpler pressurized fluid flow system and hammer
that could reduce manufacturing costs; and
= providing a sturdier piston in order for the hammer to operate at a
higher
pressure and deliver higher energy to the rock without the risk of a
catastrophic failure of the piston.
BRIEF SUMMARY OF THE INVENTION
In a first aspect of the invention, a pressurized fluid flow system has been
developed for a reverse circulation DTH hammer having a cylindrical outer
casing,
a rear sub affixed to the rear end of the casing and connected to the source
of
pressurized fluid, a centrally-bored piston slidably and coaxially disposed
inside the
outer casing,a drill bit slidably mounted in the front end of the hammer on a
driver
sub and a sample tube coaxially disposed within the outer casing, passing
through
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the central bore of the piston and extending from the rear sub to the drill
bit,
wherein the pressurized fluid flow system comprises:
a cylinder coaxially disposed in between the outer casing and the piston, the
cylinder extending from the rear sub to the drill bit guide;
a cylindrical control tube coaxially disposed in between the piston and the
sample tube, coupled to and extending forward from the rear sub, the control
tube
having pressurized fluid inlet means connected to an annular passageway formed
between the control tube and the sample tube; and
two chambers to help to respectively supply and discharge pressurized fluid
into and out of the work chambers: an internal chamber defined by a central
recess
in the inner surfaces of the piston and a discharge chamber defined by one or
more recesses in the inner surface of the outer casing, preferably a single
annular
recess.
These elements have the following configuration:
the outer sufaces of the sample tube include recessed front-end and rear
portions, and a central control portion in between;
the cylindrical control tube comprises a front-end control outer-surface
portion
and a recessed rear-end outer-surface portion;
the discharge chamber is delimited by the outer surface of the cylinder and
the inner surface of the outer casing; and
the internal chamber is delimited on the one side by the outer surfaces of the
sample tube alone or together with the outer surfaces of the control tube,
depending on the position of the piston during the operation of the hammer,
and on
the other side by the inner surfaces of the piston.
The invention is characterized by the internal chamber being permanently
filled with and connected to the source of pressurized fluid through the
annular
passageway that is formed between the control tube and the sample tube, for
supplying pressurized fluid to the front and rear chambers of the hammer. For
such
purpose, the pressurized fluid flow system of the invention is respectively
configured such that a front annular supply passage is formed in the overlap
between the front inner sliding surface portion of the piston and the recessed
front-
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end outer surface portion of the sample tube, and a rear annular supply
passage is
formed in the overlap between the rear inner sliding surface portion of the
piston
and the recessed rear-end outer surface portion of the control tube.
On the other hand, the discharge chamber is permanently communicated with
the bottom of the hole drilled by the hammer for discharging into said hole
the
pressurized fluid from the front and rear chambers of the hammer.
During the stage where the front chamber is supplied with pressurized fluid,
the inflow of pressurized fluid is controlled by the overlap of the central
control
outer surface portion of the sample tube with the front inner sliding surface
portion
of the piston. Similarly, during the stage where the rear chamber is supplied
with
pressurized fluid, the inflow of pressurized fluid is controlled by the
overlap of the
front-end control outer surface portion of the control tube with the rear
inner sliding
surface portion of the piston. With this form of control of the inflow to the
front and
rear chambers a more efficient filling of the front and rear chambers is
achieved in
every cycle of the hammer and the magnitude of the passive volumes in both
chambers is reduced.
Moreover, the flow of pressurized fluid discharged from the front and rear
chambers is controlled solely by the overlap or relative position of the outer
sliding
surfaces of the piston with the inner surface of the cylinder. There is a
front set of
pressurized fluid discharge through-ports in the cylinder for discharging the
pressurized fluid from the front chamber to the discharge chamber, and there
is a
rear set of pressurized fluid discharge through-ports in the cylinder for
discharging
the pressurized fluid from the rear chamber to the discharge chamber. However,
for channeling the pressurized fluid from the internal chamber to the front
and rear
chambers of the hammer and from these latter chambers to the discharge
chamber, no conduits or passages have been milled in the piston, thus
rendering
the piston stronger and the hammer cheaper to manufacture.
Furthermore, having the pressurized fluid flow system of the invention a
discharge chamber adjacent to the inner surface of the outer casing allows to
divert
the pressurized fluid flow to the outside of the outer casing through one or
more
. --
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end discharge ports bored in the casing's wall, and therethrough to discharge
the
pressurized fluid to the peripheral region of the front end of the drill bit.
In a second aspect of the invention, a reverse circulation DTH hammer is
provided, characterized by having the improved pressurized fluid flow system
that
has been described above and by discharging the pressurized fluid from the
discharge chamber and out of the outer casing along the sides of the front end
portion of the same, through the aforementioned end discharge ports.
Preferably the end discharge ports are connected to respective longitudinal
discharge channels formed on the outer surface of the front end portion of the
outer casing. Both the end discharge ports and longitudinal dicharge channels
are
covered by a sealing element such as a shroud or outer sealing sleeve, so as
to
direct the pressurized fluid to the peripheral region of the front end of the
drill bit
and produce a pressurized fluid flow across the front face of the drill bit
for
dragging the rock cuttings towards the inside of the continuous central
passage
formed along the center of the hammer.
To facilitate the understanding of the precedent ideas, hereinafter the
invention will be described with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Figure 1 depicts a longitudinal cross section view of the reverse circulation
DTH hammer of the invention specifically showing the disposition of the piston
with
respect to the outer casing, cylinder, drill bit, control tube and sample tube
when
the front chamber is being supplied with pressurized fluid and the rear
chamber is
discharging pressurized fluid to the bottom of the hole.
Figure 2 depicts a longitudinal cross section view of the reverse circulation
DTH hammer of the invention specifically showing the disposition of the piston
with
respect to the outer casing, cylinder, drill bit, control tube and sample tube
when
the rear chamber is being supplied with pressurized fluid and the front
chamber is
discharging pressurized fluid to the bottom of the hole.
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Figure 3 depicts a longitudinal cross section view of the reverse circulation
DTH hammer of the invention specifically showing the disposition of the piston
and
the drill bit with respect to the outer casing, cylinder, control tube and
sample tube
when the hammer is in flushing mode.
Figure 4 depicts an isometric view of the reverse circulation DTH hammer of
the invention with a cut-out outer casing for showing the disposition of the
inner
parts of the hammer when the front chamber is being supplied with pressurized
fluid and the rear chamber is discharging pressurized fluid to the bottom of
the
hole.
In these figures, the flow system of the hammer has been depicted with
respect to the solution designed under the invention to convey the pressurized
fluid
to the front chamber and rear chamber, and therefrom to the bottom of the
hole, in
all the possible modes and states, including the exhaustion of the pressurized
fluid
to the peripheral region of the front end of the drill bit for flushing the
rock cuttings.
The direction of the pressurized fluid flow has been indicated by means of
arrows.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION (Figures 1 to 4)
Referring to figures 1 to 4, a reverse circulation DTH hammer is depicted
having the following main components:
a cylindrical outer casing (1);
a rear sub (20) affixed to the rear end of said outer casing (1) for
connecting
the hammer to the source of pressurized fluid;
a centrally-bored piston (60) slidably and coaxially disposed inside said
outer casing (1) and capable of reciprocating due to the change in pressure of
the
pressurized fluid contained inside of a front chamber (240) and a rear chamber
(230) located at opposites ends of the piston (60), the piston (60) having
outer
sliding surfaces (63), and inner surfaces (64);
a drill bit (90) slidably mounted in the front end of the hammer on a driver
sub (110), the driver sub (110) being mounted in the front end of the outer
casing
rynt, w
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(1), the drill bit (90) being aligned with the outer casing (1) by means of a
drill bit
guide (150) disposed inside said outer casing (1) and limited in its sliding
movement by a drill bit retainer (210) and the drill bit supporting face (111)
of the
driver sub (110); and
a sample tube (130) coaxially disposed within the outer casing (1) and
extending from the drill bit (90) to the rear sub (20).
According to the pressurized fluid flow system of the invention the centrally-
bored piston has outer siliding surfaces (63), a front inner sliding surface
portion
(64a), a rear inner sliding surface portion (64b) and a central recess (64c)
in the
inner surfaces (64) of the piston (60); and the sample tube (130) has a
central
control outer surface portion (131c) for interacting with said front inner
sliding
surface portion (64a) of the piston.
Further, a cylinder (40) and a cylindrical control tube (170) are provided,
which are respectively disposed coaxially in between the outer casing (1) and
the
piston (60), and in between the piston (60) and the sample tube (130), the
sample
tube comprising a recessed rear-end outer surface portion (131b) such that an
annular passageway (175) is formed in between the sample tube (130) and the
control tube (170). Part of the inner surface (5) of the outer casing (1), the
drill bit
guide (150) and the rear sub (20) provide support for the cylinder (40) while
the
cylindrical control tube (170) is supported on the front inner guide surfaces
(21) of
the rear sub (20). The cylindrical control tube (170) has an inner surface
(178), a
front-end control outer surface portion (171a) and a rear-end recessed outer
surface portion (171b). The cylinder (40) extends from the rear sub (20) to
the drill
bit guide (150), and the control tube (170) is coupled by a coupling portion
(174)
thereof to, and extending forward from the rear sub (20) having inner surfaces
(178) and outer surfaces (171).
Accordingly, the rear chamber (230) of the hammer is delimited by the rear
sub (20), the cylinder (40), the control tube (170) and the rear thrust
surface (62b)
of the piston (60). In turn, the front chamber (240) of the hammer is
delimited by
the drill bit (90), the cylinder (40), the drill bit guide (150), the sample
tube (130)
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and the front thrust surface (62a) of the piston (60). The volume of these
chambers
(230, 240) is variable and depends on the piston's (60) position.
The pressurized fluid flow system of the invention further comprises a
discharge chamber (2) that, when the hammer is in operation, is in permanent
fluid
communication with the bottom of the hole drilled by the hammer for
discharging
pressurized fluid from the front chamber (240) and from the rear chamber (230)
to
the front of the hammer and therefrom to the bottom of the hole. In the
exemplary
embodiment depicted in the figures the discharge chamber (2) is composed of a
central annular space (2a) in the middle and a set of discharge passageways
(2b,
2c) extending from each of the ends of the central annular space (2a), both
the
annular space (2a) and passageways (2b, 2c) being defined by recesses in the
inner surface (5) of the outer casing (1) and internally delimited by the
cylinder
(40). It should be understood that the discharge chamber (2) could also have
other
configurations such as being formed by a single annular recess in the inner
surface
(5) of the outer casing (1).
A front set of pressurized fluid discharge through-ports (42) and a rear set
of
pressurized fluid discharge through-ports (41) are provided in the cylinder
(40) for
respectively channelling the pressurized fluid out of the front and rear
chambers
(240, 230) and into the discharge chamber (2), so the flow of pressurized
fluid
discharged from the front and rear chambers is controlled solely by the
overlap or
relative position of the outer sliding surfaces of the piston with the inner
surface of
the cylinder.
The pressurized fluid flow system of the invention also has an internal
chamber (68) for supplying pressurized fluid to the front chamber (240) and to
the
rear chamber (230). In the embodiment depicted in the figures, the internal
chamber (68) is defined by the central recess (64c) in the inner surfaces (64)
of the
piston (60), externally delimited by said central recess (64c), and it is
internally
delimited by either outer surfaces (131) of the sample tube (130) alone (see
figure
1) or the outer surfaces (131) of the sample tube (130) together with the
outer
surfaces (171) of the control tube (170) (see figure 2), depending on the
position of
the piston during the operation of the hammer.
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According to a preferred embodiment of the invention as depicted in the
figures, the control tube (170) has at its rear end thereof a set of inlet
ports (177)
that allows the pressurized fluid to flow from the rear sub (20) to the
internal
chamber (68), through the annular passageway (175) formed between the inner
surface (178) of the control tube (170) and the recessed rear-end outer
surface
portion (131b) of the sample tube (130).
When the hammer is in operation, the internal chamber (68) is in permanent
fluid communication with the source of pressurized fluid and filled with said
pressurized fluid. A front annular supply passage (67a) is formed between the
front
inner sliding surface portion (64a) of the piston (60) and the recessed front-
end
outer surface portion (131a) of the sample tube (130), and a rear annular
supply
passage (67b) is formed between the rear inner sliding surface portion (64b)
of the
piston (60) and the rear-end recessed outer surface portion (171b) of the
control
tube (170) as the piston (60) reciprocates, to respectively supply pressurized
fluid
to the front and rear chambers (240, 230) of the hammer. The inflow of
pressurized
fluid to the front and rear chambers (240, 230) is thereby controlled
respectively by
the overlap of the front inner sliding surface portion (64a) of the piston
(60) with the
central control outer surface portion (131c) of the sample tube (130) and by
the
overlap of the rear inner sliding surface portion (64b) of the piston (60)
with the
front-end control outer surface portion (171a) of the cylindrical control tube
(170).
Further, the outer casing (1) of the pressurized fluid flow system of the
invention has at its front end portion one or more end discharge ports (3)
connected to respective longitudinal discharge channels (4) milled on the
outer
surface of the front end portion of the outer casing, both the end discharge
ports
(3) and longitudinal discharge channels (4) having the function of conveying
the
flow of pressurized fluid received in the discharge chamber (2) from the front
and
rear chambers (240, 230) of the hammer, to the outside of the outer casing (1)
and
therefrom to the peripheral region of the front end of the drill bit (90). The
end
discharge ports (3) and longitudinal discharge channels (4) are covered by a
sealing element such as a shroud or a cylindrical outer sealing sleeve (190).
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Control of the state of the front chamber (240)
When in the hammer cycle the impact face (61) of the piston (60) is in contact
with the impact face (95) of the drill bit (90) and the drill bit (90) is at
the rearmost
point of its stroke, i.e. the hammer is at its impact position (see Figure 1),
the front
chamber (240) is fluidly communicated with the internal chamber (68) through
the
front annular supply passage (67a) formed in between the front inner sliding
surface portion (64a) of the piston (60) and the recessed front-end outer
surface
portion (131a) of the sample tube (130) and through a set of flow enhancing
passages (99) milled on the impact face (95) of the drill bit (90). In this
way, the
pressurized fluid can flow from the internal chamber (68) toward the front
chamber
(240) and begin the rearward movement of the piston (60).
The inflow of pressurized fluid into the front chamber (240) will stop when
the
piston (60) has traveled in the front end to rear end direction of its stroke
until the
point where the front pressurized fluid supply edge (66a) of the piston (60)
reaches
the front pressurized fluid supply edge (133) of the sample tube (130). As the
movement of the piston (60) continues further in the front end to rear end
direction
of its stroke, a point will be reached where the front pressurized fluid
discharge
edge (65a) of the piston (60) matches the front limit of the front set of
pressurized
fluid discharge through-ports (42) of the cylinder (40). As the movement of
the
piston (60) continues even further, the front chamber (240) of the hammer will
become fluidly communicated with the discharge chamber (2) through the front
set
of pressurized fluid discharge through-ports (42) of the cylinder (40) (see
Figure 2).
In this way, the pressurized fluid contained inside the front chamber (240)
will be
discharged into the discharge chamber (2) and from the discharge chamber (2)
it is
able to freely flow out of the outer casing (1). According to the exemplary
embodiment shown in the figures, the pressurized fluid from the discharge
chamber (2) is discharged through pressurized fluid discharge passageways
(151),
discharge grooves (152) and discharge ports (153) of the drill bit guide
(150), and
therethrough to the end discharge ports (3) of the outer casing (1). From said
ports
(3) the pressurized fluid is then directed to the peripheral region of the
front end of
the drill bit (90), through the longitudinal discharge channels (4) of the
outer casing
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(1). These ports (3) and channels (4) are covered by the shroud or outer
sealing
sleeve (190).
Control of the state of the rear chamber (230)
When in the hammer cycle the impact face (61) of the piston (60) is in
contact with the impact face (95) of the drill bit (90) and the drill bit (90)
is at the
rearmost point of its stroke, i.e. the hammer is at impact position (see
Figure 1), the
rear chamber (230) is in direct fluid communication with the discharge chamber
(2)
through the rear set of pressurized fluid discharge through-ports (41) of the
cylinder
(40). In this way the pressurized fluid contained inside the rear chamber
(230) is
able to freely flow to the discharge chamber (2) and from the discharge
chamber
(2) it is able to freely flow out of the outer casing (1) through the
pressurized fluid
discharge passageways (151), discharge grooves (152) and discharge ports (153)
of the drill bit guide (150), and through the end discharge ports (3) of the
outer
casing (1), from where it is directed to the peripheral region of the front
end of the
drill bit (90), through the longitudinal discharge channels (4) of the outer
casing (1).
These ports (3) and channels (4) are covered by the shroud or outer sealing
sleeve
(190).
The outflow of pressurized fluid from the rear chamber (230) will stop when
the piston (60) has traveled in the front end to rear end direction of its
stroke until
the rear pressurized fluid discharge edge (65b) of the piston (60) reaches the
rear
limit of the rear set of pressurized fluid discharge through-ports (41) of the
cylinder
(40). As the movement of the piston (60) continues further in the front end to
rear
end direction of its stroke, a point will be reached where the rear
pressurized fluid
supply edge (66b) of the piston (60) matches the rear pressurized fluid supply
edge
(172) of the control tube (170). As the movement of the piston (60) continues
even
further, the rear chamber (230) of the hammer becomes fluidly communicated
with
the internal chamber (68) of the piston (60) through the rear annular supply
passage (67b) formed in between the rear inner sliding surface portion (64b)
of the
piston (60) and the rear-end recessed outer surface portion (171b) of the
control
- - -
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tube (170) (see Figure 2). In this way, the rear chamber (230) will be filled
with
pressurized fluid coming from the internal chamber (68).
Flushing Mode Operation
In the flushing mode of the hammer depicted by Figure 3, i.e. when the
percussion of the hammer stops, the impact face (61) of the piston (60) rests
on
the impact face (95) of the drill bit (90), and the pressurized fluid is
conveyed
directly to the peripheral region of the front end of the drill bit (90)
through the
following pathway: into the rear chamber (230), through the rear sub (20),
through
the set of pressurized fluid inlet ports (177) of the control tube (170),
through the
annular passageway (175) formed in between the inner surface (178) of control
tube (170) and the recessed rear-end outer surface portion (131b) of the
sample
tube (130), to the rear chamber (230); and from the rear chamber (230) to the
discharge chamber (2) through the rear set of pressurized fluid discharge
through-
ports (41) of the cylinder (40). From the discharge chamber (2) the
pressurized
fluid is able to flow freely to the outside of the outer casing (1) through
the
pressurized fluid discharge passageways (151), discharge grooves (152) and
discharge ports (153) of the drill bit guide (150), and through the end
discharge
ports (3) of the outer casing (1), from where it is directed to the peripheral
region of
the front end of the drill bit (90), through the longitudinal discharge
channels (4) of
the outer casing (1). These ports (3) and channels (4) are covered by the
shroud or
outer sealing sleeve (190).
Pressurized fluid that flows into the front chamber (240) from the internal
chamber (68) of the piston (60), is then conveyed to the outside of the outer
casing
(1) through the pressurized fluid discharge grooves (152) and discharge ports
(153) of the drill bit guide (150) and through the set of end discharge ports
(3) of
the outer casing (1).
