Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~09SOZl
ME~HOD OF CONTROLLING ~EE REVERSING OF A D~JICE
FOR DRIVING EOLES IN EARTE AND DEVICE
~OR PERFORI~I~G s~æ
The present invention relates to construction techno-
lo~y and, ~r~ particularly it relates to a method of
co~trolliDg the reversing of a device ~or driving holes
in earth find to devices for performi~g same.
~ he inve~tion ca~ be used to utmost e~fectiveneso
for driving or making holes in compacted soil.
The present inve~tion can be also used to advantage
in drivi~g pipes and tubes into soil, e.g. at trenchless
laying o~ underground li~es.
At present various holes are drive~ in earth with a
wide use of devices actuated by pressurized fluid e.~.
compressed air. ~ore o~ten tha~ not the devices used are
re~ersible, i.e. the~ ca~ be operated in the ~orward mode
wherein they adva~ce through the soil bod~ and make a hole
therein, as well as i~ the re~erse mode, so that they can be
retracted from the soil bod~ back to surfare.
There are also know~ methods of controlling the reversing
of such percussive devices ~or dri~ing or sinking holes
in earth, based on the air suppl~ line being rotated. B~
rotating thi~ line in either direction, a member controlling
the air distributio~ in the device ~or drivin6 holes in earth
i8, respectivel~, turned either in or out in a thread bet~ee~
lO9SOZl
two extreme positions. This operation results in the ~i-
rection o~ the impacts in the percussive-action device being
reversed, which is tantamount to reversing the direction c~
the progress of the device for driving holes i~ earth.
~ his method is embodied in a percussive device for
driving holes in earth (see, for example, the USSR Inv~
entor's-Certi~icate No. 238-,424) comprising a cylindrical
a c co rr~rn o,~te~
housing with a pointed forward end. The housing ~64i~K~r#;
therein a reciprocable impa~t member having a hollow space
in the rear portion the~reo~. The space receives therein a
stepp~d-diameter tubular part secured in the housi~ by a
threaded connection. The t~bular part is movable between two
positions whereat~ respectively, the device i8 advanced in
the forward and reverse directions.
Co~nected to the reax or tail portion of the tubular
part is a compressed-air supply hose. The impact member is
arra~ged in the housing 90 that its exter~al surface defines
with the internal surface of the housing the front wor~ing
cham~er, ~hi-le the i~tex~al sur~ace of the hollow space in
the tail portion-of the impact member defines ~ith the tu-
-bular part-the rea~ wor~ing chamber. The impact member has
ma~e therein a port-ada~ted to establish commu~ication bet-
ween the two ch~mbers, to effect reciprocation of the impact --
member, t-he c-hambers being co~municated when the impact me~-
ber is in the front part of the housing.
10~021
-- 3 --
Thi~ hitherto known percussive device for driving
holes in earth operates with compressed air being supplied
via the hose and the tubular part into the rear chamber,
whereby the impact member is driven forward and delivexs an
impact upon the front part of the housing at the end of its
forward stroke. At this moment compressed air is supplied
through the port in the impact member into the front working
chamber.-
The ef~ective end face area of the impact member, actPdupon by compres~ed air in the front chamber~ being greater
than the ef~ective end face area of the same impact member,
acted upon by compressed air in the rear chamber, the force
urging the impaet member in the rea~ward direction is greate~
tha~ the force urging the impact member in the forward di-
rection. ~onsequent ly, the impact member is driven rear-
wardl7. Upon the port-of the impact member clearing the
rearmost end edge of the tubular part, compressed air is
exhausted ~rom the front chamber into ambient air.
Now the pressure of compressed air in the ~ront chamber
becomes short of the pressure in the rear cham~er, the last-
me~tio~ed pressure equalli~g the supply line pressure, ~here-
by the impact member is arrested a~d then driven forward
on~e again~ through it forward stroke.
~ hen the abGvedescrib~d cycle of the operation of the
device of the prior art in the ~orward mode repeats itself.
lO9SOZl
4 -
~ o make the de~ice for drivi~g hole~ in earth operate
in the reverse mode, the tubular part is to be set to the
position corresponding to the reverse operation. This is
done by rotating the tubular part with aid of the supply
hose connected thereto, until this tubular part is set at
its rearmost position.
Now compre~sed air is again supplied into the rear
chamber and al~o periodically supplied through the port
in the impact member into the front working chamber, driv-
i~g the impact member through successive reciprocations.
However, in this case the impact member delivers impacts
upon the rear or tail part of the housing, in which wa~
the device is retraeted through the hole made in the
course o~ the operation of the deviee in the fsrward mode~
A di~advantage of this technique of controlling the
device ~r driving hole~ in earth arises from the fact
that afte;r the hole ha8 been made to a considerable length,
it is dif~icult and in certain cases altogether impossible
to-transmit the co~trolli~g torque to the tubular part wIth
aid of the supply hose. ~oreover, thi~ man~er of switching
the device ~rom one mode o~ operation to the other one has
proved to-be time-eon~iLg.
- There is aiso known a method o~ controlling the revers-
ing o~ a percussive action device for driving hoies in earth,
~09S021
based on pulling a cable and then rotating the suppl~
hose to displace an air-distributing member, in which wa~
the advance of the device is reversed.
This method of controlling a percussive device for
driving holes in earth is performed by a device (see the
West German Patent No. 2,340,751) comprising a cylindrical
housing accomiodating therei~ a reciprocable impact member.
The impact member ha~ a hollow space in its tail portion,
receiving a tubular part secured in the housing. The
external walls of the impact member defi~e with the internal
wall of the housing the iront workin~ chamber, while the
walls of the hollow space in the impact member define with
the en~ fa¢e of the tubular part the rear working chamber.
The two chambers communicate via a port made in the impact
member.
The tubular part has two an~ular lugs with tuo long-
itudinal lug~ therebetween, limiting the displacement of
this part in the axial direction, and also two recesses
preventing rotation of this part relati~e to ths housing.
The tubular part iB mounted in the axial bore of a guide
element se¢ured in the housing and having two longitudinal
grooves and an aperture receiving a spring-urged retaining
element connected ~ith the remote-control cable. The abutment
of the retaining element in the tubular part-retaining pos-
itio~ proaects into the recess in the body of the tubular
lO950Zl
-- 6 --
part. Longitudinal grooves are made in the wall of the
axial bore of the guide element. The annular and longitu-
dinal lug8 retain the tubular part in either one of two
positions corresponding to the forward and reverse mode of
the operation of the device for driving hole in eart.
In the ~orward mode of the operation of the last-descr-
ibed device of the prior art the tubular member is poæitio
so that the pattern of air distribution in the device pro-
vides for practically simultaneous impact of the impact
member upon the foremost portion of the housing and admiss~
of compressed air into the ~ront working chamber. In this mo-
de of operatio~ the impact member is reciprocated, deliver-
in~ succes~ive impacts upon the foremost portion of the
housi~g. Should it be neces~ary to reverse the device ~or
driving holes in earth, the tubular part is to be set to the
other extreme position. ~his is attained by manually pulling
the retaiIling element remote control cable, to withdraw the
retaining abutmen~ from the recess in the tubular part. The~
the supply hoæe is rotated to rotate the tubular part with
respect of the guide element~ until its longitudinal lugY
align with the grooves o~ the guide elament. Under the
aetio~ o~ the air pres~ure in the rear chamber, the tubular
part is now displaced rearwardly of the device, into its
other position. ~o retain the tubular part in this new po-
sition, the hose is rotated to rotate the tubular part about
109~0~.
-- 7 --
the latter's axis, and the cable is released for the
retaining element to engage the tubular part.
I~ this new position it is ensured th~t the admissio~
of compressed air into the front working chamber takes
place earlier than in the forward mode, while the exhaust
takes plaee relatively later, whersby the impact member now
delivers impacts upon the rear portion of the device, which -
means that the device for driving holes in earth is now
advanced in the reverse direction.
A disadvantage o~ this reversing control method is
the very incorporation of the cable which is apt to get
tangled with the supply hose, or else to get caught by some
foreign object. Besides, the rotation o~ the hose in still
required to reverse the device, which is difficult when the
hole is relatively l~ng.
There is further know~ a method of controlling the
reversing of a pere~ssive device for driving hole~ in earth,-
wherein the reversing control function is e~fected by cutt-
ing off and re-establishing the supply of compressed air
through the feed line. In this way action is exerted onto
an elem~nt controlling the direction o~ the progress o~
the device.
~ his reversing eontrol method is performed by a percuss-
ive device for driving holes in earth (~ee the West German
Auslegeschrift ~o. 2,105,229) comprising a cylindrical
lO9~0Zl
-- 8 --
a cc~ m n~ ~ ~1 a t l r~
housing accc~vd~ting therein a reciprocable impact member.
The impact member ha~ a hollow space in the rear or tail
portion thereof, receiving therein a tubular part secured
in the housing. The external walls of the impact member de-
fine with the inte mal walls of the housing the front work-
ing chamber, while the walls of the hollow space of the im-
pact member and the front end face of th~ tubular member
define the rear working chamber. The impact member has a
port made therein through which the two chambers communicate
with each other to effect reciprocation of the impact member~
A specific feature o~ the construction o~ the device is the
incorporation of a bush rotatable relative to the tubular
member. ~he rotation of the bush relative to the tubular
part is provided ~or by the tubular part having made therein
a cam groove, and the bush having a lug rsceived in this
groove.
The tubular part has in the greater-diameter portion
thereof two rows of ports, while the bush has on the greate
diameter portion thereof two -~ows of Clo~s~ so arranged
that when the bush is rotated relative to the tubular part,
it has its wall closing one row of the ports in the tubular
member and opening up the other row. When the device for
driving holes in earth is to be operated in the forward mode,
those ports of the tubular member are closed, which are the
nearest to the front portion of ths housing, a~d those
~,og5~1
ports are open which pertain to the tail portion of the
housing. In this situation compressed air is supplied
into the front working chamber upon the ports of the impact
member having cleared the foremost edge of the tubul-ar part,
and the exhaust is ef~ected through the open ports of the
tubular part.
When compressed air is supplied via the hose and the
tubular part into the rear working chamber, the impact
member is driven toward the front portion of t~e housing,
and in its foremost position it delivers an impsct upon
the housi~g. At this moment compressed air is admitted
from the rear working chamber into the front working chamber
via the ports in the impact member. Owing to the pressure
differential acting upon the impact member, with the effort
applied thereto from the front chamber being greater tha~
from the rear one, the impact member commences its rearward
motion. Upon the ports of the impact member aligning with
the port~ o~ the tubular part, compres~ed air is exhausted-
from the front working chamber into the ambient air.
To switch over the last-described device for driving
holes in earth from forward to reverse operation, the supply
o~ compresæed air thereto is to be cut of~. A spring then
displaces the bush relative to the tubular part, a~d, owing
to the action of the cam slot, the bush is rotated relative
to the tubular part. When the compressed air supply is re-
~, ,?
10~0~
- 10 -
-established, the bush rotates some more relative to the
tubular part. Now the ports of the tubular part, which are
closer to the frQnt ~ortion of the hou~ing, become open, and
the rearmost ports therein are closed.
Now, when compressed air is supplied into the rear
working chamber, the admission of compressed air into the
front wor~ing chamber takes place earlier than at the for -
ward mode of operation, whereas, in its turn~ the exhaust -
is delayed, whereby the reC~pr!ocating impact member deli-
vers impacts upon the rear or tail portion of the device.
A shortcoming of the last-described technique of re-
versing the operation o~ a device for dIiving holes in
earth is that operating the device becomes hampered when
either the air supply thereto is incidentally cut off, or
elRe ~hen the operation is to be interrupted ~or some
reason, which involves outting off the compressed air supply,
because in both cases the mode of operation of the device is
reversed, which is quite uncalled for. This becomes particu-
larl~ aw~ward when the device is launched into earth, and
the supply of compressed air is to be repeatedly turned off-
and on to correct the hole-making direction.
It is an object of the present invention to eliminate
the disadvantages and shortcomings o~ the reversible devices
for driving holes in earth, which have been described herein-
above .
1095021
It is another object of the present invention to in-
crease the capacity of the device.
It is still another object of the present invention to
improve the reliability of the control, when the operation of the
device is to be reversed.
According to a first aspect of the invention there is
provided a method of reversing a pneumatic percussive device for
making holes in the ground, the device having a forward mode of
operation in which said device is driven into the ground and a
reverse mode of operation in which said device is retracted from
the ground, s~id device being connected to a supply of compressed
air by a feed line, said method comprising disconnecting said
feed line from the supply of compressed air, creating suction in
the feed line to switch the device from one said mode of opera-
tion to the other said mode ~} operation by actuating a valve
arrangement in said device, and re-connecting supply of compressed
air to said feed line to drive said device in said other mode of
operation.
This pattern of controlling the reversing of a percus-
sive device for driving holes in earth from one mode to theother one, e.g. from the forward mode to the reverse one, pro-
vides for reliable remote control of such reversing.
According to a second aspect of the invention there is
provided a pneumatic reversible percussive device, having a
forward mode of operation in which the device is driven into the
ground and a reverse mode of operation in which the device is
retracted from the ground, said device comprising: a hollow
housing~a reciprocable impact member accommodated in said hous-
ing and defining front and rear working chambers; a bush member,
having a stepped portion arranged axially in said housing and
adapted to be connected to a compressed air feed line, a rear
portion of said impact member being hollow and fitting over said
1095021
stepped bush member to define therewith said rear working
chamber; first port means provided in the rear hollow portion
of said impact member such that in a forward position of the
impact member said first port means provides communication
between said front and rear working chambers, said first port
means co-operating with the stepped portion of the bush member
to be first closed off thereby as said impact member moves to
the rear of said housing, and then to communicate said front
working chamber with a further chamber in the rear of said
housing as said first port means moves beyond said stepped
portion of said bush member, said further chamber being commun-
icable with the atmosphere, said impact member thereby recip-
rocating in said housing when compressed air is supplied to
said bush member by the feed line; second port means at an
intermediate position in the stepped portion of the bush member;
a valve arrangement in said bush member actuable by suction
applied to the feed line to open and close alternately said
second port means; said first port means passing said second
port means during each stroke of the impact member, said device
being arranged such that with said second port means closed,
said impact member strikes the front of said housing during
successive strokes so as to drive the device in the forwards
direction, whereas, with said second port means open, said front
working chamber communicates with said rear working chamber
as said first port means passes said second port means during
each stroke and said impact member thereby strikes the rear of
the housing during successive strokes so as to drive the device
in the rearwards direction.
~-, -12-
lO950Zl
It is expedient that the aspirator should include an
a~piration nozzle and a control valve operable to connect
the aspiration nozzle to the air feed line and disconnect
it therefrom.
~ he present invention will be further described in
connection with a preferred embodiment thereof, with refer-
ence being had to the accompanying drawings, wherein:
Fig. 1 schematically illustrates a system depicting the
method of controlling the reversing of pneumatic percussive
devices for making hole~ in earth in accordance with the in-
vention, in the forward mode of the operation of the device;
~ ig. 2 shows the same, as ~ig. 1, with the operation
mode being reversed;
Fig. 3 is a longitudinal sectional view of the area
A in Fig. 1 of the pneumatic reversible device for driving
holes in earth~ according to the invention;
~ ig. 4 ~hows an involute (rotated through 90) of the
e~ternal surface of the hollow valve element at the diame-
ter D;
Fig. 5 is a sectional view taken on line V-V o~
Fig. 3 Swith the port~ o~ the bush and the valve element
driven apart);
Fig. 6 is the same sectional view, as in Fig~ 5, with
the ports of the bush and o~ the valve element aligned.
,
1095021
- 14 -
~ he method of controlling the reversing of a pneumatic
reversible percussive ~levice for making holes in earth, in
accordance with the invention, includes the operation of
supplying compressed air from an e~ternal source into the
air feed line and into the reversible device for making
holes in earth, as indicated with arrows in ~ig. 1. ~o
clarify the description of the method, some of the elements
of the device performing this method will be re~erred to
hereinbelow. In the forward mode of the operation, when a
hole is driven or made in earth, an impact member 1 acco~ -
odated in a housing 2 delivers successive impacts upon the
frontmost part of the housing 2. ~he gate 3 of a control
t O ~ t~
valve 4 is i~ a position whereat the aspiration~ozzle 5
of an aspirating means is disconnected from an air feed li-
ne 6, so that the reversible percussive device 7 for making
holes in earth is connected via the air ~eed line 6 to a
compressecl air source 8.
- Should it be necessar~ to reverse the operation of the
percussive device 7 for ma~ing holes in earth, in accor-
dance with the inventio~, the compressed air supply to the
device 7 is cut off, e.g. by setting the gate 3 o~ the con--
trol valve vertically, as shown in Fig. 2, thus creating
suction in the percussive action reversible device 7 for
making holes in earth by withdrawing air therefrom. This
direction of the air flow in indicated with the arrow in
1095021
- 15 -
Fig~. 2. ~he suction thus created acts upon an element
controlling the operation mode of the device 7, this ele-
ment being displaced, switching over the device 7 to opera-
tion in the alter~ative mode, i.e. the reverse mode of ope-
ration.
It is deemed appropriate to illustrate the herein
disclosed method of controlling the reversing o~ the device
7 by describing the operation of the reversible percussive
device for making holes in earth.
~ he pneumatic reversible percussive device 7 (~ig. 1)
~or driving or making hole~ i~ earth, performing the herein
disclosed reversing control method, includes the housing 2
in the form o~ a ~ollow cylinder with a pointed foremost or
front end, i.e. the end which acts upo~ the soil to ma~e a
hole therei~. The housing 2 accom~odates therein the reci-
procable impact member 1 having in the tail portion thereof
a cylindrical space defining the rear working chamber 9. ~he
external surface of the impact member 1-defines with the in-
ternal ~ur~ace of the housing 2 the front wor~ing chamber
10. When the impact member 1 of the rever~ible device 7 for-
making hole~ in earth reciprocates, the working chambers 9
and 10 vary their volume. The front and rear wor~ing chambe~s
10 and 9 communicate via ports 11 made in the impact member
109~02~
~ he tail space o~ the impact ~member 1 receives there-
in a stepped-diameter bush 12 (Figs 3 and 1) which is
coaxial with the impact member 1, and, hence, with-the
housin~ 2, the bush 12 having its greater-diameter portion
or stage received in the hollow space of the impact member
1, while its smaller-diameter portion or stage is secured
to the tail portion of the housing 2 by means of a nut 13
haYing an opening 14 therethrough for exhausting spent com-
presse~ air into ambient medium. The stepped-diameter air
supply bush 12 has in the greater-diameter ~tage thereof
ports 15 which are intended to supply compressed air from
the rear working chamber 9 into the front working chamber 10
when the pneumatic reversible percussi~e device 7 for making
holes in earth is operate~ in the reverse mode.
~ eceived within the greater-diameter stage of the
stepped-diameter air supply bush 12 is a spring-urged
hollow valve element 16 having in the surface thereof, coo-
perati~g with the air supply bush 12, ports 17. ~hese ports
17 are alignable with the ports 15 in the steppsd-
-diameter air supply bush 12 upo~ the hollow valve element
16 having been rotated accordingly about its longitudinal
axis. ~he hollow valve element 16 has made in the cylind~-
ical surface thereof, cooperating with the ~tepped-diameter
air suppl~ bush 12, a zigzag-shaped groove 18 movably rec~
eiving therein a lug 19 ~ast with the greater-diameter
10950~1
- 17 -
portion or stage of the air supply bush 12. Fig. 4 of the
appended drawings shows an involute (rotated through 90)
of the external surface of the valve element 16 at the
diameter D (~ig. 3). The end face of the hollow valve ele-
ment 16, facing the smal~er-diameter portion or stage of
the air supply bush 12, has made there-through apertures
20 associated with valves 21. ~he hollow valve element 16
is urged forwardly of the housing 2 by a compression spring
22. The stepped-diameter air supply bush 12 carries a valve
member 23 preventing ingress of soil into the reversible
de~ice 7~
The air feed line 6 incorporates an aspirator 5 ~ith
two conduits 24 25 and a control Yalve 4 having a gate 3
rotatable betwee~ a horizontal position and a vertical one.
In one of its positions (the horizontal one) the valve 4
eonnects the pneumatic reversible percussive device 7 for
making holes in earth to the compressed air source B, while
in its other position, the vertical one, the reversible de-
vice 7 is connected to the suction conduit 24 of the aspira-
tor 5, whereas the compressed air source is connected to the
aspiration nozzle conduit 25 of the aspirator 5.
The aforedescribed pneumatic reversible percussive
device 7 for making holes in earth operates, as follows.
To operate the pneu~atic reversible pexcussive device
7 for making holes in earth in the ~orward, or hole-ma~ing
10950~1.
- 18 -
mode, the gate 3 is turned into its horizontal position,
and the reversible device 7 is connected to the compressed
air source 8. Under the combined action of the spring 22
and compressed air the hollow valve element 16 is held in
its foremost position~ In this position the lug 19
of the stepped-diameter air supply bush 12 sets at the peak
or apex o~ the zigzag-shaped groove 18, facing the rear
portion of the housing 2, and the ports 15 of the stepped-
-diameter air supply bush 12 are closed with the wall of the
hollow valve element 16, as shown in Fig. 5. Shown in Fig. 1
of the appended drawings is the foremost position of the
impact member 1, whereat the impact member 1 strikes the
housing 2 (which correspond~ to the forward mode of operati~
of the reversible device 7 for ma~ing holes in earth).
~ hen the air is supplied now via the feed line 6 into
the rear working chamber 9, it is admitted into the front
working chamber 10 through the ports 11 in the impact mem- -
ber 1. ~he pressure of the compressed air in the rear and
~ront working chambers 9 and 10~ respectivel~, being roughly
equal, an~ the e~fective area of the end face surface of
the impact me~ber 1, acted upon by compressed air in the
front working Ghamber 10, being greater than the effective
face area o~ the same impact member 1, acted upon by com-
pressed air in the rear working chamber 9, the efforts
acting upon the impact member 1 from the front and rear
10~5021
- 19 -
working chambers 10 and 9, respectively, are different, the
effort developed in the front working chamber 10 being
greater. Consequently, the impact member 1 is bci~g dis-
placed toward the rear portion o~ the housing 2. Upon the
ports 11 in the impact member 1 becoming closed off by the
wall of the greater-diameter stage o~ the stepped-diameter
air supply bush 12, compressed air is no lon~er admitted
into the front ehamber 10. The volume of the latter increas-
es~ as the impact member continues its rear~ard motion, and
the compressed air contained therein e~pands. Upon the ports
11 in the impact member 1 having cleared the rear face edge
of the greater-diameter stage of the air supply bush 12, the
front wor~ing c-hember 10 becomes connected to the ambient
medium via the ports 11 in the impact member 1 and the
openingrs 14 in the ~ut 13. The compressed air coming from
the fro~t working chamber 10 opens the val~e 23 and escapes
into the ambient medium, whereby the pressure in the ~ork-
ing eha~ber 10 becomes roughly equal to atmospheric press-
ure; so that there is no longer a~ e~fort applied to the
impact member 1 from the side of the front end of the
housing 2. At the same time, from the side of the rear
working chamber 9 continuously connected with the compressed
air source ~ there acts upon the impact member 1 an effort
developed b~ the action of compressed air upon the end sur-
face of the impact member 1, facing the rear wor~ing chamber
9.
lO9S021
- 20 -
The laqt-mentioned ef~ort, first, arrests the rearward
motion of the impact member 1 and then drives it forwardly
until its foremost end strikes the housing 2. Approximately
at the same mome~t the ports 11 in the impact member 1
clear the foremost edge of the greater-diameter stage of the
air supply bush 12, and compressed air is admitted into the
front working chamber 10. The impact member 1 is driven
rearwardly, a~d the abovedescribed cycle repeats itself.
~ o reverse the operation o~ the pneumatic reversible
device 7 ~or making holes i~ earth, the gate 3 of the con-
trol valve 4 is turned into its vertical position.
The compre~sed air source 8 now supplies compressed
air via the feed line 6 into the conduit 25 of t~e aspirator
5 where the dynamic head of the air stream is converted into
a static sub-atmospheric pressure. This creates suction in
the suction conduit 24 o~ the aspirator 5, and, hence, in
the pneumaltic reversible device 7 for making holes in earth.
The air being withdrawn creates 3uction in the internal
space of the stepped-diameter air supply bush 12 of the
reversible pneumatic de~ice 7 ~or making holes i~ earth,
and there is devel~ped an air ~low from the stepped-diameter
air supply bush 12 towaId the aspirator 5. There is created
a pressure drop betwee~ the rear working chamber 9 and the
air in the internal space of the stepped-diameter air supply
bush 12~ The ~auge pressure of the air in the rear working
~095()21
_ 21 -
chamber 9 drives the valve 21 of the hollow valve element
16 to the end wall of the latter, which precludes a flow of
air from the rear working chamber 9 into the internal space
of the stepped-diameter air supply bush 12, through the port
20 of the hollow valve element 16. Under the action of the
air from the rear working chamber 9 upon the end wall of
the hollow valve element 16, the latter is driven rearwardly
of the housing 2. While bei~g thus axially displaced, this
hollow valve eleme~t 16, owing to its operative connection
with the stepped-diameter air supply bush 12 with aid of the
zigzag-shaped groove 18 in the surface of the valve element
16 and the lug 19 of the bush 12, received therein, is rotat
ed about its longitudinal axis through a-specified angle.
With the hollow valve element 16 having been thus driven
into its rearmost posi~ion, the lug 19 of the air supply
bush 12 fi~d~ itself at the apex of the zigzag-shaped groove
18, facing the front portion of the housing 2.
Now, when the gate 3 of the control valve 4 is reset to
its horizontal position, or else when no more suction is
supplied to the reversible percussive device 7 for making
holes in earth, the valve element 16 is returned by the
spring 22 into its foremost position. While being thus
displaced axially, the hollow valve element 16 is rotated
thf~ough a certain angle about its longitudinal axis, owing
to its operative connection with the stepped-diameter air
10~50Zl
-- 22 --
supply bush 12, because throughout this axial displacement
of the hollow valve element 16 the lug 19 remains i}~mobile,
while the walls of the zigzag-shaped groove 18 of the hollow
valve element 16 cooperate with this lug 19 and thus rotate
the valve element 16. In the foremost position of the hollow
valve element 16 the lug 19 finds itself in the rearmost
blind end (although, the different one from the abovemention-
ed) of the zigzag-shaped groove 18.
In this angular position o~ the hollow valve element 16.-
it~ ports 17 align with the ports 15 in the stepped-diame-
ter air supply bush 12, as shown in Fig. 6.
With compressed air now being fed from the supply sour-
ce 8 via the feed line 6 ~with the gate 3 of the valve 4
restored to its horizontal position, as sho~ in ~ig. 13
into the percussive reversible device 7 ~or driving or mak-
ing holes i~ earth, the impact member 1 is sent forward under
the action of compressed air filling the rear working chamber
9, toward the front portion of the reversible device 7 for
mR~ing holes i~ earth. Upon the ports 11 in the impact
member 1 having estab~hed communication with the ports 15
i~ the greater-diameter stage of the stepped-diameter air
æupply bush 12, compressed air is admitted from the rear
working chamber 9 through the ports 17, 15, respectively, o~
the hollow valve element 16 and the stepped-diameter air
supply bush 12 into the front working chamber 10. As it has
~09~;02~.
-- 23 --
been already stated, the effective area of the end surface
of the impact member 1 in the front working chamber 10 is
greater than that in the rear working chamber 9, and so the
effort acting upon the impact member 1 from the front work-
ing chamber 10 iæ greater than that acting upon the same
impact member 1 ~rom the rear working chamber 9. ~his diffe-
rence of the efforts starts slowing down the impact member
1. As the latter mo~es on forward, the ports 11 in the
impact member 1 become closed of~ with the wall of the
stepped-diameter air supply bush 12, while the volume of
the ~ront workin~ chamber 10 continues to diminish, whereby
the air pressure is rapidly built therein. This built-up
pressure increases still further the effort applied to the
impact member 1 from the ~ront working chamber 10. Under
this effort the impact member 1 is arrested and starts mov-
ing rearwardly, and at the end of its rearward stroke it
delivers an impact upon the tail portion of the housing 2,
i.e~ upon the nut 13, to be more precise. As a result of
repeated impacts of this kind, the percussive reversible
device for making holes in earth is dri~en backward, iØ
it is driven in the reverse mode o~ its operation. ~he
ports in the impact member 1 clear the end edge of the
greater-diameter stage of the air supply bush 12, whereby
the compressed air is exhausted from the front working
chamber 10 into the am~ie~t medium. Under the action of
109~0~1
- 24 -
compressed air filling the rear working chamber 9 the impact
membex is sent forward once again, and the abovedescribed
cycle of the reverse mode repeatæ itself.
Should it be necessary now to switch over the pneumatic
reversible percussive device 7 from the reverse mode to the
forward one, the sequence of switching it over from the
forward to reverse mode is to be repeated, i.e. the gate
3 of the valve 4 is to be set to its vertical position, to
create suction in the reversible device 7.
The hollow valve element 16 would be displaced into
its rearmost position, while rotating through a certain
angle about its longitudi~al axis. Then the supply of suc-
tion is discontinued~ and the hollow valve element 16 is
restored into its original ( i.e. the extreme foremost) posi-
tion, whereat its wall closes off the ports 15 in the
greater-diameter stage of the stepped-diameter air supply
bush 12.
