Reversible air-operated apparatus of the percussive type for driving holes in ground by compacting same

The apparatus consists of a hollow body wherein there is contained a striker which divides the space inside the body into a forward operating chamber and a rear exit chamber. The striker is provided with ports for admitting compressed air into the forward operating chamber and for allowing the emission of spent air from the chamber. The striker is also provided with an interior space, the rear end face of said striker being left open. Said hollow body includes passages and a pipe for placing said interior space of said striker in communication with a source of compressed, the pipe being positioned for longitudinal travel relative to the body. For holding fast the pipe in its extreme positions and for determining the direction of movement, which can be either forward or in reverse, the apparatus is provided with a means in the form of a member which exerts radial springy action, is of annular cross section and is disposed inside the body of the apparatus, one of the surfaces of the springy member being exposed to the pressure of compressed air and the other to the pressure of the surrounding medium.

The present invention relates to air-operated apparatus of the percussive 
type for driving holes in the ground, and more specifically to reversible 
air-operated apparatus of the percussive type for driving holes in the 
ground by compacting same. The apparatus disclosed may be used in laying 
pipelines, power and communication cables, etc. by the trenchless method. 
There are known in the art reversible air-operated apparatus of the 
percussive type for driving holes in the ground by compacting same (cf., 
for example, FRG Pat. No. 1,634,417 of the Federal Republic of Germany). 
The known apparatus has a hollow cylindrical body, which is tapering in the 
direction of driving the hole, wherein there is contained a striker with a 
provision for longitudinal travel is, said striker being provided with an 
interior space, being open at the rear end face and having side ports. The 
striker divides the space inside the body into a forward operating chamber 
and a rear exit chamber, and reciprocates due to the pressure of 
compressed air striking against the body. The apparatus is provided with 
an air-distributing pipe built into the body and so arranged with its 
forward portion inside the space in the striker that the side ports of the 
striker are alternately closed and opened by said forward portion of the 
pipe when the striker moves back and forth, thus placing the forward 
operating chamber in communication with either the space in the striker or 
the rear exit chamber. For reversing the apparatus, the forward portion of 
the pipe is made so that it is capable of displacing relative to the body 
into either of the extreme positions, i.e., forward or back, a threaded 
connection between the pipe and body providing for said longitudinal 
travel. The requisite displacement of the pipe is obtained in this case 
due to the rotation of a flexible air hose attached to the pipe. When the 
apparatus is in operation, the friction between the male and female 
threads holds fast the pipe in the given position. 
In another embodiment of the invention disclosed in the above Patent, the 
pipe is made up of several members. The forward portion consists of a 
sleeve slipped on the tubular rear portion of the pipe secured immovably 
relative to the body. Interposed between the sleeve and the rear portion 
of the pipe is a spring which sets the sleeve into the extreme foremost 
position wherein the sleeve is held fast by a ball resting in a hole 
provided in the rear portion of the pipe. The ball is pressed against the 
sleeve by the outward tapered surface of a spring-loaded tube accommodated 
inside the rear portion of the pipe. For setting the sleeve of the pipe 
into either of the extreme positions as required, it is sufficient to 
release the ball by moving rearward, with the aid of the hose, the 
spring-loaded tube accommodated inside the rear portion of the pipe. Once 
released, the ball does not prevent the sleeve from moving so that the 
compressed air admitted into the apparatus causes the sleeve to travel 
backwards as far as it will go and to stay there until the flow of air 
into the apparatus is cut off. The sleeve is returned to its forward 
position due to the action of the spring when no compressed air is 
admitted into the apparatus. 
A disadvantage of the apparatus disclosed in the FRG Pat. No. 1,634,417 is 
low reliability of the way the pipe is being held fast in its extreme 
positions. When use is made of the threaded joint between the pipe and 
body as envisaged in the first embodiment of the invention, it is possible 
that the pipe will move on its own accord if the air hose is turned by 
accident, as this may be the case in practice, for the friction between 
the male and female threads may be too low to hold the pipe in place when 
the striker strikes against the body. Moreover, the pipe may fail to be 
moved by the air hose which may lack rigidity to overcome the resistance 
in the threaded joint between the pipe and body if said joint is clogged 
up. In the other embodiment of the invention disclosed in said Patent, the 
snap ball may become released due to an accidental pull on the hose during 
operation so that the sleeve will move backwards under the pressure of 
air, causing the apparatus to change the working direction from "forward" 
to "back." If the apparatus is being reversed, an accidental interruption 
of the flow of compressed air into the apparatus, no matter how short this 
interruption may be, will change the working direction of the apparatus to 
"forward," because in this case the sleeve will be moved by the spring 
into the foremost position and locked there by means of the ball. Summing 
up, because of the low reliability of the way the pipe is held fast in the 
requisite position relative to the body inherent in the apparatus 
disclosed in said Patent are involuntary changes of the direction in which 
the apparatus is set to operate, said changes occuring due to the turning 
or pulling of the air hose by accident or due to the interruption of the 
flow of compressed air into the apparatus. 
Said disadvantages are eliminated in an apparatus disclosed in FRG Pat. No. 
2,340,751 also granted by the Federal Republic of Germany. Said apparatus 
features a hollow cylindrical body, which is tapered in the forward 
direction and is in the form of a pike at the front while the rear portion 
of the body is closed by a flange rigidly attached thereto. Accommodated 
inside the body is a reciprocating striker the fore-and-aft strokes 
whereof being limited by the front part of the body at one end and by the 
flange rigidly attached to the rear of the body at the other end. Built 
into the rear of the body, i.e., into the flange, with a provision for 
rotation and longitudinal displacement relative to the body is an 
air-distributing pipe which is provided with stops serving to limit the 
amount of its longitudinal displacement; also disposed in the flange is a 
means for preventing the rotation of the pipe relative to the body. The 
striker divides the space inside the body into two chambers, a forward 
operating chamber and a rear exit chamber. Said rear exit chamber is 
connected to a surrounding medium through longitudinal passages in the 
flange whereas the striker has an interior space, is open at the rear end 
face and has ports at the sides. The forward portion of the 
air-distributing pipe is arranged in the space inside the striker so that 
it can either close the side ports in the striker or open them depending 
on the position of the striker. The stops limiting the amount of 
longitudinal displacement of the pipe are given the form of projections on 
the side surface of the pipe. Said projections can enter longitudinal 
grooves provided in the flange, if the projections are placed opposite the 
grooves, thereby enabling the pipe to move longitudinally. By turning the 
pipe through a certain angle it can be placed into a position wherein the 
projections on the pipe fail to align with the longitudinal grooves in the 
flange and, as a result, no longitudinal displacement of the pipe relative 
to the body is possible. When placed in any of such positions, the pipe is 
locked against rotation by means of a ball with a control device built 
into the flange. The control device is a spring-loaded pin in contact with 
the ball with one of its ends while attached to the other end there is a 
wire used to control the operation of the ball from a distance. When the 
pipe is placed into its foremost position, the apparatus is set to operate 
forward. This implies that the striker, reciprocating under the pressure 
of compressed air, strikes against the forward part of the body, i.e., 
against the pike. When the pipe is placed into its rearmost position, the 
apparatus is set to operate backward in which case the striker strikes 
against the rear part of the body, i.e. the flange, while reciprocating. 
The main disadvantage of the apparatus disclosed in the FRG Pat. No. 
2,340,751 is the complicated procedure of changing over from one working 
direction to the other. For reversing the apparatus, it is necessary to 
cut off the delivery of compressed air into the apparatus, to pull the 
wire so as to release the ball and then, holding the wire taut, to turn 
the pipe through a certain angle by turning the air hose. Next, the pipe 
is shifted into its rearmost position by pulling the hose, turned through 
the requisite angle by turning the air hose and only then the wire is 
released of the tension applied thereto so as to lock the pipe against 
rotation. The procedure of changing over from working in reverse to 
working forward is the same only in the reversed order of events. However, 
when the apparatus operates under the ground, said changing over poses 
extreme difficulties, if being possible at all, for it is hardly possible 
to shift the pipe into its foremost position as required by applying a 
force to the hose which is too flexible to transmit same to the pipe. 
It is the object of the present invention to provide a reversible 
air-operated apparatus of the percussive type for driving holes in the 
ground by compacting same which, featuring a reliable way of holding fast 
the pipe in its extreme positions relative to the body, poses no 
manufacturing problems and is more convenient in operation than all known 
apparatus of the same type. 
Said and other objects are attained by a reversible air-operated apparatus 
of the percussive type for driving holes in the ground by compacting same 
which incorporates a hollow cylindrical body, which is tapered in the 
direction of driving the hole. Contained in the body is a striker dividing 
the space inside the body into at least one operating chamber and one exit 
chamber of variable volumes. The striker reciprocates under the action of 
compressed air admitted into the apparatus and, moving so, strikes against 
the body. The striker is provided with at least one side port for 
admitting compressed air into the forward operating chamber and for 
allowing the emission of spent air from said chamber. The striker is also 
provided with an interior space and is left open at the rear end face. The 
apparatus is provided with an air-distributing pipe which is accommodated 
inside the body, connected to a line supplying compressed air, provided 
with at least one longitudinal passage and disposed so that the forward 
portion of the pipe is contained in the space inside the striker, thus 
connecting same to the source of compressed air. The rear portion is built 
into the rear of the body with a provision for longitudinal travel 
relative to the body between its foremost and rearmost positions. The rear 
part of the body is provided with passages connecting the exit chamber to 
the surrounding medium. The apparatus is provided with a means for holding 
fast the pipe in its extreme positions relative to the body. In accordance 
with the invention, the means of holding fast the pipe in its extreme 
positions consists of at least one member which exerts a radial springy 
action, is of annular cross section and is so disposed inside the body of 
the apparatus that the outward side surface of said member faces the 
inward side surface of the body and the inward side surface faces the 
longitudinal axis of the apparatus, one of said surfaces of the springy 
member being exposed to the pressure of compressed air and the other to 
the pressure of surrounding medium. 
By virtue of the present invention there is provided a reversible 
air-operated apparatus of the percussive type for driving holes in the 
ground by compacting same which, featuring a reliable way of holding fast 
the pipe in its extreme positions relative to the body, poses no 
manufacturing problems and is more convenient in operation than all known 
apparatus of the same type. 
It is preferred that a sleeve with holes piercing its walls and, which is 
immovably attached to the body, is provided inside the striker, said 
striker being interposed between said body and the forward portion of the 
air-distributing pipe, said pipe being so arranged in said sleeve that the 
holes in the sleeve are closed by said pipe when it is placed into its 
foremost position and are opened when the pipe is shifted into the 
rearmost position. A plan like this is conducive to reducing the distance 
the air-distributing pipe is bound to cover in order to set the apparatus 
to operate in reverse. 
It is also preferred that the member exerting radial springy action is made 
in the form of an elastic hose attached to the air-distributing pipe so 
that the bore of said hose forms a part of the longitudinal passage of the 
air-distributing pipe. This arrangement allows the employment of the air 
hose as the member exerting radial springy action. 
It is also preferred that grooves running obliquely to the longitudinal 
axis of the apparatus are provided in the inward side surface of the body 
and in the outward side surface of the springy member facing said inward 
surface or, alternatively, a layer of material displaying high friction is 
applied to each of said surfaces to improve the reliability of the way the 
air-distributing pipe is held fast in its extreme positions relative to 
the body. 
It is preferable to provide inserts between the body and the elastic hose 
so that said inserts deform the hose in the transverse direction, thus 
requiring less stringent requirements for the manufacture of the elastic 
hose than ever before. 
It is preferable to interpose between the springy member and the body a 
sleeve attached to the air-distributing pipe and provided with 
longitudinal slots as well as with external projections and to provide 
inside the body recesses aligning with said projections so that said 
projections fit into said recesses when compressed air is being admitted 
into the air-distributing pipe. As a result, said pipe is held fast in the 
given position relative to the body, and the elastic hose is protected 
from wear. 
It is also preferable to provide projections on the outward surface of the 
springy member and to provide in the inward surface of the rear part of 
the body recesses which are disposed opposite said projections so that 
said projections enter said recesses when compressed air is being admitted 
into the pipe. This adds to the strength of the joint between the pipe and 
body so that the pipe is held fast in the given position relative to the 
body in a more reliable way. 
It is also preferable that the member exerting radial springy action be 
made in the form of elastic rings and the air-distributing pipe be 
provided with external grooves wherein said elastic rings are 
accommodated, the pipe being pierced with holes placing the grooves in 
communication with the longitudinal passage of the pipe. This solution 
offers the prospect of using prefabricated standard parts as the springy 
member. 
Finally, it be preferred that the springy member is made in the form of an 
elastic cup attached to the body with its outward surface while the inward 
surface of said cup contacts the outward surface of the rear portion of 
the air-distributing pipe, the space enclosed by said cup, the body, the 
sleeve, which is immovably attached to the body, and by the pipe being 
placed in communication with the longitudinal passage in said pipe through 
a hole with which the pipe is provided with, so that, when compressed air 
is admitted into the apparatus, the pipe is held fast in its extreme 
positions relative to the body by said cup pressed against the pipe. An 
arrangement like this simplifies the design of the apparatus.

The apparatus shown in FIGS. 1 and 2 consists of a hollow body 1 which has 
a forward pointed part 2 and a rear part 3 featuring an end face of extra 
thickness wherein there are provided longitudinal passages 4 placing the 
the interior of the body 1 in communication with the surrounding medium. 
Disposed inside the body with a provision for longitudinal travel is a 
striker 5 with an interior space 6 and which is open at the rear end face 
and which has side ports 7. The striker divides the space inside the body 
into two chambers -- a forward operating chamber 8 and a rear exit chamber 
9 -- and reciprocates inside the body due to the action of compressed air 
striking against the body in the course of said displacements. Serving the 
purpose of admitting compressed air into the forward chamber and of 
emitting spent air from leaving said chamber into surrounding medium, 
there is provided in the apparatus an air-distributing pipe 10. The rear 
portion 11 of said pipe 10 is built into the rear part 3 of the body 1 
with a provision for longitudinal travel relative to the body between the 
foremost and rearmost positions, and the forward portion 12 of the pipe 
extends into the space 6 inside the striker. 
For holding fast the air-distributing pipe in its extreme positions, the 
rear portion of said pipe is provided with a member exerting radial 
springy action. Said member is made in the form of an elastic hose 13 
attached to the pipe so that the bore of said hose forms a portion of a 
longitudinal passage 14 in the pipe which communicates with a source of 
compressed air (not shown) wherefrom air is supplied over a flexible line 
15 attached to the rear portion of the pipe. By benefit of this 
arrangement, the space 6 in the striker is always connected to a source of 
compressed air. A compression spring 16 placed between the forward portion 
of the air-distributing pipe and the rear part of the body serves to set 
said pipe in its foremost position. 
When the apparatus is set to operate forward, compressed air is admitted 
into the space 6 of the striker from the air line 15 through the 
longitudinal passage 14 of the air-distributing pipe. The air, exerting 
its action on the elastic hose 13, causes its outward side surface to come 
into contact with the inward side surface of the rear part 3 of the body 
so as to hold fast the air-distributing pipe in its foremost position, as 
indicated in FIG. 1. When the striker is in its foremost position, the 
ports 7 are not closed by the forward portion 12 of the air-distributing 
pipe as shown in FIG. 1 and compressed air enters the forward operating 
chamber 8 from the space 6 through said ports 7. Since the area of the 
striker whereto the pressure of the air in the chamber 8 is applied is 
larger than the area of the striker which is subject to the pressure in 
the space 6 of the striker, said striker is urged to move towards the rear 
part 3 of the body. As it progresses in said direction, the forward 
portion 12 of the pipe closes the ports 7 and the striker continues its 
travel due to inertia and the expansion of compressed air in the forward 
operating chamber 8. Next, the ports 7 of the striker become open again, 
placing the forward operating chamber 8 in communication with the rear 
exit chamber 9. Said chamber, in its turn, is connected to the surrounding 
medium through the passages 4 in the rear part of the body, enabling spent 
air to escape from the chamber 8 into the surrounding medium. After that, 
the striker stops due to the pressure of compressed air in the space 6 and 
starts its travel towards the forward part 2 of the body. In the course of 
the progress of the striker, the ports 7 therein are again closed by the 
forward portion 12 of the pipe to be opened at a later stage so that the 
forward operating chamber is again filled with compressed air. Once 
compressed air is admitted into the chamber 8, the striker reaches the 
forward part 2 of the body 1, strikes against said part and starts moving 
rearward. Said cycle is regularly repeated and the body, being struck by 
the striker, is caused to drive the hole. The reactions of those forces 
which impart motion to the striker when the apparatus is in operation are 
taken up by the body, yet they fail to bring about any displacement of the 
body in the opposite direction because they are by far smaller than the 
frictional forces coming into play between the walls of the apparatus and 
the walls of the hole being driven. 
The procedure of setting the apparatus to operate in reverse is as follows. 
The feed of compressed air into the apparatus is cut off and, 
consequently, the air-distributing pipe is released of the grip of the 
member 13, because the member 13 exerting radial springy action decreases 
in cross section and fails to produce as much friction as is required to 
take hold of the pipe. After that, the pipe 10 is shifted in its rearmost 
position shown in FIG. 2 by pulling the air line 15, and compressed air is 
admitted into the apparatus while the air line is being held taut. When 
shifted into its new position, the pipe is again held fast in the same way 
as when set into its foremost position, i.e., the springy member (elastic 
hose) 13 expands due to the pressure of compressed air so that its outward 
side surface is pressed against the inward side surface of the rear part 3 
of the body and the pipe is consequently held fast. Once the pipe has been 
set into its new (rearmost) position, compressed air is admitted into the 
forward operating chamber 8 and spent air is released from said chamber in 
the same way as occurs when the pipe is in the foremost position, and the 
striker 5 also reciprocates inside the body. Yet, when the pipe 10 is set 
into this new position, compressed air is admitted into the forward 
operating chamber 8 somewhat earlier in the cycle than was the case when 
the pipe was in its foremost position and, owing to that, the striker 
stops short of the forward part 2 of the body without striking same. When 
the striker is on the backstroke, being acted upon by the pressure of 
compressed air in the forward operating chamber 8, spent air is released 
from said chamber somewhat later in the cycle than is the case when the 
pipe was in its foremost position and, owing to that, the pressure in the 
space 6 is too low to stop the striker which consequently reaches the rear 
part 3 of the body and strikes against same. Yielding to the strikes the 
striker delivers against the rear part of the body, the apparatus returns 
along the hole driven and reaches its head. 
For changing the direction of travel from back to forward, it is necessary 
to stop the flow of compressed air into the apparatus. As a result, the 
springy member 13 releases its hold on the pipe which is returned, due to 
the action of the spring 16, into its foremost position wherein the 
apparatus operates forward. 
The rear part of the apparatus illustrated in FIG. 3 differs from the rear 
part of FIGS. 1 and 2 in that grooves 17 and 18 running obliquely to the 
longitudinal axis of the apparatus are provided in the outward side 
surface of the rubber hose 13 and in the contiguous surface of the body of 
the apparatus. This adds to the forces of cohesion between the pipe and 
body so as to improve the reliability of the way the pipe is being held 
fast. Serving the same purpose, as this can be noted from FIG. 4, are 
layers 19 and 20 of a high-friction material which are applied to the 
contiguous surfaces of the rubber hose 13 and the body. 
Referring to FIG. 5, additional members in the form of inserts 21 which 
deform the hose 13 in a transverse direction are interposed between the 
hose 13 and the body of the apparatus The recourse to inserts allows less 
stringent requirements for the manufacture of the hose 13, for the 
adequate contact required to hold fast the pipe can be assured whatever 
the degree of change in the diameter of the hose. 
When compressed air is admitted into the apparatus illustrated in FIG. 3, 
the rubber hose 13 expands under the pressure so that its outward surface 
with the grooves 17 is pressed against the contiguous surface of the body 
with the grooves 18. The grooves 17 and 18 increase the cohesive force and 
render the way the pipe is being held fast in its extreme positions more 
reliable. The hose 13 shown in FIG. 4 operates on a similar principle. In 
this case, the holding fast of the pipe in a reliable way is obtained by 
virtue of the layers 19 and 20; change high-friction material which 
increase the frictional forces between the pipe and contiguous inward 
surface of the body of the apparatus. The hose 13 of FIG. 5 is pressed not 
to the body directly, when compressed air is being admitted into the 
apparatus, but to the inserts 21 interposed between said hose and the 
body, this action of the hose holding fast the pipe relative to the body. 
As far as other aspects of operation are concerned the apparatus 
illustrated in FIGS. 3, 4 and 5 do not differ in principle from the 
apparatus shown in FIGS. 1 and 2. 
Depicted in FIGS. 6 and 7 is the rear part of the apparatus of another 
embodiment. Compared with the rear part of the apparatus shown in FIGS. 1, 
2 and 3, a new component is introduced thereinto in the form of a sleeve 
22 attached to the air-distributing pipe and provided with longitudinal 
slots 23 as well as with external projections 24 on the sides, said 
projections being disposed opposite recesses 25 provided in the rear part 
of the body of the apparatus. When the apparatus is in operation, the 
elastic hose 13 expands under the pressure of compressed air and exerts a 
force on the projections 24 which enter the recesses 25 in the body, thus 
holding fast the air-distributing pipe in a given position relative to the 
body. Other aspects of the operation of the apparatus are the same as 
those in FIGS. 1 and 2. 
FIGS. 8 and 9 illustrate another embodiment of the rear part of the 
apparatus which differs from the rear portion of the apparatus shown in 
FIGS. 1 and 2 in that there are projections 26 attached to the elastic 
hose 13 and disposed opposite recesses 27 in the body when the 
air-distributing pipe is set to either of its extreme positions relative 
to the body. Following the admission of compressed air, the elastic hose 
13 expands so as to be pressed against the contiguous surface of the body 
of the apparatus, thereby holding fast said pipe. The projections 26 
provided on said hose enter the recesses 27 in the body, adding to the 
reliability of the link up between the pipe and body. Otherwise, the 
apparatus operates according to the same principles as the apparatus shown 
in FIGS. 1 and 2. 
FIG. 10 illustrates another embodiment of the rear part of the apparatus 
which differs from the rear part shown in FIGS. 1 and 2 in that there is a 
new component in the form of a sleeve 28 with side holes 29 which is 
immovably attached to the body and is disposed in the space 6 of the 
striker 5 between said striker and the forward portion 12 of the 
air-distributing pipe. The side holes 29 are closed by the forward portion 
12 of the pipe when said pipe is shifted inside the sleeve 28 into its 
foremost position. Said holes remain open when said pipe is set into its 
rearmost position. For holding fast the pipe in its extreme positions 
relative to the body, the springy member is made, for example, in the form 
of rubber rings 30 accommodated in grooves 31 provided in the rear portion 
11 of said pipe. The grooves 31 are permanently connected to the 
longitudinal passage 14 of the pipe, being admitted thereinto compressed 
air, by means of holes 32 provided in said pipe. 
The apparatus shown in FIG. 10 operates forward when the air-distributing 
pipe 10 is set into its foremost position, i.e., when the holes 29 in the 
sleeve 28 are closed by the forward portion 12 of said pipe. This is in 
contrast to the apparatus shown in FIG. 1, wherein the ports 7 of the 
striker 5 are closed and opened, when said striker reciprocates under the 
pressure of compressed air applied to the forward operating chamber 8 and 
the space 6 in the striker, by the sleeve 28 interposed between the 
striker 5 and the air-distributing pipe 10 and not by the forward portion 
12 of said pipe. In addition, said pipe is held fast by elastic rings 30 
which, while expanding under the pressure of compressed air entering the 
grooves 31 through the holes 32, are pressed by their outward side surface 
to the contiguous surface of the body, thus giving rise to friction 
between the body and the rings 30 fitted on the pipe which is sufficiently 
high to hold fast the pipe. 
For reversing the apparatus shown in FIG. 10, it is necessary to cut off 
the flow of compressed air, to shift the air-distributing pipe into its 
rearmost position by pulling the air line 15 and then to admit compressed 
air again into the apparatus. When the air-distributing pipe is in its new 
(rearmost) position, the holes 29 in the sleeve 28 are open so that 
compressed air is admitted into the forward operating chamber through said 
holes in said sleeve when the striker is on the forward stroke or, in 
other words, the induction takes place in this case somewhat earlier in 
the cycle than when the air-distributing pipe is in its foremost position. 
Because of an early induction of compressed air into the forward operating 
chamber 8, the air pressure applied to said chamber stops the striker, 
which is on the forward stroke, short of the front part 2 of the body 
without striking same and causes the striker to reverse its stroke. When 
the striker is on the backstroke, the induction of compressed air into the 
forward operating chamber 8 is interrupted somewhat later in the cycle 
than is the case when the air-distributing pipe is in the foremost 
position. Owing to that, by the time spent air leaves the forward 
operating chamber, the kinetic energy of the striker is much higher than 
the kinetic energy the striker displays in moving when the 
air-distributing pipe is in the foremost position. Under the circumstances 
like this, it appears that pressure of compressed air applied to the space 
6 is not sufficiently high to bring the striker to a strikeless halt, and 
the striker ends its backstroke by striking against the rear part 3 of the 
body of the apparatus. 
It can be noted that the rear part of the apparatus illustrated in FIGS. 11 
and 12 differs from that of the apparatus shown in FIGS. 1 and 2 in that 
provided in the wall of the rear portion 11 of the air-distributing pipe 
are through holes 33, wherein there are accomodated pins 34 which are 
located opposite annular recesses 35 provided in the rear part of the 
body. The springy member made in the form of an elastic (e.g., rubber) 
ring 36 embraces all the pins 34 so as to keep them flush with the edges 
of the holes 33. In said embodiment, the air-distributing pipe is held 
fast by the pins 34 which, by overcoming the resistance of the elastic 
ring 36, yield to the pressure of air in the passage 14 of said pipe and 
extend from the holes 33 so as to enter the annular recesses 35 in the 
body when compressed air is being admitted into the apparatus. When the 
flow of compressed air into the apparatus is interrupted, the pins 34 are 
forced by the action of the elastic ring 36 out of the annular recesses 
35, and due to that the air-distributing pipe is free to shift rearwards 
so as to set the apparatus to operate in reverse. In other respects, the 
operation of said apparatus does not differ from the operation of the 
apparatus shown in FIGS. 1 and 2, i.e., compressed air is admitted into 
the forward operating chamber 8 and spent air leaving said chamber is 
disposed of when the striker is on the move exactly in the same way as in 
the apparatus of FIGS. 1 and 2. 
The rear part of the apparatus shown in FIG. 13 differs from that of the 
apparatus represented in FIG. 10 by the fact that the member exerting 
radial springy member is in the form of an elastic cup 37 made, for 
example, of rubber which is immovably attached to the body and embraces 
the outward surface of the rear portion 11 of the air-distributing pipe 
10. In addition, there is a hole 38 in the forward end face of the pipe 
wherethrough a space 39 enclosed by said pipe, by the outward surface of 
the cup 37, by the sleeve 28 and by the body is connected to the source of 
compressed air. Other details of the rear part 3 of the apparatus shown in 
FIG. 13 are a nut 40 screwed into the body and a shock absorber 41 
attached to said nut. The sleeve is attached to the body not directly but 
by means of the shock absorber 41. The operating principle of the 
apparatus shown in FIG. 13 is the same as that of the apparatus 
illustrated in FIG. 10. The only difference is in the way the 
air-distributing pipe is being held fast. This is accomplished with the 
aid of the elastic cup 37 which is immovably attached relative to the body 
and is pressed to the air-distributing pipe by the pressure of air 
admitted into the space 39 through the hole 38 in said pipe so as to hold 
fast same in the given position relative to a body.