CA1308314C - Pneumatic percussive device - Google Patents

Abstract

ABSTRACT
A pheumatic percussive device has a casing accommoda-ting a movable hammer piston dividing the interior space of the casing into two chambers. One of these chambers alternately communicates, by means of an air distribution arrangement having a movable actuator member, with a compres-sed air source and with the environment. In addition, said chamber communicates, via a throttling passage, with a cavity of the air distribution arrangement the pressure in which ensures movement of the actuator member to one of its limit positions.
The invention is most preferably used for forming holes in the construction of engineering lines of various uses by moling.

Description

PNæUMATIC P~RCUSSI~B DEVICE
The present inventiDn relates tD the mining tecbnDlDgy, and more specificall~, it deals with a pneumatic percus-9 ive dev iC9 .
The present invention may be most advanta~3Dusly used in pneumatic percussive tD~ls such as pnsumatic mDles de-si~ned for for~in, bDrehDles in sDil and rDcksc KnDwn in the art are pneu~atic percussive devices having valve a~d spDol ~ir distribution arrangements and pneumatic devices in which air distributiDn is effected bg the hammer pistDn. All such devices ~re characterized by the provisiDn of a system Df passages made either in tbe casin, walls Dr in the bammer pistDn, which are naces-sary for cDntrDlling DperatiDn D~ the spDDl or valve and also for supplying cD[npressed air tD wDrking chambers of the device and for discharging exhaust air from these chambers. The prDvisiDn of such passages results, on the Dne hand, in a decrease in the net area of the ha~mer piston which, in turn, lowers the specific impact power and, on the Dther hand, complicates the hammer piston and thus bringing abDut sup~rfluDs stress cDncent-rators so as to substantially reduce service life of these parts. This is true to the largest exte~t fDr undergrDund tools such as pneumatic mDles in which diameter D~ the casing, h~nce of tha hammer piston, is limited by th0 diameter of the hole, and the impact loads are taken up nDt only by the hammer piston, but als~ by the casing ~ihich functions as a ,vorking member as well q.~

Known in the art is a pnsuMatic percussivs device (D~, C, 1132067) cDmprising a pile hammer lowered intD
a borehole and an independent air distribution ar~an~e-ment i~stalled Dn the ground level. The pile hammer i5 in the fDrm Df a trivial impact ~lDrk CDnsisting D~ a tubular casing clDsed at bDtl ends snd a hammer pistDn mDunted therein for axial movement. The ham~er piston d~vides the interior space of the tubular casing into t~lo chambers cDm-municati~ with each other ~ither thrDugh a throttling pas-~a~e, or through a passage having a check valve, Dr by means o~ both. At least Dne of these chambers, which i9 referred to as the cDntrol chamber, communicates thrDu~h a hose with tbe air distribution arran6emcnt prDvided Dn the grDund level.
~ he air distribution arrangement is generally in the fDrm o~ an oscillating system consistin~ Df a spool valve box and an actuatDr provided tharein and mada in the fDrm of a spDol Dr a ~lve adapted tD perform Dscillations either autDmatically or positively under the action Df a drive mechanism, e.g. a cam drive. ~he self-Dscillating spoDl is connected by means o~ levers and pivot joints to a pendulum having an adjustable weighb~
FDr putting the pile hammer in ~peratiDn, the actuator of the air distributiDn arrangement is autDmatically Dr posi-tively driven to pe~form Dscillations. During ~scillations o~ the spoDl the hose connecting the controlled chamber Df tbe pile hammer tD the air di9tributiDn arr-ngement alter-nately communicates wlith a coinpr~ssed air source and ~ith ~ 31~

the environment depending Dn pDsition D~ th~ SPDD1~ I,vh~reby the con~rolled chamber of the pile haramer also alternately CQmmunicates with the compre~sed air so~ ce and wi.th the envirDnment. CD nsaquently, pulsating pressure is built up in the contr~lled chamber. As bDth chambers of the pile hammer cDmmunicate ~ith each other throu~. the thrDttling passage Dr through the passaQe incorporati~ a check valve7 rather than thrDu,h a free passaQ~e, pressure in ~hese chambers is always different. Under the action o~ the pres-sure difference in the chambers, the harnmer pistDn per-~orms reciprocations durin~ which it imparts blows either tD a workin~ implement or to the casin~-in the oppDsite di~
rection. The desired directiDn Df blDWS iS ensured by a pre-set combination of parameters of the air distributi~n ar-rangement chosen by way Df eXPerir.1entS.
In certain embodiments of tbe pile hammer tbere are no passages in the hammer L~)iston and casin, ?ltogether. This makes the abovedescribed device advantageDus over priDr art pneumatic percussive devices having a spool or valve air distributiDn arrangements that cannot be ~mpelemented without a system of passages which are required fDr control-linæ the spoDl Dr valve and fDr discharging wasta air from the chambers and admittinQ compressed air to the chambers.
~ he provision Df a hose connecting the contrDlled chamber tD the air distribution arrangement which is located at a substantial distance from the pile hammer reslllts in an increase in the "dead volume" Df this chamber by th~

amDunt o~ tha volume of the interiDr sp~ce Df the ho,se.
At the s~me bime, an increase in the "dsad volume" of the chamber is known to result in an 2ddi~ional unproduc-tive cDnsumption of compxessed air, hence in a lo~er e~-~iciency9 In addition~ a subistarltial ],engtb of the h~se limits the rate of pressure pulses ef~ectively transmitted tD the chamb3r, i.~c limits impact pDwer of tbe pil~ hammer.
In an ideal case~ the rate of pressure pulses ~f~ectively transmitted through the hose per unit of ti-i~e is deter-mined by the formula herein ~3 is the rate o~ pulses:
is the hose length;
~ is the velocity Df sound in the air.
In real life devices, the rate Df effectively trans-mitted pulses is still lower.
Known in the art is a pneumatic percussive device (SU~ A, 2613~9), comprisin,, a casin~ and a hammer piston mDunted in the casing fDr movementr ~he hammer pistDn divi das the interior space Df the casing into tWD chambers.
A working implement is incorpDrated in the ~rDnt end part o~ the casing~ A massive balancin~ pistDn is pro-vided in the rear end part of the casin~ w~~ich is in the form of a spDol adapted to per~orm sel~- ~scillatDry movement when compressed air is supplied to th~ device.
A longitudinal passage provideed in the spool permanently communicates with a controlled chamb~r on Dne side and is cDmmunicable with e~ther a 90U~C~ of compressed air or ~ 31 ~

the environment on the Dther side dep~nding on position Df the spoDl. Owing to the fact that the indepandent air distribution arran~ement is inc3rporated i~ the casing of the percussive device, there is no need tD use a hose fDr con~unicatiDn Df the controlled chamber with the air distributiDn arrangement as was the case in the priDr art pneumatic percus 9 ive device Df DE,C, 1132067.
When cDmpressed air is supplied tD this device, the spool providad in the rear end part Df the casinO~ per-forms self-oscillations v~ith respect to the casingO Depen-ding Dn pDsition D~ the spDDl during its Dscillatory move-ment, the controlled chamber alternately cDmmunicates thrDugh tbe longitudi~al passage Df the spDol with the comprassed air`source and with the environment~ Therefore7 bhe balan-cing pistDn which is made in the form of the spool functions not Dnl~ as a balancing inertia member but also as an in dependent air distribution device establishin~ communica-ti~n alternately between the controlled chamber of the de-vice and the cDmpressed air source and the environment, Under the acti~n of pulsating prassure in the control-led chamber and air pressure in the ~ther chamber, the hammer piston performs raciprocations during which it imparts blDws tD ~he wDrking implement.
HDwevar, as the balancing pistDn functiDns as a balan-cing member as wall~ it has suhstantial dimensiDns and mass as well as the amplitude of DscillatiDns 3D that the size and mass o~ the device as a whole alsD increasH without bringing about any increase in bhe impact pDver. Consequently, ths speci~ic impact power of the device is lo;erGd. ht~
tsmpts mads t-o reduce mass and size oi this ~rior art ds-vice bv way o~ rGtional choice of dimensiDns, rla~s and swing Df DSCill~tions Df ths bala~cin$ i~istDn and by lo-~sring a~plirude Df DSCil1atiOnS D~ the balancing .vistDn by means OL limitin, abutments failed. ~hus reducin~ r~ ss of the balancin~ pistDn tD lov7er Iriass Df the device as a wbole inevitably result in an increase in amplitude Df its oscil' tio~s so that length D~ bh~ casinæ increasas and the reduction ~f mass o~ the device as a whDle is nDt achieved because Df an increase in masS of the casin;;. Re-ducinæ amplitude D~ D5Ci11atiOnS 0~ the balancin~ pistDn by r,leans D~ the limitin:; abutlments as is the case in InDwn pneumatic psrcussive àsvices ~lith valve air distribution arrangements in which the valve rdmain3 statiD.lar~! alter-natel~ in one and Dther pDsition is also impossible ~or tWD
reasDns. ~irstly, the balancing pisGDn cannot bs stopped i~
~ne w~ants it to per~Drm its lunctiDn. ~ecDndly, this pistDn being a sel~-oscillatinO member, it cannot remain stationary a~ter its engaga~ant ~,iththe abutment since the very principle DL? its selL?-DscillatiDn mDvement involves the development Df a rebound ~orce under the action D~ which tha balancing piston is instantly reversed after its st~p-pa~e. As a result, ~requency o~ oscillatory mDvement o~ the balancing piston is only determined b~ a very short tims o~ its shift between the tWD abutments and it will become tDo high SD as to rule out normal DperatiDn o~ the device.

~4~

It is an object of` the invention to sub3tantially reduce mass and size of the device as a wbole while re-taining advantages of pneumatic percussive devices havin~
a sirlgle controlled chamber and cDmparatively high impact power.
~ hes~ and Dther ob~cts ar3 accomplished by that in a pneu~atic percussive device having a casing accDmmodating a movable hammer piston dividing the interiDr space Df the casing into tWD chambers, the first chamber bein~ de-fined by th~ casing walls and the hammer piston and the second chamber being defined by the hammer pist~n an~ an air distribution arrangement accDmmodated in the casi ~
and having a movable actuator member dividing the interior space o~ the air distributiDn arran~eLIent into at least two cavities, the pressure in the first cavity ensuring mDvement of tha actuator member to ons of its limit posi-tions, the second cavity permanently communicating with the secDnd chamber and alternately communicatin~ with a cD~npres sed air source and the environment, accDrding to the in-ventiDn, the first cavity of the air distribution arrange-ment communicates with the second chamber via a throttling passage.
The provision of the throttling passage establishing communicatiDn between said secDnd chamber and first cavity prevents an instantaneous develo~ment of a forcs that cbanges direction of movement o~ the actuator member a~ter its stoppage in Dne of its limit positions~ Durin~ its self-oscillatDry movement between the two abutm~nts, the 3(,~ 3 -'-3ctuatDr member can thus stop in each Df its limit p~8i-tiDn3, the stDppaJ,e time in Dne pDsitiDn bein~ equal to the time fDr filling said first cavity D~ the air distributiDn arrangement with air through the throttlin, pas~age and the stDppage time in tbe other positiDn being equ~l tD
the ti~lla for discharging cDmpressed air thr~ugh this pas-sage frDm said first cavity. ~he law of oscilla~Dry mDve-ment of the actuator member in this case is determined by parameters Df the thrDttling passage and said ~irst cavity Df the air distribution arrangement, but it dDes nDt sub-stantially depend Dn its inertia properties. As a result, an actuatDr member may be used the size and amplitude Df Dscillations Df which can be reduced to the values suffi-cient not only fDr enabling ~ree admissiDn and discharge Df air. In comparison with the davice disclDsed in SU, A, 261319, size and mass of this device ~re reduced as a whDle withDut a reduction in its impact p~wer SD that the specific impact power, i.eO the impact pDwer-tD-~mass Dr volume ratiD Df the device increases.
It is preferred that tha first cavity ~f the air dist-ribution arrangement and the second chamber o~ the casing cDmmunicate with each Dther through at least Dne au~iliary thrDttling passage, the Dutlet opening Df which Dn the side Df the first cavity Df the air distribution arrange-ment is provided with a check valve secured to a wall of the air distribùti~n arrangement.
This facility allows a~ Dptimum time for admis~i~n Df cDmpressed air to said 3econd chamber to be chDsen wibh --9~
a preset tim~ for exhaust of w~ste air thare~rDm, ~ o prDvlde ~Dr the pDssibility o~ choice of an optim~m ti~a fDr dischax~e Df compre~3ed air ~ro~ sa1d second cham~
ber with a prese~ tim~ for air ~dmis~ion the~stD~ it i~
pre~srred that the interior space o~ the air distribution arrangement and the ~econd cha~ber o:e the casin~; communica-te with e~ch other ~hrcu~h at le~st Dne 3~xiliary thrDttling passage haviog ~n outlet Dpeni~g therso~ on the side o~ th~
second chambar o~ the casin~ provided with a check valv0 sacured tD a wall Df the air distribution arra~gement.
~ o prevent uncontrDlled air over~lDws ~r~m the ~ir line i~to tha ~irsb cavi~y D~ the air distribubion arrange-ment, it i5 pre~erred, D~ the cDntrary, that ~ di~phra~m be prD~ided on the surface o~ the actuatDr member acted upo~ by cDmpr~ssed air pressure in said ~irst cavity, bhe diaphragm being secured to the periphery o~ the air distri~
bution casing.
The invention will nDw be described with r~erence to a specific embod$ment illustrated i~ the accompan~ing dra-wings, in which:
Figure 1 is a ganeral view o~ a pneumatic percussive device according tD the invention;
~ igure 2 i~ an embodiment of an air distributio~ ar-rangeme~ having its actuator member which is in a position allowing compressed air t~ be admitted tc o~e o~ chambers D~
~he device;
Figura 3 i~ ditto of Figure 2 showing a positiou o~ the 3~

~10-actuator me~ber allswing waste air tD be exhausted from said chsmber o~ the device;
~ i~ure 4 ie an embodiment o~ an air distribubion ar-rangement U5i~g a spring, shown in a position allowin~
~ompressed air to be admitted to one of chamber~ of the device;
Figure 5 is ditto of Figure 4, but shDwing the actuatDr member in a position allowing waste air to be e~hausted from said chamber D~ the device;
Figure 6 is an embodiment of an air distributiDn ar-rangement having two throttling passages allowin~ compres-sed air to be admitted to one chamber D~ the ~evice only;
Fiæure 7 is an embodiment Df an air distribution ar-ran~ement having tWD thrDttling passag~s allowing cDmp-ressed air to be admitted only to the interiDr space of the air distribution arrangement;
Figure 8 is an embodiment of an air distributiDn ar-ran~ement usin~ a diaphragm.
A pneumatic percussive device comprises a casing 1 (Figure 1), e.g. of a tubular shape.
A working implement 2 is abtached to Dne end face of the casing, and an air distribution arrangement 3 vvith an air supply hose 4 is provided at the other end of the ca-sing. A hammer piston 5 is mounted for axial movement in the casing 1. ~he hammer piston 5 dividea the i~ erior space of the casing into two chambers 6, 7. The first chamber 6 i5 defined by the walls o~ the casing 1, the hammer piston 5 and the workin~ implement 2. ~he second chamber 7 is defined by the ~115 of the c~5ing 1~ hammor ~3~

pistDn 5 and th~ air distribution ar~angament 3~ The f'irst and second chambers 69 7 communicate with sach otber bg any apprDpriate known means (not s~own), limiting overf~Dws of air f`rom the second chamber 7 tD the first cbamber 6.
A known means Li~iting overf'lDws of air betwec~ the first and secDnd cha~bers 6 and 7 may be in the form of a t~.rot-tling passa~e v~hich ma~ be in the ~orm Df an annular space between the hammer pist~n 5 a~d the casing 1 or in the form o-f a passage incDrporating a check valve, or bDth~
~ he air distribution arrangerrlent 3 has a movable ac-tuator me~b~r 8 (Figu~e 2) dividing the interiDr space o*
a casing 9 of the air distribution arrangement 3 intD at least two cavities~ and in this particular case, intD three cavities 10, 11, 12 since the actuator member 8 i9 made in the form o~ a stepped spDol mDunted coaxially with the hammer piston 5 (f'iOure 1) in the casing 9 (Fi~ure 2) of the air distribution arrangement 3 f'or r~cipr DC ati D ns bet-ween abutments.13 and 14 provided in the casing 9 of the air distribution.arrangement 3. ~he f`irst cavity 10 i~
de~ined by the walls of the casing 9 of the air distribu-tion arrangement 3 and an end f'ace 15 of' the actuator mem-ber 8. Pressure in the first cavity 10 ensures a shift of the actuator me~ber 8 t~ one of its limit positions~ ~he secDnd cavity 11 is d0fined by the walls of the casing 9 and annular end ~aces 16 and 17. ~he second cavity 11 permanently communicates thrDugh communicating radial and lDngitudinal passages 18 and 19, respectively, with the second chamber 7 of the device. The acbuatDr member 8 ha~ a cavity 20 i~ the form of a ~leevc having a bottom 21.

3~L

The cavity cDrnmunicatos, via a passage 22, with ~ha air supply hose 4 and, via a radial passa~e 239 with the seeDnd eavity 11, and the seeond cavity 11~ d0pending Dn pDsition of the aCtUatDr member 8 alt~rnatel~ c~mmu-nicates witb tbe air sup,)ly line when in Dne positiDn, via the radial passage 23, and, via th0 radial passage 14, with the envirDnment when the actuator memb3r ~ is in the other p~sition (Fi~ure 3). The third cavit~ 12 defined by an end faee 25 and the walls of th~ easing 9 Df the air distribu-tion deviee permanently eDmmunicates with the enVirDnment via a radial passa~e 26 (Fi~ure 2)~ ~be first cavity 10 permanently communicates with the seeond chambar ? via 3 throttling passage 27 and functions as a reeeiver.
Fi~ures 4, 5 show an emb~diment ~f a casin~ 28 Df the air distribution arrangemsnt 3 and an actuatDr membsr 29 of anDther type in which th3re is nD cavitg in ths form Df a slseve inside the acbuator member 29, In this case a first cavity 30defined by the ;ialls of the casin~, 2~ and an end faee 31 Df the actuator membsr 29, direetly com-munieates, via a thrDttling passage 229 with the seeDnd ehamber 7 of the device and funetions as a reeeive~0 A
seeond cavity 33 defined by a wall ~ the easing 2~ and annular end faees 34 and 35 permanentl~ comr.unicates with tbe seeond ehamber 7 through CDmmUniCatin~ radial and lDn~itudinal passa~0s ,~ and ,7, respeetively. Dependin~
Dn pDsitiDn Df ~he aetuator member 29, tbe seeond eavity 33 may eDmmunicate eithsr with the snvirDnrnent tbrough a radial passage 38 ~n tbe pDsitiD~ shDwn in ~igurs 4) Dr with the interior of the air suppl.y hose 4 thrDu~h pas.ia~es 39 and 22 (in the position of ~he actua~or m~mbe~ 29 shown in Figure 5). ~ third cavity 40 defined b~ the ~alls Df the casing 28 and an end face 41 of the aC~UatDr mem-ber 29 permarently CDmmunicates~ via the pas~a~3 22, with the air supply hose 4. A spring 42 is prDvided in the first cavity 30 batween the wall Df the casing 28 a~d tha end face 31 of the actuator member 29, the force of the spring placing the actuatDr member 29 in the pDsitiDn shown in ~igure 4 in which the second chamber 7 cDmmu-nicates with the environment.
To allow fDr a choice Df an optimum ~ime for e~;haust Df co~pressed alr from the second chamber 7 with a preset time for air admission theretD, the first cavity 1 ~Figure 6) cDmmunicates with khe secDnd chamber 7 through an auxiliary thrDttling passage 43. '~he outlek opening ol the throttlin~
passage Dn the`side of the secDnd chambar incDrporates a check valve 44 secured tD the wall Df the casing 9 of the air distribution arrangement 3 fDr allowin~ air to pass t D the secDnd chamber 7 only.
If it is desired tD make choice of an Dptimum time fDr cDmpressed air admission tD the sacDnd chamber 7 with a preset time for e~baust Df waste air therefrom.9 the outlet Dpening of the auxiliary tbrottling passage 43 incDrporates Dn the side Df the first cavity 1 a check valve 45 secured tD ~he wall D~ the casin~ 9 of tho ai.r distributiDn ar~
rangement 3 which allDws compressed air to be Dnly admitted tD the fir~t cavity 10.

J~

_ '1 L~~
Fi~ure 8 shDws an embDdiment D~ the air dlsbributiDn arrang~ment 3 similar to that described with re~erenc~
tD F~gure 19 but having a diffsrent structural form D~ an actuator member 460 This actuator member 46 has an en~
~ace defining a first cavity 47 in the fDrm o~ a ~le~ible diaphragm 48 secured to the periphery vf the casing 9 Df ths air distributiDn arrangement 30 ~ he pneumatic percussive d0vice accDrding tD the in-ventiDn functions in the ~ollowing manner.
When compressed air is ~ed to the device accordi~g tD the inventiDn through the air supply hDse 4 (~igure 2) from a compressed air source (not shDwn), the actuator mem-ber 8 in the fDrm Df a stepped spoDl moves under the ac-tion of cDmpressed air pressure upon tbe bDttom 21 of th3 sleeve 24 until it e~gages ~Jith the abutment 13, i.e. until it is in a positiDn in which compressed air sup~lied through the hose 4 ~ills the secDnd chamber 7 of bhe casin~ 1 thrDugh the,passage 22, the caviby 20, the radial passage 23 of the acbuatDr member 8, the second cavit~ 11, the radial and longitudinal passages 1~ and 19 of the casing 9 D~ the air distribubion arran~emant 3. Whe~ compressed air is ad-mitted tD the second chamber 7, an additiDnal force applied Dn the part of the secDnd csvity 11 to the end face 16 acts upon the actuator member 8 to press ti'e ~ctuator mem-bsr 8 against the abutment 13.
At the same time, prsssure in the first cavity 10 increases gradually si~ce its chargin~ with compressed air 3~

DCCU~S thrD ugh tbe tbr~tling passa~;~ 27 cDnn~ctin~ this ~irst cavity ~unctioning as a receiv~r to the sacond chamber 7. Admis~iDn of cDmpressed air to the secDnd chamber 7 lasts until air pressure in the ~irst cavity 10 reaches duri~g its filling a value which is su~Picient to shi~t the actuator membar 8 to the Dth~r pDsitiDn9 iOe.
until its en~a~ement witb the abutme~t 14 as shown in Figure 3.
In the ~ew positio~ o~ the actu~tor member 8~ admis-~iDn D~ c~mp~esse~ air tD the second chamber 7 is stopped as the radial passage 23 is shut-off, and wsste air i~
exhau~ted , i.e. in this position o~ the actuat~r member 8 the secDnd chamber 7 cD~municates with the envirDn~ent via the lo~itudinal and radial passages 19 and 18 Df tha casing 9 o~ the air distribution arran6ement 3, it9 sec~nd cavit~ 11 and radial pass~ge 24. During air exhaust~ air pressure in the second chambar 7 abrupbly decre~ses, but pressure in bhe ~irst cavit~ 10 decre~ses gradually since its dischar~e OCCUr9 through the thrDttLing passa~e 27.
~he acbuator membsr 8 remains in this position until pres-sure in the ~irst cavity 10 decreases tD a value ~t whicb the force o~ pressurs acting upon the end ~ace 15 D~ the ac-tuator member 8 becDmes lDwer tha~ tha force D~ the ~ir line pressure in the cavity Z0 actin~ upDn the botbom 21.
Then the abDvedescribsd process Df the sclf-~scillati moveme~t of ~he actuator membar 8 with stoppages at bwD
limit positio~9 is regularly repeated.

Dependin~ on position ln which the actuator mem~
ber 8 is lDcated, tbe second cbamber 7 cDmm~nicate.s either witb ~ ~surce 9~ c~mpressed a ~ and i9 ineul~tad ~r~m the environment3 sr with t~ envirDn~ent and is insulat~d ~rom the sDurc~ Df cDmpr~ssed air. ~hsrefora, puls~ting pres-surs devalDps in the secDnd chamber 7 of the device when compresssd air is supplied thrDugh the air supply hDse 4~
As the first chamber 6 (Figure 1) and the 3econd chamber 7 commun~cate through any appr~priate kaown maans (nDt shown) restricting air passage from one chamber 7 (6) tD ansther rather than through an unobstructed passage, pressure in the ~irst and second chambers 6, 7 is differ~nt~ Under the action o~ the pressure dif~erence between the chambers 6, 7 Df the device, the hammer piston 5 per~Drms reciproca-tiDns in the casing 1. One can chD~se such a c~mbinatiDn Df parameters of the air distributiDn arrangement 3 by w~y D~ expsriments that the ha~mer piston 5 will impart blows tD
the workinO implemenb 2 during reciprocations in bhe ca-sing 1 every cycle o~ operatiDn of tha air di~tributi~n arrangement 3.
OperatiDn ~f the air distributiDn arrangement 3 bhe amb~diment Df which i3 sh~wn in Figures 4, 5 is identical to ~peratiDn of the air distributiDn arrangement 3 shown in Fi~ures 2, 3 as regards functions.
When cDmpressed air i9 admitted tD the device, thrDugh the air supply hDse 4 ~Fi~ure 4), the actuator member 29 is moved under the actiDn o~ air pr0ssure up~n tha end face 41 thereof in a positio~ (Figur~ 5) in which bbe secDnd chamber 7 of the ca9ing 1 communicates, via the pas-~t~ ~ 3l4 sages 37, 36, 39 and 22, with a cDmpre:ised air sDurce SD
that ccmpre~sed air is admitted to the second chamber 7.
During admissiDn of compressed air, an additiDnal ~orce eDunteracting the force o~ the spring 42 and caused by pressure acting upon the end face 34 acts upon the act~atDr member 29. ~he admission lasts until pres~ure i~ the first eavity 30 during its filling with compressed ~ir through the throttling passa~e 32 reaches a value which is suflicient for shifting the actuator member 29 to a positiDn in which the secDnd chambsr 7 (Figure 4) communicates, via the pas-sagas 37, 36 and 38, with the environment. In tbis positiDn of the actuator member 29 waste air is exhausted frcm the seeond chamb~r 7. Simulatneously with the exhaust, bhe first cavity 30 functioning as a receiver is discharg~3d through the throttling pessage 32 so that the actuator member 29 is again shifted to a position allowing cDrl~)ressed air tD be admitted tD the second chambar 7~ ~he abovedescribed process is then repeated~ Operation of the device as a whole is 9imilar to Dperation of the ~evice with the air disbribution arrangement described 1;/ith reference to Fi-gures 2, 3.
Oparation of bbe device accordin~ to the invention using the air distributivn arranrement 3 having an au~iliary throttling passage 43 (Figure 7 ) .1lith an Dutlet opening thereof incorporating bhe check valve 45 differs from that described above only in the fact that ch~rging o~ the ~irst cavity 10 is effeet~d through th~ throtbling passage 27 and ~8~ ~ ~

the auxiliary throttlin~ pas,sa~,e 43 and discharg~ is e~fected thrDu~h the throttling passage 27 Dnly.
If the outlet openin~ of tha au~iliary throttli~
passag3 43 is prDvided with the check valve 44 (Figure 6), the first cavity 10 is discharged through the throttlinO
passage 27 and tha auxiliary throttling passage 43.
OperatiDn of the device using the air distribution arrangement 3 with the diap~ragm 48 (Figure 8) is similar to operatiDn D~ the devica described with re~erence tD
~igures 2, 3. The di.fferenc~ rasid~s in that the diaphragm ~8 functions aa ~he end face de-~ining the first cavity 47 comr.1unicating with the secDnd chamber 7 thrDugh the thrott-ling passage 47.
~ he number Df embodiments of the actuator member 8 and air distributiDn arrangement 3 is nDt li.~ited to the two er.bodiments shDwn in Figures 2, 3 and -~75.~ir distri-bution arran-.,ements havinO different designs o~ the actuator member can ba used~ ~cwever, with any embodim~nt thareDf, it is necessar~ that there shall be at least one throttling passa~3 e_tablis,.ing cDmmunication between a chamber D~
the casing alternately communicatinO with a cDm~pressad air source and the environment with a cavit~ Df the air distributiDn arr'angement the pressure in which ensures move-ment o~ the actuator member to one of its limit positionsO
In comparison with the prior ~,rt, the pneumatic per-cussive device accordin~ to the invention has an air distri-bution arrangement D~ minimum mass and si~e. ~his makes it possible tD lower size and mas~ ~f the device as a whole WithDUt cDmpr~misin~ its ir~pac~ po-i~er ~/hila r~taininb all advantag~s D~ pneumatie percussiv~ devices havin~ a single eontrDlled ehamb3r~ A~ a r~sult, th~ spscifie ir.ipaet pDwer, i.e~ the power-tD-mass Dr volume ratiD Df the deviee increases. On the other hand, if mass and size Df the d~vie~ according tD t'ne inventiDn remain the same as befDrs, absDluta i:..pact power Df th~ devics inereases b~ virtue Df an increase in its specific pow~r which, in ths snd Df the day, results in an increase in prDduc-tivity in applicatiDns cf this devieeO

1'1

Claims (4)

1. A pneumatic percussive device, comprising a casing, a movable hammer piston accommodated in the casing dividing the interior space of the casing into two chambers, the first chamber being defined by walls of the casing and the hammer piston, and the second chamber being defined by the hammer piston and an air distribution arrangement accommodated in the casing and having a movable actuator member dividing the interior space of the air distribution arrangement into at least two cavities, the pressure in the first of these cavities communicating through a throt-tling passage with the second chamber ensuring movement of the actuator member to one of its limit positions, the second cavity permanently communicating with the second chamber and alternately communicating with a compressed air source and the environment.

2. A pneumatic percussive device according to claim 1, wherein the first cavity of the air distribution arrangement and the second chamber of the casing communicate with each other through at least one auxiliary throttling passage having its outlet opening on the side of the first cavity of the air distribution arrangement incorporating a check valve secured to a wall of the air distribution arrangement.

3. A pneumatic percussive device according to claim 1, wherein the first cavity of the air distribution arrangement and the second chamber of the casing communicate with each other through at least one auxiliary throttling passage having its outlet opening on the side of the second chamber of the casing incorporating a check valve secured to a wall of the air distribution arrangement.

4. A pneumatic percussive device according to claim 1 wherein a diaphragm is provided on the surface of the actuator member acted upon by compressed air pressure in the first cavity, the diaphragm being secured to the pe-riphery of a casing of the air distribution arrangement.