US1798642A - Multiple-piston pneumatic tool - Google Patents

Description

March 31, l931- F. 1 o. wADswORTH MULTIPLE PISTON PN-EUMATIC TOOL s sheets'fsheet 1 E a mi 3&5 Q E.

Filed Julfy 26, 1921 March 3,1, 1931.

F. L. O. WADSWORTH MULTIPLE PISTON PNEUMATIC TOOL 1921 C5 Sheds-Sheet 2 Filed -July 26 /N VEN TOR rA W March 31, 1931- F. L.. o. wADswoRTH 1,798,642

MULTIPLE PISTON PNEUMATIC TOOL Filed July 26, 1921 3`Sheets-She'efI 3 hNmHli mmm I.mwawwmnh A Patented Mar. 31, 1931 STT Application led July 26, 1921.

This linien ion relates to fluid actuated impact mechanisms, such as pneumatic riveting and chipping hammers, compressed air drills ad the like, which comprise freely movable piston members that are reciprocated at a high speed to deliver a rapidly recurring succession ,of blows against the heads of relatively stationary toolelements (such as a rivet set or chisel, or a percussion drill); and

one ofthe p imary objects of my present improvement-s is to greatly increase the driving, or cutting or penetrating power of such devices, without adding to their weight or bulk.

Under the usual conditions of operationwhere the action of these tools lis dependent only on an impact effect-the maximum capacity of this type of mechanism is determined, in part by the force of each `blow and in part bythe number of blows delivered per minute. T ie first factor Vis measured by the driving energy of the pistonat the instant of its impact with the operating tool element; and this, in turn, depends on the mass or weight of the reciprocating member and on its maximum velocity, or speed of travel, at that instant of impact. Under a given actuating pressure on the reciprocating members, which is generally fixed by practical conditions, the velocity imparted thereto is directly proportional to the square root of the length oftravel, or the stroke, of the piston, and is inversely proportional to the square root of its mass. lt lfollows from ,this

that the momentum of each impact blow is directly proportional to the square root of the piston stroke and also to the square root of the piston weight, and that the driving or cutting power of each impulse may therefore be increased Vby using either a larger piston or a longer piston cylinder, or both. But the increase in either of these factors increases the bulk and weio'ht of lthe mechanism in a much more rapid ratio than the individual 5 power impulse is augmented; and the increase 'in the effective length of stroke decreases the possible number ofstrokes per minute. rhe aggregate driving power or working capacity of these tools, as ordi- 3 narily constructed, cannot therefore ybe `.in-1

Serial No. 487,589.

creased without a great disproportionate enlargement ofthe size, and weight ofthe more important parts of the organization; and this in turn adds not only to the first cost of construction and the subsequent expense of yoperation and maintenance, but also increases the difculty and the labor of manipulating these laroer and heavier mechanisms.

in my improved construction I avoid 'all of the dny'ncultieskabove mentioned, and ob- 60 tain certain new and important results by .utilizing a. plurality of piston elements to iinpart a properly controlled series of blows to a single operating tool. All of the recipron eating members are preferably made of substantially the same size and weight and are capable of making substantially the same length of stroke, which is varied according to an arbitrary rating of capacity (e. g. a ten inch stroke for a No. 10 hammer, atwelve inch 70 stroke for a No. 12 hammer, etc), and the reciprocative movements of the piston elements are controlled timed, preferably by a single distribution valve., in such manner that when one of the said elements is making T5 its forward or impact stroke, another one is making its rearward or return stroke. rlhe number of blows per minute mayV thus be increased to any desired ratio, by increasing the number of co-operatively controlled pis- So tons, without vany decrease either in the .mass or the stroke of each reciprocating element,

- andwithout any diminution., therefore, in the driving force of Veach impulse. A multiple piston tool of my improved construction will, "3 for this reason, possessa driving power which may be two or three times as great asthat possessed .by .the single piston tool of the ordinary construction and of the same rated stroke; and for reasons which will hereafter appear this relatively great increase in the operating capacity of the new type of mechanism may be accompanied by an actual decrease in the bulk and weight of any given size or number (e. g. No. 10) of hammer.

Another object of this invention is to improve the operating balance of reciprocating- ,piston-.impact tools, by the counteracting momentum effects of voppositely moving piston elements,and thus diminish the transmis- 100 sion of shock and vibration to the hands of the operators.

A. further object of my improvements is to produce a fluid actuated impact tool which does not require the introduction of any change of live air, o1' live inotivefluid, at the front end of the piston chamber, to effect the rearward or return movement of the reciprocating member, and which does not therefore require, or necessitate, the use of long supply and exhaust passages extending from the distribution valve to the tool receiving end of the piston cylinder.

Other objects of my present improvements are to produce pneumatic hammer constructions, which are relatively simple in design and can be readily manufactured without the use of special tools; which are easily disassembled and repaired; and which can be operated at low cost.

As illustrative of my invention I have shown, in the accompanying drawings, three (3) forms or exemplifications of the multiple piston type of impact tools; and in the following description of these exemplifications I have, as far as possible, used the same, or similar reference numerals to denote or designate the same or corresponding parts and elements of the several exemplary organizations.

On the first sheet of drawings, Figure 1 is a longitudinal section through the center of a twin npiston pneumatic hammer that embodies my improvements; Fig. 2 is an enlarged cross section on the plane 2 2 of Fig. 1 (or Figs. 3 and 5) Fig. 3 is a fragmentary sectional elevation on the plane 3 3 of Fig. 2; Fig. 4 is a partial section on this same plane, but showing the distribution valve element in another position; Fig. 5 is another fragmentary section on the i plane 5 5 of Fig. 2 (at right angles tothe plane of the sections shown in Figs. 1, 3 and 4) and Fig. 6 is a cross section on the plane 6 6 of Fig. 1.

rlhe second sheet of dra-wings illustrate a second embodiment of my improvements.

Fig. 7 is a side elevation, partially in section, of this form of construction; Fig. 8 is an enlarged longitudinal section of a part ofthe' hammer shown in Fig. 7; Fig. 9 is another 1 similar view of this same part with the distribution valve element at the opposite end of its movement; and Figs. 1l) and 11 are crossscctional views that are respectively taken on the planes 10-10 and 11 11 of 7.

Figs. 12 to 17, inclusive, depict a third exemplification of my invention. In these views Fig. 12 is a central longitudinal section through the rear or handle end of a pneumatic riveting hammer; Fig. 13 is a sectional elevation, on the same plane as Fig. 12, of the front or rivet set end of this tool; Fig. 14 is a transverse cross section on the plane 14 14 of Figs. 12-13; Fig. 15 is a longitudinal section on an enlarged scale on the planes 15 15 of Figs. 12-14; Fig. 16 is a transverse section on the plane 1 6 16 of Figs. 12 and 15; and Fig. 17 is another view on a still larger scale on this same plane, and shows the distribution valve elements in another position.

In the construction shown in Figs. 1 to 6 inclusive the hammer barrel 4 is provided with two parallel cylindrical chambers, 7 and 8, which extend from the rivet set collar, or sleeve 9, at the front end of the said barrel, to an enlarged cylindrical cavity that receives the valve box 12 at the rear end thereof. The valve box 12 is provided with two openings, which are of the saine diameter as the chambers, 7 and 8, and which register therewith, and form extensions thereof when the valve box is in place. Each of these chambers contains a suitable piston element 17, which is adapted to reciprocate freely therein; and which is preferably provided with a slightly convexed striking face that is adapted to engage with the surface of a curved rib 18 on the inner end of the rivet set shank 19, at such an angle that thek force of the blows delivered by the piston elements is directed toward the center of the rivet head or other object on which the tool is operating.

The valve box 12 is also provided with two recesses 20 and 21, which are disposed on opposite sides of the piston cylinder extensions therein; and which are adapted to receive respectively the distribution valve element 22 and the control valve 23 that regulate the admission of air to the opposite ends of the piston chambers. Live air is admitted to the rear ends of these recesses through the lateral passages, 24 and 25` which open into the annular chamber 26 that surrounds the rear end of the valve box and communicates at one side with the usual supply duct 27 inthe hammer handle. The live air thus admitted to the recess 20 enters the open end of the hollow distribution valve 22 and passes therefrom, through the ring of ports 28, to one or the other of two annular grooves 29 and 30; which are in communication, through the passages 31 and 32, respectively, with two drilled and plugged cavities 33 and 34 (see Fig, 3). The cavity 33 is provided with a transverse opening 35, similar in form to that indicated at 41 in Fig. 2, which enters the side of an eccentric groove 36 in the valve box section of the piston chamber 7 and the cavity 34 is provided with a similar opening 37 that communicates l in like manner with the eccentric groove 38 in the valve box section of the other piston chamber 8. The valve box sections of these chambers are further provided with two other eccentric grooves 39 and 40, which are similar in form to the grooves 36 and 38 and which are positioned at a fixed distance in advance of the latter; and these forward channels are in communication with the transverse openings 41 and 42, that enter the drilled and plugged cavities 43 and 44. rlhe cavity 43 is in communications through an tothe annular chambers which The space in fron1L of the head 6T elongated port l5., with an ecceY tric groove lo surroundingl the distribution valve und the cavity lll is in communication., through a similar port l?, with a revcrselv oilsct eccentric groove d8. The recess cont 'ng the trioution valve is also provided wl eccentric groove which communicates through the port with the exhaust passage 51 that leads to the outside of the hanne barrel (as best shown in Fig.

The hollow distribulion valve 22 has an cnlarged central portion, which terminates in the two shoulders 52 and 58 (see l? l), and which carries a ge /-l that slices in a chamber 55; and this central enlargement is provided with a peripheral channel 5G whose width is just sutlicient to cover the two adjacent grooves llQ-/lS (when the valve is in the position of 3 or the t ro adjacent grooves 4G i9 when the valve is in the position of Fig, l The shell of the valve is perforated by the restricted ducts 57 and which serve to adn it air, from the recess 20,

are respectively located in the rear of the shoulder and in front of the shoulder 53. The e2:- treme rear end of the iirst of these annular chambers is provided with a passageway :E9 which leads forwardly to a port Q in the valve box section of the cylinder and the opposite end of the other chamber, in front of the shoulder` 53, is provided with a passageway 61 that leads to a correspondi positioned port 62 in the piston cylincer 8. The front end of the chamber 55, which the ange l reciprocates, is connected to another port 63, in the front portion the cylinder 7, by means the passageway l; and the rear end of this same chai iber i" connected ito a correspondingly posi@` cned por@ 65 inthe cylinc er 8,-by means of the passageway 66.

rlhe control valve which is positionecl line recess 21 comprises plunge i 23 and a head 67, that is in cate freely in a two-part t The annular chamber behind the l-.eao 5 connectedL to the live air channel 25, b n of the groove and the duct opening inthe rear o; the sten 231i to the exhaust channel 51, by means of tno ducts 72 and 73 and the peripheral groove le.

is in 'co-minunication with front part of the recess 21 through the port 75; and a passageway T6 leads from the said recess to an opening 7'? in the partition wall betwee. the cylinders 7 and 8 (see 1). The valve plunger 23-67 is so proportioned that the area of the head portion 67 is about four times the area of the annular shoulder between kthe said head and the stem and the latter perforated by restricted duct 78, that serves to connect the ,diferentialarea ,chambers on the two sides of the said head, when the valve plunger is in the position shown in Fig. 5.

rllho various bearing surfaces of the reciprocating valve elements and 23-67) are ground to form close but easy sliding lits with: their respective casings; and the longitudinal movements .of these elements are limited by the bushing caps or sleeves 8O and 58 that enand cover the front ends thereof. The assembled valve box parts are clamped in po-H sition inthe cylindrical recess at the rear end of the hammer barrel l by screwing on the handleV 1, and locking it in place by means of suitable ratchet and dog connections 81-82 (such for example as have been fully illus--5v trated and described in my co-pending appliation VSerial No. 788,79l, led July 11, 1921) and in order to prevent leakage of liveair from the annula space 26 to the exhaust passages @-51 a compressible wedge-shapedV e xacl-ring ring S3, of aluminum or lead alloy-or similar material, is inserted between the end of the hammer barrel 4land an internally turned flange on the recessed hub of the handle member 1. i Sl--SQ and the exhaust openings 51 are covered by a spring ring or clip Se that it provided on one side with discharge openings 85 that direct the exhaust away from the handle oortion of the hammer.

The operation of this double piston hammer is as follows: lliencompressed air, or other motive fluid, is admitted to the passage 2'? and the annular chamber 26 (by means of the usual thumb valve on the handle grip),

it will force the controlvalve 23-67 toits forward position, as shown in Fig. 5, and permit the motive fluid to flow through the 'passages and ports ZS-T-ZG and 77 until the pressure in the front 'end of the piston ff, .-1

chambers, and the space between the two pistons therein, is a little less than V30% of that inthe annular supply reservoir 26. The pressure on the front face of the valve'head 67 then overbalances the pressure on the anl r shoulder between this head and the stem 23 and the valve is inovedrearwardly, thus closing the entry end of the-*duct 78 and cutting oil 'the further flow of motive fluid to the front of the piston chambers, but leaving that space charged with' air at the reduced pressure just indicated. Yllhe opening of the lsupply passage 27 also admits motive fluid, at the full eservoir pressure, to the interior of l the 'hollow distribution valve 22; and thence to the rear end ofone of the piston chambers 'Z or 8. lfthe distribution valve is in the position of Fig. 3, the high pressureair flows through .the communicating ports and passages 28-29-31-33-35-36 into the rear end ofthe piston chamber 7' and forces the piston ,therein forwardly. ln this position of the valve the rear end of the other piston chamber 8 is open to the external air through the communicating ports and channels 40- rlhe vlocking connections D 42-44-47-48-49-50-5l and 85; and the piston in this chamber is therefore driven rearwardly by the low pressure fluid which ias been admitted through the control valve 23-67 and trapped in the space between the oppositely moving piston elements.

luring the first part of this movement the ports 68 and 65 and passages 64 and 66 are open to the low pressure air and the forces acting on the two sides of the valve flange 54 are balanced (see Figs. l and ln this part of the movement the port 60 is open to the high pressure air in the rear part of the chamber 7 and the port 62 is open to the exhaust. 'lf he pressure on the rear of the valve shoulder 52 is therefore greater than the pressure on the front face of the shoulder 58, and the valve is maintained in the position shown in Fig. 8. But when the advancing piston in the cylinder 7 reaches and passes the port 68 the front face of the valve flange 54 is exposed to the high pressure air in the rear of the said piston, while the opposite face is still subjected to the lower pressure of the air that is trapped between the reciprocating members. The valve may be so designed that this superior pressure on the front of the flange 54 will suffice to move the valve rearwardly; but in order to maintain a more perfect and c ntrolled timing between the two piston movements l prefer to make the area of the flange 54 considerably less than the area of the shoulders 52 and 53; and thus delay the throw of the valve until the rearwardly moving piston has reached and covered the port 62. lfVhen this occurs the escape of air from the space in front of the shoulder 58 is arrested and the live air flowing into this space through the vents 58 immediately raises the pressure therein sufficiently to move the valve rearwardly to the position shown in Fig. 4. This movement placesV the valve openings 28 in communication with the channel 30 and admits live motive fluid, through the p-orts and passageways 32-84-37 38, to the rear end of the cylinder 8; and simultaneously establishes tween the rear end of the cylinder 7 and the external air through the ports and passages 39-41`43-45-46-49-50-51-85. The piston in the cylinder 8 is thus driven forward from the dotted line of position of Fig. l, while the piston in the cylinder 7 is returned by the pressure of the air that remains trapped between the two reciprocating elements. The valve 22 is maintained in the position shown in Fig. 4 by the pressure of the live air on the front shoulder 58, until the advancing piston has passed thel port (thus exposing the rear of the flange 54 to the motive fluid pressure back of said advancing piston) and the rearwardly moving piston has-simultaneously or subsequentlycovered the port 60 and permitted the live air pressure to build up in the rear of the communication be-L shoulder 52 and throw the valve forwardly, to initiate another cycle of co-operative piston m vements. Each piston is thus caused to move in forced time relationship with its mate and to deliver a regularly recurring series of blows on the rivet set or other operating tool at the forward end of the hammer; and the time ordinarily lost by the return of the piston element to the rear of the hammer barrel (in preparation for the succeeding stroke) is completely eliminated.

ln the construction shown in Figs. 7 to l1, inclusive7 the two piston elements 17a and 176 are co-aXially mounted in concentric piston chambers 7 a and 8a, which are separated from each other by a tube 86, and which are connected at their front ends by the port openings 77a and 77 Z). The tube 86 is engaged at its forward extremity by a block 87 which is set in the end of the rivet set 19, and which is grooved on its sides to form the equalizing ports 77 b; and it is held at its rear end in a flanged sleeve 88 that is, in turn, clamped between the end wall of the hammer handle l and the adjacent recessed end of the valve bonv 12a. The outer surface of the sleeve 88 and the inner concentric surface of the valve box, are finished to form the bearing surfaces for the reciprocating distribution valve element 22a; and the enlarged forward p-ortion of this valve constitutes the rear end of the outer annular piston chamber 8a. rlhe engaging portions of the tube 86 and the sleeve 88 are pierced with a row of ports 81a, which are in radial alignment with the ports 28a that pass through the rear endof the valve box and open directly into the annular reservoir 26 in the hammer handle. rEhe inner tube 86 is further perforated with a second row of openings 39a that open into an annular channel 46a between the members 86 and 88; and this channel in turn communicates with another row of openings 45a in the outer sleeve 88. The adjacent inner face of the valve box 12a is provided with a groove or channel 49a which is opposite the openings 45a, and which communicates, through the passages 50a and the annular space 51a, with the radial exhaust ports 51?). The rear portion of the distribution valve, which reciprocates in the annular space between the sleeve 88 and the concentric bearing surface of the valve casing, is provided with an end flange 52a (that traverses the ports 28a-31a) and with an intermediate channeled rib 56a which is pierced with the ports 90-90 and which traverses the opposing openings 45a and 49a.

The front part of the valve boX 12a-which receives and guides the enlarged forward portion of the hollow valve 22a-is provided with two grooves or channels 88a and 40a which communicate respectively with the annularV live air reservoir 26 (through the longitudinal passageways 82a) and with the eX- haust openings lmthrough the radial ducts 47a. The corresponding portion of the valve shell is perforated with two rows of main ports 91 and 92, which are adapted to register respectively with the channel 38a (when the valve is in the positionshown in Fig. 8) and with the groove a (when the valve is in the position shown in Fig. 9) and with a third row of auxiliary ports 93, that register with the first-named channel when the valve is in its last-mentioned position (Fig. 9). valve bonv is further provided with one or more restricted ducts 57a that lead from the live air reservoir 26 to the annular space in the rear of the valve flange 52a; and also with similar ducts 78a that lead from the passages 32a to the space behind the front shoulder 53a of the distribution element. A longitudinal passage 76a leads from the forward end of the annular piston chamber Sa to a point ust back of the live air groove 38a; and this passage is provided with two radial ducts or ports, 94 and 95, one of which registers with the ports 92 (when the valve is in The i the position of Fig. 8) and the other of which opens into the space behind the shoulder 53a and communicates with the ducts 78a, when the valve has been thrown forward (to the position shown in Fig. 9). The inner piston chamber 7a is also provided with a. row of ports 96-96 which open into the eXtreme rear end of the annular space behind the rear valve flange 52a.

The operation of the last described mecha-V nism is as follows: lVhen the thumb latch of the handle is depressed and live motive fluid is admitted to the annular reservoir 26, one or the other of the piston elements will be d l en forward by the flow of the high pres; sure air, either through the ports 3l@ or through the ports 91-and a restricted amount of wire drawn Huid ill be simultaneously admitted to the front of the piston chambers, an d between the two piston elements, through one or the other of the ports 94 or 95 and the passageway 76a. lf the distribution valve is in the position shown in Fig. 8, the motive fluid will enter the rear end of. the cylinder 8a. (through the passages and ports 32a* liSd-9i) and drive the annular piston 175 forwardly. ln this position the rear end of the central cylinder Ya is open to the external air through the ports and passages 39e-A6@- Lia 90-50a-5la-5lb-85; and the piston 17a will therefore be forced rearwardly by the low pressure air that is between it and the advancing piston lia. During the maj or part of this movement the rear face of the valve flange 59a is not subjected to any substantial presvbecause the air can escape to the open exhaust, through the ports 96, more rapidly than it can flow in through the restricted ducts ct-and the pressure on the front face of the shoulder 53a is considerably greater than the diderential pressure on the rear face thereof, because of the difference in the areas of these two faces. The valve 22a is therefore held in its retracted position until the rearwardly moving piston laphas covered the ring of ports 39a and thus cut off any further escape of air from the rear end of the cylinder 7a.' The pressure bacl; of the valve flange 52a is then raised sufhciently to overcome the previously unbalanced pressure on the front shoulder 53a and the valve is moved forward to the position shown in F ig. 9. This movement closes the ports 91 and opens the ports 31a-thus admitting live motive fluid to the rear of the piston 17a and driving the latter forward-and it also closes the ports a and opens the ports 92, thereby permitting the air back of the piston 17?) to escape to the atmosphere, through the passageways 40a-7a-51b-85, and allowing this member to be` returned by the air that is trapped between the two pistons, and is now maintained at the desired pressure by the slow flow of high pressure fluid through the restricted ducts 'T8Q-95. During the major period of this reversed action of the piston. valve mechanism the front face of the valve shoulder 53a is relieved of pressure-by the escape of air through the open exhaust ports 92-and the distribution element is held in. its advanced position by the full live airv pressure on its rear flange 52a. But when the piston 175 has, in its return movement, reached and covered the exhaust ports 92 (as shown in Fig. 9) the fluid in the rear of this member is trapped in the space between it and the valve flange 53a; and the pressure thereon is increased-by the joint effect of the live air flowing through the restricted ducts 93 and the compression ofthe trapped fluid by the rearwardly moving piston-until it is sufficient to overcome the opposing forward pressures on the valve flanges; and the distribution element is then thrown to the position shown in Fig. 8. This initiates a new cycle of the previously described movements.

ln the operation of this second exemplifies.- tion Vof my improved multiple piston organisation, the maintenance of the desired pressure between the'reversely moving pistons is effected by the relatively slow but continuous iiow of motive fluid into. the passageway either through the duct 94, or the ducts 78a and 95-and this flow is so regulated (by a. proper proportioning of the areas of the supply passages) as to just compensate for any .lealrages,`from the front of the piston chambers, through the rivet set mounting, or

past the rearwardly moving piston to the errhaust. pressure on the reciprocating piston elements is not as sensitive anduniversal in its action as the automatic reduction pressure valve 23-67 which is described in connection with the construction shown in Figs. l to 6; but itl This means of controllin the return CIT cure the desired operation of the hammer under very considerable variations in the motive iiuid pressure.

rEhe third illustrative embodiment of my invention, which is depicted in Figs. 12 to 17, inclusive7 presents several features of structure which are common to both of the previously described mechanismsand which need not therefore be redescribed in detailbut it presents other features of construction which require additional explanation. For example: The two organizations shown in Figs. 1 'to 11, inclusive, are each provided with two pistons; whereas the organization now under consideration has four pistons which operate in pairs in the symmetrically disposed cylinder chambers 76-70, and 86-86. rEhe cylinders T6-7c, and the pistons (170) which work therein, are of somewhat smaller cross-sectional area than the cylinders 868c and the corresponding piston elements (17(6) and in order to make the two pairs of reciprocating members of snbstantially equal weight the length of the pistons 170 is somewhat greater than that of the pistons 176?. The greater length of the firstmentioned members requires a greater length of'piston chamber for the maintenance of an equal length of stroke; and this is secured by extending the cylinders 'Z6-7c through the valve box 126, (as best shown in Fig. 12) and terminating the cylinders 86-80 at the forward end of that box as shown in Fig. 15)

The distribution valve of this four cylinder construction is made in two parts 226-220, and is mounted transversely of the valve box between the extensions of the piston chambers 7 6 7 c. These valve parts are mounted in ground and hardened bushings 98 and 99 which are inserted from opposite sides of the valve box 126, and are held in place, when the valve box is inserted in the end of the hammer barrel, by the extension sleeve 100 at the rear end thereof. The rear sides of these bushings 98 and 99 are provided with segmental slots 101 and 102 which open into a transverse groove 103 on the back of the valve box 126, and the ends of this transverse slot communicate with the live air chamber 26 at the base of the hammer handle (see Fig. 12). The valve box 126 is further provided with two sets of longitudinal passageways which are arranged symmetrically on opposite sides of the valve bushings 98 and 99; and which communicate through lateral passageways with two lines of ports in the side walls of the said bushings. The four longitudinal passageways 336 are provided with lateral ports 356 which open into the rear end of the piston cylinders 76 and 70; and these passageways communicate, through rows of openings 316 with two annular spaces between the inner surface of the valve bushings 98 and 99 and the intermediate channeled portions 104 and 105 of the distribution valve sections 226 and 220. The four longi-l tudinal passageways 346 a-re provided, at their inner ends with transverse ports 376 that open into the rear ends of the cylinders 86 and 8c (best shown in Fig. 15) and at their rear ends with transverse passages 326, that also communicate with the annular spaces last referred to. The four longitudinal passages 446 are provided, at their inner ends with transverse ports 426 that also open into the rear end of the cylinders 86 and 8c (see Fig. 15), and these passages communicate at their rear ends with the sides of two peripheral grooves 486 on the exteriors of the bushing elements 98 and 99. The adjacent portions of these bushings are perforated with rows of radial ports 476 which serve, in certain positions of the valve elements, to connect the groove 486 with the interior of the hollow distribution valve. The ends of the bushings 98 and 99 are cut away on one side to form forwardly extending slots or channels 106 that register with the rear ends of a series of exhaust passages 510 in the rear end of the hammer barrel 4. The dividing web between the four symmetrically disposed piston chambers is further provided with a transverse passage 416 that connects therear ends of the cylinders 7 6 and 7c; and this transverse passage is connected with an oval channel 436 that opens, at its rear end, into the central portion of the distribution valve recess.

The valve box 126 is also provided with two sets of restricted ducts V57 6 and 586, which lead respectively from the live air channel 103 to the annular chambers at the outer and inner sides of the valve flanges 526 and 536; and the adjacent portions of the valve shells, are perforated with rows of small ducts 107 and 108, that are adapted to put the said annular chambers in communication with the interior of the valve when the adjacent flanges are moved away from the contiguous ends of the valve recesses. The portions of the valve casing in which the reduced ends of the valve sections reciprocate are further provided with restricted ports 596 and 616; and these ports communicate respectively with the ports 606 and 626 in the rear ends of the piston cylinders i6-70 and 86-80.

The forward ends of the four piston cylinders are all connected with each other by an annular opening 109 at the rear of the rivet set sleeve 9; and this annular opening is in communication-through the longitutudinal passageway 766-with a pocket 21 that contains an automatic control valve 23 which is similar to that illustrated in detail in Fig. 5.

n explaining the operation of this third embodiment of my invention it will be assumed that the live motive iuid is admitted to the handle when the valveparts are in the 1position shown in the enlarged view of Fig. 17. rllhe high pressure air will then pass, through the slots 101 and 10Q and the passages Slo-SS-Sb, int-o the rear ends of the cylinders fband drive the two pistons therein Jorwardly. In this position the rear ends of the cylinders `822- are open to the external air through the communicating ports and passageways i26- stelo-'LS-d @-106-510 and 85; and the pistons 17d are therefore ree to move earwardly under the effect of the low pressure air which is admitted to the front end of the piston cylinders through the passageway 76?) by the previously described action of the automatic control valve 943-67. Buring this phase of the operation the pressures on the opposite shoulders 52?) and 53?) of the distribution valve elements are substantially balanced, because the live air which is admitted to the annular chambers back of the shoulders 586 (through the ducts 58o) is allowed to pass to the exhausted ends of the cylinders 8b and 8c through the now opened ports 612) and 62?); and the live air that enters the chambers in front of the valve shoulders 52h (through the ducts 57o) is allowed to pass to the exhaust directly through the vents 107. But the valve sections are maintained in position, in part by the frictional resistance to their movement, and in part by the kinetic pressure edect of the'streams of live motive fluid that are flowing 'ir-om the slots 101 and 102 inwardly toward tne port openings 315. But when the rearwardly moving pistons 17d cover the exhaust 1sorts 426 the escape of air from behind the valve flanges 53?) is retarded; and when the continued rearward movement of the pistons has covered the port 62?) suoli escape is completely arrested; and the rapid resultant building up of the pressure in the now closet chambers back 'li the ilanges 536 throws the valve sections 225 and 22o outwardly from the position shown in Fig. 1'? to that shown in Figs. 15 and 16.

In this second position of the parts the ports 31o are closed and the ports v326 are opened, thus allowing the live motive fluid to flow into the rear ends'orn tl eA piston chainbers S-Sc and drive the pistons therein forwardly. The outward movement orn the alve sections also opens the elongated eX- haust port 482), and allows the air in the rear ends of the piston chambers N2-'Zo to i'low through the interior of the hollow valve sections and pass to the outside of the hammer through the passageways 10G-510 and 85. ln this phase of the operation the pressures on the end flanges of the distribution valve sections are balanced by the escape of air Vfrom the annular chamber back of the flange 53?) through the now opened vents 108 and by the escape of air from the annular chamber outside of the flange 52o through the ports 595 and 605; but the valve parts are maintained in position, as betere, by the rictional resistance to their movement and by the kinetic pressure effects of the live air flow through the slots 101 anl 10QJ to the port openings 32?). When the rearwardly moving pistons 17@ reach and close the eX- haust openings el?) the -further escape oi air from the chambers in front of the shoulders 525 is retarded; and when these pistons, in their continued rearward movement reach and cover the ports 605 that escape is coinpletely stopped. rlhe instantly augmented live air pressure on the outer shoulders of the valve elements then throws these elements to the iirst described position (illustrated in Fig. 17) and the various parts are in position to repeat the above-described cycle of movements.

in order to obtain the most eifiiciently synized action of the reversely moving pis- 'n some cases, desirable to so proeleuients 'hat they will have the l' period Yl3 reciprocation rather lt we ignore the retardiction (which is usually very etiect oic gravity (which may e movement) and assume that essure of the motive fluid on piston remains substantially the lull stroke thereof; the

ellective .L the race or tl L '1 constant o.

time, t, oi' each recurrent movement is where m is the mass o the piston, s is the distance through which it has moved from resti. e., the stroke of the hammer-Agis the area exposed to the motive fluid and p is the eil-fective pressure. ln the case of cylindrical pistons, the mass is equal to the area, A., multiplied 'by the length, Z, and the density, D, oi3 the reciprocating element, and the above eX- pression may therefore be written ln the particul form of construction illustrated in Figs. 1 to 5, the two piston elements 1 r i and character, and have ln'this case, both equal lengths of strolre ,f s). the masses and t cation of the two elements are the same. But in the constructions shown in Figs. 7 to 11 anl 1Q to 1?', inclusive, one set of piston elenints (17a or lo) is longer than the other t 1'4"?) or 17d) and each reciprocating member as substantially the saine stroke 3. It the lrainn er is to be so designed that each piston rave the saine natural period of recipro- (25 the product DZ must remain constant; and the mean density of the longer pistons must therefore be less than that oli' `e natural periods of reciproy the shorter pistons. This result can be attained most conveniently by making the lon er pistons (17a or 170) of the form shown in Fig. 1 or Fig. 1n this form the rear end of the piston is provided with a` cavity 110, which may either be covered by a cap 11ithat is pressed and welded in place to form a substantially integral part of the piston body-or may be left open as shown in Fig. 7.

The hollow or recessed form of piston last described may also be employed with advantage in certain types of hammer construction in which either single or multiple pistons are used. ln percussion impact tools, the useful etico (e) each blow ls determined in part by the kinetic energy of the movingpiston at the time impaetwhich is ieasured by the product of the mass times the square of the velocity (o2) of the piston element-and in part by the character of the work to be perfori'ned-whieh controls the ratio between the kinetic energy of impact and the useful work accomplished by the impact actuated member. The aggregate effect (E) of a succession of blows depends upon the individual effect (c) of each blow and upon the total number (N) of such blows; and the driving or cutting power (P) of the tool is, in general, measured by the integrated effect of these two factors in a fixed interval (or unit) of time.

Under the conditions assumed in the preceding paragraph, the velocity imparted to a piston of length Z and density D and having i stroke s is V 2fs :JW Dl where f is the force acting, and if we assume that the time of the return stroke is approximately the same as that of the impact stroke, Ahe number of complete reciprocations (or blows) of a. single piston in a given interval of time (T) will be T Z" r Marzi/rit 1f all of the kinetic energy of each blow could be converted into useful work the e'eet (em) of such blow would be f and the driving power of each piston element or for unit of time (T21) wie P 2te/@V Under such circumstances, the eEect of each blow (em) would be independent of the mass of the piston but would be directly proportional to the cross-sectional area of the reciprocating member and to the length of its stroke. But the aggregate effect (Em) of a succession of impacts, on a uniformly resistant object, would vary inversely as the square root of the mass (m) of the striking member; and in such a case it would, therefore, be an advantage to decrease that mass, without oecreasing the cross-sectional area (il), or the bearing length Z, by the use of the form of hollow piston element that is shown in Figs. 1 and 7.

Under other conditions of operation, the practical efl'eot (e) of each impact stroke represents considerably less than the maximum kinetic energy (em) that is imparted to the striking piston; and in many cases this effect (e) is more nearly proportional to the momentum of piston movement (me) than it is to the energy thereof 2 me 2 such cases i e cumulative action of a series of such blows (each of which produces the same leffeet) is represented by or for unit time (T=1) 1f the charac-ter of the work is such that the momentive edect of initial individual blows is of relatively great importance-as in certain hot riveting or forging operaionshit will be of advantage to increase the mass (m) ofthe striking piston; and this can be best accomplished by increasing its density D (in such a manner as is described in my copending application Serial No. 488,794 filed July 11, 1921, Jlatent No. 1,739,338 granted Dec. 10, 1929) without increasing its length and thereby diminishing its possible length of stroke (s). But when the aggregate effect of recurrent succession of uniformly acting impulses is to be considered (as in the majority of chipping and drilling` operations) and the cumulative momentive action (E) or effective power (P) is of primary importance, the density of the'piston member, and its length of stroke, are immaterial, and the cross-sectional area (A) is the only factor that requires consideration. Under such circumstances also, it is advantageous to employ the hollow or recessed form of piston element (shown in Figs. 1 and 7) because that form is lighter than a solid form having the same pressure-receiving area (A) and the same bea-ring length (Z). This last advantage is particularly characteristic of the four piston construction shown in Figs. l2 to 17 because in that embodiment of my invention the ratio between the effective pressure area (A) of the moving pistons and the mass thereof 1s increased both by the utilization of the recessed form of construction for the pistons 17o-170, and also by the division of each impact element into two cylindrical members, whose aggregate cross-sectional area 1s considerably greater than that of a single piston of the normal and usual size and weight.

While I have illustrated and described several embodiments of my invention, it will be apparent to those skilled in the art that other modifications, additions and omissions may be made in the apparatus illustrated without departing from the spirit and scope of the invention, as set forth by the appended claims.

I claim as my invention:

1. In a pneumatic tool, a casing, two piston chambers enclosed within said casing and in open communication at their forward ends, a free piston located in each chamber, means for delivering motive fluid to the communicating ends of said chambers between the pistons, and means responsive to variations of pressure within the chambers for controlling the delivery of motive fluid to and the discharge of motive fluid from the rear ends of said chambers.

2. In a pneumatic tool, a casing, two pis- "f ton chambers enclosed thereby, having their forward ends in open communication, a free piston located within each chamber, means responsive to the fluid pressure trapped in said chambers between said pistons for controlling the delivery of motive fluid to the communicating ends of said chambers, and mea-ns for controlling the delivery of fluid to and the discharge of fluid from the rear ends of said chambers.

3. In a pneumatic tool, a casing, two concentric cylinders located therein, a separate piston operating in each cylinder, a valve box located in the casing and surrounding the rear ends of said cylinders, and a sleeve valve located in said box and surrounding the rear ends of Jthe cylinders for controlling the delivery of operatineV fluid to said cylinders.

4. In a pneumatic tool, a casing, two concentric cylinders located therein and in communica-tion at their forward ends, a separate piston operating in each cylinder, a valve box located within said casing at the rear of said cylinders and in line therewith, a sleeve valve, located within the box and encircling the rear ends of the cylinders, for controlling the delivery of operating fluid to the rear of said pistons, and for maintaining a decreased fluid pressure at the forward ends of said cylinders in front of said pis-y tons.

5.l In a pneumatic tool, a casing enclosing two piston chambers in open communication at their forward ends, a separate free piston located in each chamber, a member extending into said casing and engaged by both of said pistons at the forward limit of their strokes, means for alternately delivering high pressure motivel fluid to said chambers behind said pis-tons and for alternately exhausting said chambers, and means for maintaining a reduced operating pressure in the communicating ends of said chambers ahead of said pistons.

6. In a pneumatic tool, a casing enclosing a plurality of piston chambers in open communication at their forward ends, a separate free piston in each chamber, a member extending into said casing forming a closure for the forward end of all of said chambers, and adapted to be engaged by said pistons, a distributing Valve responsive in operation to variations in fluid pressure within said chambers for delivering high pressure fluid first to one and then another of said chambers and for exhausting one and then another of said chambers and means `for maintaining a reduced fluid pressure in the com municating ends of said chambers.

7. In a pneumatic hammer, a casing enclosing two piston chambers in open communication at their forward ends, a free piston operating in each chamber, a rivet set extending into said casing and adapted to be engaged by both of said pistons, means responsive to variations in pressure in both chambers for controlling the delivery of fluid to and the discharge of fluid from the rear ends of said chambers and for maintaining a determined fluid pressure in the communicating ends of said chambers.

8. In a pneumatic tool, a casing enclosing two concentric piston chambers, in open communication at their forward ends, a member extending into the forward end of said casing and adapted to be engaged by both pistons, means for controlling the delivery of motive fluid to and the discharge of motive fluid from the rear ends oil said chambers, and means for maintaining a predetermined operating pressure in communicating ends of said chambers.

In testimony whereof, I have hereunto subscribed my name this 25th day of July. i 1921.

FRANK L. O. WADSWORTH.

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