US3870113A

US3870113A - Pneumatic drill apparatus

Info

Publication number: US3870113A
Application number: US442350A
Authority: US
Inventors: Newell E Slawson
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-02-14
Filing date: 1974-02-14
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11

Abstract

A pneumatic drilling apparatus using repetitive impacts on drill bits to drill holes in rock and the like and particularly to drill large holes in earth formations. The apparatus includes a housing secured to the end of a drill stem and having a pair of cylinders therein with each cylinder having a piston reciprocably mounted therein dividing each cylinder into two chambers. Air supply means communicate with said chambers on opposite ends of the respective piston to selectively supply compressed air thereto for effecting the reciprocating movement of the pistons. A valve is included in the air supply means and is operable to control the flow of air into the chambers by selectively opening and closing conduits to each of said chamber wherein the valve functions automatically in response to pressure differentials thereon. The pistons impact the drill bits on their power stroke to effect the drilling and the pressurized air used in reciprocally moving the pistons is exhausted through passages into the drill hole for clearing away drilling debris.

Description

tilted States Patent [1 Slawson PNEUMATIC DRILL APPARATUS [76] Inventor: Newell E. Slawson, 319 Cleveland Ave., Garnett, Kans. 66032 22 Filed: Feb. 14, 1974 21 Appl. No.: 442,350

[52] US. Cl. 175/96, 175/101 [51] Int. Cl. 1521b l/06, E2lb 3/08 [58] Field of Search 175/92, 100, 101, 105, 175/189, 296; 173/101 [56] References Cited UNITED STATES PATENTS 574,589 l/1897 Treman 173/101 X. 995,593 6/1911 Gilman 173/101 X 1,461,713 7/1923 Gilman et a1. 175/96 1,612,338 12/1926 Wilson et al...... 175/96 X 1,710,925 4/1929 Hardsocg 175/96 X 2,937,619 5/1960 Kurt 175/296 X 2,942,850 6/1960 Heath 175/96 3,297,099 1/1967 Adams et al 175/101 X FOREIGN PATENTS OR APPLICATIONS 345,592 10/1922 France...... I 173/101 1,338,995

4/1963 France 175/96 1 Mar. 11, 1975 Primary Examiner-David H. Brown Attorney, Agent, or FirmFishburn, Gold & Litman [57] ABSTRACT A pneumatic drilling apparatus using repetitive impacts on drill bits to drill holes in rock and the like and particularly to drill large holes in earth formations. The apparatus includes a housing secured to the end of a drill stem and having a pair of cylinders therein with each cylinder having a piston reciprocably mounted therein dividing each cylinder-into two chambers. Air supply means communicate with said chambers on opposite ends of the respective piston to selectively supply compressed air thereto for effecting the reciprocating movement of the pistons. A valve is included in the air supply means and is operable to control the flow of air into the chambers by selectively opening and closing conduits to each of said chamber wherein the valve functions automatically in response to pressure differentials thereon. The pistons impact the drill-bits on their power stroke to effect the drilling and the pressurized air used in reciprocally moving the pistons is exhausted through passages into the drill hole for clearing away drilling debris.

9 Claims, 8 Drawing Figures PNEUMATIC DRILL APPARATUS The principal objects of the present invention are: to provide a drilling apparatus using compressed air to urge reciprocating movement of pistons; to provide impact ondrill bits for effecting drilling of a hole through rock and the like; to provide such a drilling apparatus wherein pressurized air is supplied to chambers on both sides of the pistons to effect the reciprocating movement thereof; to provide such an apparatus with exhaust means which conduct the pressurized air used in moving the pistons into the drill hole to clear the drilling debris away from the drill bits; to provide such a drilling apparatus with means for selectively closing and opening the exhaust passages on both sides of said pistons wherein the pressurized air is exhausted at a predetermined position of the pistons; to provide such a drilling apparatus with an automatically operating valve that is responsive to pressure differentials thereon which selectively opens and closes air passages to the chambers on both sides of said pistons; to provide such an apparatus with air passages to the cylinders with spaced inlet parts and a rocking valve plate controlling entry of air thereto; to provide such an apparatus that has a minimum number of moving parts that is simple in construction and positive in operation; and to provide such a drilling apparatus that requires a minimum of maintenance and that is well adapted for its intended use.

Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings wherein are set forth by way of illustration and example, certain embodiments of the present invention. FIG. 1 is a side elevational view of the drilling apparatus.

FIG. 2 is a section view of the drilling apparatus showing structural details thereof.

FIG. 3 is a sectional view of the drilling apparatus taken along the line 3-3, FIG. 2.

FIG. 4 is a sectional view of the drilling apparatus taken along the line 44, FIG. 2. 7

FIG. 5 is a sectional view of the drilling apparatus taken along the, line 5-5, FIG. 2.

FIG. 6 is a secti nal view of the drilling apparatus taken .along the line 6-6, FIG. 2.

FIG. 7 is an enlarged fragmentary view of the upper portion of the cylinder and piston with portions broken away to show structural details thereof.

FIG. 8 is an enlarged fragmentary view of a lower portion of the-cylinder and piston with portions broken away to show structural details thereof.

Referring more in detail to the drawings.

As required, detailed embodiments 'of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention which may be embodied in a drill shaft 4 operatively supported and connected to a rotary drill structure for raising and lowering and for effecting rotation of the drilling apparatus during hole drilling operations. The drilling apparatus 1 also includes a housing 5 having at least two substantially identical impact providing means therein which as illustrated include a cylinder 6 with a piston 7 reciprocably mounted therein. The pistons 7 divide each of the cylinders 6 into two

chambers

8 and 9 on each end of the piston 7. The drill bits 2 are each movably mounted in a respective cylinder 6 for engagement witn portions of the piston 7 on the power stroke or the downstroke of the piston 7 with the engagement being an impact type engagement to effect breaking or pulverizing of the material to be drilled through. Each of the

chambers

8 and 9 have means cooperating therewith for conducting pressurized fluid thereto to effect the reciprocating movement of the piston on the power stroke and areturn stroke with the flow of pressurized fluid being automatically controlled by a pressure responsive valve means 10.

In the illustrated structure, the housing 1 is comprised of a drill head 12 having an elongate tubular shroud 13 with the shroud 13 enclosing a pair of spaced apart cylinders 6 extending substantially the length of the shroud 13. It is to be noted that one or more pairs of impact providing means can be used although only one pair is shown. In the form shown the cylinders 6 are suitably secured to the drill head 12, such as by welding, and have a plate member 14 suitably secured to the lower disposed ends of the cylinders 6 in any suitable manner such as by welding. The plate 14 is received within the shroud 13 adjacent the lower end thereof and a lower locking plate 15 is secured to the plate 14 such as with fasteners 16 wherein the shroud 13 is retained between the drill head 12 and the locking plate 15 by engaging shoulder portions thereon with the shroud providing protection for the cylinders 6.

The drill head 12 has the valve means 10 thereon and secured between same and the adapter 3. The valve means 10 in the illustrated structure include a valve body 19 having a portion 20 thereof receivable within a recess 21 of the drill head 12. The adapter 3 and the valve body 19 are suitably secured to the drill head and in the illustrated structure the adapter and valve body each have

flanges

22 and 23 with fasteners 24, such as bolts, extending therethrough and threadably engaging the drill head 12 for securing same thereto. The valve means 10'includes a chamber 26 formed between the adapter 3 and the valve body 19 and as shown, the

adapter 3 has a hollow portion formed therein and the valve body 19 which has a valve seating surface 27 partially defining the chamber 26. A flow passage 28 extends through the adapter 3 and opens into the chamber 26 and is operable for supplying pressurized fluid thereto. As illustrated the seat surface 27 has two

inclined surface portions

29 and 30 meeting at an apex 31 wherein the

inclined surfaces

29 and 30 are substantially flat and incline downwardly from said apex. A plurality of

flow passages

33, 34, 35 and 36 extend through the valve body 19 and the drill head 12 communicating with the chamber 26 and open on a surface of the drill head 12 in the interior of the housing 5. The

passages

33 and 34 open on the inclined surface 29 and the

passages

35 and 36 open on the inclined surface 30 and are surrounded by seating surface portions.

The valve means includes a valve member 38 operable for selectively opening and closing the

passages

33, 34, 35, and 36 in response to pressure differentials thereon. in the form shown, the valve member 38 is a rocker type valve member and has a substantially flat surface 39 engaging the apex 31 and pivotal thereon from overlying and closing relation to the

passages

33 and 34 to overlying and closing relation to the

passages

35 and 36. The valve member 38 preferably is made of a rigid material such as steel, hard rubber and the like and is such as to sealingly engage the

surfaces

29 and 30 around the openings of the

passages

33, 34, 35 and 36 for selectively closing same. A hold down member 41 is suitably secured to the adapter 3 in the chamber 26 and having an edge 42 engaging the valve member 38 for holding same in engagement with the apex 31 and still allowing same to freely pivot thereon. The valve member 38 is held in position in the chamber 26 by suitable means such as dowel pins 43 secured to the valve body 19 and extending through elongate slots through the valve member 38 wherein the slots 44 hold the valve member 38 in position in the chamber 26 and still allow free pivotal movement thereof. As illustrated the peripheral edge of the valve member 38 is positioned adjacent to an interior wall of the chamber 26. Openings or notches 45 are provided in the valve member 38 and as illustrated extend inwardly from the peripheral edge thereof and are in opposed relation. The openings 45 allow free passage of the pressurized air between the valve member 38 and the chamber defining side wall.

EAch of the cylinders 6 are provided with a member 46 positioned in the upper end thereof in the respective chamber 8 with the member having a plurality of ports 47. communicating with the chamber 8 for supplying pressurized fluid thereto. A groove 48 extends around the member 46 and connects the ports 47 to supply the pressurized fluid to each of. the ports. Conduits or pipes 50 connect the passage 33 and the passage 35 to respective cylinders 6 for conducting the pressurized fluid from the passages to the ports 47 and the chambers 8. Preferably, the members 46 each have an elongate stem 51 depending therefrom into the chamber 8 and receivable within an exhaust passage or bore 52 maintainingvsame closed until a predetermined position on the downstroke or power stroke of the piston is reached wherein the stem 5 1 is clear of the exhaust passage 52 allowing pressurized air in the chamber 8 to be exhausted therethrough on the power stroke of the piston 7. The length of the stem 51 is less than the length of the power stroke of the piston 7.

Conduits or pipes 54 communicate between the chambers 9 and the

passages

34 and 36 for conducting pressurized fluid thereto. The pipes 54 are suitably secured in position such as by welding. The pipes 54 open into a circumferential groove 55 which extends around the exterior of a wear sleeve 56 which is fixed in the cylinder 6 and has the piston 7 reciprocably received extending from one side thereof and is receivable in a guide member 58. It is to be noted that the openings 55' open into the chamber 9 a short distance above the top of the guide member 58 whereby downward movement of the piston 7 will close the openings 55 trapping air in the lower portion of the chamber forming a cushion to reduce or eliminate the force off engagement between the piston and the guide member on the power stroke. The entrapped air also helps in reversing directions of movement of the piston upon completion of the powerstroke. Adjacent to the lower disposed end of the reduced diameter portion 57, a plurality of circumferentially spaced grooves 61 are provided on the exterior of the reduced diameter portion 57 whereupon when the piston 7 reaches a predetermined position on the upstroke, the grooves 61 move into the chamber 9 and form exhaust passages between the chamber 9 and the interior of the guide member 58.

The drill bits 2 each have an elongate shank portion 62 received within the respective cylinders 6 having an exhaust passage 63 therethrough and an upper disposed end 64 engageable with the end 59 of the piston 7 whereby on the downstroke of power stroke of the piston, the

ends

59 and 64 engage, with the engagement being an impact type engagement, to drive bits 2 into the material being drilled to break same for removal. Preferably, the diameter of the shank 62 is greater than the diameter of the piston portion 57 whereby the guide member 58 acts as a stop for upward movement of the drill bits 2. A wear sleeve 65 is fixed in the cylinder 6 and receives therein a head portion 66 of the shank 62. A bit retainer sleeve 67 is suitably fixed in the cylinder 6, such as by having an enlarged circumferential flange portion 68 retained in a groove 69 formed in the plate 14 and locking plate 15 wherein the bit retainer retains the bit wear sleeve 65, the guide member 58, and the piston wear sleeve 56 within the respective cylinders 6. As illustrated, the inside diameter of the bit retainer sleeve 67 is slightly less than the inside diameter of the bit wear sleeve 65 and the head portion 66 has adiameter substantially the same as the diameter of the bit wear sleeve 65 whereby a shoulder 70 is formed on the upper end of the bit retainer sleeve to retain the shanks 62 in the cylinder 6. The head 66 ,is provided with a circumferential groove 71 having lock rings 72 therein to engage the shoulder 70 and prevent withdrawal of the drill bits 2 from the respective cylinder 6. The drill bit 2 may be of any suitable type which are conventional wherein the drill bits 2 have a drilling end 73 which can have tungsten carbide inserts thereon for a wear resistant drill bit. Preferably the drilling ends 73 extend outwardly of the housing 5 so as to drill a hole larger in diameter than the housing.

The present invention is more fully understood by a description of the operation thereof. Pressurized fluid, such as compressed air, is supplied from a source (not shown) through a passage 76 in the drill pipe 4 and through the passage 28 into the chamber 26 wherein the pressurized air will flow through one set of two sets of passages which comprise a set of

passages

33 and 34 and a set of

passages

35 and 36. As shown in FIG. 2 the valve member 38 is in overlying and closing relation to the

passages

35 and 36 wherein the

passages

33 and 34 are open and pressurized air will flow to the chamber 8 in the right hand cylinder 6 and the chamber 9 in the left hand cylinder 6, effecting a power stroke of the right hand piston 7 and the return stroke of the left hand piston 7. The right hand piston 7 moves downwardly on the power stroke until impact engagement with the end 64 of the drill bit 2 and at a predetermined position on the power stroke, the piston exhaust passage 52 is open allowing the pressurized fluid in the chamber8 to be exhausted therethrough and through the drill bit exhaust passage 63 which includes a plurality of outlets 77 directing the exhaust air out into the drill hole to clear drilling debris-andcuttings away from the drill bits. During the return stroke of the left hand piston 6 of the grooves 61 move out of the guide member 58 and allow the pressurized air in the chamber 9 to be exhausted into the guide member 58 and through the exhaust passage 63 to clear drilling debris from the drill bit 2. Upon nearing the completion of the power stroke of the right hand piston 7, and nearing the completion of the return stroke of the left hand piston 7, air is pressurized in the

chambers

9 and 8 respectively thereby causing same to reverse flow through the

passages

35 and 36 and the

respective conduits

50 and 54 creating a pressure differential on the valve member 38 thereby causing same to pivot on the apex 31 and move to close the

passages

33 and 34. After pivoting movement of the valve member 38, the

passage

35 and 36 are open allowing pressurized fluid to flow into the chamber 8 of the left hand cylinder 6 and the chamber 9 of the right hand cylinder 6 causing the respective pistons 7 therein to move in opposite directions with the left hand piston 7 moving on the power stroke and the right hand piston 7 moving on the return sroke, wherein the valve is recycled as described to effect continuous reciprocal movement of the pistons and effect automatic operation of the valve 10. Preferably, the

pistons 7 will change directions of movement before engaging either the member 46 or the guide member 58. It is to be noted that in the particular form of the invention shown, the pistons 7 reciprocate in opposite directions or out of phase.

It is to be understood that while I have illustrated and described certain forms of my invention, it is not to be limited to the specific form or arrangement of parts herein described and shown.

What I claim and desire to secure by Letters Patent 1. A.pneumatic drilling apparatus adapted to be secured to the end of a drill pipe and rotatable thereby for drilling, said apparatus comprising:

a. a housing having at least two cylinders therein;

b. a piston reciprocably mounted in each said cylinder, said pistons each having first and second ends;

c. a chamber in saidhousing and being partially de-' fined by a seat surface;

d. passages communicating between said chamber and said cylinders on opposite ends of said pistons for selectively allowing pressurized air to flow to said cylinders and effect reciprocating movement of said pistons, said passages opening on said seat surface and being surrounded thereby;

e. drill bits mounted in said cylinders and having opposed ends with one end of each adjacent a portion of respective said piston whereby movement of said piston on a power stroke urges said piston portion to engage said one drill bit end, said engagement being an impact type engagement;

a valve member movably mounted in said chamber and having surface portions overlying said seat surface and selectively movable into sealing engagement with portions thereof for closing certain of said passages and opening other said passages effecting reciprocating movement of said pistons and the impact engagement of same with said drill bits, said valve member moving in response to pressure differentials thereon;

' g. exhaust passages communicating with said cylinders on each end of said piston;

h. means cooperating with said exhaust passages for selectively opening and closing same at predetermined positions of said pistons for selectively permitting exhaust of air from said cylinders;

i. means on said housing for securing same to a rotatable drill shaft wherein said drill shaft effects rotation of siad housing;

j. said seating surface having two inclined surface portions meeting at an apex with said inclined surface portions being inclined downwardly from said apex, each said inclined surface portion having certain of said passages opening thereon;

k. said valve member having a substantially flat surface engaging said apex wherein said valve member pivots thereon from overlying relation on one inclined surface portion to overlying relation on the other inclined surface portion; and

1. means in said chamber engaging a portion of said valve member and holding same in engagement with said apex and permitting said valve member to freely pivot on said apex.

2. The apparatus as set forth in claim. 1 wherein said passages include:

a. a pair of first passages each communicating with a respective said cylinder on one end of said piston and operable forconducting pressurized air thereto and urging said pistons to move on a power stroke, each said first passage opening on a respective said inclined surface portion; and

b. a pair of second passages each communicating with a respective said cylinder on the other end of said piston ,and operable for conducting pressurized air thereto and urging said pistons to move on a return stroke, each said second passage opening on a respective said inclined surface portion wherein the first and second passages for each of said cylinders are on different said inclined surface portions.

3. The apparatus as set forth in claim 2 wherein:

a. said pistons dividing said cylinders into first and second chambers with said first chamber being on the one end of said piston having said first piston end partially defining said first chamber and with said second chamber being on the. other end partially defining said first chamber and with said second chamber being on the other end of said piston having said second piston end partially defining said second chamber, the size of said chambers varying upon movement of said pistons; and

b. said first passages communicating with said first chambers and said second passages communicating with said second chambers.

4. The apparatus as set forth in claim 3 wherein said exhaust passages includes:

' a. a first exhaust passage through each of said pistons and extending between said first and second ends; and

b. said cooperating means includes a member receivable in a respective first exhaust passage for normally closing same, said first exhaust passage opening at a predetermined position on the power stroke of the pistons and closing at a predetermined posistion on the return stroke of the piston whereby pressurized air in said first chamber exhausts through said first exhaust passages at said power stroke predetermined position and air is pressurized in said first chamber on the return stroke of said pistons and reverse flowing through respective said first passages and urging said valve member to move and open said first passage for supplying pressurized fluid thereto and effect the power stroke of said piston, said pistons normally moving in opposite directions.

5. The apparatus as set forth in claim 4 wherein:

a. said pistons each having a reduced diameter portion on the respective opposite side thereof with said second end being a free end of said reduced diameter;

b. said cylinders each having a reduced diameter portion for slidably receiving said piston reduced diameter portion therein; and

c. said exhaust passages including second exhaust passages communicating between said second chambers annd said cylinder reduced diameter portion, said piston reduced diameter portion opening and closing a respective said second exhaust passage at a predetermined position of said piston.

6. The apparatus as set forth in claim 5 including:

a. means forming third exhaust passages each communicating with a respective said first exhaust passage and a respective said second exhaust passage for conducting fluid therefrom to the exterior of said housing, said third exhaust passages being through respective said drill bits and directed for clearing debris away from said drill bits.

7. A pneumatic drilling apparatus adapted to be secured to an end of a drill pipe and rotatable thereby for drilling, said apparatus comprising:

a. a housing having at least two cylinders therein; b. a piston reciprocably mounted in each said cylin: d er with said pistons dividing said cylinders into first and second chambers with said first chamber being on a first end of said piston and said second chamber being on a second end of said piston, said pistons each having a reduced diameter portion extending from said second end and through said second chamber, said pistons each having an exhaust passage longitudinally therethrough;

c. a pressure responsive valve in said housing;

d. a passage communicating with said valve for conducting pressurized air thereto;

e. passages communicating between said valve and said first and second chambers for selectively conducting pressurized air thereto for effecting reciprocating movement of said pistons within said cylinders;

f. drill bits mounted in said cylinders and having opposed ends with one end of each adjacent a portion of a respective said piston whereby movement of said piston on a power stroke urges said piston portion to engage a respective said drill bit end, said engagement being an impact typeengagement, said drill bits each having an exhaust passage communicating between said cylinders and the exterior of said housing;

g. a member in each said cylinder selectively receivable in a respective piston exhaust passage for closing same until a predetermined position of the power stroke of said piston is reach wherein said exhaust passage is opened for allowing pressurized air in said first chambers to be exhausted through respective said piston exhaust passages and respective said drill bit exhaust passages;

h. means forming an exhaust passage between said second chambers and said respective drill bit exhaust passages; and

i. means cooperating with said piston reduced diameter portion for closing said respective second chamber exhaust passages until a predetermined position of a return stroke of said pistons is reached wherein pressurized air is allowed to be exhausted from said second chambers into said respective drill bit exhaust passages.

8. The drill apparatus as set forth in claim 7 wherein:

a. said means forming said second chamber exhaust passages including at least one channel in each of said pistons reduced diameter portions adjacent a free end thereof; and

b. said cooperating means including a reduced diameter portion in said cylinder slidably receiving said piston reduced diameter portion therein whereby when said piston reaches a predetermined position on the return stroke thereof, said channel communicates between said second chamber and said drill bit exhaust passage forming an exhaust passage therebetween.

9. A pneumatic drilling apparatus adapted to be se cured to the end of a drill pipe and rotatable thereby for drilling, said apparatus comprising:

a. a housing having at least two cylinders therein;

c. a chamber in said housing and being partially defined by two inclined seating surfaces, said inclined seating surfaces meeting at an apex with said inclined seating surfaces being inclined downwardly from said apex;

d. passages communicating between said chamber and said cylinders on opposite ends of said pistons for selectively allowing pressurized air to flow to said cylinders and effect reciprocating movement of said pistons, said passages opening on said seating surfaces and being surrounded thereby. said passages opening on one seating surface communicating with one cylinder on the first end of the respective piston and with the other cylinder on the second end of the respective piston and the said passages opening on the other seating surfae communicating with said other cylinder on the first end of the respective piston and with said one cylinder on the second end of the respective piston whereby in reciprocation of the pistons one moves in the opposite direction to the movement of the other piston;

e. drill bits mounted in said cylinders and having opposed ends with one end of each adjacent a portion of a respective said piston whereby movement of said piston on a power stroke urges said piston portion to engage said one drill bit end, said engagement being an impact type engagement;

f. a valve member movably mounted in said chamber and pivoting about said apex with portions extend- 9 a Y 10 ing therefrom and overlying said seating surfaces, g. means in the chamber engaging a portion of said said valve member being selectively movable into v lv d holding same for freely pivoting about sealing engagement with the seating surfaces for Said apex;

closing certain passages and opening othersaid passages said valve member pivoting from overlyders on each end of Said piston; mg relation on one Inclined seating surface to overlying relation on the other inclined seating surface, mean? cooperatlng wlth Sald exhaust passages for effecting reciprocating movement of said pistons selecnvelxsmenmg 9 (flosmg Same at 'predeter' and impact engagement of same ith a respectiv mlned positions of said pistons for selectively perdrill bit, said valve member moving in response to 10 ng BXhfluSI of air from aid ylinders. pressure differentials thereon;

h. exhaust passages communicating with said cylin-

Claims

1. A pneumatic drilling apparatus adapted to be secured to the end of a drill pipe and rotatable thereby for drilling, said apparatus comprising: a. a housing having at least two cylinders therein; b. a piston reciprocably mounted in each said cylinder, said pistons each having first and second ends; c. a chamber in said housing and being partially defined by a seat surface; d. passages communicating between said chamber and said cylinders on opposite ends of said pistons for selectively allowing pressurized air to flow to said cylinders and effect reciprocating movement of said pistons, said passages opening on said seat surface and being surrounded thereby; e. drill bits mounted in said cylinders and having opposed ends with one end of each adjacent a portion of respective said piston whereby movement of said piston on a power stroke urges said piston portion to engage said one drill bit end, said engagement being an impact type engagement; f. a valve member movably mounted in said chamber and having surface portions overlying said seat surface and selectively movable into sealing engagement with portions thereof for closing certain of said passages and opening other said passages effecting reciprocating movement of said pistons and the impact engagement of same with said drill bits, said valve member moving in response to pressure differentials thereon; g. exhaust passages communicating with said cylinders on each end of said piston; h. means cooperating with said exhaust passages for selectively opening and closing same at predetermined positions of said pistons for selectively permitting exhaust of air from said cylinders; i. means on said housing for securing same to a rotatable drill shaft wherein said drill shaft effects rotation of said housing; j. said seating surface having two inclined surface portions meeting at an apex with said inclined surface portiOns being inclined downwardly from said apex, each said inclined surface portion having certain of said passages opening thereon; k. said valve member having a substantially flat surface engaging said apex wherein said valve member pivots thereon from overlying relation on one inclined surface portion to overlying relation on the other inclined surface portion; and l. means in said chamber engaging a portion of said valve member and holding same in engagement with said apex and permitting said valve member to freely pivot on said apex.

2. The apparatus as set forth in claim 1 wherein said passages include: a. a pair of first passages each communicating with a respective said cylinder on one end of said piston and operable for conducting pressurized air thereto and urging said pistons to move on a power stroke, each said first passage opening on a respective said inclined surface portion; and b. a pair of second passages each communicating with a respective said cylinder on the other end of said piston and operable for conducting pressurized air thereto and urging said pistons to move on a return stroke, each said second passage opening on a respective said inclined surface portion wherein the first and second passages for each of said cylinders are on different said inclined surface portions.

3. The apparatus as set forth in claim 2 wherein: a. said pistons dividing said cylinders into first and second chambers with said first chamber being on the one end of said piston having said first piston end partially defining said first chamber and with said second chamber being on the other end partially defining said first chamber and with said second chamber being on the other end of said piston having said second piston end partially defining said second chamber, the size of said chambers varying upon movement of said pistons; and b. said first passages communicating with said first chambers and said second passages communicating with said second chambers.

4. The apparatus as set forth in claim 3 wherein said exhaust passages includes: a. a first exhaust passage through each of said pistons and extending between said first and second ends; and b. said cooperating means includes a member receivable in a respective first exhaust passage for normally closing same, said first exhaust passage opening at a predetermined position on the power stroke of the pistons and closing at a predetermined position on the return stroke of the piston whereby pressurized air in said first chamber exhausts through said first exhaust passages at said power stroke predetermined position and air is pressurized in said first chamber on the return stroke of said pistons and reverse flowing through respective said first passages and urging said valve member to move and open said first passage for supplying pressurized fluid thereto and effect the power stroke of said piston, said pistons normally moving in opposite directions.

5. The apparatus as set forth in claim 4 wherein: a. said pistons each having a reduced diameter portion on the respective opposite side thereof with said second end being a free end of said reduced diameter; b. said cylinders each having a reduced diameter portion for slidably receiving said piston reduced diameter portion therein; and c. said exhaust passages including second exhaust passages communicating between said second chambers and said cylinder reduced diameter portion, said piston reduced diameter portion opening and closing a respective said second exhaust passage at a predetermined position of said piston.

6. The apparatus as set forth in claim 5 including: a. means forming third exhaust passages each communicating with a respective said first exhaust passage and a respective said second exhaust passage for conducting fluid therefrom to the exterior of said housing, said third exhaust passages being through respective said drill bits and directed for clearing debris away from said driLl bits.

7. A pneumatic drilling apparatus adapted to be secured to an end of a drill pipe and rotatable thereby for drilling, said apparatus comprising: a. a housing having at least two cylinders therein; b. a piston reciprocably mounted in each said cylinder with said pistons dividing said cylinders into first and second chambers with said first chamber being on a first end of said piston and said second chamber being on a second end of said piston, said pistons each having a reduced diameter portion extending from said second end and through said second chamber, said pistons each having an exhaust passage longitudinally therethrough; c. a pressure responsive valve in said housing; d. a passage communicating with said valve for conducting pressurized air thereto; e. passages communicating between said valve and said first and second chambers for selectively conducting pressurized air thereto for effecting reciprocating movement of said pistons within said cylinders; f. drill bits mounted in said cylinders and having opposed ends with one end of each adjacent a portion of a respective said piston whereby movement of said piston on a power stroke urges said piston portion to engage a respective said drill bit end, said engagement being an impact type engagement, said drill bits each having an exhaust passage communicating between said cylinders and the exterior of said housing; g. a member in each said cylinder selectively receivable in a respective piston exhaust passage for closing same until a predetermined position of the power stroke of said piston is reach wherein said exhaust passage is opened for allowing pressurized air in said first chambers to be exhausted through respective said piston exhaust passages and respective said drill bit exhaust passages; h. means forming an exhaust passage between said second chambers and said respective drill bit exhaust passages; and i. means cooperating with said piston reduced diameter portion for closing said respective second chamber exhaust passages until a predetermined position of a return stroke of said pistons is reached wherein pressurized air is allowed to be exhausted from said second chambers into said respective drill bit exhaust passages.

8. The drill apparatus as set forth in claim 7 wherein: a. said means forming said second chamber exhaust passages including at least one channel in each of said pistons reduced diameter portions adjacent a free end thereof; and b. said cooperating means including a reduced diameter portion in said cylinder slidably receiving said piston reduced diameter portion therein whereby when said piston reaches a predetermined position on the return stroke thereof, said channel communicates between said second chamber and said drill bit exhaust passage forming an exhaust passage therebetween.