AU692825B2 - Automatic leveling system for blasthole drills - Google Patents

Description

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PA()01001 I Regulation 3.2

AUSTRALIA

Patents Act 1990 COOMPLETE SPECIFICATION FOR A STANDARD PATENT GE.0

ORIGINAL

Does Do* aa Name of Applicant: Actual Inventor: Address for service in Australia: HARNISCHF EGER CORPORATION Timothy R. KiERRIGAN CARTER SMITH BEADLE 2 Railway Parade Camberwell Victoria 3124 Australia AUTOMATIC LEVELING SYSTEM FOR

DRILLS

Invention Title: BLASTHOLE The following statement is a full description of this invention, including thle best method of performing it known to us 1 1--11~-31 I AUTOMATIC LEVELING SYSTEM FOR BLASTHOLE DRILLS BACKGROUND OF THE INVENTION Blasthole drills are extremely large machines used in mining operations to drill holes for explosives. A conventional blasthole drill moves on crawlers and must be stabilized and leveled before it drills a hole. This is done by the drill's hydraulic leveling jacks. Automatic leveling systems, which automatically control the leveling jacks to level the drill, are .ee.

known. See, for example, U.S. Patent No. 4,679,489.

After a drill completes a hole, the leveling jacks must be fully retracted so that the drill can move to a new location without damaging the jacks. Upon reaching a new location, a oe° drill must be leveled again. The time required to level a drill is setup time, not production time. Automatic leveling systems reduce the setup time by efficient use of the controls.

The movement of the jacks toward the ground by the automatic leveling system is referred to as "auto level raise" because this action raises the blasthole drill frame. Retraction (upward movement) of the jacks by the automatic leveling system is referred to as "auto level lower" because this action lowers the blasthole drill frame.

On one well-known blasthole drill, a P&H® 120 manufactured by Harnischfeger Corporation of Milwaukee, Wisconsin, the leveling jacks trai-el an average of 28 inches from their fully retracted positions to ground contact. The time required for the -4 ~L L I 51C- I ~P- II ii 2 jacks to travel this distance is most of the leveling cycle time.

The average leveling cycle time is 45 seconds.

SUMMARY OF THE INVENTION The invention provides an automatic leveling system which reduces the time required for the jacks to make ground contact.

This is done by using a hydraulic regeneration circuit or

O.

"regen". The regeneration circuit is applied to a jack cylinder to allow the piston rod to extend at a faster rate. The regeneration circuit connects the rod end to the bore end via a regeneration valve. Fluid from the pump is joined by fluid from the rod end, and the combined flow is directed to the bore end.

As a result, the pump acts only against the area of the rod. The .99 piston therefore moves faster but with less force.

The increase in piston or rod speed is equal to the ratio of the bore area to the rod area. A jack cylinder with a nine inch bore and a six inch rod has a bore area of 63.62 square inches and a rod area of 28.27 square inches. The ratio of bore area to rod area is 2.25:1. Therefore, the jack moves to ground contact 2.25 times faster with the regeneration circuit.

Other features and advantages of the invention will become apparent to those skilled in the art upon view of the following detailed description, claims and drawings.

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3 DESCRIPTION OF THE DRAWINGS Fig. 1 is a side elevational view of a blasthole drill embodying the invention.

Fig. 2 is a vertical sectional view of a jack assembly.

Fig. 3 is a schematic view of the auto level hydraulic system.

Fig. 4 is a portion of Fig. 3 showing auto level raise without regeneration.

Fig. 5 is the same portion of Fig. 3 showing auto level 10 raise with regeneration.

Fig. 6 is the same portion of Fig. 3 showing auto level lower.

"Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

IsilC- IIIP~TT I C' 1. I 1 -I 4 DESCRIPTION OF THE PREFERRED EMBODIMENT A blasthole drill 10 embodying the invention is illustrated in Fig. 1. The blasthole drill 10 comprises a frame 14 supported by crawlers 18 for movement over the ground. A mast 22 is moveable relative to the frame 14 and relative to a vertical position. A rotary head 24 moves along the mast 22 for rotating a drill pipe (not shown) and for driving the drill pipe into the ground.

The blasthole drill 10 also comprises (see Fig. 3) an automatic leveling system 26. The automatic leveling system 26 includes (see Figs. 1 and 3) jacks 30, 34, 38 and 42 at the four corners of the frame 14. The jacks 30, 34, 38 and 42 are substantially identical, and only the jack 30 will be described in detail. The jack 30 includes (see Fig. 2) a sleeve 46 and a spud 50 slidably housed within the sleeve 46. A jack shoe 54 is pivotally connected to the lower end of the spud 50, and a cylinder 58 is housed within and connected to the spud 50 for common movement therewith. The cylinder 58 slides relative to a piston 62 connected to a piston rod 66 having an upper end fixed to the frame 14. The piston 62 divides the cylinder 58 into a first or lower chamber 70 (the bore end) and a second or upper chamber 74 (the rod end) through which the piston rod 66 extends.

An extension conduit 78 extends through the piston rod 66 to the lower chamber 70, and a contraction conduit 82 extends through the piston rod 66 to the upper chamber 74. This jack c- P~ 81 -L 5 construction is conventional and will not be described in greater detail. It should be noted that the jacks 30, 34, 38 and 42 are represented only schematically in Figs. 3-6.

The automatic leveling system 26 also incluues (see Fig. 3) a fluid source 86 and a pump 90 having an inlet 94 communicating with the fluid source 86. The pump 90 also has an outlet 98.

The automatic leveling system 26 also includes three sub-circuits 102, 106 and 110. The sub-circuit 102 controls the rear jack 0 4.

the sub-circuit 106 controls the rear jack 34, and the subcircuit 110 controls the front jacks 38 and 42. The sub-circuits eta 102, 106 and 110 are substantially identical, and only the subcircuit 102 will be described in detail. Common elements have S been given common reference numerals.

The sub-circuit 102 includes (see Fig. 4) a pump conduit 114 having one end 118 communicating with the pump outlet 98 and S having an opposite end 122. The pump conduit 114 has therein a flow control valve 124. A return conduit 126 has one end 130 communicating with the fluid source 86 and has an opposite end 134. The sub-circuit 102 also includes (see Fig. 4) a first conduit 138 having one end 142 and having an opposite end 146 communicating with the extension conduit 78 and thereby with the first chamber 70 of the jack 30. (The extension conduit 78 is not shown in Figs. 3-6 but is shown in Fig. 2. Because the jacks are shown only schematically in Figs. 3-6, the first conduit 138 is shown in Figs. 3-6 communicating directly with the bore end of ul c_ IL -I Q ~II L~I -r I 6 the cylinder 58.) A pressure switch 148 communicates with the first conduit 138 and sends a signal to a PLC (not shown) when the pressure in the conduit 138 exceeds a predetermined value.

The reason for this is explained below. A second conduit 150 has one end 154 communicating with the contraction conduit 82 and thereby with the second chamber 74 of the jack 30. The second conduit 150 has an opposite end 158.

The first conduit 138 has therein (see Fig. 4) a counterbalance valve 162 allowing flow in the direction away from the first chamber 70 (upwardly in the drawings) only when a pilot

E

pressure from the second conduit 150 is applied to the counterbalance valve 162 via a pilot line 166. The counterbalance valve 162 includes a check valve 170 allowing flow toward the first chamber 70 (downwardly in the drawings). The second conduit 150 has therein (see Fig. 4) a counterbalance valve 174 allowing flow in the direction away from the second chamber 74 (upwardly in the drawings) only when a pilot pressure from the first conduit 138 is applied to the counterbalance valve 174 via a pilot line 178. The counterbalance valve 174 includes a check valve 182 allowing flow toward the second chamber 74 (downwardly in the drawings).

The sub-circuit 102 also includes (see Fig. 4) a third conduit 186 having one end 190 and having an opposite end 194 communicating with the first conduit 138 between the opposite 7 -I I~ I~C pell -r 1 7 ends thereof. A fourth conduit 198 has one end 202 and has an opposite end 206.

The sub-circuit 102 also includes (see Fig. 4) a raise/lower valve 210 which is preferably a three-position, four-way valve controlled by solenoids 214 and 218. The solenoids 214 and 218 are ,ntrolled by the PLC. The raise/lower valve 210 is selectively operable between first, second and third modes or 4 upper, lower and center positions. In the first mode of the raise/lower valve 210 (shown in Fig. the end 122 of the pump conduit 114 communicates with the end 142 of the first conduit 138 and the end 134 of the return conduit 126 communicates with the end 206 of the fourth conduit 198. In the second mode of the 4* raisey'lower valve 210 (shown in Fig. the end 122 of the pump conduit 114 communicates with the end 206 of the fourth conduit 198, and the end 134 of the return conduit 126 communicates with the end 142 of the first conduit 138. In the third mode of the raise/lower valve 210 (not shown), the end 122 of the pump conduit 114 is blocked and the ends 142 and 206 of the first and fourth conduits 138 and 198 communicate with the end 134 of the return conduit 126. "he raise/lower valve 210 is spring-biased to the third mode (the center position), is moved to the first mode (the upper position) when the solenoid 218 is energized, and is moved to the second mode (the lower position) when the solenoid 214 is energized.

I I L I I LI I -L 8 The sub-circuit 102 also includes (see Fig. 4) a regeneration valve 222 which is preferably a two-position, threeway valve. The regeneration valve 222 is selectively operable between first and second modes or right and left positions. In the first mode (shown in Fig. the regeneration valve 222 connects the end 158 of the second conduit 150 to the end 190 of the third conduit 186. That is, the regeneration valve 222 diverts fluid from the second conduit 150 to the first conduit 138, or connects the second conduit 150 to the first conduit 138 I0 via the third conduit 186. In the second mode (shown in Fig. 4), the regeneration valve 222 connects the end 158 of the second conduit 150 to the end 202 of the fourth conduit 198. The S regeneration valve 222 is spring-biased to the left position (second mode) and is switched to the right position (first mode) when a pilot pressure is applied to the regeneration valve 222 via a pilot line 226.

The sub-circuit 102 also includes (see Fig. 4) a control valve 230 which is preferably a two-position, three-way valve.

The control valve 230 is selectively operable between first and second modes or left and right positions. In the first mode (shown in Fig. the control valve 230 connects the pilot line 226 to the first conduit 138 via a pilot line 234 so 'hat a pilot pressure is applied to the regeneration valve 222 when the first conduit 138 is under pressure. In the second mode (shown in Fig.

the control valve 230 connects the pilot line 226 to the -r I I r Il L E I -I I 9 fluid source 86 so that a pilot pressure is not applied to the regeneration valve 222. The control valve 230 is spring-biased to the second mode (the right position) and switches to the first mode (the left position) when a solenoid 238 is energized by the

PLC.

The auto level system 26 operates each of the sub-circuits 102, 106 and 110 in four different modes: the "AUTO LEVEL RAISE O*c 9 WITHOUT REGEN" mode; the "AUTO LEVEL RAISE WITH REGEN" mode; the "AUTO LEVEL LOWER" mode; and the "STATIONARY" mode. These modes 10 will be described in connection with the sub-circuit 102.

9 Operation of the sub-circuits 106 and 110 is substantially identical.

The AUTO LEVEL RAISE WITHOUT N mode is illustrated in Fig. 4. During AUTO LEVEL RAISE WITHOUT REGEN, the valve 210 is in its first mode that the first conduit 138 communicates with the pump outlet and the fourth conduit 198 communicates with the fluid source. The pressure in the first conduit 138 acts on the counterbalance valve 174 through the pilot line 178 so that fluid can flow away from the jack 30 (upwardly in Fig. 4) through the counterbalance valve 174. Also, the valve 230 is in its second mode so that the pilot line 226 communicates with the fluid source and the valve 222 is therefore in its second mode, whereby the second conduit 150 communicates with the fourth conduit 198.

Consequently, fluid from the pump flows through the pump conduit 114 to the valve 210, through the valve 210 to the first conduit I I I II 10 138, through the first conduit 138 to the counterbalance valve 162, through the counterbalance valve 162 v3a the check valve 170, and through the remainder of the first conduit 133 to the chamber 70 of the jack 30. From the chamber 74 of the jack fluid flows through the second conduit 150, through the counterbalance valve 174, through the remainder of the second conduit 150 to the valve 222, through the valve 222 to the' fourth conduit 198, through the fourth conduit 198 to the valve 210, through the valve 210 to the return conduit 126, and through the "'10 return conduit 126 to the fluid source.

The AUTO LEVEL RAISE WITH REGEN mode is illustrated in Fig.

During AUTO LEVEL RAISE WITH REGEN, the valve 210 is in its first mode so that the first conduit 138 communicates with the pump outlet and the fourth conduit 198 communicates with the fluid source. The pressure in the first conduit 138 acts on the counterbalance valve 174 through the pilot line 178 so that fluid can flow away from the jack 30 (upwardly in Fig. 5) through the counter} ,lance valve 174. The valve 230 is in its first mode so that pressure applied to the valve 222 via the pilot lines 234 and 226 places the valve 222 in its first mode. With the valve 222 in its first mode, the second conduit 150 communicates with the third conduit 186. As a result, fluid from the pump floxs through the pump conduit 114 to the valve 210, through the valve 210 to the first conduit 138, through the first conduit 138 to the counterbalance valve 162, through the counterbalance valve

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I 'I 'I 11 162 via the check valve 170, and through the remainder of the first conduit 138 to the chamber 70 of the jack 30. From the chamber 74 of the jack 30, fluid flows through the second conduit 150, through the counterbalance valve 174, and through the remainder of the second conduit 150 to the valve 222. Because 'he valve 222 is now in its first mode, fluid form the second conduit 150 flows through the valve 222 and the third conduit 186 to the first conduit 138, instead of returning to the fluid source 86, and then flows with fluid from the pump 90 to the bore *0"i10 end of the cylinder 58. As explained above, the pump therefore acts only against the area of the piston rod 66. The piston 62 therefore moves faster but with less force than during AUTO LEVEL RAISE WITHOUT REGEN.

e The AUTO LEVEL LOWER mode is illustrated in Fig. 6. During 15 AUTO LEVEL LOWER, the valve 210 is in its second mode so that the 44 first conduit 138 communicates with the fluid source and thr fourth conduit 198 communicates with the pump outlet. The valve 230 is in its second mode 30 that the pilot line 226 communicates with the fluid source and the valve 222 is therefore in its second mode. With the valve 220 in its second mode, the second conduit 150 communicates with the fourth conduit 198. The pressure in the second conduit 150 acts on the counterbalance valve 162 through the pilot line 166 so that fluid can flow away from the jack 30 (upwardly in Fig. 6) through the counterbalance valve 162. Fluid from the pump flows through the pump conduit I I 12 114 to the valve 210, through the valve 210 to the fourth conduit 198, through the fourth conduit 198 to the valve 226, through the valve 226 to the second conduit 150, through the second conduit 150 to the counterbalance valve 174, through the counterbalance valve 174 via the check valve 182, and through the remainder of the second conduit 150 to the chamber 74 (the rod end) of the jack 30. From the chamber 70 (the bore end) of the jack fluid flows through the first conduit 138, through the so 0 6 *4w .4 counterbalance valve 162, through the remainder of the first conduit 138 to the valve 210, through the valve 210 to the return conduit 126, and through the return conduit 126 to the fluid

S

source.

:a"During the STATIONARY mode (not illustrated), the valve 210 is in its third mode so that the end 122 of the pump conduit 114 is blocked and the ends 142 and 206 of the first and fourth conduits 138 and 198 communicate with the fluid source.

Consequently, neither of the first and fourth conduits 138 and 198 is pressurized, so that neither of the counterbalance valves 162 and 174 is opened to allow fluid flow away from the jack This effectively locks the jack 30 in position.

The "raise" cycle of the auto level system 26 is started when the drill operator engages an "auto level raise" control (not shown). At this point, the PLC energizes the solenoids 218 and 238 to place the valves 210 and 230 of the three sub-circuits in their first modes, so that the sub-circuits all operate in i i ~llli i' i I 13 their AUTO LEVEL RAISE WITH REGEN modes. When a jack makes ground contact, the pressure increase in the first conduit 138 causes the pressure switch 148 to signal the PLC, at which time the PLC de-energizes the solenoid 238 to switch the valve 230 to its second mode and thereby switch the sub-circuit to the AUTO LEVEL RAISE WITHOUT REGEN mode. Once all of the jacks have made ground contact, the PLC operates the sub-circuits in the AUTO LEVEL RAISE WITHOUT REGEN modes as necessary to raise the low part of the blasthole drill 10 to the level position. Once the drill 10 is level, the PLC de-energizes all solenoids to place the sub-circuits in their STATIONARY modes.

The "lower" cycle of the automatic leveling system 26 is also initiated by the drill operator. The PLC energizes the solenoids 214 of the sub-circuits to place the sub-circuits in their AUTO LEVEL LOWER modes. As explained above, the AUTO LEVEL LOWER modes operate without the regeneration circuit.

Various features of the invention are set forth in the following claims.

Claims (14)

1. An automatic leveling system for a blasthole drill or the like, said system comprising a jack including a cylinder, and a piston dividing said cylinder into first and second chambers, a pump having an outlet, a fluid source, a first conduit having one end communicable with said pump outlet and having an opposite end communicating with said first chamber, a second conduit having one end communicating with said second chamber and having an opposite end communicable with said S fluid source for returning fluid from said second chamber to said fluid source, and a regeneration valve for selectively diverting fluid from said second conduit to said first conduit when fluid from said pump is being su.,±ied to said first chamber via said first conduit. II 15

2. A system as set forth in Claim 1 and further comprising a third conduit having one end communicating with said valve and having an opposite end communicating with said first conduit between said pump outlet and said first chamber, wherein said valve is selectively operable between a first mode wherein said valve connects said opposite end of said second conduit to said one end of said third conduit, and a second mode wherein S. said valve connects said opposite end of said second conduit to said fluid source.

3. A system as set forth in Claim 2 wherein said valve is normally in said second mode and switches to said first mode when a pilot pressure is applied to said valve, and wherein said system further comprises a control valve selectively S" operable to apply a pilot pressure to said regeneration valve.

4. A system as set forth in Claim 3 wherein said control valve is selectively operable between a first mode in which a pilot pressure is applied to said regeneration valve and a second mode in which a pilot pressure is not applied to said regeneration valve, and wherein said control valve is normally in said second mode and is selectively switched to said first mode by a solenoid. C I 16 A system as set forth in Claim 2 and further comprising a fourth conduit having one end communicating with said regeneration valve and having an opposite end, wherein said regeneration valve connects said opposite end of said second conduit to said one end of said fourth conduit when said regeneration valve is in said second mode, and wherein said system further comprises a pump conduit having one end communicating with said pump outlet and having an opposite end, a S. return conduit having one end communicating with said fluid .0 source and having an opposite end, and a raise/lower valve selectively operable between a first mode wherein said opposite end of said pump conduit communicates with said one end of said first conduit and said opposite end of sa 4 d return conduit communicates with said opposite end of said fourth conduit, and a second mode wherein said opposite end of said pump conduit communicates with said opposite end of said fourth conduit and said opposite end of said return conduit communicates with said one end of said first conduit in said second mode.

6. A system as set forth in Claim 1 wherein said first conduit has therein a counterbalance valve allowing fluid flow in the direction away from said first chamber only when a pilot pressure from said second conduit is applied to said counterbalance valve. 17

7. A system as set forth in Claim 6 wherein said second conduit has therein a counterbalance valve allowing fluid flow in the direction away from said second chamber only when a pilot pressure from said first conduit is applied to said counterbalance valve.

8. A system as set forth in Claim 1 and further comprising a piston rod which is connected to said piston and which extends through said second chamber. a a *~e mo o• ft a. S.Q ft 18

9. An automatic leveling system for a blasthole drill or the like, said system comprising a jack including a cylinder, and a piston dividing said cylinder into first and second chambers, a pump having an outlet, a fluid source, a first conduit having one end communicable with said pump outlet and having an opposite end communicating with said first chamber, i0 a second conduit having one end communicating with said second chamber and having an opposite end communicable with said fluid source for returning fluid from said second chamber to said fluid source, and a regeneration valve for alternatively and selectively connecting said opposite end of said second conduit to either said first conduit or said fluid source. 19 A system as set forth in Claim 9 and further comprising a third conduit having one end communicating with said valve and having an opposite end communicating with said first conduit between said pump outlet and said first chamber, wherein said valve is selectively operable between a first mode wherein said valve connects said opposite end of said second conduit to said one end of said third conduit, and a second mode wherein said valve connects said opposite end of said second conduit to said fluid source. 9e80

11. A system as set forth in Claim 10 wherein said valve is normally in said second mode and switches to said first we' mode when a pilot pressure is applied to said valve, and wherein said system further comprises a control valve selectively S" operable to apply a pilot pressure to said regeneration valve.

12. A system as set forth in Claim 11 wherein said control valve is selectively operable between a first mode in which a pilot pressure is applied to said regeneration valve and a second mode in which a pilot pressure is not applied to said regeneration valve, and wherein said control valve is normally in said second mode and is selectively switched to said first mode by a solenoid. 20

13. A system as-set forth in Claim 10 and further comprising a fourth conduit having one end communicating with said regeneration valve and having an opposite end, wherein said regeneration valve connects said opposite end of said second conduit to said one end of said fourth conduit when said regeneration valve is in said second mode, and wherein said system further comprises a pump conduit having one end communicating with said pump outlet and having an opposite end, a return conduit having one end communicating with said fluid source and having an opposite end, and a raise/lower valve selectively operable between a first mode wherein said opposite end of said pump conduit communicates with said one end of said first conduit and said opposite end of said return conduit communicates with said opposite end of said fourth conduit, and a second mode wherein said opposite end of said pump conduit S communicates with said opposite end of said fourth conduit and said opposite end of said return conduit communicates with said one end of said first conduit in said second mode.

14. A system as set forth in Claim 9 wherein said first conduit has therein a counterbalance valve allowing fluid flow in the direction away from said first chamber only when a pilot pressure from said second conduit is applied to said counterbalance valve. 21 A system as set forth in Claim 14 wherein said second conduit has therein a counterbalance valve allowing fluid flow in the direction away from said second chamber only when a pilot pressure from said first conduit is applied to said counterbalance valve.

16. A system as set forth in Claim 9 and further comprising a piston rod which is connected to said piston and *e which extends through said second chamber. 9.9 S S

22- 17. An automatic leveling system for a blasthole drill or the like, said system comprising a jack including a cylinder, a piston dividing said cylinder into first and second chambers, and a piston rod which is connected to said piston and which extends through said second chamber, a pump having an outlet, a fluid source, a first conduit having one end and having an opposite end communicating with said first chamber, a second conduit having one end communicating with said second chamber and h--ing an opposite end, a third conduit having one end and having an opposite end communicating with said first conduit between said one end and said opposite end of said first conduit, a fourth conduit having one end and an opposite end, a pump conduit having one end communicating with said pump outlet and having an opposite end, a return conduit having one end communicating with said fluid source and having an opposite end, a raise/lower valve selectively operable between a first mode wherein said opposite end of said pump conduit communicates with said one end of said first conduit and said opposite end of said return conduit communicates with said opposite end of said fourth conduit, and a second mode wherein 0* 0 0* C 28 April 1998 I .4 23 said opposite end of said pump conduit communicates with said opposite end of said fourth conduit and said opposite end of &-id return conduit communicates with said one end of said first conduit in said second mode, and a regeneration valve selectively operable between a first mode wherein said valve connects said opposite end of said second conduit to said one end of said third conduit, and a second mode wherein said valve connects said opposite end of said second conduit to said one end of said fourth conduit. 10 18. A system as set forth in Claim 17 wherein said S regeneration valve is normally in said second mode and switches S to said first riode when a pilot pressure is applied to said S regeneration valve, and wherein said system further comprises a control valve selectively operable between a first mode in which a pilot pressure is applied to said regeneration valve and a second mode in which a pilot pressure is not applied to said regeneration valve, and wherein said control valve is normally in said second mode and is selectively switched to said first mode by a solenoid. -24- 19. A system as set forth in Claim 18 wherein said first conduit has therein a counterbalance valve allowing fluid flow in the direction away from said first chamber only when a pilot pressure from said second conduit is applied to said counterbalance valve, and wherein said second conduit has therein a counterbalance valve allowing fluid flow in the direction away from said second chamber only when a pilot pressure from said first conduit is applied to said counterbalance valve. An automatic levelling system substantially as hereinbefore described with reference to the accompanying figures. DATED: 27 April 1998 CARTER SMITH BEADLE Patent Attorneys for the Applicant: HARNISCHFEGER CORPORATION S S. S S S o• 0 RNM:GM:#17453,RSI 27 April 1998 I: ABSTRACT An automatic leveling system (26) for a blasthole drill (10) or the like the system comprising a jack (30) including a cylinder and a piston (62) dividing the cylinder into first (70) and second (74) chambers, a pump (90) having an outlet a fluid source a first conduit (138) having one end (142) communicable with the pump outlet (98) and having an opposite end (146) communicating with the first chamber a second conduit (150) having one end (154) communicating with the second chamber (74) and having an opposite end (158) communicable with the fluid source for returning fluid from the second chamber (74) to the fluid source and a regeneration valve (222) for selectively diverting fluid from the second conduit (150) to the first conduit (138) when fluid from the pump (90) is being supplied to the first chamber (70) via the first conduit (138). t* **V *o *oo 0' *P Vo TJHJL:#17453 9 March 1995 i I