US5101907A — Differential actuating system for downhole tools

Claim 1

Independent Claim 170 words

A downhole tool apparatus for use in a well having a well bore and a tubing string suspended within said well bore so that a well annulus is defined between said well bore and said tubing string, said apparatus comprising: a power piston having first and second sides; and operating valve means having a first position for selectively communicating annulus pressure from said well annulus with said first side of said power piston and simultaneously communicating said second side of said power piston with a zone of said well isolated from said annulus pressure so that a pressure differential between said well annulus and said zone moves said power piston in a first direction, and having a second position for subsequently communicating said annulus pressure with said second side of said power piston and simultaneously communicating the first side of said power piston with said zone so that said pressure differential between said well annulus and said zone moves said power piston in a second direction opposite said first direction.

Claim 2

Dependent Claim 170 words

A downhole tool apparatus for use in a well having a well bore and a tubing string suspended within said well bore so that a well annulus is defined between said well bore and said tubing string, said apparatus comprising: a power piston having first and second sides; and operating valve means having a first position for selectively communicating annulus pressure from said well annulus with said first side of said power piston and simultaneously communicating said second side of said power piston with a zone of said well isolated from said annulus pressure so that a pressure differential between said well annulus and said zone moves said power piston in a first direction, and having a second position for subsequently communicating said annulus pressure with said second side of said power piston and simultaneously communicating the first side of said power piston with said zone so that said pressure differential between said well annulus and said zone moves said power piston in a second direction opposite said first direction.

Claim 3

Dependent Claim 20 words

The apparatus of claim 1, wherein: said operating valve means is endlessly cyclable between its said first and second positions.

Claim 4

Dependent Claim 19 words

The apparatus of claim 1, wherein: said zone of said well is an interior zone of said tubing string.

Claim 5

Dependent Claim 22 words

The apparatus of claim 3, wherein: said interior zone of said tubing string is communicated with a rat hole of said well.

Claim 6

Dependent Claim 22 words

The apparatus of claim 3, wherein: said interior zone of said tubing string is isolated from a rat hole of said well.

Claim 7

Dependent Claim 20 words

The apparatus of claim 1, wherein: said zone of said well is communicated with a rat hole of said well.

Claim 8

Dependent Claim 70 words

The apparatus of claim 1, said well including a packer sealing said annulus between said tubing string and said well bore to separate said well annulus into an upper well annulus above said packer and a lower well annulus below said packer, wherein: said annulus pressure is the pressure of said upper well annulus above said packer; and said zone of said well is communicated with said lower well annulus.

Claim 9

Dependent Claim 17 words

The apparatus of claim 1, wherein: said annulus pressure is greater than a pressure in said zone.

Claim 10

Dependent Claim 57 words

The apparatus of claim 1, further comprising: isolation means for providing fluid pressure communication between said operating valve means and each of said well annulus and said zone of said well, while isolating said operating valve means and said power piston from contact with well fluids contained in said well annulus and said zone of said well.

Claim 11

Dependent Claim 50 words

The apparatus of claim 9, wherein: said isolation means is further characterized as a means for providing endless fluid pressure communication between said operating valve means and both said well annulus and said zone of said well and for thereby permitting an unlimited number of movements of said power piston.

Claim 12

Dependent Claim 166 words

The apparatus of claim 9, wherein said isolation means comprises: a first isolation chamber having a first isolation piston reciprocably disposed therein and dividing said first isolation chamber into a first tool side chamber portion and a first well side chamber portion, said first tool side chamber portion being in open flow communication with said operating valve means; a second isolation chamber having a second isolation piston reciprocably disposed therein and dividing said second isolation chamber into a second tool side chamber portion and a second well side chamber portion, said second tool side chamber portion being in open flow communication with said operating valve means; and reversing valve means for alternatively communicating said well annulus with one of said first and second well side chamber portions while simultaneously communicating said zone of said well with the other of said first and second well side chamber portions, so that well fluids from said well annulus can flow into and out of said well side chamber portions.

Claim 13

Dependent Claim 34 words

The apparatus of claim 11, further comprising: actuating means, interconnecting said power piston and said reversing valve means, for changing a position of said reversing valve means upon each stroke of said power piston.

Claim 14

Dependent Claim 65 words

The apparatus of claim 12, further comprising: time delay means for delaying communication to said power piston of pressure changes in said first and second isolation chambers; and fluid pressure accumulator means for maintaining a pressure between said power piston and said time delay means, after said reversing valve means begins reversing position for a sufficient time to complete a stroke of said power piston.

Claim 15

Dependent Claim 76 words

The apparatus of claim 1, wherein said operating valve means comprises: a main operating valve means for directly controlling fluid pressure communication between said power piston and each of said well annulus and said zone; a differential pressure actuating piston means, operably associated with said main operating valve means, for moving said main operating valve means; and a pilot valve means for selectively applying a second fluid pressure differential across said differential pressure actuating piston means.

Claim 16

Dependent Claim 39 words

The apparatus of claim 14, further comprising: a low pressure dump chamber defined within said apparatus; and wherein said second fluid pressure differential is the differential between said annulus pressure and the pressure in said low pressure dump chamber.

Claim 17

Dependent Claim 51 words

The apparatus of claim 14, further comprising: isolation means for providing fluid pressure communication between said power piston and each of said well annulus and said zone of said well, while isolating said power piston from contact with well fluids contained in said well annulus and said zone of said well.

Claim 18

Dependent Claim 49 words

The apparatus of claim 16, wherein: said isolation means is further characterized as a means for providing endless fluid pressure communication between said power piston and both said well annulus and said zone of said well and for thereby permitting an unlimited number of movements of said power piston.

Claim 19

Dependent Claim 170 words

The apparatus of claim 16, wherein said isolation means comprises: a first isolation chamber having a first isolation piston reciprocably disposed therein and dividing said first isolation chamber into a first tool side chamber portion and a first well side chamber portion, said first tool side chamber portion being in open flow communication with said power piston; a second isolation chamber having a second isolation piston reciprocably disposed therein and dividing said second isolation chamber into a second tool side chamber portion and a second well side chamber portion, said second tool side chamber portion being in open flow communication with said power piston; and wherein said main operating valve means is a means for alternately communicating said well annulus with one of said first and second well side chamber portions while simultaneously communicating said zone of said well with the other of said first and second well side chamber portions, so that well fluids from said well annulus can flow into and out of said well side chamber portions.

Claim 20

Dependent Claim 47 words

The apparatus of claim 14, further comprising: pressure differential supply means for providing fluid pressure communication between said pilot valve means and each of said well annulus and said zone, so that said second fluid pressure differential is the differential between said well annulus and said zone.

Claim 21

Dependent Claim 173 words

A downhole tool apparatus, comprising: a power chamber; first and second isolation chambers; a power transfer element disposed in said power chamber; a first isolation piston slidably disposed in said first isolation chamber and dividing said first isolation chamber into a first tool side chamber portion and a first well side chamber portion; a second isolation piston slidably disposed in said second isolation chamber and dividing said second isolation chamber into a second tool side chamber portion and a second well side chamber portion; conduit means for communicating said first and second tool side chamber portions with said power chamber; and reversing valve means having a first position for communicating a high pressure zone of said well with said first well side chamber portion while simultaneously communicating a low pressure zone of said well with said second well side chamber portion, and having a second position for communicating said high pressure zone with said second well side chamber portion while simultaneously communicating said low pressure zone with said first well side chamber portion.

Claim 22

Dependent Claim 173 words

A downhole tool apparatus, comprising: a power chamber; first and second isolation chambers; a power transfer element disposed in said power chamber; a first isolation piston slidably disposed in said first isolation chamber and dividing said first isolation chamber into a first tool side chamber portion and a first well side chamber portion; a second isolation piston slidably disposed in said second isolation chamber and dividing said second isolation chamber into a second tool side chamber portion and a second well side chamber portion; conduit means for communicating said first and second tool side chamber portions with said power chamber; and reversing valve means having a first position for communicating a high pressure zone of said well with said first well side chamber portion while simultaneously communicating a low pressure zone of said well with said second well side chamber portion, and having a second position for communicating said high pressure zone with said second well side chamber portion while simultaneously communicating said low pressure zone with said first well side chamber portion.

Claim 23

Dependent Claim 89 words

The apparatus of claim 20, wherein: said power transfer element is a power piston slidably disposed in said power chamber and dividing said power chamber into first and second power chamber portions; and said apparatus further includes operating valve means for communicating one of said first and second tool side chamber portions with a selected one of said first and second power chamber portions while simultaneously communicating the other of said first and second tool side chamber portions with the other of said first and second power chamber portions.

Claim 24

Dependent Claim 83 words

The apparatus of claim 21, wherein: said first and second power chamber portions and said first and second tool side chamber portions are filled with clean hydraulic fluid which flows between said power chamber portions and said tool side chamber portions through said operating valve means as said power piston moves in said power chamber; and said isolation pistons provide a means for isolating said clean hydraulic fluid from contamination by well fluids in said high and low pressure zones of said well.

Claim 25

Dependent Claim 53 words

The apparatus of claim 21, further comprising: pressure supply control means, operably associated with said reversing valve means, for switching said reversing valve means alternately between its said first and second positions so that fluid pressure from said high pressure zone of said well is substantially continuously communicated to said operating valve means.

Claim 26

Dependent Claim 38 words

The apparatus of claim 21, further comprising: actuating means, interconnecting said power piston and said reversing valve means, for moving said reversing valve means between its said first and second positions upon each stroke of said power piston.

Claim 27

Dependent Claim 67 words

The apparatus of claim 24, further comprising: time delay means for delaying communication to said power piston of pressure changes in said first and second isolation chambers; and fluid pressure accumulator means for maintaining a pressure between said power piston and said time delay means, after said reversing valve means begins a change in position, for a sufficient time to complete a stroke of said power piston.

Claim 28

Dependent Claim 80 words

The apparatus of claim 21, further comprising: said operating valve means having a fixed high pressure inlet from said isolation chambers and a fixed low pressure outlet to said isolation chambers; high pressure shuttle check valve means for communicating said fixed high pressure inlet with the one of said isolation chambers which is communicated with said high pressure zone; and low pressure shuttle check valve means for communicating said fixed low pressure outlet with the other of said isolation chambers.

Claim 29

Dependent Claim 30 words

The apparatus of claim 20, further comprising: remote control means for controlling said operating valve means in response to a command signal transmitted from a surface location adjacent said well.

Claim 30

Dependent Claim 32 words

The apparatus of claim 20, further comprising: pressure supply control means, operably associated with said reversing valve means, for switching said reversing valve means alternately between its said first and second positions.

Claim 31

Dependent Claim 37 words

The apparatus of claim 28, wherein: said reversing valve means is an electric solenoid operated reversing valve means; and said pressure supply control means is a means for controlling said electric solenoid of said reversing valve means.

Claim 32

Dependent Claim 85 words

The apparatus of claim 28, wherein: said reversing valve means includes a hydraulic actuator means for moving said reversing valve means between its said first and second positions; and said pressure supply control means includes a first fluid accumulator means for sensing a position of said first isolation piston and for directing pressurized hydraulic fluid to said hydraulic actuator means of said reversing valve means to switch the position of said reversing valve means when said first isolation piston nears an end of its stroke.

Claim 33

Dependent Claim 85 words

The apparatus of claim 20, further comprising: said power chamber having a high pressure inlet and a low pressure outlet; high pressure shuttle check valve means, disposed in said conduit means, for communicating the one of said isolation chambers which is communicated with said high pressure zone with said high pressure inlet of said power chamber; and low pressure shuttle check valve means disposed in said conduit means for communicating the other of said isolation chambers with said low pressure outlet of said power chamber.

Claim 34

Dependent Claim 25 words

The apparatus of claim 31, wherein: said power chamber is further characterized in that said high pressure inlet and said low pressure outlet are fixed.

Claim 35

Dependent Claim 22 words

The apparatus of claim 20, wherein: said power chamber includes a high pressure inlet and a low pressure outlet which are reversible.

Claim 36

Dependent Claim 52 words

The apparatus of claim 20, further comprising: a differential pressure actuating piston means, operably associated with said reversing valve means, for moving said reversing valve means between its said first and second positions; and a pilot valve means for selectively applying a fluid pressure differential across said differential pressure actuating piston means.

Claim 37

Dependent Claim 47 words

The apparatus of claim 34, further comprising: a low pressure dump chamber; and wherein said pilot valve means is further characterized in that said fluid pressure differential is a differential between said high pressure zone of said well and the pressure in said low pressure dump chamber.

Claim 38

Dependent Claim 46 words

The apparatus of claim 34, further comprising: pressure differential supply means for providing fluid pressure communication between said pilot valve means and each of said first and second isolation chambers, so that said fluid pressure differential is the differential between said high and low pressure zones.

Claim 39

Dependent Claim 72 words

The apparatus of claim 36, further comprising: time delay means for delaying communication to said pilot valve means of pressure changes in said first and second isolation chambers; and fluid pressure accumulator means for maintaining a pressure between said pilot valve means and said time delay means, after said reversing valve means begins a change in position, for a sufficient time to complete a stroke of said differential pressure actuating piston means.

Claim 40

Dependent Claim 98 words

The apparatus of claim 36, further comprising: said pilot valve means having a fixed high pressure inlet from said pressure differential supply means and a fixed low pressure outlet to said pressure differential supply means; high pressure shuttle check valve means, disposed in said pressure differential supply means, for communicating said fixed high pressure inlet with the one of said isolation chambers which is communicated with said high pressure zone; and low pressure shuttle check valve means, disposed in said pressure differential supply means, for communicating said fixed low pressure outlet with the other of said isolation chambers.

Claim 41

Dependent Claim 16 words

The apparatus of claim 20, wherein: said power transfer element is a rotating power transfer element.

Claim 42

Dependent Claim 81 words

A downhole tool apparatus, comprising: a housing having a power chamber defined therein, and having power passage means defined in said housing for providing fluid pressure communication between said power chamber and first and second zones of a well; pressure transfer control means for applying a pressure differential between said first and second zones of said well across said power chamber to operate said downhole tool apparatus regardless of which of said first and second zones contains the higher fluid pressure.

Claim 43

Dependent Claim 81 words

A downhole tool apparatus, comprising: a housing having a power chamber defined therein, and having power passage means defined in said housing for providing fluid pressure communication between said power chamber and first and second zones of a well; pressure transfer control means for applying a pressure differential between said first and second zones of said well across said power chamber to operate said downhole tool apparatus regardless of which of said first and second zones contains the higher fluid pressure.

Claim 44

Dependent Claim 47 words

The apparatus of claim 40, further comprising: a power piston slidably disposed in said power chamber; and wherein said pressure transfer control means is further characterized as a means for applying said pressure differential across said power piston repeatedly in alternating directions to repeatedly operate said tool.

Claim 45

Dependent Claim 61 words

A downhole tool apparatus, comprising: a housing having a power chamber defined therein; power passage means for providing fluid pressure communication between said power chamber and first and second zones of a well; and pressure transfer control means for using a pressure differential between said first and second zones of said well as an endless power source to said power chamber.

Claim 46

Dependent Claim 61 words

A downhole tool apparatus, comprising: a housing having a power chamber defined therein; power passage means for providing fluid pressure communication between said power chamber and first and second zones of a well; and pressure transfer control means for using a pressure differential between said first and second zones of said well as an endless power source to said power chamber.

Claim 47

Dependent Claim 42 words

The apparatus of claim 42, further comprising: a power piston slidably disposed in said power chamber; and wherein said pressure transfer control means is further characterized as being a means for moving said power piston through an unlimited number of operating strokes.

Claim 48

Dependent Claim 28 words

The apparatus of claim 42, wherein: said pressure transfer control means is further characterized as being responsive to command signals transmitted from a surface location adjacent said well.

Claim 49

Dependent Claim 17 words

The apparatus of claim 42, further comprising: a rotating power transfer element disposed in said power chamber.

Claim 50

Dependent Claim 80 words

A downhole tool apparatus for use in a well, comprising: a housing having a power chamber defined therein; a power transfer element disposed in said power chamber; and energy conversion means for converting a hydraulic differential pressure potential energy between first and second zones of said well into mechanical kinetic energy of said power transfer element as well fluid flows from said first zone of said well through said downhole tool apparatus and into said second zone of said well.

Claim 51

Dependent Claim 80 words

A downhole tool apparatus for use in a well, comprising: a housing having a power chamber defined therein; a power transfer element disposed in said power chamber; and energy conversion means for converting a hydraulic differential pressure potential energy between first and second zones of said well into mechanical kinetic energy of said power transfer element as well fluid flows from said first zone of said well through said downhole tool apparatus and into said second zone of said well.

Claim 52

Dependent Claim 61 words

The apparatus of claim 46, wherein: said power transfer element is a power piston reciprocable disposed in said power chamber; and said energy conversion means is further characterized in that said well fluid flows through said apparatus simultaneous with movement of said power piston and at a rate proportional to a rate of displacement of volume by said moving power piston.

Claim 53

Dependent Claim 39 words

The apparatus of claim 47, wherein: said energy conversion means is further characterized as a means for temporarily retaining in said downhole tool apparatus all well fluid flowing therethrough during a plurality of operating strokes of said power piston.

Claim 54

Dependent Claim 27 words

The apparatus of claim 46, further comprising: isolation means for isolating said power transfer element from contact with said well fluid flowing through said downhole tool apparatus.

Claim 55

Dependent Claim 97 words

The apparatus of claim 46, wherein: said power transfer element is a power piston reciprocably disposed in said power chamber; and said energy conversion means further includes: passage means, defined in said housing, for communicating said pressure differential with said power piston; and operating valve means for intermittently reversing a direction of said pressure differential across said power piston and for flowing a volume of well fluid from said first zone into said downhole tool to displace said power piston while simultaneously displacing an equal volume of well fluid from said downhole tool into said second zone.

Claim 56

Dependent Claim 21 words

The apparatus of claim 46, wherein: said power transfer element is a rotating power transfer element disposed in said power chamber.

Claim 57

Independent Claim 76 words

A method of moving a power transfer element of a downhole tool in a well, comprising: (a) isolating first and second well zones from each other; (b) flowing well fluid from said first zone through said downhole tool into said second zone; and (c) converting a hydraulic differential pressure potential energy between said first and second well zones into mechanical kinetic energy of said power transfer element as said well fluid flows through said downhole tool.

Claim 58

Independent Claim 76 words

A method of moving a power transfer element of a downhole tool in a well, comprising: (a) isolating first and second well zones from each other; (b) flowing well fluid from said first zone through said downhole tool into said second zone; and (c) converting a hydraulic differential pressure potential energy between said first and second well zones into mechanical kinetic energy of said power transfer element as said well fluid flows through said downhole tool.

Claim 59

Dependent Claim 56 words

The method of claim 52, wherein: said step (c) is further characterized in that said power transfer element is a reciprocable power piston and said well fluid flows through said downhole tool simultaneous with movement of said power piston and at a rate proportional to a rate of displacement of volume by said moving power piston.

Claim 60

Dependent Claim 39 words

The method of claim 53, wherein: said step (c) is further characterized in that all well fluid flowing through said downhole tool is temporarily retained in said downhole tool during a plurality of operating strokes of said power piston.

Claim 61

Dependent Claim 18 words

The method of claim 52, further comprising: isolating said power transfer element from contact with said well fluid.

Claim 62

Dependent Claim 80 words

The method of claim 55, wherein said steps (b) and (c) further comprise: communicating said pressure differential with said power transfer element, said power transfer element being a power piston; and intermittently reversing a direction of said pressure differential across said power piston and flowing a volume of well fluid from said first zone into said downhole tool to displace said power piston while simultaneously displacing an equal volume of well fluid from said downhole tool into said second zone.

Claim 63

Dependent Claim 38 words

The method of claim 52, wherein: said step (a) is further characterized in that said first zone is a well annulus and said second zone is a tubing string bore communicated with a rat hole of said well.

Claim 64

Dependent Claim 24 words

The method of claim 52, wherein: said step (c) is further characterized in that said power transfer element is a rotating power transfer element.

Claim 65

Independent Claim 86 words

A method of operating a downhole tool in a well having a well bore and a tubing string suspended within said well bore so that a well annulus is defined between said well bore and said tubing string, said method comprising: (a) isolating said well annulus from another zone of said well; and (b) using a pressure differential between said well annulus and said other zone of said well as an endless power source to move said downhole tool through an unlimited number of operating cycles.

Claim 66

Independent Claim 86 words

A method of operating a downhole tool in a well having a well bore and a tubing string suspended within said well bore so that a well annulus is defined between said well bore and said tubing string, said method comprising: (a) isolating said well annulus from another zone of said well; and (b) using a pressure differential between said well annulus and said other zone of said well as an endless power source to move said downhole tool through an unlimited number of operating cycles.

Claim 67

Dependent Claim 36 words

The method of claim 59, further comprising: (c) applying pressure to said well annulus at a surface location of said well to increase fluid pressure in said well annulus at said downhole tool above hydrostatic pressure.

Claim 68

Dependent Claim 26 words

The method of claim 60, wherein: said step (c) is further characterized as maintaining said fluid pressure in said well annulus at a substantially constant value.

Claim 69

Dependent Claim 40 words

The method of claim 60, wherein: said step (c) is further characterized as intermittently applying a temporary pulse of pressure to said well annulus to temporarily increase fluid pressure in said well annulus at said downhole tool above hydrostatic pressure.

Claim 70

Dependent Claim 32 words

The method of claim 62, wherein: said step (b) is further characterized as using said pressure differential regardless of whether said well annulus or said other zone contains the higher fluid pressure.

Claim 71

Dependent Claim 50 words

The method of claim 59, wherein: said step (a) is further characterized as sealing between said tubing string and said well bore with a packer thereby isolating said well annulus above said packer from a lower zone of said well below said packer, said lower zone being said other zone.

Claim 72

Dependent Claim 116 words

The method of claim 59, wherein: said step (b) is further characterized as: (b)(1) communicating annulus pressure from said well annulus to a first side of a power piston of said downhole tool while simultaneously communicating a second side of said power piston with said other zone of said well so that said pressure differential moves said power piston in a first direction; (b)(2) subsequent to step (b)(1), communicating annulus pressure with said second side of said power piston while simultaneously communicating said first side with said other zone of said well so that said pressure differential moves said power piston in a second direction opposite said first direction; and (b)(3) repeating steps (b)(1) and (b)(2).

Claim 73

Dependent Claim 27 words

The method of claim 65, further comprising: isolating said power piston from contact with well fluids from said well annulus and said other zone of said well.

Claim 74

Dependent Claim 30 words

The method of claim 65, wherein: said step (b) is further characterized in that steps (b)(1) and (b)(2) are performed in response to command signals transmitted from a surface location.

Claim 75

Dependent Claim 34 words

The method of claim 59, wherein: said step (b) is further characterized as using said pressure differential as an endless source to rotate a rotatable power transfer element through an unlimited number of revolutions.

Claim 76

Dependent Claim 114 words

A position sensing apparatus for sensing a position of a structure relative to a base, comprising: displacement means for displacing hydraulic fluid as said structure moves from a first position to a second position relative to said base; a hydraulic accumulator means including an accumulator chamber for accumulating an increasing volume of said hydraulic fluid from said displacement means at a pressure increasing in relation to said increasing volume; and dump value means, in fluid flow communication with said accumulator chamber for discharging at least a portion of said volume of hydraulic fluid into a discharge conduit when said pressure of said volume of hydraulic fluid in said accumulator chamber reaches a predetermined level.

Claim 77

Dependent Claim 114 words

A position sensing apparatus for sensing a position of a structure relative to a base, comprising: displacement means for displacing hydraulic fluid as said structure moves from a first position to a second position relative to said base; a hydraulic accumulator means including an accumulator chamber for accumulating an increasing volume of said hydraulic fluid from said displacement means at a pressure increasing in relation to said increasing volume; and dump value means, in fluid flow communication with said accumulator chamber for discharging at least a portion of said volume of hydraulic fluid into a discharge conduit when said pressure of said volume of hydraulic fluid in said accumulator chamber reaches a predetermined level.

Claim 78

Dependent Claim 56 words

The apparatus of claim 69, wherein said structure is an isolation piston for separating two fluid chamber portions while transferring pressure therebetween, said apparatus further comprising: hydraulically actuated reversing valve means, operatively responsive to said discharging of hydraulic fluid from said dump valve means, for reversing the direction of a pressure differential across said isolation piston.

Claim 79

Dependent Claim 39 words

The apparatus of claim 69, further comprising: return means for returning said discharge portion of said hydraulic fluid to said displacement means as said structure moves from said second position back to said first position relative to said base.

Claim 80

Dependent Claim 47 words

The apparatus of claim 71, wherein: said return means includes a return conduit between said discharge conduit and said displacement means, and a check valve means in said return conduit for allowing flow therethrough toward said displacement means and for preventing flow therethrough from said displacement means.

Claim 81

Dependent Claim 155 words

The apparatus of claim 69, wherein said dump valve means comprises: a two stage dump piston having first and second differential areas defined thereon, said first area being in continuous communication with said accumulator chamber; pilot valve means, defined on said dump piston and having a closed position wherein said second differential area of said dump piston is isolated from said accumulator chamber and an open position wherein said second differential area is communicated with said accumulator chamber; and resilient biasing means for biasing said dump piston toward said accumulator chamber, said biasing means having a spring rate such that said pilot valve means moves to its said open position when said pressure in said accumulator chamber reaches said predetermined level and said spring rate further being such that upon opening of said pilot valve means said dump piston is moved to a fully open position thereof communicating said accumulator chamber with said discharge conduit.

Claim 82

Dependent Claim 49 words

The apparatus of claim 69, wherein: said accumulator means includes an accumulator piston slidably disposed in said accumulator chamber, and a biasing spring means for biasing said accumulator piston against said volume of hydraulic fluid with a force that increases relative to the compression of said biasing spring means.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1995-04-07	1995-10-07	1996-04-07	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1999-04-07	1999-10-07	2000-04-07	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2003-04-07	2003-10-07	2004-04-07	$7700.00	Window Closed / Lapsed

Differential actuating system for downhole tools

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