AU779463B2 - Actuators for borehole plugs - Google Patents

Description

1'.

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 TROUPERDALE PTY LTD

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "ACTUATORS FOR BOREHOLE PLUGS" The following statement is a full description of this invention, including the best method of performing it known to us: 1Q ACTUATORS FOR BOREHOLE PLUGS This invention is concerned with improvements in actuators for inflatable borehole plugs.

An inflatable borehole plug generally is used in the mining industry to create a "deck" within a borehole to distribute explosive charges within the borehole to avoid the necessity to completely fill the borehole with an explosive composition such as ANFO or an emulsion explosive.

An early type of inflatable borehole plug comprised a resilient S. 10 bladder having a hollow injection nozzle tube piercing the wall thereof. The free end of the nozzle tube was connected to an air hose in turn connected to a compressor. After lowering the bladder to a desired depth by the air hose, the bladder was inflated and the nozzle withdrawn leaving the resilient bladder wall to seal the nozzle 15 aperture by resilient contraction. Generally these devices were found to be quite unreliable.

Inflatable borehole plugs usually comprise a sealed gas tight flexible bag containing a source of pressurized fluid which source, when actuated has a time delay property to enable the flexible bag to be lowered into a borehole to a predetermined depth before expanding against the borehole wall to form a deck.

Typically the source of pressurized fluid comprises an aerosol can with a conventional valve stem and a mechanical actuator which, 2 when actuated holds the valve in an open position to discharge the entire contents of can in a manner similnr tn inscrtiride "hnmhe" n r other aerosol fumigants.

The aerosol can contains a quantity of non-expansive liquid usually water, and a quantity of expansive propellant such as a hydrocarbon or halohydrocarbon which remain in separate phases with the water at the bottom of the can and the propellant in a gas/liquid space thereabove.

A tube extends from the interior inlet port of the valve to the 10 base of the aerosol can and when actuated water is discharged first and when substantially all of the water volume is discharged, the propellant gas is then discharged. In this manner, the water acts as a time delay fluid enabling the inflatable borehole plug to be lowered to a predetermined depth in a borehole before the propellant gas enters 15 the flexible bag body of the plug to expand the body against the borehole wall.

The period of time delay can range from as low as 5 seconds to as much as 5 minutes and is influenced by the volume of water in the aerosol can and/or the diameter of the discharge orifice in the valve and/or actuating cap.

Prior art borehole plug systems and particularly inflatable borehole plug systems are described in Australian Patent 656051.

While generally effective for their intended purpose, the 3 inflatable borehole plugs of Australian Patent 656051 suffer a number oZ practical disadvan which nriLe from tho recinn anrd nnortinn 01 IUI J V III r- of the inflation system employed therein.

The pressurized inflating vessel of Australian Patent 656051 comprises a conventional pressurized aerosol-type container and valve assembly with a conventional latchable valve actuating means of the type employed with aerosol pesticide "bombs" and other fumigants.

These latchable valve actuators comprise a fairly rigid plastics e 10 mounting ring which frictionally engages over the valve sealing rim of the aerosol-type container. Extending from an integrally formed hinge too on one side of the mounting ring is a generally circular valve actuating member with an integrally formed extension opposite the hinge. A latch member extends from an underside of the extension and is 15 engagable with an inwardly directed abutment on the mounting ring.

In the centre of the valve actuating member at its upper side is an upstanding nozzle with a fine orifice. On the lower side of the valve actuating member is a tubular orifice which, in use, locates over the valve stem of an aerosol-type container to direct the pressurized fluid from the container to atmosphere via the fine nozzle orifice, the interior wall of the tubular orifice has a downwardly divergent taper to form a fluid seal with the valve stem when the latchable actuator is actuated.

Our co-pending Australian Patent Application 10114/00, the disclosure of which is incorporated herein by referencr. dpals with improvements in inflatable borehole plugs and describes a single phase expansive fluid with controllable expansion delay. The single phase, dual purpose fluid comprises a mixture of dimethyl ether, water and ethanol wherein the dimethyl ether is soluble in water and initially acts as a delay fluid whilst soluble but later acts as an expansive fluid as it comes out of solution at ambient temperatures and pressures.

10 The inflatable bladder or bag is preferably a tough flexible film which is capable of withstanding relatively high internal gas pressure but otherwise is resistant to puncture or tearing in a borehole.

Typically the bladders or bags are formed by a heat welding process from a polyethylene, polypropylene, nylon film or a coextrusion such 15 as nylon/surlyn or polyethylene/nylon/polyethylene to achieve toughness with low gas permeability.

Preferably the inflatable bladder is formed from PET 9 (polyethylene terephthalate) film alone or in coextrusion or laminate with one or more other polymer films.

For added durability, the inflatable bladder or bag may be loosely located in a sleeve or sack formed from a woven or nonwoven synthetic fibre. The outer sleeve or sack provides greater resistance to damage when inserting in a borehole and during inflation of the bladder or bag therein.

In regions where ambient temperatures excped 35°r it has been determined that inflatable borehole plug of the type described in Australian patent 656051 can perform unreliably to the extent that they do not inflate fully. Unreliable decking systems are completely intolerable for mining companies as the failure or partial failure of explosive detonation, even in only a few of a large "string" of boreholes, is a costly and time consuming exercise for miners.

Investigations have revealed that the unreliability of prior art 10 inflatable borehole plugs can be attributed in most cases to a failure of the latchable valve actuator to remain latched whereby the entire contents of the pressurized container are released.

When an inflatable borehole plug with incorporated pressurized container is exposed to elevated ambient temperatures at between 15 say, 35°C to 50'C in direct sunlight, the latchable valve actuator, being composed of thermoplastics material can reach a temperature exceeding ambient air temperatures. Moreover, this can cause the liquid/gaseous contents of the pressurized container to rise to a similar temperature and substantially increase the internal pressure in the container as these prior art systems have comprised a quantity of water as a delay fluid and a gaseous expansive fluid having properties not dissimilar to an ideal gas.

Typically, when these prior art systems are exposed to elevated temperatures prior to actuation, the heated expansible fluid passes from the aerosol container into the flexible hag tinder hinher nrPiiessure and at a greatly increased flow rate than otherwise would occur at lower temperatures. This sudden and high pressure inflation of the bag subjects the welded seams to an impact force often sufficient to tear the seam thus allowing the bag to deflate.

In practice it has been found that after actuating the pressurized container, valve by depressing the latchable valve actuator, thermal deformation of the valve actuating member can 10 cause the latch to become disengaged thereby causing the valve to close long before the entire contents of the pressurized container are released.

In some cases the latch will release before even the delay liquid has been evacuated from the container. In other cases the latch will release when the inflatable chamber of the borehole plug is fully inflated. Either way, a non expansive delay fluid such as water will generally have reached the same temperature as the cap and thus has little or no cooling effect on the valve actuating member to prevent or retard the rate of thermal deformation, particularly as the pressurized fluids are constrained to pass entirely through the fine nozzle orifice in the centre of the valve actuating member.

Another disadvantage of the pressurizing containers of the type described in Australian Patent 656051 is that the use of a hydrocarbon or halohydrocarbon expansive fluid or like expansive Flii;r ;ic that tho ciihctantiIl inr-ra ac in intornal rnntninar nracciira -t elevated temperatures exacerbates the problem of thermal deformation of the valve actuating member leading to premature latch release.

Yet another problem associated with prior art inflatable borehole plug pressurized containers of the aforementioned type is that any contamination in the pressurized fluids can readily cause a blockage in the fine nozzle orifice in the valve actuating member.

10 Such contamination may arise during filling of the containers or by chemical reaction with polymeric container lining materials or container flange sealants.

Whether or not the nozzle blockage causes unlatching of the valve actuator, incomplete inflation of the borehole plug arises.

15 A difficulty with incomplete borehole plug inflation is that it is not possible to determine from ground level whether the plug has fully inflated other than when the pressurized container valve closes before any expansive gas is released into the inflatable plug.

Accordingly, insufficient plug inflation may be discovered only when a deck collapses under the weight of a charge of explosive composition giving rise to a borehole base charge much greater than required.

It is an aim of the present invention to overcome or ameliorate at least one of the problems associated with prior art inflatable 8 borehole plugs.

According to one aspect of the invention there is provided a latchable valve actuator for pressurized fluid containers, said actuator comprising:a body member engagable with an upper portion of a pressurized fluid container; a latchable valve actuator extending from one side of said body member to an opposite side of said body member, said valve actuator having a latch member adjacent a free end thereof, said valve o 10 actuator, being resiliently deformable to enable engagement between said latch member and said body member to retain in an open S. position a valve in fluid communication with the interior of said container whereby, in use, at least portion of the fluid escaping said valve is allowed to come into contact with said valve actuator for 15 cooling thereof by adiabatic expansion of at least one component of said fluid.

Suitably the body member is engagable over a joining flange between a valve cap and a top wall of said container.

The latchable valve actuator may be pivotally coupled to said body member.

Preferably the latchable valve actuator is integrally formed with said body member.

If required, the valve actuator may include a valve locating recess on an underside thereof.

Prefe rha, the valve locating recess is adrlpted to aIniw at lpaq.t portion of the fluid escaping from the valve to come into contact with said valve actuator.

Suitably the valve locating recess includes a generally cylindrical wall having one or more fluid apertures therein.

If required the valve actuator may include a fluid orifice extending from an upper side thereof to said valve locating recess.

Preferably an upper part of said body member forms a fluid 10 retaining wall between said joining flange and said valve actuator.

*The valve actuator may include a lever extension.

:According to another aspect of the invention there is provided an inflatable borehole plug incorporating a container of expansive ~fluid, said container including a latchable valve actuator according to 15 a first aspect of the invention.

According to yet another aspect of the invention there is provided a method of locating an inflatable borehole plug in a borehole wherein a latchable valve actuator of a container of expansive fluid is cooled by release of expansive fluid to reduce thermal deformation of said valve actuator in a latched position.

In order that the invention may be more readily understood and put into practical effect, reference will now be made to a preferred embodiment illustrated in the accompanying drawings in which:- FIG 1 shows a part cross sectional view of a valve actuation eomh! fittel tn n cnntniner nf epYnqnixP flidrl FIG 2 shows a top plan view of the actuator of FIG 1.

FIG 3 shows an enlarged part cross-sectional view of the engagement between the valve stem of a container of expansive fluid and the valve actuator of FIG 1.

FIG 4 shows a graph of fluid pressure vs temperature of the fluid in a pressurised container.

In FIG 1 the valve actuator 1 has a circular body 2 which :10 frictionally engages over the rolled flange joint 3 between a valve cap 4 and a pressurized fluid container 5, the valve cap 4 incorporating valve 6 and valve stem 7 being of the type normally employed in aerosol insecticide sprays or the like. A flexible tube 8 connects the inlet port of the valve 6 with a region adjacent the base (not shown) of the container 5. Preferably the container is a three piece steel container rather than a one piece drawn aluminium container with an integrally formed base as prior art aluminium containers under extreme ambient conditions have been known to burst. Three piece steel containers can expand in the region of the top cap to accommodate excess internal pressure.

Body 2 includes a tapered entry portion 9 to enable fitment over the flange joint 3 and a small shouldered abutment 10 which engages on the free edge 11 of the flange portion of valve cap 4.

11 An upstanding part circular wall portion 12 has connected at nne side. thereof a !atchnhe vinlle acituatnr 1-1 wAthich inrludesic n central nozzle aperture 14, a latch member 15 and a lever extension 16. As shown the valve actuator 13 is in an unlatched position.

On the underside of valve actuator 13 is a valve stem locating recess 17 in the form of a cylindrical wall 18 having an upwardly convergent inner wall 19. Wall 18 includes opposed slots 20, the purpose of which will be described later.

An arcuate projection 21 extend upwardly from lever extension S. 10 16 to assist in obtaining finger grip through a multi-walled inflatable borehole plug.

In use, an operator presses lever extension downwardly by finger or thumb pressure until latch member 15 engages under shouldered abutment 22 formed on body 2.

15 When latch member 15 is engaged on body 2, valve 6 is retained in an open position to release the expansive fluid within container 5, which fluid preferably includes at least one component 4 capable of undergoing adiabatic expansion. Such a fluid may, for example, comprise a single phase mixture of dimethyl ether and water in the ratio of from 10:1 to 1:10 with about 6% or more of ethanol and, if required, an anti-corrosive additive to minimise corrosion of container When valve 6 is latched in an open position, the single phase 12 liquid mixture, which is pressurized primarily by the partial pressure of the dimethyl ether, is driven un tubeh 8 via valve 6 and thence to exit valve stem 7 in the valve stem locating recess 17.

Part of the liquid exits via nozzle orifice 14 directly into the interior of the inflatable borehole plug, and part exits via slots 20 into the interior space defined by the annular well 3 surrounding valve 6 and upstanding wall 12 of valve actuator 1.

Once the expansive fluid is exposed to ambient pressure, the dimethyl ether component comes out of solution and begins to boil at 10 ambient temperature and pressure and the gaseous phase undergoes adiabatic expansion.

As described in co-pending Australian patent application 10114/00, inflatable borehole plugs comprise a single or multi-walled plastics bag which may comprise a single compartment or two or 15 more compartments into which the expansive fluid may expand.

For the present invention a single compartment plastics bag, preferably of co-extruded nylon or a single film PET is effective. In a non-inflated state the bag is of a flat rectangular configuration with the pressurized fluid container located adjacent one edge. The bag is folded and/or rolled into a compact elongate cylindrical shape not dissimilar to a rolled newspaper and is retained in this cylindrical state by resiliently deformable members such as elastic rubber bands.

As the single phase fluid mixture emerges from the pressurized 13 container it flows into the generally confined space between adjacent layers of plastics material forming the wall of the bag and, as the cylindrical package is suspended in a bore hole in a vertical state, the fluid flows towards the bottom of the bag in the confined space.

When initially released, the partial pressure of the dissolved gaseous element in the fluid mixture is at its greatest as the concentration of the gaseous element in the fluid mixture is greatest.

Initially, with a relatively small volume of fluid in the bag, the surface area of the fluid is minimised in the confined space of the 10 folded bag and this contributes to an initially reduced rate of escape of the gaseous component from the liquid mixture.

As the bag expands, the pool of liquid in the bottom thereof develops a larger surface area to permit a more rapid rate of escape of the gaseous component into the hollow interior of the bag.

15 Depending upon the ratio of gaseous solute to liquid solvent in the mixture and the overall volume thereof, the borehole plug, when fully expanded permits an equilibrium state in the residual solute/solvent mixture to maintain a constant internal pressure in the bag.

Any suitable liquid mixture of at least two components storable in a pressurized container in a single liquid phase would be suitable for the invention.

The criteria for such mixtures are that it must form a single 14 phase liquid in a pressure range of from 10kPa to 350 kPa, the Cc. Omnnnent max/ h i\ q hnilinn noint in the ranae of from 1000C to 100C at ambient pressure.

Accordingly, the expansive component would normally be in a gaseous state at ambient temperature and pressure conditions and would be soluble or at least miscible in the delay fluid when stored under pressure in the pressurized container.

The solute gas would thus possess a relatively high absorption coefficient for the solvent and preferably would obey Raoult's Law for S: 10 ideal systems. Depending upon the nature of the system however and other factors which may affect the rate of escape of the gas from the liquid phase, the system may be selected to exhibit either a positive or negative deviation from the ideal law.

For example, while many hydrocarbons and halohydrocarbons 15 form a liquid phase at relatively low pressures, they are neither soluble or miscible in an inexpensive, non-flammable, non-toxic solvent such as water. A non polar liquid solvent such as a low I viscosity mineral or synthetic oil may be preferable for such hydrocarbon and halohydrocarbon expansive fluids either alone or as a stabilized water in oil or oil in water emulsion.

Similarly for polar gases such as dimethyl ether a polar solvent system comprising a mixture of water and ethanol has been found to be inexpensive but otherwise quite satisfactory.

With a pool of expansive fluid contained in well 3 and with liquid Pxnn.sivP fluid being spraved over the inside surfaces of valve actuator 1, the entire valve actuator is cooled by the adiabatic expansion of the dimethyl ether as it undergoes a phase change from liquid to vapour.

The resultant rapid cooling of the valve actuator retains the integrity of the latching engagement between latch 15 and shouldered abutment 22 by resisting the tendency for thermal deformation in valve actuator 13, which deformation might otherwise allow the latch S: 10 to disengage after a period of time to close valve 6.

A wide range of operating pressures are permitted with o :inflatable borehole plugs and expansive fluids employed therein as the capacity of a plug to form a supportive deck for an explosive charge o:ooo weighing up to 5 tonnes is a function of frictional engagement with 15 the wall of the borehole. Thus a large surface area inflatable bladder with a low internal pressure of say 35kPa may be just as effective as *a smaller bladder with an internal pressure of 150kPa.

~FIG 2 shows a top plan view of the latchable valve actuator of FIG 1.

Latch member 15 is movable between an unlatched position and a latched position by downward pressure on lever extension 16 whereby because of the discontinuity of upstanding wall 12 and the formation of slots 24 between wall 12 and valve actuator 13, 16 actuator 13 undergoes flexure in the region between the inner ends of FIG 3 shows an enlarged part-cross sectional view of an alternative embodiment through X-X in FIG 2. In FIG 3 like reference numerals are employed to describe like features in FIGS 1 and 2.

In FIG 3, the central portion of the valve actuating member 13 has fluid apertures 30 extending radially outwardly from valve stem locating recess 17 to direct expansive fluid issuing from the container (not shown) directly onto the inner surface 31 of the actuating member 13. This ensures more rapid cooling of actuating member 13 to resist disengagement of latching member 15 as a result of thermal deformation of the valve actuating member 13.

Fluid in a liquid state is collected in the well 23 as shown in FIG 1.

Additionally or alternatively, one or more apertures 32 may extend from the inner chamber 33 above valve stem locating recess 17 to direct expansive fluid in a liquid phase on to the upper surface 34 of valve actuating member 13 to provide additional cooling thereof or otherwise to provide a sole source of coolant to the valve actuating member 13.

One or more apertures 32 may extend in a generally horizontal position or in a downwardly inclined fashion shown to direct fluid onto selected surface regions of valve actuating member 13.

17 FIG 4 shows graphically a plot of fluid pressure vs temperature .r....riced cnntaine.r nf delay/expansive fluid combination as earlier described.

This graph illustrates the progressively non-ideal behaviour of the expansive fluid as the temperature of the fluid contents of the container rises to elevated ambient temperatures as may be encountered in certain geographical locations.

It readily will be apparent to a skilled addressee that many modifications and variations may be made to the invention without 10 departing from the spirit and scope thereof.

**For example, the valve actuating member may comprise a barlike member hingedly connected at one end to body 2 and having a latch member depending therefrom for engagement with body 2. The bar-like member may be of metal or a stiffer plastics material than body 2 whereby the valve actuating member is less susceptible to thermal deformation at elevated temperatures.

The valve actuating members of the various aspects of the invention may include stiffening structures such as webs to resist thermal deformation.

Throughout the specification, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

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Claims (19)

1. A latchable valve actuator for pressurized fluid containers, said actuator comprising:- a body member engagable with an upper portion of a pressurized fluid container; a latchable valve actuator extending from one side of said body member to an opposite side of said body member, said valve actuator having a latch member adjacent a free end thereof, said valve actuator, being resiliently deformable to enable engagement between said latch member and said body member to retain in an open position a valve in fluid communication with the interior of said container whereby, in use, at least portion of the fluid escaping said valve is allowed to come into contact with said valve actuator for cooling thereof by adiabatic expansion of at least one component of said fluid.

2. An actuator as claimed in claim 1 wherein the body member is *o engagable over a joining flange between a valve cap and a top wall of said container.

3. An actuator as claimed in claim 1 or claim 2 wherein the latchable valve actuator is pivotally coupled to said body member.

4. An actuator as claimed in any one of claims 1 to 3 wherein the latchable valve actuator is integrallv formed with said hndy member.

An actuator as claimed in any preceding claim including a valve 21 IocatInCrgn, rcef on n i ndenrsrd -n*hro"f IVCI III 1 I l Jl I C4I u UI 8 I1 IU Ur i

6. An actuator as claimed in claim 5 wherein the valve locating recess is adapted to allow at least portion of the fluid escaping from the valve to come into contact with said valve actuator.

7. An actuator as claimed in claim 5 or claim 6 wherein the valve locating recess includes a generally cylindrical wall having one or more fluid apertures therein.

8. An actuator as claimed in any one of claims 5 to 7 including a fluid orifice extending from an upper side thereof to said valve locating recess.

9. An actuator as claimed in any one of claims 2 to 8 wherein an upper part of said body member forms a fluid retaining wall between said joining flange and said valve actuator.

10. An actuator as claimed in any preceding claim including a lever 15 extension.

11. An inflatable borehole plug incorporating a container of expansive fluid, said container including a latchable valve actuator according to any one of claims 1 to

12 An inflatable borehole plug according to claim 12 wherein said container includes an expansion system including an expansive fluid and a delay fluid, said expansive fluid being substa hntia!!y soluble in said delay fluid at a pressure greater than ambient pressure, said expansion system characterised in that said expansive fluid behaves as a non-ideal gas under conditions of elevated temperature and at 22 ambient pressure expands adiabatically.

13. A npiug a s crimed in crlim 11 nr rliim 19 wherein said Peynnsive fluid exhibits a positive deviation from Raoult's Law at elevated temperatures.

14. A plug as claimed in claim 11 or claim 12 wherein said expansive fluid exhibits a negative deviation from Raoult's Law at elevated temperatures.

A method of locating in a borehole an inflatable borehole plug according to any one of claims 11 to 14 wherein said latchable valve actuator of is cooled by release of expansive fluid to reduce deformation of said valve actuator in a latched position.

16. A valve actuator substantially as hereinbefore described with reference to the accompanying drawings.

17. An inflatable borehole plug substantially as hereinbefore described with reference to the accompanying drawings. 15

18. A method of locating an inflatable borehole plug in a bore hole substantially as hereinbefore described with reference to the accompanying drawings.

19. An expansion system for the inflatable borehole plug of any one of claims 11 to 14 substantially as hereinbefore described with reference to the preferred embodiments. o go