Pumps can be used to pump base emulsions, which contain oxidisable salts but are generally not explosive on their own, doped emulsions which are base emulsions containing particulate material, such as ammonium nitrate, which may be explosive in its own right, and emulsion explosives which may be doped but which are base emulsions that have been sensitised by the inclusion of a multitude of small compressible voids. All of these are included within the term "emulsion compositions for explosives", as are base emulsions, doped emulsions and emulsion explosives containing other ingredients.

The pumping of emulsion compositions for explosives is generally the most hazardous activity routinely performed by personnel handling bulk emulsions in this field. The compositions are vulnerable to thermal decomposition at increased temperatures in the pump, for example due to crystallisation of the salts, phase separation and discolouration, and it is generally accepted that a pump which is used for pumping emulsion compositions for explosives can fail safe at temperatures up to about 170°C. Emulsion compositions which are heated to above this temperature are at increased risk of deflagration or explosion. This may lead to the destruction of the pump, with a risk of damage to other plant and equipment in the vicinity of the pump and/or of serious injury to personnel or loss of life particularly if the deflagration or explosion of emulsion composition in the pump leads to the detonation of explosives material external to the pump.

Temperature build-up in pumps capable of pumping emulsion compositions for explosives can arise for a variety of reasons, including dead head pumping, dry running and trapped air compression.

Dead head pumping occurs when the outflow from a pump is blocked. Such a blockage may occur at an outlet from the pump or may occur in a conduit leading from the pump outlet.

During dead head pumping the drive energy supplied to the pump is converted to heat which is absorbed by the material entrapped within the pump.

Dry running occurs when a pump is operating without materials being fed into the pump.

During dry running, friction generated by the pumping mechanism can result in the generation of heat which is not able to be dissipated through the material being pumped. The resultant temperature rise may result in decomposition of any residual material within the pump.

Trapped air compression arises when air in the pump is repeatedly compressed and expanded by the ongoing pumping motion, usually during dead head pumping. Very high temperatures can result from this type of pump failure.

A variety of safety mechanisms have been designed for pumps used in the explosives industry to counter these failure modes. Electronic safety systems have been used based on temperature and pressure sensors, whereby the drive mechanism of the pump is shut off at a critical temperature, pressure and/or flow rate. Whilst these safety mechanisms will alleviate the problem when they are operational, they are expensive to install and maintain and can be readily disabled or bypassed by operators in the field.-Even if they are operational, such sensors may be located in regions of the pump remote from where the highest temperatures and/or pressures may be reached in a particular failure mode, such that the sensors do not accurately measure the relevant criteria.

Most importantly, however, the electronic sensor based safety systems have not proven to be robust and are therefore not suited to many pumping systems for emulsion compositions for explosives, including sled-based mobile pumping systems and other pumping systems used underground. Underground mines present an extremely difficult and demanding working environment so that equipment used there must be simple, robust and reliable.

A number of more robust mechanical fail safe systems for pumps have been proposed, such as in EP-A-0255336 and WO 97/47886 and its US equivalent 5,779,460. These integral fail safe mechanisms involve a remote temperature sensitive connection between a drive shaft and a rotor member in a progressive cavity pump which melts to terminate the drive relationship above a critical temperature. Such mechanisms rely on heat being conducted through the rotor member to the temperature sensitive connection, with the risk that the temperature of the material being pumped or residual material in the pump becomes critical in that time.

Similarly, in GB 1379434, in a mechanical seal device for a rotary pump comprising stationary and rotatable seal rings which engage each other, it is proposed to provide temperature sensitive means spaced from the region of engagement and arranged to become soft at a predetermined temperature to allow the seal rings to separate.

In US 5,318,416 it is proposed to provide for pressure relief in a progressive cavity pump before a critical pressure potential which may result in the explosion of explosive in the pump is reached. This is achieved by providing the stator housing with a weakened area which parts in response to pressure build-up in the stator.

In other proposals, it is suggested that pressure relief or the interruption of drive to a pump or compressor be provided by melting a fusible plug at a critical temperature. For example, in US 5,603,608 the melting of a fusible plug at one end of the rotor of a progressive cavity pump relieves fluid pressure and thereby interrupts drive to the rotor. In SU 1002664, a fusible plug provided in a compression chamber of a piston compressor melts at a critical temperature to

allow pressure relief from the chamber. In SU 981381 the reduced pressure difference in a piston compressor on opposite sides of a fusible plug when it melts actuates a relay which stops the compressor motor. Similarly, in AU 17335/20 pressure relief when a fusible plug in an air compressor melts is used to stop the compressor and signal a warning. In US 1,426,206, melting of a fusible plug adjacent the bearings of a centrifugal pump actuates a release mechanism whereby power supply to the pump motor is interrupted.

As with the safety systems involving electronic sensors, the above proposals involving fusible plugs suffer from the disadvantage that the fusible plug may not be disposed at a location in the pump to quickly sense localised temperature increase in the material being pumped.

It is an object of the invention to alleviate these disadvantages of prior art pumps and proposals.

According to the present invention there is provided a pump comprising a housing defining a working chamber having an inlet and an outlet and a pump member which is relatively movable in the working chamber to displace material worked by the pump through the working chamber from the inlet to the outlet, and wherein at least a working surface of a component of the pump which in use is in contact with material being worked in the working chamber is formed of a material which is rigid at a normal operating temperature of the component but which is fusible at a predetermined temperature greater than the normal operating temperature but no more than about 170°C.

By the present invention, in use the fusible material of-at least the working surface of said component (or of two or more such components) will deform when it is heated to above the predetermined temperature in a failure mode of the pump, and thereby stop or at least reduce the work being performed on the material in the pump and alleviate the build-up of heat. Since the or each said working surface is in contact with the material being worked by the pump, any delay in stopping or reducing the work being performed on the emulsion composition in the

event of a failure of the pump may be alleviated. Furthermore, forming the entire working surface of the one or more components of said fusible material may alleviate the same disadvantages of the previously proposed fusible plugs when overheating of the product being worked in the pump is localised.

The type of component of the working chamber whose working surface at least may be formed of the fusible material will depend upon the kind of pump, but it will be directly involved in the working of the emulsion composition through the working chamber, whether as a fixed or movable component. Thus, the at least one component may for example be selected from the pump displacement member or a component thereof, the pump housing, a valve component of a flow control valve for the emulsion composition, if present, and any combination of two or more of these.

It will be appreciated that the phrase"a material which is rigid at a normal operating temperature of the component"means that the material is sufficiently rigid for the desired work to be performed by the component. The material could in some embodiments have a degree of resilience at the normal operating temperature (usually no more than about 80°C and preferably in the range of about 30 to 50°C).

Preferably the predetermined temperature is substantially below the accepted fail safe temperature of emulsion compositions for explosives of about 170°C, and most preferably the predetermined temperature for the fusible material is no more than about 140°C so as to leave an adequate safety margin.

Advantageously, the entire structure of the at least one component is formed of the fusible material. If only the working surface of the or each said component is formed of the fusible material, the fusible material preferably has a minimum thickness of 5 mm, preferably at least 7 mm, and more preferably at least 10 mm. Advantageously, other parts of said at least one component not formed of the fusible material and/or other components of the pump which are in contact with the material being worked in the working chamber are formed of a robust

engineering material such as stainless steel, optionally lined as discussed below.

The fusible material may be a metallic material such as an alloy as described in the aforementioned prior art, but is preferably a polymeric engineering material having a softening temperature of the predetermined critical temperature. Suitable polymeric materials include acetal, polyethylene, polyethylene copolymers and polyethylene blends. Preferably the fusible material is an ultra high molecular weight polyethylene. One example of such a material is sold under the trade mark TIVAR 1000 by Cadillac Plastics, Australia and has an observed melting range of about 130 to 135°C and a Vicat softening point of about 138 to 140°C.

In one aspect, the pump may be of a kind including a rotor or impeller mounted in a stator or housing for rotation and any of the rotor or impeller and stator or housing is formed of the fusible material at least at the surface thereof.

In a preferred embodiment of this aspect of the invention the pump is a progressive cavity pump in which the rotor comprises a rigid helical rotor member and the stator has a longitudinal cavity therethrough which defines a helical groove. When rotated within the stator cavity, the rotor makes contact with the stator to form a series of cavities which move in an axial direction to form a positive displacement pump. In this embodiment, it is preferable to manufacture the helical rotor member entirely from the fusible material. It has been found that manufacturing the helical rotor member from the fusible material allows the rotor member to be readily manufactured in varying configurations. The ability to redesign the configuration of the rotor member has practical advantage with pumping material of differing viscosities and solids content. Alternatively, the helical rotor member may be lined with the fusible material, in which case the core of the rotor member may be of, for example, stainless steel.

In this embodiment the stator may be formed of a rigid engineering material such as stainless steel. While it is common to line the stator cavity of a progressive cavity pump with a resilient

material such as an elastomer to facilitate the pumping action, the use of a rotor having at least the surface formed of the fusible material may permit the resilient material to be omitted. The resilient material, if present, may form a lining in the working chamber of the stator, or the stator may be formed entirely of the resilient material. One example of a suitable elastomer is rubber. Clearly, the resilient material should not fuse at a temperature up to the predetermined temperature, if at all. Alternatively, the stator could be lined with or formed of the fusible material, but generally this is not as convenient as providing the fusible material as at least part of the rotor member.

In another aspect, the present invention may be applied to a gear pump. A gear pump generally comprises two intermeshing gears which rotate in opposing manner to urge the pumpable material therebetween. In some embodiments of gear pump the vanes of the gears are lobe shaped, in which case the gear pump may be known as a lobe pump. The gears are mounted for rotation within a housing. Generally the gears are manufactured from a rigid material such as steel with a resilient lining such as of rubber or another elastomer, to provide a seal. In one embodiment, therefore, the housing may be lined with or formed from the fusible material.

Alternatively, the gears may be lined with, or manufactured entirely from, the fusible material thereby eliminating the need for a resilient lining on the gears in order to provide the requisite interference fit for the pumping mechanism.

In another aspect, the present invention may apply to a piston pump in which a piston is displaceable in a housing to work the material through a working chamber in the housing. In this embodiment the piston crown member or cup which engages the housing and/or the housing may have at least its working surface formed of the fusible material. Either of these components may be lined with the fusible material, but preferably the piston crown member is formed entirely of the fusible material. The piston crown member may be engaged with a support component of the piston by means of at least one interengaging formation, such as a

rib, in which case, in addition to deformation of the piston crown member and/or housing, the melting of the at least one interengaging formation may cause the piston crown member to disengage the support component and thereby stop or further alleviate work on the material in the working chamber of the pump.

The piston pump may comprise one or more valves for controlling the flow of the material as it is pumped through the working chamber by the piston. Alternatively to or in addition to the piston crown member and/or housing comprising the fusible material, the valve or any of the valves may have at least a working surface formed of the fusible material. Thus, in the event of a pump failure, heating of the or each valve component comprising the fusible material to above the predetermined temperature may result in the valve becoming inoperative so that working of the material in the working chamber becomes ineffective. In a preferred embodiment, the or each valve is a check ball valve and one or both of the ball and valve seat is formed of or lined with the fusible material. Preferably, the ball is formed entirely of the fusible material.

Advantageously, we have found that the use in accordance with the invention of a polymeric fusible material for at least the working surface of a pump displacement member such as a rotor, gear or piston component or of a pump stator or housing may also reduce the friction between the pump displacement member and working chamber contact surfaces. This reduces the energy requirements required to run the pump, reduces torque requirements and reduces the heat generated under normal operating conditions. Such use may also reduce the rate at which the temperature increases in the event of a pumping failure.

Three embodiments of a pump in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic part-sectional representation of a progressive cavity pump according to the invention;

Figure 2 is a sectional view of a piston pump according to the invention; Figure 3 is an enlargement of the circled portion of Figure 2; Figure 4 is an elevational view of a gear pump according to the invention with a housing front cover removed; Figure 5 is a graph of temperature and motor torque output illustrating the results of the test described in Example 1; and Figure 6 is a graph of temperature and time illustrating the results of the test described in Example 2.

Figure 1 shows a two-lobed progressive cavity pump 1 which comprises a housing 2 in which there is disposed a stator base 3 of stainless steel lined with an elastomeric material 4, such as nitrile rubber. The elastomeric lined stator defines a helical groove or working chamber in which a rotor 9 rotates to pump material from an inlet 5 to an outlet 6. A rotational drive motor 7 drives a drive shaft 8 which in turn rotates the rotor. The rotor 9 is formed of a fusible material comprising an ultra high molecular weight polyethylene known as Tivar 1000 developed by Poly Hi Solidur/Menashe Corporation having an observed melting range of 130 -135°C and a maximum continuous operating temperature of about 80°C at which the material is rigid. In normal use, the material being pumped from the inlet to the outlet helps to dissipate any heat build-up between the rotor working surface 10 and the stator lining 4.

In the event of dry running, at least the UHMWPE working surface 10 will heat up and deform as it softens to reduce the frictional contact between the working surface and the elastomeric lining 4. In the event of dead head running, the working surface 10 will deform as it softens with increasing temperature and substantially reduce the energy input from the rotor 8 to the emulsion composition being pumped as the material will be able to pass between the deformed rotor 8 and the stator.

Referring now to Figures 2 and 3, there is shown a piston pump 11 comprising a housing 12 defining a working chamber 14 in which a piston 16 is reciprocally displaceable. The

reciprocating motion is provided by, for example, an air or hydraulic motor (not shown) which drives the piston 16 through a connecting rod 18.

The housing 12 has an inlet housing 20 at an inlet end thereof and an outlet housing 22 at an outlet end thereof. The inlet housing 20 has an inlet portion 24 for connecting the pump to a source of material to be pumped. The outlet housing 22 has an outlet 26 from the working chamber 14 and supports a bearing end member 28 for the piston 16. A packing seal 30 is disposed between the outlet housing 22 and end bearing member 28, and two wear rings 32 are supported by the end bearing member. The end bearing member 28 also supports a lip seal- type scraper ring 34. The fact that the scraper ring 34 is in the form of a lip seal may help to alleviate heat build-up in the piston in the event of dry pumping.

Referring particularly to Figure 3, the piston 16 comprises a piston member 36 connected to a piston rod 38 by threaded fasteners 40 passing through respective tubular spacers 42. The piston member 36 has a piston crown 44 located thereon by means of an annular rib 46 which is held in place by means of a retaining member 48 and the fasteners 40. The piston crown 44 has an annular groove around its outer periphery in which is received a further lip seal scraper ring 50. Again, the lip seal scraper ring may alleviate heat build-up in the piston crown in the event of dry running.

The piston member 36 is annular and defines a valve seat 52 of an outlet check ball valve of which the ball 54 is free to move between the seat and the end of the piston rod 38 and is confined in such movement by the spacers 42.

The inlet housing 20 defines a valve seat 56 of an inlet check ball valve, with the ball 58 of the inlet check ball valve being free to move between the valve seat 56 and a keeper pin 60 and confined in such movement by pins 62.

In use, as the piston 16 is displaced in an output direction, to the right in Figure 2, by the drive motor, material in the working chamber 14 on the output side of the piston closes the outlet

check ball valve and is forced out of the pump through the outlet 26. At the same time, a suction is created on the input side of the piston which, combined with any positive pressure on the material in the inlet 24, draws that material through the open inlet valve. As the piston cycle is completed by displacing the piston to the left in Figure 2, pressure on the material in the working chamber 14 on the input side of the piston forces the ball 58 of the inlet check ball valve to close against the seat 56 and forces the ball 54 of the outlet check ball valve to move away from the seat 52 so that the material moves through the valve seat 52 and between the spacers 42 into the output side of the working chamber.

In order to avoid excessive heat build-up in the event of pump failure particularly due to dead head operation, especially when combined with air or void compression in the working chamber, the piston crown 44 is formed of the ultra high molecular weight polyethylene Tivar 1000. If the temperature of the emulsion composition in the working chamber and of the piston does increase beyond the continuous operating maximum temperature of about 80°C for the Tivar piston crown, the material of the crown begins to soften and deform and will eventually fail as the temperature approaches the melting range of 130-135°C. At this stage work on the emulsion composition in the working chamber 14 may be reduced if the emulsion composition is able to pass between the piston crown and the housing 12. If the material softens sufficiently, the annular rib 46 of the piston crown will deform such that the piston crown may no longer be retained on the reciprocating piston member 36. In these circumstances, the remainder of the piston 16 will be free to reciprocate relative to the piston crown 44, thereby substantially reducing the work being performed on the material in the working chamber 14.

The balls 54 and 58 of the outlet and inlet check ball valves, respectively, are also formed of the same ultra high molecular weight polyethylene so as to also deform as temperature in the working chamber increases and thereby no longer seat properly on the respective valve seat.

Again, this will reduce the work being performed on the emulsion composition in the working chamber if the emulsion composition is able to pass around one or both balls, thereby reducing further heat build-up in the material.

As described, the likelihood of an increase in temperature to anywhere near 170°C, the emulsion explosive decomposition temperature, is dramatically reduced by the provision of the fusible piston crown and by the fusible valve members.

Referring now to Figure 4 there is shown a gear pump 60 comprising a housing 62 in which two intermeshing gears 64 and 66 are rotatable in opposite directions to displace emulsion composition through the working chamber 68 from an inlet 70 to an outlet 72.

Each of the gears 64 and 66 is supported for rotation by a respective spindle 74 and 76, with one or both of the spindles being driven by an external motor (not shown). If only one of the gears is driven by the motor, the other will be counter-rotated by its interengagement with the one gear.

One or both of the gears 64 and 66 is made of the aforementioned ultra high molecular weight polyethylene so that in the event of a pumping failure due to dry pumping or dead head pumping heat build-up in the pump will cause the or each gear to soften and deform so that it is either no longer driven by the respective spindle or other gear or no longer displaces the emulsion composition through the working chamber 68 even though it may still rotate.

Optionally, the housing may be lined with an elastomeric material such as nitrile rubber so as to reduce friction engagement between the gears 64 and 66 and the surface of the housing defining the working chamber 68. However, this is advantageously not necessary when both gears 64 and 66 are formed of the UHMWPE.

EXAMPLES Example 1 A Mono E041 progressive cavity pump having a 40 mm diameter rotor was modified so as to be as described with reference to Figure 1. Thus, the stainless steel rotor was replaced by

a rotor of identical shape made of the UHMWPE Tivar 1000.

The modified pump was driven at 460 rpm, initially with water in the stator, but then dry so as to simulate dry running. The standard stator was instrumented with temperature sensors at its axial centre (a) and at the discharge outlet (b), and the torque output of the motor (c) was monitored. The results are shown in Figure 5. As may be seen, temperature rise was rapid, reaching almost 140°C in under 4 minutes. At the same time, motor torque output increased from a start of about 4kW to about 4.2 kW after about 75s and then dropped to about 3.1 kW after about 200 s. This significant reduction in torque indicates a reduced energy input as the rotor heated up and deformed. This was confirmed when the rotor was removed from the stator; it was observed to have flattened peaks due to deformation and shedding of material.

The rotor could be flexed by hand while still hot-at an estimated temperature of about 80 to 90°C.

Example 2 A Maxi-Pump displacement piston pump as described with reference to Figures 2 and 3 and driven by a linear drive air motor limited to a maximum pump pressure of 4000 kPa was tested under controlled conditions simulating dead head pumping with void compression. To provide these conditions both the inlet to and the outlet from the pump were blocked with the pump's deadspace cavities filled with bulk base emulsion phase and the pump inlet chamber precharged with pressure regulated compressed air.

The motor was started, cyclically compressing the air void in the pump at an approximate ratio of 2.0: 1 (outlet chamber to inlet chamber) and generating pressures up to 2500 kPa. Due to a small air leakage between the outlet and inlet chambers (the outlet chamber is between the piston and the outlet, the inlet chamber is between the piston and the inlet check ball valve) arising from clearances in the pump's piston retainer, the air void was not progressively compressed (ie. pressure did not increase with every pump cycle) but maintains a cyclic pressure ratio. Nevertheless, the inlet power from the drive motor was transferred to the air

void, resulting in heating the air void in the outlet chamber.

The temperature in the pump working chamber was measured at three locations, (a) midway along the piston housing or cylinder, (b) adjacent the outlet or piston check ball valve in the inlet chamber, and (c) in the outlet chamber, and the results are shown in Figure 6. As may be seen, the temperature in the outlet chamber increased to over 130°C in about 30 minutes, with increases to about 125°C in the inlet chamber and about 110°C at the housing over a similar period. The lower temperature increase at the housing was due to its better thermal conductivity and to heat loss from the pump.

From about 130°C in the outlet chamber, it may be seen from Figure 6 that the temperature began to fall even though the pumping conditions were maintained. This was due to deformation of the piston crown or cup and of the ball of the piston or outlet check ball valve at the elevated temperature, thereby preventing further pressurisation of the air void in the outlet chamber.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within its spirit and scope. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word"comprise", and variations such as"comprises"and"comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge.