FIELD OF THE INVENTION

This invention relates to pumping of liquids. In particular, the invention relates to a check valve assembly and to a pump using the check valve assembly. More particularly, the invention relates to a check valve assembly and to a pump using the check valve assembly for use in the pumping of pumpable explosives, including explosives gels.

BACKGROUND TO THE INVENTION

In a system where two-part explosives gels are pumped into blast holes in the mining or other industries, mobile or semi-fixed pumping units are commonly used. These pumping units are designed to deliver the required mass ratio of the two gel components into a blast hole.

Many different types of pumps are available and are currently used to pump these gels in accurately measured quantities. One specific pump type that is in common use is a positive displacement pump. For this application both progressive cavity (mono) pumps and piston-type positive displacement pumps have been used. To date the progressive cavity-type pumps have mostly been implemented on larger semi-fixed installations, while positive displacement pumps are common in mobile units typically designed to be carried by a single person. In order to achieve a positive displacement pumping action from a piston-type pump, a piston is located for reciprocal movement within a bore and a set of seals prevents leakage between the piston and bore. In addition, two one-way or check valves are used and so oriented that a flow of liquid is allowed to enter through an inlet port and then via a first check valve when the piston retracts and allowed to exit via a second check valve through a delivery port when the piston advances.

In the pumpable explosives industry one of the design challenges has been to design valves that will consistently and reliably operate when the liquids being pumped have stones and other particulate material entrapped therein.

All of the valves presently in use require that the fluid pressure opens the check valves and that the check valves are maintained in an open state as a result of a pressure drop that across the valve as the liquid flows through the valve. This pressure drop is problematic, especially when a special class of pumpable explosives known as "water- gels" is pumped, as it can cause the fluid that keeps the in suspension to separate from the mixture and so cause the solids to coagulate and cause blockages.

Furthermore, most of these valves also require structural ribs or other strengthening features to support valve closing means. These ribs or other features are generally orientated across the flow of liquid, which tends to an increase in the likelihood of crystallization or agglomeration and a buildup of residue on the valve components, especially when water-gels are being pumped. The valves commonly in use for the purpose of pumping explosives are, in many instances, fitted with springs, bearings, shafts, etc. in order to achieve valve closure and sufficient alignment of the valves to seat adequately. All these features tend to form pockets and obstructions on which water-gels have shown a tendency to crystallize or agglomerate, inhibiting operation of the valve.

OBJECT OF THE INVENTION It is an object of this invention to provide a novel valve arrangement for use, particularly, but not exclusively, in the pumping of water-gels that at least partly overcomes the problems set out above. The invention extends to a pump incorporating the valve arrangement.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a check valve for a positive displacement fluid pump having a piston operable for reciprocating movement within a bore, the valve including an annular channel defined on one of a wall of the piston or a wall of the bore; and an annular seal mounted on the other of the wall of the piston or the wall of the bore and at least partially received within the annular channel, the channel and seal being shaped, dimensioned and configured so that the- channel seats against the annular seal at least during a part of its operating stroke in a-. first direction and is spaced from the annular seal at least during a part of its reverse stoke in the reverse direction, thereby to permit axial flow of the fluid in a fluid passageway defined between the piston and the bore when spaced from the seal and; restricting axial fluid flow in the fluid passageway when seated against the seal.

The channel and seal may be shaped, dimensioned and configured so that the channel seats against the annular seal at least during a part of its operating stroke in a first direction and at the extremity of its operating stroke and is spaced from the annular seal at least during a part of its reverse stoke in the reverse direction and at the extremity of its reverse stroke,

The channel and the seal may be shaped and dimensioned so as to permit relative axial movement between the channel and the seal, a side wall of the channel seating against a side of the annular seal at least when the piston is at the extremity of its stroke in its first direction. The annular channel may be wider in cross-section than that portion of the annular seal that is received within the channel, a side wall of the channel seating against a side of the annular seal at least when the piston is at the extremity of its stroke in its first direction.

At least one of the annular seal and the annular channel may include stop means for preventing the channel from seating sealingly against the seal during the reverse stroke of the piston. Then, the stop means may comprise a series of angularly spaced axial ribs provided on the piston within the channel. Instead, the stop means may comprise a series of angularly spaced axial ribs provided on the annular seal.

In a preferred embodiment of the invention, the annular channel is defined on the wall of the piston and the annular seal is mounted within the bore of the pump.

The seal may be operable to slide on the bore with the reciprocal motion of the piston during at least a part of the operating and reverse strokes of the piston.

The annular seal may be resiliently compressible and may be inserted into the bore of the pump in a compressed condition so that when in place within the bore, the seal: exerts an outwardly directed radial force on the bore, thereby to provide an axial frictional force between the seal and the bore.

The annular seal may include urging means for applying an outwardly directed radial force against the bore, thereby to provide an axial frictional force between the seal and the bore. Then, the urging means may comprise a compressed helical spring mounted to form an annulus within the annular seal concentric with the seal.

The annular seal may be of a unitary construction. Instead, the annular seal may comprise two annular seal parts that are fitted together before insertion in the pump. Where the annular seal comprises two annular seal parts that are fitted together before insertion in the pump, the urging means may be entrapped therebetween. The annular seal, when viewed in axial cross section, may have a generally flat outer circumferential base for seating against the bore and extends radially inwardly from the base to form a dome. The outer circumferential base may have a groove pattern defined thereon to inhibit the formation of liquid films between the seal and the bore, in use. Then, the groove pattern may comprise a series of axially spaced circumferential grooves or a helical spiral or other suitable pattern.

The seal may further include an annular insert provided in the outer circumferential base, the insert being of a wear-resistant material. Then, the insert may have a groove pattern defined on an outer circumferential surface thereof to inhibit the formation of liquid films between the seal and the bore, in use. Further, the insert may have an incised or relief pattern defined on its inner circumferential surface to improve mating with material of the annular ring.

The annular seal may have an annular resiliently flexible seating skirt extending radially inwardly to provide an additional seating formation against which the channel may seat. Further, the annular seal may have a first resiliently flexible sealing skirt extending from a side of the seal facing in a downstream direction with respect to fluid flow through the valve, the skirt being outwardly angled and extending radially outwardly beyond the circumferential base of the seal when in a relaxed state. Still further, the annular seal may have a second resiliently flexible sealing skirt extending from a side of the seal facing in a upstream direction with respect to fluid flow through the valve, the skirt being outwardly angled and extending radially outwardly beyond the circumferential base of the seal when in a relaxed state.

According to a second aspect of the invention there is provided a positive displacement fluid pump having a piston operable for reciprocating movement within a bore and defining an axial fluid passageway between the piston and the bore, the fluid passageway defining a fluid flow path between an inlet and an operating chamber of the pump, and the pump including a check valve as hereinbefore described operatively positioned within the fluid passageway. The positive displacement fluid pump may have a series of axially spaced check valves operatively positioned within the fluid passageway.

The positive displacement fluid pump may include guide means for inhibiting lateral movement of the piston with respect to the bore, the guide means being located proximate or on the, or one of the, check valves.

According to a third aspect of the invention there is provided a method of pumping a fluid using a positive displacement fluid pump having a piston operable for reciprocating movement within a bore, the method including defining an axial fluid passageway between the piston and the bore, the fluid passageway providing a fluid flow path between an inlet and an operating chamber of the pump; and providing a check valve within the fluid passageway, the check valve being operable to restrict axial flow of the fluid in the fluid passageway defined between the piston and the bore when the piston moves in a first, operating direction and to allow axial fluid flow in the fluid passageway when the piston moves in the reverse direction.

The check valve may be as hereinbefore described.

According to a yet further aspect of the invention there is provided a seal for use in a check valve for a positive displacement fluid pump having a piston operable for reciprocating movement within a bore, the seal substantially as herein described.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to the following diagrammatic drawings. In the drawings:

Figure 1 shows a schematic view of a general arrangement of a typical explosives gel delivery system incorporating an explosives gel pump; Figure 2 shows a schematic sectional view of a portion of a typical positive displacement fluid pump having a piston operable for reciprocating movement within a bore (Prior Art);

Figure 3 shows a schematic sectional view of a portion of a positive displacement fluid pump in accordance with the invention;

Figure 4 shows a sectional detail of the check valve of the pump of Figure 3 in a closed configuration;

Figure 5 shows a sectional detail of the check valve of the pump of Figure 3 in an open configuration;

Figure 6 shows a sectional detail of a further embodiment of the check valve of the invention in an open configuration;

Figure 7 shows a sectional detail of the embodiment of the check valve of Figure 6 in a closed configuration;

Figure 8 shows a sectional detail of a pair of check valves of the invention operating in series in place pump;

Figure 9 shows a sectional detail of a seal of a check valve in accordance with the invention, through a section IX-IX on Figure 10;

Figure 10 shows a plan view of the seal of Figure 9;

Figure 11 shows an exploded view of the seal of Figure 9;

Figure 12 shows a perspective view of the seal of Figure 9;

Figure 13 shows a sectional view of a series of check valves in place in a piston and bore of a positive displacement explosives gel pump; and Figure 14 shows a sectional side view of a further embodiment of a seal in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In Figure 1 , a typical e xplosives delivery system 10 fo r the charging of a two-part explosive gel 12 into a blast hole 14 in the mining or other industries is shown. In such a system, mobile or semi-fixed pumping units 16 are used. These pumping units 16 are designed to deliver the required mass ratio of the two explosives gel components into a blast hole 14 that has been drilled into a rock face 18.

Typically, a positive displacement pump 2 0 is used in such an explosives delivery system, a portion of which is shown in Figure 2. In a positive displacement piston-type pump 20, a piston 22 is slidingly located within a bore 24 for reciprocal motion. A set of seals 26 prevents leakage between the piston 22 and bore 24. In addition, one-way valves 28,30, also known as check valves, are used and so oriented that the fluid being pumped is permitted to enter the pumping chamber 32 from an inlet port 34 under the control of a first check valve 28 as the piston 22 retracts and is permitted to exit through an exit port 36 under the control of a second check valve 30 as the piston 22 performs its positive or operating stroke.

The pump of the present invention, generally indicated by reference numeral 40 in the drawings, uses the movement of the piston 42 relative to the bore 44 to open and close a check valve 50, instead of using the more conventional differential pressure and flow directions of the pumped fluid to control the opening and closing actions of the check valve.

In the valve of the invention, generally indicated by reference numeral 50 in the drawings, an annular seal 52 is used to prevent leakage between the piston 42 and the bore 44 of the pump 40 during the operating stroke of the piston 42, but also serves the function of a check valve in co-operation with a annular channel 58 that provides a seat defined on a wall 56 of the piston 42. Thus, in a pump 40 using a check valve 50 of the invention, the fluid flow path through the pump 40 follows an annular passageway 54 defined between the wall 56 of the piston 42 and the bore 44 in a generally axial direction, the fluid flow being controlled by the check valve 50. This is in contradistinction to typical pumps of this type where an attempt is made to prevent the axial flow of the pumped fluid between the piston and the bore by means of seals.

In the embodiment of the pump 40 shown in Figures 3 to 5, a seal 52 is mounted within the bore 44 and is partially received within an annular channel 58 defined on the piston wall 56, the channel seating against the seal 52 when the valve 50 is in its closed position, as shown in Figure 4. The construction of the seal 52 and channel 58 together allow reciprocal axial movement of the piston 42 within the bore 44, firstly since the channel 58, when viewed in cross-section, is wider than that part of the seal 52 received within the channel 58 and secondly, because the seal 52 is operable to move together with the piston 42 once the piston 42 has abutted the seal 52. In addition, the seal 52 and channel 58 are shaped to provide radial clearance between them to allow for fluid to flow through an annular gap 60 formed between the piston 42 and seal 52, when the valve 50 is not in its closed position, as shown in Figure 5.

In operation, when the piston 42 begins its operating stroke the check valve 50 is in its open position, as shown in Figure 5. The piston 42 then begins its operating stroke and shortly thereafter a first wall 62 of the channel 58 of the piston 42 engages the seal 52 to form a liquid-tight seal, as shown in Figure 4. This configuration is maintained until the piston 42 reaches the extreme of its operating stoke and the seal 52 effectively acts as a part of the piston 42 in urging fluid under pressure into the operating chamber of the pump 32. The piston 42 then begins its return stroke and travels a small distance (the difference between the effective axial widths of the channel 58 and seal 52) before it impacts stops 64 on the seal 52, as shown in Figures 3 and 5. The check valve 50 is now in its open position and a fluid flow path, indicated by the arrows 66 in Figure 5, is provided in the annular passageway 54 defined between the piston 42 and the bore 44.

A series of angularly spaced, radial ribs 68 is provided in the seal. These ribs 68 function as stops 64 against which a second wall 70 of the channel 58 of the piston 42 abuts on its return stroke. It will be appreciated that similar ribs may be provided in the channel 58 of the piston 42 rather than on the seal 52. It will also be appreciated that other means for providing a stop between the piston and the seal may be provided.

Furthermore, the seal 52 is intentionally designed for a frictional drag between the bore 44 and the seal 52. This frictional drag force results from, and is proportional to, an outwardly directed radial force acting on the inside of the bore 40, the resulting frictional force acting at the interface of the seal 52 and bore 40 to oppose relative movement between the seal 52 and the bore 40. In one preferred embodiment of the invention, a net outwardly directed radial force exerted by the seal 52 is due to an elastic preloading of the seal 52 that is applied during assembly by forcing the seal 52, which is resiliently compressible, to fit within a bore 40 of a diameter smaller than the unloaded free outer diameter of the seal 52. In addition or instead, in a preferred embodiment of the invention a shown in detail in Figures 9 to 12, an urging device in the form of a helical spring 72 is entrapped between components of the seal 52 to provide the desired outwardly directed radial force.

In use, as the piston 42 begins to move on its positive stroke, ie towards the left in Figures 3 to 5, the seal 52 remains stationary in position due to the frictional drag exerted by the seal 52 on the inside of the bore 44. The piston 42 keeps on moving to the left until it engages with the seal at 74. A first wall 62 of the channel 58 of the piston 42 then seats against the seal 52 providing a liquid-tight seal. As the piston 42 continues on its stroke, the force applied by the piston 42 is greater than the frictional drag on the seal 52 and the seal 52 is urged to move with the piston 42 to the left in the drawings, all the while maintaining the liquid tight seal. The check valve 50 is now in its closed position and the piston 42 causes liquid to flow out of the one way delivery valve 30, shown in Figure 3.

As soon as the piston 42 reaches the extremity of its operating stroke, the conventional one way delivery valve 30 closes under the influence of its spring 31. The piston 42 then commences its return stroke, to the right in the drawings. The seal 52, however, remains stationary in its last position due to the frictional drag of the seal 52 on the inside of the bore 44. As the piston 42 continues with its return stroke, it engages with the stops 64 of the seal 52 at 76. However, this engagement does not prevent liquid from flowing around the seal 52 between the seal 52 and the channel 58 of the piston 42 because of the clearance between the channel 58 and the seal 52 in this configuration indicated by the arrow at 78. Immediately after the piston 42 has engaged with the stops 64 of the seal 52, the seal 52 begins to move along with the piston 42 (to the right). As it does so, liquid is allowed to flow through the valve 50 (to the left).

As soon as the piston 42 reaches the extremity of its return stroke (is in its rightmost position), the operating chamber 32 of the pump 40 downstream of the piston 42 has been filled with liquid having flowed through the flow path provided between the seal 52 and the piston 42. A repetition of the process described above will result in a repetitive pumping action.

A beneficial feature of this arrangement is that the operation of check valve 50 is actuated and performed by movement of the piston 42 in combination with the friction forces present between the seal 52 and the inner wall 50 of the bore 44, and is not dependant on differential fluid pressures, as is the case with conventional check valve arrangements. Furthermore, the check valve 50 may be simply constructed such that there are few, or no, o bstructions that could provide areas on which a liquid may crystallize or particulates coagulate and so impede operation of the valve 50 and hence the pump 40.

Turning to Figures 6 and 7, a further embodiment 90 of the seal is shown. In these drawings, with reference to Figures 3 to 5, like components are indicated by like reference numerals. The seal 90 of this further embodiment is generally similar to that illustrated in Figures 3 to 5 and described above. However, in order to make the seal 90 more dirt tolerant, especially when seating with the piston 42, an additional flexible and resilient sealing skirt 92 is provided on the seal 90. The skirt 92 is orientated generally radially inwardly on the seal 90 and is arranged so that, after commencing its operating stroke motion, the wall 62 of the piston channel 58 engages first with the skirt 92 and only then with the seal 90 at 74. The skirt 92 is sufficiently flexible so that it folds against the side wall 62 of the channel 58 and, owing to its flexibility, engages with the piston 42 even when a small obstruction 94, such a stone or other particulate material entrained in the liquid being pumped, lodges between the seal 90 and the piston 42. The sealing skirt 92 enables the check valve 50 to function in a more dirt-tolerantly manner, because if dirt is trapped between main body of the seal 90 and the side wall 62 of the piston channel 5 8, the sealing skirt 92 provides an additional seal against the piston 42. Alternatively, if dirt is trapped under the sealing skirt 92, it is sufficiently flexible not to inhibit the normal sealing action of the check valve 50. In effect, this arrangement provides two sealing faces in series, which seal independently of each other and in so doing make the valve 50 more dirt-tolerant.

In the above description, (notwithstanding the drawings) the seal has been described as if it were an integral one-piece device, but there are advantages to constructing the seal as an assembly of several parts, each potentially performing one of the functions described above. In this regard, we turn now to Figures 9 to 12 which show the seal 52 in greater detail. The seal 52 comprises three parts, as shown in Figure 11 , the parts being assembled to provide a composite seal. The seal has an outer body 100, which provides an annular circumferential cylindrical base 102, which abuts against the bore 44 of the pump 40 in use. A series of circumferential annular grooves 104 is defined in the base 102 to assist in achieving a desired frictional drag between the seal 52 and the bore 44, by acting, much in the same way as treads on a motor vehicle tyre, to inhibit the formation of a hydrodynamic liquid film between the seal 52 and the bore 44. Such a film could significantly reduce the frictional drag that is required for the correct functioning of the valve 50. The outer body 100 of the seal 52 extends radially inwardly from the base and a groove 106 is provided on an inner face 108 of the outer body 100 of the seal 52, in which is received a helical spring 72. An inner annular body component 110 of the seal 52 is receivable within the outer body 100 of the seal 52 and has a complementary groove 112 defined in its outer face 114, the helical spring 72 being entrapped between the two body components 100,110. The inner body component 110 provides the domed portion of the seal, against which the wall 62 of the piston channel 58 seats in use. In addition, a series of six angularly spaced radially orientated ribs 68 is mounted on the inner body component 110 of the seal 52 to provide stops 64 against which the opposed wall 70 of the channel 58 abuts during the return stroke of the piston 42. It will be appreciated that any suitable number of ribs 68 may be used. When assembled, the helical spring 72 is inserted between the outer and inner body components 100,110 of the seal 52. The inner and outer components 100,110 of the seal 52 may be connected to one another by a means of a chemical bond or the one component may be cast onto the other component. In order to insert the seal 52 into the bore 44 of the pump 40, it is necessary to compress the seal 52, thereby compressing the helical spring 72. The natural tendency of the spring 72 to return to its relaxed form creates an outwardly directed radial force against the walls 8 0 o f the bore 44 of the pump 4 0, thereby providing the desired frictional force between the base 102 of the seal 52 and the wall 80 of the bore 44. The inner and outer body components 100,110 of the seal 52 may be moulded of a synthetic rubber material or any other suitable material. It will be appreciated that a seal of a similar construction may be manufactured as a single one- piece unit. Also, the seal 52 may be constructed without the spring 72 and other means for providing the frictional force may be provided, including relying on the resilience of the material of the seal itself.

The seal also has two circumferential sealing skirts 118,120 extending laterally from the base 102 of the seal 52, one on either side of the outer body component 100 of the seal 52. The skirts 118,120 are angled outwardly from the axis of the seal 52 and the ends 122 of the skirts 118,120 extend radially outwardly beyond the base 102 when the seal 52 is viewed out of the pump 40 in its relaxed state. When inserted into the bore 44 of the pump 40, the seals 118, 120 are urged against the inner wall 80 of the bore 44 and exert a force on the bore 44 to improve the sealing of the seal 52 against the bore 44. In addition, the seals 118,120 may act to sweep debris from the bore 44 and to inhibit its ingress between the seal 52 and the bore 44.

A yet further embodiment 130 of the seal is shown in Figure 14 and, with reference to the earlier Figures 9 to 12, like reference numerals indicate like components, unless otherwise stated. In this embodiment, the seal 130 has a circumferential insert 132 that is located in the base 131 of the seal 130. The insert 132 has a series of grooves 133 defined on its other surface 134 and the inner surface 136 of the insert 132 is also grooved 138 to promote adherence of the body 140 of the seal 130 to the insert 132. In a preferred embodiment of the invention, the body 140 of the seal 130 is moulded onto the insert 132. In this embodiment, the body 140 of the seal 130 comprises two component parts 142,144, but does not include a helical spring, the body 140 of the seal 130 and the insert 132 being relied upon to provide the necessary resilience to the seal 130. Of course, a spring or other urging device may be inserted or included in this embodiment, as required. This construction of the seal 130 has the advantage that a high-wear resistant material, such as an Ultra-High Molecular Weight Polyethylene (UHMWPE) may be used for the high wear component of the seal, ie the insert 132, while softer materials, such as polyurethanes of various, and possibly different, grades, may be used for the other components 142,144.

A further embodiment 150 of the pump is shown in Figures 8 and 13, in which, with reference to Figures 3 to 5, like components are indicated by like reference numerals. In this embodiment 150, a pair of similar check valves 50 is used in series, the piston 152 having a pair of axially spaced channels 58 defined on its side wall 154. As shown in Figure 8, the piston 152 of the pump 150.1 is of a unitary construction. As shown in Figure 13, the piston 152 of the pump 150.2 is constructed as a composite unit comprising three piston parts 156,158,160, held together by means of a machine screw 162. This construction facilitates the assembly and maintenance of the pump 150.2 and the insertion of the seals 52 within the bore 44 of the pump 150.2 and it is particularly advantageous to be able to assemble and disassemble the composite piston 152 and valve seals 52 from the end of the pump 150.2 from which the head of the piston 164 is accessible, ie without having to remove the entire piston assembly 152 from the bore 44 of the pump 150. By applying more than one check valve 50 in series, the dirt tolerance of the pump 150 is again improved, while at the same time making it practically possible to use relatively softer materials for the seals 52, since one of the two valves 50 will normally close fully without being affected by an obstruction, even if the other is affected by an obstruction. The obstructed valve 50 does not then have a high pressure difference across its seal 52 and is not forced to attempt to close against the obstruction.

In order for the valves 50 to function efficiently, the piston 152 must be located within the bore 44 sufficiently accurately for the seals 52,90,130 to consistently engage with the piston 152 and, in particular, lateral movement of the piston 152, or piston slap, should be inhibited. In the embodiment of Figure 3 and that of Figure 13, this is achieved by means of radially extending lugs 166 located in the side wall 168 of the piston 152. Other forms of guides, such as fins, may equally be used. Preferably, the guides are positioned in close proximity to the seal or seals 52 of the pump 150, in order to achieve accurate location of the parts of the valve 50 with one another. Instead, the piston 42 may be made to engage with a formation of the seal in order to provide lateral stability. Such radial engagement features should be so designed as to allow liquid to flow through the annular passageway 54 between the seal and the piston 42 when the valve is in its open position and could be achieved by means of a series of angularly spaced axially oriented fins or protrusions on either the piston 42 or the seal 52,90,130.

It is also foreseeable that the direction of the pumping action could be reversed without materially affecting the invention as described.