GB2538249A - Sandfalls and the like - Google Patents

Abstract

An underwater-sandfall producing apparatus 10 comprises an upwardly directed conduit 14 with an outlet 16 from the top of the conduit, pump means 20 to cause a flow of water 22 to pass upwardly along the conduit, a reservoir for the sand 241, and entrainment means 242 to enable the water for said flow to entrain sand from the reservoir through an entrainment gap between the reservoir and conduit. The apparatus is constructed so that the flow can carry the sand up the conduit to its said outlet and produce the underwater sandfall from the outlet without the use of a stream of bubbles, and direct the flow downwardly 223 from the outlet towards the reservoir. The conduit may comprise Venturi means 34 close to said entrainment gap to improve the entrainment, and a non-return valve 46 between an outlet of the pump and the sand reservoir to prevent back flow of sand to the pump when the pump is switched off.

Description

TITLE: Sandfalls and the like

Field of the Invention

This invention relates to sandfalls and the like. A sandfall is a fall of sand, somewhat like a waterfall but with sand replacing the water. The sandfall can be under water (subaqueous). In the present context, the apparatus to produce this feature is usually decorative, e.g. for use in an aquarium, in which case the apparatus may provide a continuous fall of sand or other particulate material, and the sandfall is somewhat similar to a waterfall but is under the surface of the water in the aquarium.

Background

In a proposed arrangement tried by the present inventors, sand from a reservoir near the bottom of an aquarium is entrained by a stream of bubbles of air which carries the sand upwards to a point at which the air is separated off and the sand is allowed to fall back towards the reservoir. This is intended to be a continuously recycling process for the sand. The falling sand is directed to be away from the upward stream of bubbles carrying the sand so that this stream can be hidden from view and only the falling sand can be seen, so that the falling sand will somewhat resemble a waterfall. Hiding the separated-off air entails that the apparatus should stretch up to the surface of the body of water, or preferably above it.

The Invention The inventors consider this to have the following disadvantages. The air pump required has to be quite powerful. A large quantity of air escapes at the top of the apparatus, and this is quite unsightly and distracting. The sand used has to be quite light to be entrained by the air bubble stream and, when released from the air bubble stream, tends to scatter to a greater or lesser extent outside the sand reservoir. The scattering can be reduced by carefully selecting the sand grain size and the aeration, i.e. the parameters controlling the air stream, but the inventors found these to be quite critical when they attempted to maximise the amount of sand returning to the reservoir. Also, this light sand would sometimes clog up the pump outlet when the pump was switched off.

Most of these problems disappeared when they substituted a water pump submersed in the water and an upwards water stream to entrain the sand. There were no unsightly escaping air 30 bubbles to be hidden. There was no need to have an air feed coming into the aquarium to the pump. The pump could be much less powerful, and the sand could be coarser, and in particular sufficiently coarse not to scatter when falling back into the reservoir. And all this could be done easily without requiring critical adjustments of the water flow and path, and requiring very uniform and carefully chosen sand grain size. The problem of clogging of the pump outlet when switched off could then also readily be overcome. Thus, essentially, the difficulties could be overcome by using flowing water as the vehicle to entrain the sand rather than a stream of air bubbles.

Although embodiments of the invention will be described with reference to sand and water and an aquarium, it will be readily apparent to one skilled in the art that the invention can be applied to: any suitable particulate material, even small ball bearings; any suitable liquid, e.g. oil, usually to be transparent or translucent; any suitable display, e.g. for decorative use, not confined to the case of an aquarium, or even for scientific or technical use that is not a display.

Initially, the inventors found a difficulty with the sand flow, because its vehicular water is under the surface of the body of water in the aquarium, disperses and flows sideways in all directions into that body of water, and tends to carry its sand with it, so that this sand does not return to the sand reservoir but dissipates over a large area of the bottom of the aquarium. This dispersion can be substantially reduced by suitable choice of largeness of particle size of the sand. However, the inventors then found that they could substantially improve upon even this until the spread or dissipation is almost eliminated by providing means to guide the water and sand mixture and control the direction in which the sand will flow when the water separates from it. Preferably, there is a conduit for the upwards stream of water and entrained sand and the guide means comprise guiding outlet means at the top of the conduit, e.g. by effectively bending the conduit downwardly at the top, preferably so as to direct the separating sand towards the sand reservoir for recycling (see Figures 1, 7, 8 and 9 for different arrangements to achieve this). In theory, the reservoir for recycling the sand could be simply the bottom of the aquarium at large, but this when tried did not work because more and more sand was deposited too far away from the entrainment inlet to be entrained, and because foreign matter became mixed up with the sand, and because the entrainment suction could not be made large enough to be useful (while incidentally not being dangerous in the sense of entraining small fish).

In contrast to the air pump needed to produce the stream of bubbles in the prior arrangement mentioned above, a suitable water pump to recycle the water to entrain and recycle the sand can be any one or more of: submersible in water (so that it can for example be inside the aquarium); substantially noiseless; of much lower power than any possible air pump to do the same job of entraining sand; and of much smaller size. This allows the pump, the conduit bent over at the top and the sand reservoir to be in a single unit or housing, and allows the housing to be so small (or at least of so little height) that its top can be well below the surface of the water in the aquarium.

Further, the pump may have a driving rotor able to be placed adjacent to a base or a wall of the aquarium and magnetic so that it can in turn be driven by electrically driven magnetic or electromagnetic means, e.g. a rotor, e.g. a magnetic rotor, outside said base or wall, which can avoid the need to have an electric power lead for the pump that pierces said base or wall or trails over a top edge of the aquarium. Such rotors may suitably comprise SmCo, or other powerful non-corroding magnets e.g. comprising Alnico, ceramic and/or neodymium. Preferably, the conduit comprises a vertical part, and the sand reservoir is to one side of this and opens into it through an entrainment gap so that water pumped up this conduit part can draw in a stream of water past the sand reservoir in order to entrain the sand through the entrainment gap into the upwards stream of pumped water in this conduit part. This conduit part may be narrowed close to the reservoir entrainment gap to have a Venturi effect to help draw in the sand. The conduit may comprise a non-return valve between an outlet of the pump and the sand reservoir to prevent back flow of sand into the pump when the pump is switched off. A possible alternative is indicated in Figure 2 Thus, embodiments of the invention can provide any one or more of the following features: * a sandfall apparatus adapted to produce a fall or cascade of sand within water, powered by the water, with the sand recycled by the water; * apparatus adapted to provide a sandfall powered by a stream of water, with the sandfall apparatus wholly immersed in the water of an aquarium; and therefore not having disadvantages of using air bubbles, for example needing to hide them after separating them from the sand, e.g. needing an exhaust pipe for the separated air; * a sandfall apparatus operable without bubbles and/or without air; and/or without air holes; * the sand may be replaced by any suitable particulate material; * the water may be replaced by any suitable liquid; * a sandfall apparatus which does not require a water reservoir other than the body of water in which the sandfall is, or is to be, located; * the conduit may have circular, oval, square or rectangular cross-section, at least in a vertical part thereof, possibly throughout substantially most of such vertical part; * the pump (e.g. because it can be quite powerful and/or smooth-operating) may have an outlet directly providing said stream without any intermediate pressure control means; * a sandfall apparatus operable wholly underwater; * a sandfall apparatus such as to enable sand to be recycled by falling directly from an entrained sand outlet to a sand reservoir; and preferably one in which this process occurs; * a sandfall apparatus that encourages the surface of the sand to act as a medium for containing or growing bacteria good for aquarium fish; * even in the absence of bubbles, the sand can provide a surface for nitrifying bacteria to colonise on, which can break down harmful waste from fish; * a sandfall apparatus adapted to recycle the sand so that the amount of sand used is substantially fixed and the recycled sand is able to collect in a sand reservoir from which water flow from a pump is able to draw sand to continue the cycle; * the conduit is substantially rigid so that it can provide a structured water flow; * an outlet (e.g. an exit end) of the conduit is shaped and/or arranged to inhibit the sand from spraying across the body of water; * an outlet (e.g. an exit end) of the conduit is shaped to help direct the direction of sand fall; * the pump has a cover (not shown) to protect from its moving parts any fish that might swim near it; * the apparatus is provided with a casing; and preferably, the casing is substantially watertight, or at least inhibits the flow of water out through the casing, in either case apart from a region adjacent the said outlet so that any water within the casing and outside the up-pipe (said upwards conduit) is essentially static; * a sandfall apparatus integrated with an ornamental structure; * a sandfall apparatus comprising a pump able to operate with a flow rate within a range extending from 200 to 1000 (or even greater than 1000) litres per hour; and/or a flow rate of at least 600 litres per hour; and/or a flow rate of substantially 600 litres per hour.

One aspect of the invention provides a sandfall apparatus as claimed in claim 1.

Other aspects of the invention provide a sandfall process as claimed in claim 13 or 14.

Embodiments of the invention may have any one or more of the features recited in any one or 30 more of claims 2 to 11 and 15.

Some preferred features: The upwardly directed conduit is preferably upright, preferably substantially vertical. The conduit may be tubular or a segment of a tube. The entrainment means is located after the pump means. The entrainment means is adapted to enable the entrainment by means of flowing water and/or suction and/or with or without the aid of gravity.

The pump means comprise a submersible pump.

Reference will now be made by way of example to the accompanying drawings, in which: Figure 1 is a schematic cross-section showing the principle of various embodiments of the invention (the thin horizontal lines in Figure 1 are construction lines and should be ignored); and Figures 2 to 9 are schemata indicating schematically possible alternative arrangements of parts of 10 the apparatus shown in Figure 1.

Referring to the drawings, identical references in the same Figure or different Figures refer to the same item or items that are identical or similar or have similar functions, and references with the same first two digits refer to items that are identical or similar or have similar or related functions. Referring now more particularly to Figure 1, an underwater-sandfall producing apparatus 10 adapted to operate under water to produce an underwater sandfall 12, comprises an upwardly directed conduit 14 with an outlet 16 from the top of the conduit 14, connected to the latter by a short horizontal tube segment 18, pump means 20 to cause a flow 22 of water to pass upwardly along the conduit 14, and entrainment means 24 to enable the water for said flow 22 to entrain sand 26, the apparatus 10 being constructed and arranged so that the flow 22 can carry the sand 26 up the conduit 14 to its said outlet 16 without the aid of air and produce the underwater sandfall 12 from the outlet 16.

The upwardly directed conduit 14 is upright, and substantially vertical. The conduit 14 is tubular and forms a segment of a generally upwardly-leading tube 28, 14, 18, of which the segment 28 is provided for the sake of convenience for connecting outlet 30 of pump 20 to inlet 32 of conduit 14. Relative to the flow 22, the entrainment means 24 is located after the pump means 20. The pump means 20 comprise a submersible pump 20. The entrainment means 24 is adapted to enable the entrainment by means of flowing water and suction and without the aid of gravity. The entrainment means 24 comprise a reservoir 241 for sand 26 and an entrainment inlet 242 from the reservoir 241 to the conduit 14, so constructed and arranged that the upward flow 22 in the conduit 14 can suck into itself through this inlet 241 a stream 221 of water entraining sand 26 from the reservoir 241.

As indicated in dashed lines, the entrainment means 24 may additionally comprise Venturi means 34 that locally narrow the conduit 14 to increase the rate of flow 22 there and produce lower pressure there and enhanced suction, and hence improved entrainment, e.g. as indicated above.

In the apparatus 10, the pump 20, conduit 14 and, entrainment means 24 including reservoir 241 are accommodated in a casing 36, which may be covered with decorative material, e.g. simulated rocks (not shown), resting on bottom material 38 (often gravel) in an aquarium 40 and totally immersed in water 42 practically filling the aquarium 40 and well below the free surface 44 of the water 42. The casing 36 is substantially watertight apart from a small region 161 adjacent the outlet 16 and at the entrainment gap inlet 242; so that it is substantially watertight to outgoing flow except in the region 161. Therefore, the body of water 421 within casing 36 is static and will ensure that flow 222 of water and entrained sand will exit from outlet 16 as a downward flow 223. Thus, the outlet 16 comprises means (the shaping of outlet 16 in conjunction with the static water 421 in the region 162) to direct downwardly the flow 222 of water and entrained sand as this flow 223 is outgoing from the outlet 16. Since casing 36 comes to a lower edge 361 at this point, the available flow cross-section in the region 161 just after the outlet 16 and edge 361 is substantially larger, e.g. at least 50 times larger, than the flow cross-section at the outlet 16 just above this region 161, the flow 223 of water from the outlet 16 can readily distribute laterally, which it does in directions such as 224. However, if the coarseness of the sand has been chosen judiciously, the sand 26, due to its downward motion imparted by flow 223, will continue to fall downwardly towards reservoir 241, constituting sandfall 12 when the flow of water 224 from the outlet 16 distributes laterally. For this purpose, the sand 26 is chosen for its particle size to have a diameter substantially in the range of from 1 mm to 3 mm. The sand reservoir 241 can readily be constructed and arranged to be of such size and position as to catch substantially all of the sand 26 outgoing from the outlet 60. Thus the apparatus 10 is adapted to recycle the sand 26.

We can also use gravel, i.e. greater than 3 mm diameter, e.g. in a large public/commercial aquarium the size might be 3 to 10 mm or even larger, e.g. at least 10 mm.

There may be any one or more of the following variations of the arrangement seen in Figure 1. The sand reservoir 241 may extend much further to the left (as seen in Figure 1) from the vertical tube portion 14, e.g. up to twice as far as the horizontal length of the horizontal conduit segment 18, and possibly extend to that length to the left of casing 36. The roof portion 101 of the housing 10 may be lowered until it is touching or almost touching the horizontal segment 18. The baffle end 362 of casing 32, instead of being substantially vertical as shown, may slope down and backwards (to the right as seen in Figure 1) to its edge 361, e.g. sloping at substantially 45° to the vertical, at least in its lower part towards its edge 361, and may be curved from upper horizontal roof portion 101 to facilitate the directing of flow 222 into flow 223 with reduction of possible turbulence. The pump means 20 may be mounted on the outside (to the right as seen in Figure 1) of the lower part 363 of the vertical wall of casing 36 (rather than being inside casing 36 as shown in Figure 1); outlet 30 will then have to lead through wall part 363 to segment 28.

Since the pump means 20 precedes (in order along the flow path 22) the entrainment means 24, its outlet 30 might easily become clogged by sand 26 falling in conduit 14 when the pump 20 is switched off. To prevent this, there can be provided a one-way valve 46 between the pump means 20 and the entrainment means 16, e.g. in the form of a simple flap-valve 46, as indicated in Figure 1. An alternative (or additional) device to avoid clogging is to position pump means 20 higher than inlet 32 so that the pump outlet 30 feeds into a downpipe 48 to the inlet 32 to conduit 14, as indicated schematically in Figure 2.

As indicated schematically in Figure 3, an alternative entrainment method could be obtained by providing a gravity feed of sand from a suitably positioned reservoir 241 into flow 22 from pump 20. In theory, the gravity entrainment could be arranged to occur prior to pump 20, as indicated schematically in Figure 4, provided pump 20 can handle a mixture of water and sand. Similarly, non-gravity entrainment, operating in exactly the same manner as shown in Figure 1, could be arranged to occur prior to pump 20, as indicated schematically in Figure 5.

The pump 20 is powered by electricity through a cable 50 from e.g. a wall plug 52. The cable 50 trails over a top edge of aquarium 40. An alternative, indicated schematically in Figure 6 (which corresponds to the bottom right-hand part of Figure 1), is for the pump 20 to have two parts 201, 202, one part 201 having a driving rotor (not shown) to drive the pumping action, this part 201 being able to be positioned inside the wall 401 of aquarium 40 adjacent the wall 401, the rotor being magnetic so that it can in turn be driven by electrically driven magnetic or electromagnetic means, e.g. a magnetic rotor, (not shown) in part 202 positioned adjacently to part 201 but outside the wall 401, powered by electricity through a cable such as 50. This can avoid the need to have an electric power lead for the pump 20 that pierces said wall 401 or trails over a top edge of the aquarium 40.

It will be seen that the foregoing apparatus when in use provides a process of producing an underwater-sandfall. In this process, there is used apparatus which is operated under water to produce an underwater sandfall, comprising an upwardly directed conduit with an outlet at the top, pump means that cause a flow of water to pass upwardly along the conduit, and entrainment means that enable the water for said flow to entrain sand, whereby the flow carries the sand up the conduit to its said outlet without the aid of air and produces the underwater sandfall from the outlet.

In a particular embodiment, e.g. that shown in Figure 1, the pump means 20 have a flow rate, within a range extending from 200 to 1000 litres per hour, of substantially 600 litres per hour, and the conduit 14 (apart from the region of the Venturi means 34) has a circular cross-section of diameter substantially 2.5 cm, producing a speed of flow 22 of substantially 34 cm/s. The size of this cross-section is substantially the same all the way from the Venturi 34 to just before region 161. The flow rate might usefully be for example within the range of from 15 to 100 cm/sec.

Whilst the outlet 16 comprises means (the shaping of outlet 16 in conjunction with the static water 421 in the region 162) which is effective to direct downwardly the flow 222 of water and entrained sand as this flow 223 is outgoing from the outlet 16, there is likely to be some turbulence in the region 161, although nothing like as much as was caused in the proposed arrangement using air bubbles. Figures 7-9 show in a very diagrammatic form various means to improve the downflow 223, improve the directing of the sandfall 12 towards the reservoir 241, and/or reduce turbulence at the outlet 16. In the Figure 7 embodiment, the horizontal segment 18 of pipe conduit 14 has been extended into a downwardly directed portion 181 providing outlet 16. In the Figure 8 embodiment, the downwardly directed portion 181 has been substantially extended downwardly to give more direction and smoothness to the flow 223. In the Figure 9 embodiment, the horizontal segment 18 has been smoothly shaped into a curve 18 starting at the top of the upwardly directed part of conduit 14 and ending with a downwardly directed portion 181 constituting outlet 16. The Figure 9 arrangement gives even more direction and smoothness to the flow 223 and (not shown) this portion 181 may be extended downwardly in the manner shown in Figure 8 and for even further improvement in directing and smoothing the flow 223. Also (not shown), the sandfall 12 may be directed at a downward angle inclined to the vertical, e.g. up to 45°, preferably up to 25°, e.g. in a direction away from conduit 14 (e.g. to the left as seen in Figure 1), provided the reservoir 241 extends sufficiently far horizontally to receive the sandfall 12. The outlet 16, the portion 181, and the curve 18 in Figure 9, constitute means to reduce, inhibit and/or substantially eliminate turbulence. _g

Any such apparatus or process as described above may be modified, so as to be suitable for any other suitable particulate material to be used in place of the sand, though we prefer coral sand.

Any such apparatus or process may be modified, so as to be suitable for any other suitable liquid to be used in place of the water.

Many variations of the invention and embodiments herein described will be apparent to people skilled in the art. For example, features of the different embodiments disclosed herein may be omitted, selected, combined or exchanged in order to form further embodiments. Again, where a preference or particularisation is stated, there is implicit the possibility of its negative, i.e. a case in which that preference or particularisation is absent. The invention is considered to extend to any new and inventive embodiments formed by said variations, further embodiments and cases.

Claims (18)

1. -10 -CLAIMS1. An underwater-sandfall producing apparatus adapted to operate under water to produce an underwater sandfall, comprising an upwardly directed conduit with an outlet from the top of the conduit, pump means to cause a flow of water to pass upwardly along the conduit, and entrainment means to enable the water for said flow to entrain sand, the apparatus being constructed and arranged so that the flow can carry the sand up the conduit to its said outlet without the aid of air and produce the underwater sandfall from the outlet.
2. 2. Apparatus as claimed in claim 1, in which the entrainment means comprise a reservoir for sand and an inlet from the reservoir to the conduit, so constructed and arranged that the upward 10 flow in the conduit can suck into itself through this inlet a stream of water entraining sand from the reservoir.
3. 3. Apparatus as claimed in claim 2, in which the entrainment means comprise Venturi means.
4. 4. Apparatus as claimed in any preceding claim, adapted to recycle the sand.
5. 5. Apparatus as claimed in any preceding claim, in which the said outlet comprises means to 15 direct downwardly the flow of water and entrained sand as it is outgoing from the outlet.
6. 6. Apparatus as claimed in claim 5, in which the flow cross-section just after the outlet is substantially larger than the flow cross-section at the outlet, whereby the flow of water from the outlet can readily distribute laterally.
7. 7. Apparatus as claimed in claim 6, in combination with the sand, which is so chosen it will 20 continue to fall downwardly when the flow of water from the outlet distributes laterally.
8. 8. Apparatus as claimed in claim 7, in which the sand is chosen for its particle size to have a diameter substantially in the range of from 1 mm to 3 mm.
9. 9. Apparatus as claimed in any one of claims 5 to 8, comprising a sand reservoir constructed and arranged to catch substantially all of the sand outgoing from the outlet.
10. 10. Apparatus as claimed in any preceding claim, in which the pump means precedes the entrainment means, comprising a one-way valve between the pump means and the entrainment means.
11. 11. Apparatus as claimed in any preceding claim, in which the pump means is connected through a downpipe to the conduit.
12. 12. A sandfall-producing apparatus, adapted to produce a sandfall without the aid of air, substantially according to any example hereinbefore described with or without reference to the 5 accompanying drawings.
13. 13. Apparatus in use for, or a process of, producing an underwater-sandfall, in which there is used apparatus as claimed in any preceding claim.
14. 14. Apparatus in use for, or a process of, producing an underwater-sandfall, in which there is used apparatus which is operated under water to produce an underwater sandfall, comprising an upwardly directed conduit with an outlet from the top of the conduit, pump means that cause a flow of water to pass upwardly along the conduit, and entrainment means that enable the water for said flow to entrain sand, whereby the flow carries the sand up the conduit to its said outlet without the aid of air and produces the underwater sandfall from the outlet.
15. 15. Apparatus or process as claimed in claim 13 or 14, in which the pump means have a flow rate 15 within a range extending from 200 to 1000 litres per hour.
16. 16. A process substantially according to any example hereinbefore described with or without reference to the accompanying drawings.
17. 17. A modification of apparatus or process as claimed in any preceding claim, suitable for any other suitable particulate material in place of the sand.
18. 18. A modification of apparatus or process as claimed in any preceding claim, suitable for any other suitable liquid in place of the water.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWSCLAIMS1. Apparatus adapted to operate underwater to produce a visual effect, comprising an upwardly directed conduit with an outlet from the top of the conduit, pump means to cause a flow of water to pass upwardly along the conduit, and entrainment means to enable the water for said flow to entrain particulate material, the apparatus being constructed and arranged so that the flow can carry the material up the conduit to its said outlet without the aid of air and thereby produce an ejection of the material from the outlet, the apparatus being constructed to direct downwardly the flow of water and entrained material as it is outgoing from the outlet so as to give a visual effect that simulates a fall of sand.2. Apparatus as claimed in claim 1, constructed to direct said outgoing flow of water at a downward angle inclined to the vertical up to 45°.3. Apparatus as claimed in claim 2, constructed to direct said outgoing flow of water at a downward angle inclined to the vertical up to 25°.4. Apparatus as claimed in claim 3, constructed to direct said outgoing flow of water at a downward angle which is substantially vertical.5. Apparatus as claimed in any preceding claim, in which the entrainment means comprise a cr) reservoir for particulate material and an inlet from the reservoir to the conduit, so constructed and arranged that the upward flow in the conduit can suck into itself through this inlet a stream of water entraining particulate material from the reservoir.COO6. Apparatus as claimed in claim 5, in which the entrainment means comprise Venturi means.CO 7. Apparatus as claimed in claim 5 or 6, in which the reservoir has an inlet mouth and the apparatus is constructed to direct said outgoing flow of water and entrained material downwardly towards said mouth.8. Apparatus as claimed in any preceding claim, adapted to recycle the particulate material.9. Apparatus as claimed in any preceding claim, in which the flow cross-section just after the outlet is substantially larger than the flow cross-section at the outlet, whereby the flow of water from the outlet can readily distribute laterally.10. Apparatus as claimed in claim 8, in combination with the particulate material, which is so chosen it will continue to fall downwardly when the flow of water from the outlet distributes laterally.11. Apparatus as claimed in claim 10, in which the particulate material is chosen for its particle size to have a diameter substantially in the range of from 1 mm to 3 mm.12. Apparatus as claimed in any one of claims 9 to 11, comprising a particulate material reservoir constructed and arranged to catch substantially all of the particulate material outgoing from the outlet.13. Apparatus as claimed in any preceding claim, in which the pump means precedes the entrainment means, comprising a one-way valve between the pump means and the entrainment means.14. Apparatus as claimed in any preceding claim, in which the pump means are connected through a downpipe to the conduit.15. Apparatus as claimed in claim 14, in which the pump means have a flow rate that is within a range extending from 200 to 1000 litres per hour.16. Apparatus for use in the production of an underwater visual effect, adapted to produce an underwater fall of particulate material without the aid of air, substantially according to any example hereinbefore described with or without reference to the accompanying drawings.17. Apparatus in use for, or a process of, producing an underwater visual effect, in which there is used apparatus as claimed in any preceding claim.18. Apparatus in use for, or a process of, producing an underwater visual effect, in which there is used apparatus which is operated under water, comprising an upwardly directed conduit with an outlet from the top of the conduit, pump means that cause a flow of water to pass upwardly along the conduit, and entrainment means that enable the water for said flow to entrain particulate cr) material, whereby the flow carries the material up the conduit to its said outlet without the aid of air and thereby produces an ejection of the material from the outlet, the flow of water and entrained material being directed downwardly as it is outgoing from the outlet so as to simulate a fall of sand.COO19. Apparatus or process as claimed in claim 18, in which the flow of water is directed at a CO downward angle inclined to the vertical up to 45°.20. Apparatus or process as claimed in claim 19, in which the flow of water is directed at a downward angle inclined to the vertical up to 25°.21. Apparatus or process as claimed in claim 20, constructed to direct the flow of water at a downward angle which is substantially vertical.22. Apparatus or process as claimed in any one of claims 18 to 21, in which the entrainment means comprise a reservoir for particulate material and an inlet from the reservoir to the conduit, so constructed and arranged that the upward flow in the conduit can suck into itself through this inlet a stream of water entraining particulate material from the reservoir.23. Apparatus or process as claimed in claim 22, in which the entrainment means comprise Venturi means.24. Apparatus or process as claimed in claim 22 or 23, in which the reservoir has an inlet mouth and the apparatus is constructed to direct said outgoing flow of water and entrained material downwardly towards said mouth.25. Apparatus or process as claimed in any one of claims 18 to 24, adapted to recycle the particulate material.26. Apparatus or process as claimed in any one of claims 18 to 25, in which the flow cross-section just after the outlet is substantially larger than the flow cross-section at the outlet, whereby the flow of water from the outlet can readily distribute laterally.27. Apparatus or process as claimed in claim 26, in combination with the particulate material, which is so chosen it will continue to fall downwardly when the flow of water from the outlet distributes laterally.28. Apparatus or process as claimed in claim 27, in which the particulate material is chosen for its particle size to have a diameter substantially in the range of from 1 mm to 3 mm.29. Apparatus or process as claimed in any one of claims 26 to 28, comprising a particulate material reservoir constructed and arranged to catch substantially all of the particulate material outgoing from the outlet.30. Apparatus or process as claimed in any one of claims 18 to 29, in which the pump means precedes the entrainment means, comprising a one-way valve between the pump means and the entrainment means.31. Apparatus or process as claimed in any one of claims 18 to 30, in which the pump means are connected through a downpipe to the conduit.(r) 32. Apparatus or process as claimed in claim 31, in which the pump means have a flow rate that is within a range extending from 200 to 1000 litres per hour.CO 33. Apparatus or process as claimed in any preceding claim, in which the particulate material comprises sand.CO 34. Apparatus or process as claimed in any preceding claim, in which the particulate material comprises gravel.35. A process substantially according to any example hereinbefore described with or without reference to the accompanying drawings.36. A modification of apparatus or process as claimed in any preceding claim, suitable for any other suitable liquid in place of the water.