EP3083144A1

EP3083144A1 - A device for feeding media to a blasting machine, and a closure for the device

Info

Publication number: EP3083144A1
Application number: EP14818894.9A
Authority: EP
Inventors: Nicolas GANSHOF VAN DER MEERSCH
Original assignee: Swiss Industrial Consulting and Technology SA; Swiss Ind Consulting and Tech SA
Current assignee: Swiss Industrial Consulting and Technology SA; Swiss Ind Consulting and Tech SA
Priority date: 2013-12-19
Filing date: 2014-11-26
Publication date: 2016-10-26
Also published as: WO2015090875A1

Abstract

18 ABSTRACT "A material conveying device"" A material conveying device comprises a cylinder (2) and a dividing wall (5) disposed within 5 the cylinder defining an upper (6) and lower (7) chamber within the cylinder. The dividing wall (5) comprises an inlet aperture (10) for conveying material from the upper chamber (6) to the lower chamber (7), and a pressure equalisation aperture (21) for equalisation of pressure between the upper and lower chambers. Closure means for the inlet and pressure equalisation apertures (20, 21) are provided, the closure means being disposed under the dividing wall (5) 10 and comprising a support member (22, 24), a first closure (23) for the pressure equalisation aperture (21) fixed to the support member, and a second closure (25) for the inlet aperture (20) fixed to the support member by means of a resiliently deformable member (26) such that the second closure (25) is vertically movable relative to the support member from an extended position to a retracted position, and is biased into the extended position. Actuation means for 15 the closure means configured to open the inlet and pressure equalisation apertures by moving the support member (22, 24) and closures (23, 25) away from the apertures to open the outlet and pressure equalisation apertures, wherein the pressure equalisation aperture (21) is opened prior to the inlet aperture (20). (Figs 2A and 2B) 20

Description

Title

A device for feeding media to a blasting machine, and a closure for the device

Background to the Invention

The invention relates to device for feeding media to a blasting machine of the type that projects a particulate media at a surface for the purpose of cleaning the surface.

Blasting machines of the above-referenced type are known and generally comprise a tank/reservoir for the media, an air/media mixing chamber where the media is mixed with compressed air and accelerated into a delivery line, and a nozzle in fluid communication with the mixing chamber for directing the media/air mixture at a surface to be treated. A machine of the above-referenced type is described in Applicants International Patent Application No:PCT/EP2007/002421. In order for this machine to operate correctly, and particularly to enable consistent and smooth delivery of media from the reservoir/tank to the mixing chamber, it is necessary to equalise the pressure between the tank and the mixing chamber. In PCT/EP2007/002421, this is achieved by employing a pressure equalisation conduit that provides fluid communication between the pressurised mixing chamber and the interior of the media tank, which results in the tank being pressurised. A problem with this arrangement is that when the tank needs to be re-filled with media, the machine needs to be switched off, as otherwise the opening the tank will release the pressure in the tank and consequently release the pressure in the mixing chamber due to the pressure equalisation conduit.

It is an object of the invention to overcome this problem.

Statements of Invention

In a first aspect, the invention provides a material conveying device comprising:

- a cylinder;

- a dividing wall disposed within the chamber defining an upper and lower chamber within the cylinder, the dividing wall comprising an outlet aperture for conveying material from the upper chamber to the lower chamber, and a pressure equalisation aperture for equalisation of pressure between the upper and lower chambers; - closure means for the outlet and pressure equalisation apertures, the closure means comprising a support member, a first closure for the pressure equalisation aperture fixed to the support member, and a second closure for the outlet aperture fixed to the support member by means of a resiliently deformable member such that the second closure is at least vertically movable relative to the support member from a first extended position to a second retracted position, and is biased into the extended position; and

- actuation means for the closure means configured to open the inlet and pressure equalisation apertures by moving the support member and closures away from the apertures to open the outlet and pressure equalisation apertures, wherein the pressure equalisation aperture is opened prior to the inlet aperture .

Thus, the use of a resiliently deformable member for mounting the second closure allows vertical movement of the closure relative to the support member, which allows the pressure equalisation aperture open prior to the inlet aperture (See Figs 1 and 2). This allows pressure equalisation between the chambers before the inlet aperture is opened.

Preferably, the closures are disposed under the dividing wall, in which the actuation means is configured to open the inlet and pressure equalisation apertures by raising the support member and closures. Thus, when the lower chamber is pressurised and the upper chamber is not pressurised, both the tension exerted by the resiliently deformable means and the pressure in the lower chamber will keep the second closure in engagement with the inlet aperture. However, opening of the pressure equalisation aperture and subsequent pressure changes in the chambers helps force the second closure down to open the inlet aperture. Typically, the support member comprises an actuation rod configured to extend longtitudinally through an aperture in the dividing wall, and a base member fixed to the actuation rod and extending laterally of the actuation rod.

Suitably, at least one of the closures is mounted to the base member, wherein the actuation means is operatively connected to the support member to raise and lower the support member.

Typically, the actuation rod extends through one of the outlet and pressure equalisation apertures. Suitably, one of the first and second closures is axially mounted to the actuation rod and another of the first and second closures is fixed to the base member.

Ideally, the actuation rod extends through the pressure equalisation aperture, wherein the first closure is axially mounted to the actuation rod and the second closure is mounted on the base member. This is an ideal arrangement as the first closure which opens the pressure equalisation conduit is exposed to the greatest stress, so mounting it on the actuation rod provides the best support. In one embodiment, the dividing wall comprises more than two apertures, and the closure means comprises a separate closure for each aperture.

Suitably, the first chamber comprises a pressure equalisation conduit configured to provide fluid communication from the pressure equalisation aperture to an upper part (i.e. a top) of the first chamber.

Preferably, the actuation rod is at least partially disposed within the pressure equalisation conduit. Ideally, at least one, and preferably both, of the closures comprises an inverted cone-shaped member. Typically, the cone-shaped member has a frusto-conical shape.

Suitably, the support member is generally L-shaped. Ideally, the resiliently deformable member is a helical spring. An advantage of the helical spring is that it allows the closure a degree of lateral play, thus facilitating self-centering engagement between the closure and its associated aperture. Other types of resiliently deformable members are possible, for example other types of spring members, or pneumatic or hydraulic piston devices. In one embodiment, both closures are mounted to the support member by means of a helical spring to allow some lateral play of the closures with respect to the support members and self-centering during engagement with apertures. The invention also relates to a closure means for outlet and pressure equalisation apertures of a material conveying device of the inve, the closure means comprising:

- a support member,

- a first closure for the pressure equalisation aperture fixed to the support member, and - a second closure for the outlet aperture fixed to the support member by means of a resiliently deformable member such that the second closure is vertically movable relative to the support member from a first extended position to a second retracted position, and is biased into the extended position. Typically, the resiliently deformable member is a helical spring.

Suitably, the support member comprises an actuation rod that in use is configured to extend longtitudinally through an aperture in the dividing wall, and a base member fixed to the actuation rod and extending laterally of the actuation rod, in which at least one of the closures is suitably mounted to the base member.

Typically, one of the first and second closures is axially mounted to the actuation rod and another of the first and second closures is fixed to the base member. Preferably, the first closure is axially mounted to the actuation rod and the second closure is mounted on the base member.

Suitably, one or both of the closures comprises an inverted cone shaped member. In one embodiment, the actuation means for the closure means comprises a reciprocating cam operatively connected to the support member of the closure means, ideally operatively connected to a top end of the actuation rod. Suitably, the actuating means is disposed above the upper chamber, away from the media. The invention also provides a closure means according to the invention, the closure means comprising:

- a support member comprising an actuation rod and a base member fixed to a lower part of, and extending laterally of, the actuation rod, - a first closure axially mounted to the lower part of the actuation rod, and

- a second closure fixed to the base member, in a spaced-apart relationship to the first closure, by means of a helical spring such that the second closure is vertically movable relative to the base member from a first extended position to a second retracted position, and is biased into the extended position,

wherein each of the first and second closures comprises an inverted cone shaped member.

The invention also provides a blasting machine of the type having a pressurised tank for media, the machine comprising:

a pressurised tank for media;

a dosing device adapted to receive media from the pressurised tank and dose the media into a supply of compressed air;

a nozzle adapted to receive the mixture of media and compressed air and direct the mixture at a surface to be treated; and

an autofeed device for continuously feeding media from an unpressurised container or hopper to the pressurised tank, wherein the autofeed device comprises a material conveying device according to the invention.

The invention also provides a blasting machine comprising:

a tank for media;

a mixing chamber for mixing media with compressed fluid;

a dosing device adapted to receive media from the tank and dose the media into the mixing chamber;

a nozzle adapted to receive the mixture of media and compressed fluid and direct the mixture at a surface to be treated;

wherein the dosing device comprises a material conveying device according to the invention.

The invention also provides a method for continuously feeding media from a first environment having a first pressure to a second environment having a second pressure without substantially altering the pressure in the second environment, which method employs a material conveying device of the invention, the method comprising the steps of: actuating the closure means for the outlet and pressure equalisation apertures in the dividing wall to open the apertures in sequence with the pressure equalisation aperture being opened prior to the outlet aperture, whereby the pressure in the second chamber is equalised with the pressure in the first chamber just prior to the media in the first chamber falling into the second chamber; and

actuating the closure means for the inlet and pressure equalisation apertures in the dividing wall to close the apertures.

In this specification, the term "unpressurised" means ambient pressure. In this specification, the term "pressurised" means a pressure significantly greater than ambient, for example 0.1 to 20.0 Bar, more typically 0.5 to lOBar.

Although the embodiments of the invention described herein primarily relate to a device for continuously feeding media from an unpressurised environment to a pressurised environment, it will be appreciated that it could likewise function in feeding media from a pressurised environment to an unpressurised environment, or between high pressure environments having different pressures or low pressure environments having different pressures.

In this specification, the term "media" is primarily intended to mean media that is employed for blasting a surface, for example sand or calcium carbonate, however the term also encompasses other flowable materials, for example powders, flakes, pellets, particulates, granulates and the like.

Brief Description of the Figures

The invention will be more clearly understood from the following description of some embodiments thereof, with reference to the accompanying drawings, in which:

Figs. 1A and IB are elevational views of a closure means according to the invention;

Figs. 2A and 2B are sectional elevational views of a material conveying device according to the invention incorporating the closure means of Figs. 1A and IB; Fig. 3 a sectional elevational view of an auto-feed device according to the invention, shown with both chambers empty;

Fig. 4 is a detailed view of the auto-feed device of Fig. 3 showing the inlet aperture in the top and bottom wall closed, and the inlet aperture in the dividing wall open;

Fig.5 a sectional elevational view of an auto-feed device of Fig. 3, shown with the first chamber charged with a dose of media; and the inlet aperture in the dividing wall closed and the pressure equalisation conduit in the dividing wall open to allow pressure equalisation between the first and second chambers;

Fig. 6 is a detailed view of the auto-feed device of Fig. 5;

Fig. 7 is detailed view of the auto-feed device of Fig. 5 shown from a different angle, and showing the aperture in the dividing wall open and the apertures in the top and bottom walls closed;

Fig.8 a sectional elevational view of the auto-feed device of Fig. 3, shown with the first chamber empty and the second chamber charged with media, the inlet aperture in the dividing wall open, the inlet aperture in the bottom wall closed, and the pressure equalisation aperture in the bottom wall open;

Fig. 9 is a detailed view of the auto-feed device of Fig. 8, showing the dose of media in the second chamber and a dose of media in the inlet chamber above the first chamber;

Fig. 10 is a detailed view of the auto-feed device of Fig. 8, showing the apertures in the dividing wall closed and pressure equalisation aperture in the bottom wall open to equalise pressure between the second chamber and outlet and inlet aperture in the bottom wall to allow the dose of media fall into the outlet;

Fig. 11 is a sectional elevational view of the auto-feed device of Fig. 3, showing the inlet aperture in the top wall open and a dose of media in the first chamber, and the inlet aperture in the bottom wall open and a dose of media in the outlet; Fig. 12 is an illustration of a blasting system comprising a blasting machine, a hopper for media and a device according to the invention; and

Fig. 13 is an illustration of a blasting machine which employs a device according to the invention as a dosing device.

Detailed Description of the Invention

Referring to the drawings, and initially to Figs. 1A and IB, there is illustrated a closure device according to the invention comprising a support member having an actuation rod 22, a transverse arm 24, a first conical closure member 23 axially mounted to the actuation rod 22, and a second conical closure member 25 mounted to the transverse arm 24 by means of a helical spring 26. The second conical closure member 25 is biased into an extended position shown in Fig. 1A by the helical spring, and is movable upon application of a force F into a retracted position shown in Fig. IB.

Referring to Figs 2A and 2B, there is illustrated a material conveying device according to the invention incorporating a closure means of Figs 1A and IB, and in which parts identified with reference to Figs. 1A and IB are assigned the same reference numerals. The conveying device comprises a cylindrical body 2 having a dividing wall 5 defining first (upper) chamber 6 and a second (lower) chamber 7. The dividing wall 5 comprises an inlet aperture 20 and a pressure equalisation aperture 21. The closure means is disposed within the cylindrical body 2 with the actuating rod 22 projecting through the pressure equalisation aperture 21, and the first and second closure members 23, 25 disposed underneath the pressure equalisation and inlet apertures 21, 20, respectively. In Fig. 2A, the closure means is raised and the two closure members 23, 25 are engaged with the apertures 21,20, closing the apertures. It should be noted that in this position, the helical spring 26 is compressed and the second closure 25 is retracted with respect to the lateral arm 24. Referring to Fig. 2B, where the closure member has been partially lowered, the first closure member 23 has moved out of contact with the pressure equalisation aperture 21, thus opening the pressure equalisation aperture, while the second closure member 25 is now in an extended position and still in contact with the inlet aperture, keeping the inlet aperture closed (in practice, the delay in pressure equalisation between the two chambers also helps keep the inlet aperture closed). This allows pressure equalisation between the chambers before the inlet aperture 20 is opened. Further lowering of the closure member (not shown) results in the second closure member 25 being moved out of engagement with the inlet aperture, thus opening the inlet aperture.

Referring Figs. 3 and 4, there is illustrated a device for continuously feeding media from an unpressurised container to a pressurised chamber, indicated generally by the reference numeral 1. In this case, the device is an auto-feed device for feeding media from a hopper (not shown) to a pressurised tank of a blasting machine (not shown) of the type described in PCT/EP2007/002421. The device 1 comprises a generally cylindrical body 2 having a top wall 3, a bottom wall 4 and a dividing wall 5, in which the top wall 3 and dividing wall 5 define a first chamber 6 and the dividing wall 5 and bottom wall 4 define a second chamber 7. An inlet chamber 8 is provided above the first chamber, and is adapted to engage an outlet of the hopper. An outlet chamber 9 is provided below the second chamber, and in use is adapted to sealingly engage with an inlet of the pressurised tank of the blasting machine. Referring particularly to Fig. 4, the top wall 3 includes a media inlet aperture 10 and a pressure equalisation aperture 11 that remains open, and a closure means that can be actuated to open and close the aperture 10, the closure means comprising an actuation rod 12 that projects through the pressure equalisation aperture 11 in the top wall 3, a transverse arm 14 and a conical closure member 15 mounted to the transverse arm by means of a helical spring 16.

Referring particularly to Figs. 3 and 9, the dividing wall 5 includes a media inlet aperture 20 and a pressure equalisation aperture 21, and a closure means that can be actuated to open and close the apertures 20 and 21 in sequence, the closure means comprising an actuation rod 22, a first conical closure member 23 mounted to the base of the rod 22, a transverse arm 24 and a second conical closure member 25 mounted to the transverse arm by means of a helical spring 26. A pressure equalisation conduit 27 is provided for providing fluid communication from the second chamber 7 to a top of the first chamber 6 via an aperture 28 in the conduit 27. The pressure equalisation conduit 27 extends through the top wall 3, and the actuation rod 22 is mounted in the pressure equalisation conduit. A seal (not shown) is mounted in a top of the pressure equalisation conduit allow movement of the actuation rod without a change of pressure in the conduit.

Referring particularly to Figs. 3 and 4, the bottom wall 4 includes a media inlet aperture 30 and a pressure equalisation aperture 31, and a closure means that can be actuated to open and close the apertures 30 and 31 in sequence, the closure means comprising an actuation rod 32, a first conical closure member 33 mounted to the base of the rod 32, a transverse arm 34 and a second conical closure member 35 mounted to the transverse arm by means of a helical spring 36. A pressure equalisation conduit 37 is provided for providing fluid communication from the second chamber 7 to a top of the first chamber 6 via an aperture 38 in the conduit 37. The pressure equalisation conduit 37 extends through the dividing wall 5 and the top wall 3, and the actuation rod 32 is mounted in the pressure equalisation conduit. A seal (not shown) is mounted in a top of the pressure equalisation conduit allow movement of the actuation rod without a change of pressure in the conduit.

In practice, the top, dividing and bottom walls will have a generally concave shape to ensure that media falls towards the respective inlet apertures.

An important aspect of the present invention is the equalisation of pressure between chambers prior to transfer of media from one chamber to another. Without pressure equalisation, the transfer of media is not possible. The inlet chamber located above the first chamber will generally always be at ambient pressure, and the outlet chamber located below the second chamber (which in the above embodiment is in fluid communication with the pressurised media tank) will always be pressurised. Thus, when the first chamber contains a dose of media, it will be at ambient pressure and the second chamber will be pressurised. In order to transfer media from the first chamber to the second chamber, the pressure equalisation aperture 21 in the dividing wall 5 needs to be opened while the media inlet aperture 20 is still closed (as in Figs. 3 and 4) to allow equalisation of pressure between the two chambers. The pressure equalisation conduit 27 ensures that the media in the first chamber is not unduly disturbed during pressure equalisation, by the provision of the aperture 28 in the conduit 27 in an upper part of the chamber, above the level of the media. Once pressure is equalised (which in practice will occur quickly), the inlet aperture is opened to allow media fall into the second chamber 7.

Thus, the closure means for the apertures in the top, bottom and dividing walls need to ensure that the apertures open and close in sequence, with the pressure equalisation aperture opening first and the media inlet aperture opening afterwards, in practice immediately afterwards. This is achieved by employing an actuating rod with two closures operatively connected to the rod, a first closure for the pressure equalisation aperture which is fixed to the rod for movement therewith, and a second closure for the inlet aperture which is fixed to the rod by means of a lateral arm, and is fixed to the arm by means of a resiliently deformable member that is biased into an extended position, for example a spring such as a helical spring, which allows a relative movement between the rod and the closure. Thus, when both closures are engaged with their respective apertures, downward movement of the rod will move the first closure out of engagement with the pressure equalisation aperture, whereas the second closure will remain in engagement with the inlet aperture due to the biasing effect of the spring until the spring is fully extended at which point further downward movement will open the inlet aperture. In this manner, a temporal and sequential opening of the apertures is achieved. The device also includes control means for controlling the closure means associated with the top, dividing and bottom walls. Various control means may be employed, including a cam mechanism, pistons, or motors controlled by a processer, the details and construction would be known to a person skilled in the art and which will not be described in more detail herein. In one embodiment, the actuation means comprises two cams mounted on a drive shaft for rotation of the cams about an axis of the shaft, wherein a first cam is operatively connected to an actuation rod of the closure means for the top and bottom walls, and the second cam is operatively connected to an actuation rod of the closure means for the dividing wall. Typically, the actuation means is adapted to actuate the closure means of the top and bottom walls to open the associated closures, and actuate the closure means of the dividing wall to close the associated closures, at substantially the same time.

The sequence of opening and closing of the closures means associated with the three walls is generally as follows: Stage 1: at a start of the process, the closures associated with the top and bottom walls will be closed and the closures associated with the dividing wall will be open. In this configuration, the first and second chambers will be unpressurised. Media is located in the inlet chamber above the first chamber (Figs 3 and 4). Stage 2. the closures associated with the dividing wall will be closed first, and the closures associated with the top and bottom walls will then be opened. In this configuration, the first chamber will be unpressurised, and the second chamber pressurised. Media will fall into the first chamber (Figs 5 and 6). . Stage 3: the closures associated with the top and bottom walls will be closed first, and the closures associated with the dividing wall will be opened second. In this configuration, the first and second chambers will be unpressurised and the media will fall into the second chamber (Figs 7, 8 and 9).

Stage 4: the closures associated with the dividing wall will be closed first, and the closures associated with the top and bottom walls will be opened second. The second chamber will be pressurised prior to the dose of media falling into the outlet chamber. Simultaneously, a dose of media will fall from the inlet chamber into the first chamber, both of which will be unpressurised (Figs 10 and 11).

Repeating these steps in sequence will enable a continuous feeding of media from the unpressurised container (i.e. hopper) to the pressurised tank of the blasting machine without compromising the operating pressure in the tank.

Referring to Fig. 12, there is illustrated a blasting system according to the invention and indicated generally by the reference numeral 50, and comprising a blasting machine having a pressurised media tank 51, dosing device and mixing chamber 52, pressurised fluid line 53 feeding pressurised air into the mixing chamber 52, pressurised media supply line 54 leading to a nozzle 55. A pressure equalisation conduit (not shown) is provided between the tank 52 and the mixing chamber 52. The hopper 56 is provided for containing media, the hopper having an outlet 57 that feeds media into an auto-feeding device of the invention 58. In use, media is continuously fed into the auto-feed device 58 from the hopper 56, and the auto-feed device feeds doses of media into the pressurised media tank 51 without any substantial pressure drop in the tank, then enabling the blasting machine to continue operating while the tank is being filled.

Referring to Fig. 13, an alternative embodiment of the invention is described in which parts similar to that described with reference to the previous embodiment are assigned the same reference numerals. In this embodiment, the auto-feed device of the invention is employed as a dosing device for the blasting machine, to feed media from an unpressurised hopper 56 into a mixing chamber 59. In use, the device of the invention acts as a dosing and metering device for dosing media from the hopper 56 into the pressurised mixing chamber 59 of the blasting machine. The rate of dosing of the media may be controlled by altering the timing of the opening and closing of the apertures to speed up or slow down the dosing rate as is required.

The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail without departing from the spirit of the invention.

Claims

A material conveying device comprising:

- a cylinder (2);

- a dividing wall (5) disposed within the cylinder defining an upper (6) and lower (7) chamber within the cylinder, the dividing wall (5) comprising an inlet aperture (10) for conveying material from the upper chamber (6) to the lower chamber (7), and a pressure equalisation aperture (21) for equalisation of pressure between the upper and lower chambers;

- closure means for the inlet and pressure equalisation apertures (20, 21), the closure means comprising a support member (22, 24), a first closure (23) for the pressure equalisation aperture (21) fixed to the support member, and a second closure (25) for the inlet aperture (20) fixed to the support member by means of a resiliently deformable member (26) such that the second closure (25) is at least vertically movable relative to the support member from an extended position to a retracted position, and is biased into the extended position; and

- actuation means for the closure means configured to open the inlet and pressure equalisation apertures by moving the support member (22, 24) and closures (23, 25) away from the apertures to open the outlet and pressure equalisation apertures, wherein the pressure equalisation aperture (21) is opened prior to the inlet aperture (20).

A device as claimed in Claim 1, in which the closures are disposed under the dividing wall (5), in which the actuation means is configured to open the inlet and pressure equalisation apertures by raising the support member (22, 24) and closures (23, 25)

A device as claimed in Claim 1 or 2 in which the support member comprises an actuation rod (22) configured to extend longtitudinally through an aperture in the dividing wall (5), and a base member (24) fixed to the actuation rod and extending laterally of the actuation rod, in which at least one of the closures (23, 25) is mounted to the base member, wherein the actuation means is operatively connected to the support member to raise and lower the support member.

4. A device as claimed in Claim 3 in which the actuation rod (22) extends through one of the inlet and pressure equalisation apertures (20, 21), wherein one of the first and second closures (23, 25) is axially mounted to the actuation rod (22) and another of the first and second closures (23, 25) is fixed to the base member (24).

5. A device as claimed in Claim 3 in which the actuation rod (22) extends through the pressure equalisation aperture (21), wherein the first closure (23) is axially mounted to the actuation rod (22) and the second closure (25) is mounted on the base member (24).

6. A device as claimed in any preceding Claim in which the first chamber (6) comprises a pressure equalisation conduit (27) configured to provide fluid communication from the pressure equalisation aperture (21) to an upper part of the first chamber.

7. A device as claimed in Claim 5 and 6 in which the actuation rod (22) is at least partially disposed within the pressure equalisation conduit (27).

8. A device as claimed in any preceding Claim in at least one of the closures comprises an inverted cone-shaped member (23, 25).

9. A device as claimed in any preceding Claim in which the support member is generally L-shaped.

10. A device as claimed in any preceding Claim in which the resiliently deformable member is a helical spring (26).

11. A device as claimed in any preceding Claim in which the actuation means comprises a rotating cam means operatively connected to the support member.

12. A closure means for outlet and pressure equalisation apertures of a material conveying device of any of Claims 1 to 11, the closure means comprising:

- a support member,

- a first closure (23) for the pressure equalisation aperture (21) fixed to the support member, and

- a second closure (25) for the outlet aperture (20) fixed to the support member by means of a resiliently deformable member (26) such that the second closure (25) is vertically movable relative to the support member from a first extended position to a second retracted position, and is biased into the extended position.

13. A closure means as claimed in Claim 12 in which the resiliently deformable member is a helical spring (26).

14. A closure means as claimed in Claim 12 or 13 in which the support member comprises an actuation rod (22) that in use is configured to extend longtitudinally through an aperture in the dividing wall, and a base member (24) fixed to the actuation rod and extending laterally of the actuation rod, in which at least one of the closures (23, 25) is mounted to the base member (24).

15. A closure means as claimed in Claim 14 in which one of the first and second closures (23, 25) is axially mounted to the actuation rod (22) and another of the first and second closures (23, 25) is fixed to the base member (24).

16. A closure means as claimed in Claim 15 in which the first closure (23) is axially mounted to the actuation rod (22) and the second closure (25) is mounted on the base member (24).

17. A closure means as claimed in any of Claims 12 to 16 in which one or both of the closures comprises an inverted cone shaped member.

18. A closure means according to Claim 12, the closure means comprising:

- a support member comprising an actuation rod (22) and a base member (24) fixed to a lower part of, and extending laterally of, the actuation rod,

- a first closure (23) axially mounted to the lower part of the actuation rod (22), and

- a second closure (25) fixed to the base member (24), in a spaced-apart relationship to the first closure, by means of a helical spring (26) such that the second closure is vertically movable relative to the base member from a first extended position to a second retracted position, and is biased into the extended position,

19. A blasting machine of the type having a pressurised tank for media, the machine comprising:

a pressurised tank for media (51);

a dosing device (52) adapted to receive media from the pressurised tank and dose the media into a supply of compressed air;

a nozzle (55) adapted to receive the mixture of media and compressed air and direct the mixture at a surface to be treated; and

an autofeed device for continuously feeding media from an unpressurised container or hopper to the pressurised tank, wherein the autofeed device comprises a material conveying device of any of Claims 1 to 11.

20. A blasting machine comprising:

a tank for media (56);

a mixing chamber (59) for mixing media with compressed fluid;

a nozzle (55) adapted to receive the mixture of media and compressed fluid and direct the mixture at a surface to be treated;

wherein the dosing device comprises a material conveying device according to any of Claims 1 to 11.

21. A method for continuously feeding media from a first environment having a first pressure to a second environment having a second pressure without substantially altering the pressure in the second environment, which method employs a material conveying device of any of Claims 1 to 11, the method comprising the steps of:

actuating the closure means for the outlet and pressure equalisation apertures in the dividing wall to open the apertures in sequence with the pressure equalisation aperture being opened prior to the outlet aperture, whereby the pressure in the second chamber is equalised with the pressure in the first chamber just prior to the media in the first chamber falling into the second chamber; and