GB2158813A

GB2158813A - Powder flow control valve

Info

Publication number: GB2158813A
Application number: GB08412802A
Authority: GB
Inventors: Philip John Lloyd
Original assignee: Loughborough Consultants Ltd
Current assignee: Loughborough Consultants Ltd
Priority date: 1984-05-18
Filing date: 1984-05-18
Publication date: 1985-11-20
Also published as: GB8412802D0; GB2158813B

Abstract

A powder flow control valve (1) has a powder flow path surrounded by a frusto-conical perforated boundary surface (3) of e.g. porous plastics material. Means, e.g. a pump, is provided for creating a drop in pressure across the boundary surface (3) with the higher pressure on the powder flow path side of the boundary surface. The pump can alternatively be used to fluidise the powder to cause powder flow through the valve. <IMAGE>

Description

SPECIFICATION Powder flow control valve This invention relates to a powder flow control valve and to a method of controlling powder flow.

When a container is to be filled with a powder, it may be desirable to measure the weight of powder accurately. For example in the food industry it may be necessary to fill a container with a measured weight of powder such as coffee or milk powder. It is desirable that the measurement of the weight of powder should be as accurate as possible since a minimum quantity of powder must be provided in the container but once that minimum weight is reached any extra powder in the container is wasted.

Various problems have to be overcome in producing an accurate measurement of the powder but one problem is providing a valve that can operate reliably over a prolonged period and that is not too difficult to maintain and in particular clean. The valve may also have to be sterilisable.

According to the invention there is provided a powder flow control valve in which a powder flow path is surrounded by a perforated boundary surface and means are provided for creating a drop in pressure across the boundary surface with the higher pressure on the powder flow path side of the boundary surface.

When the pressure drop is created powder flowing through the valve is drawn towards the boundary surface and held there so that flow of powder through the valve is terminated. A major advantage of this design is that there need be no moving parts in the powder flow path resulting in a very simple design which is also easy to clean.

The means for creating a drop in pressure across the boundary surface preferably operates by reducing the pressure on the opposite side of the boundary surface to the powder flow path without reducing (or without reducing so much) the pressure along the powder flow path. Alternatively but less desirably it could operate by increasing the pressure along the powder flow path without increasing (or without increasing so much) the pressure on the opposite side of the boundary surface.

Preferably the boundary surface has rotational symmetry and preferably includes a substantially frustoconical portion with the smaller diameter portion downstream of the large diameter portion. In use the axis of rotational symmetry of the boundary surface is advantageously substantially vertical.

The precise dimensions and shape of the boundary surface may be chosen by experiment and different dimensions and shapes may be used for different powders.

The perforated boundary surface may be made of a porous material, for example sintered metal powder, glass or a plastics material, or may be made by a component with apertures formed therein at a multiplicity of predetermined locations. In the latter case the locations are preferably evenly distributed around the boundary surface.

In addition to providing means for creating a pressure drop across the boundary surface with the higher pressure on the powder flow path side of the boundary surface means may be provided for creating a pressure rise across the boundary surface with the lower pressure on the powder flow path side of the boundary surface. When the pressure rise is created powder flowing through the valve is inhibited from adhering to the boundary surface or forming a stable arch. This technique of preventing powder sticking to a surface is already known per sue but its use in a valve according to the invention is original.

According to another aspect of the invention there is provided a method of controlling the flow of a powder in which a portion of the path along which powder flows is surrounded by a perforated boundary surface and powder flow is stopped by creating a drop in pressure across the boundary surface with the higher pressure on the powder flow path side of the boundary surface.

By way of example a powder flow control valve embodying the invention will be described with reference to the accompanying drawing which is a side sectional view of the valve.

The control valve 1 is sited at the bottom of a shaft 2 of circular cross-section and includes a frustoconical part 3 made of porous plastics material which in this particular example is that sold under the trademark PORVAIR. Immediately below the frusto-conical part 3 is a cylindrical part 4 leading to an outlet 5 of the valve. A plenum chamber 6 is defined between the outside of the frusto-conical part 3 and the walls of the shaft 2. The plenum chamber 6 is connected to a pump (not shown) which can be arranged to suck air out of or pump air into the chamber 6.

In use, powder is supplied to the top of the shaft 2 and falls down the shaft. When air is being sucked out of the plenum chamber 6 then air is caused to flow from the shaft through the frusto-conical part 3 onto the chamber 6 and this causes powder in the shaft 2 to adhere to the surface of the part 3 and no powder reaches the outlet 5; this situation corresponds to the "closed" state of the valve. If, on the other hand, air is blown into the plenum chamber 6 the air flow through the part 3 is reversed and powder is prevented from stacking to the part 3 and falls through the outlet 5; this situation corresponds to the "open" state of the valve.

The valve 1 can therefore be used very effectively to control powder flow.

One particular example of a valve and powder that have been used successfully together will now be described In this example the shaft 2 had an internal diameter d, of 60 mm, the frusto-conical part 3 had a height h of 42 mm and a minimum internal diameter d2 of 15 mm. The inclination a of the frustoconical boundary surface to the horizontal was 60o. The powder used was granular coffee which when subjected to a sieve analysis gave the results shown in the Table below: TABLE Sieve Size (liy) Cumulative Weight % 2800 97 2400 91.2 2000 79.3 1680 73.8 1400 66.8 1200 61 1000 53.1 850 46.1 500 22.8 In the "closed" state of the valve, the pressure in the plenum chamber 6 was 15" Hg below atmospheric pressure and there was an air flow rate of 48 litres per minute (at atmospheric pressure). In the "open" state of the valve, the pressure in the plenum chamber was 6 psi above atmospheric pressure and there was an air flow rate of 47 litres per minute (at atmospheric pressure).

The same valve was also tested with powdered milk and proved entirely satisfactory. Nonetheless it should be understood that the dimensions of the valve may need to be altered for different powders and in particular the dimensions d2 may need to be varied. It may also be possible to omit the cylindrical part 4 at the outlet of the valve without affecting the operation of the valve.

Claims

1. A powder flow control valve in which a powder flow path is surrounded by a perforated boundary surface and means are provided for creating a drop in pressure across the boundary surface with the higher pressure on the powder flow path side of the boundary surface.

2. A valve as claimed in claim 1 in which the means for creating a drop in pressure across the boundary surface operates by reducing the pressure on the opposite side of the boundary surface to the powder flow path without reducing, or without reducing so much, the pressure along the powder flow path.

3. A valve as claimed in claim 1 in which the means for creating a drop in pressure across the boundary surface operates by increasing the pressure along the powder flow path without increasing, or without increasing so much, the pressure on the opposite side of the boundary surface to the powder flow path.

4. A valve as claimed in any preceding claim in which the boundary surface has rotational symmetry.

5. A valve as claimed in claim 4 in which the boundary surface includes a substantially frusto-conical portion 1 with the smaller diameter portion downstream of the larger diameter portion.

6. A valve as claimed in claim 4 or 5 in which the axis of rotational symmetry of the boundary surface is substantially vertical.

7. A valve as claimed in any preceding claim in which the perforated boundary surface is made of a porous material.

8. A valve as claimed in any of claims 1 to 6 in which the perforated boundary surface is provided by a component with apertures formed therein at a multiplicity of predetermined locations.

9. A valve as claimed in claim 8 in which the locations are evenly distributed around the boundary surface.

10. A valve as claimed in any preceding claim further including means for creating a pressure rise across the boundary surface with the lower pressure on the powder flow path side of the boundary surface.

11. A powder flow control valve substantially as herein described with reference to and as illustrated by the accompanying drawings.

12. A method of controlling the flow of a powder in which a portion of the path along which powder flows is surrounded by a perforated boundary surface and powder flow is stopped by creating a drop in pressure across the boundary surface with the higher pressure on the powder flow path side of the boundary surface.

13. A method as claimed in claim 12 in which the drop in pressure is created by reducing the pressure on the opposite side of the boundary surface to the powder flow path without reducing, or without reducing so much, the pressure along the powder flow path.

14. A method as claimed in claim 12 in which the drop in pressure is created by increasing the pressure along the powder flow path without creasing, or without increasing so much, the pressure on the opposite side of the boundary surface to the powder flow path.

15. A method as claimed in any of claim 12 to 14 in which the boundary surface has rotational sym metry.

16. A method as claimed in claim 15 in which the boundary surface includes a substantially frustoconical portion with the smaller diameter portion downstream of the larger diameter portion.

17. A method as claimed in claim 15 or 16 in which the axis of rotational symmetry of the boundary surface is substantially vertical.

18. A method as claimed in any of claims 12 to 17 in which the perforated boundary surface is made of a porous material.

19. A method as claimed in any of claims 12 to 18 in which the perforated boundary surface is provided by a component with apertures formed therein at a multiplicity of predetermined locations.

20. A method as claimed in claim 19 in which the locations are evenly distributed around the boundary surface.

21. A method as claimed in any of claims 12 to 20 further including the step of creating a pressure rise across the boundary surface with the lower pressure on the powder flow path side of the boundary surface.

22. A method of controlling the flow of a powder, the method being substantially as herein described with reference to and as illustrated by the accompanying drawing.