GB2256156A

GB2256156A - Decanting columns and pipe joints

Info

Publication number: GB2256156A
Application number: GB9111571A
Authority: GB
Inventors: William Joseph Hunt
Original assignee: Enpure Ltd
Current assignee: Enpure Ltd
Priority date: 1991-05-30
Filing date: 1991-05-30
Publication date: 1992-12-02
Also published as: GB9111571D0

Description

DECANTING COLUMNS AND IMPROVEMENTS IN JOINTS The present invention relates to decanting columns for use in liquid treatment apparatus and to improvements in joints between interfitting members, such as interfitting pipes.

Decanting columns are used in water treatment plant to control the level of liquid in a treatment tank such as a flotation tank. Water containing impurities to be removed (e.g. sewage) is introduced into a flotation tank continuously. Solids are collected from the top of the tank and cleaner water is removed continuously from a low level in the tank. In order that the level of water in the tank is maintained at a desired level the water removed from the tank is led up the side of the tank in a decanting column and is allowed to overflow a weir at the top of the decanting column. It is necessary to be able to adjust the level of the weir by altering the effective length of the decanting column so as to be able to adjust the level of liquid in the flotation tank and so as to be able to bring different decanting columns on the same tank into balance with one another.Generally, such an adjustment will be made infrequently. Decanting columns are also used elsewhere in water treatment plant, for instance for decanting supernatant liquid from sludge drying beds.

In previous designs of decanting columns, a first tubular member has been provided having an inlet end for connection to water treatment apparatus and an outlet end in which is slidingly received the inlet end of a second tubular member whose opposite end constitutes an outlet weir. A cage of vertical rods is connected to the outlet end of the first tubular member. An apertured plate carried by the weir end of the second tubular member slides on the rods of the cage and provides a central threaded boss on the axis of the tubular members in which is received a threaded adjustment rod, the upper end of which is supported in a support plate carried by the top of the cage of rods.

The height of the weir may be adjusted by rotation of the threaded adjustment rod up and down which the apertured plate carrying the second tubular member can be screwed to adjust the height of the weir.

Such an arrangement is relatively expensive to fabricate, having a number of metal parts. The flow of liquid out of the weir end of the second tubular member is in part obstructed and made more turbulent by the apertured plate carrying the second tubular member and the liquid continuously washes over the threaded connection between the apertured plate and the adjustment rod so that these components need to be made of corrosion resistant metal such as stainless steel.

It will be desirable to provide a decanting column of simplified design.

The present invention provides a decanting column for use in liquid treatment apparatus, comprising a first tubular member having an inlet end for connection to said apparatus and an outlet end, and a second tubular member having an inlet end which is connected in a liquid tight manner to the outlet end of said first tubular member and a free outlet end forming a weir, wherein said connected ends of the first and second tubular members have co-operating internal and external threaded portions allowing length adjustment of the decanting column by rotation of said second tubular member.

Preferably, the thread on the threaded portion of one of said first and second tubular members is produced by winding a thread producing elongate member helically about an end portion of said first or second tubular member and attaching said elongate member thereto. The elongate member may be wound internally around the larger diameter one of the first and second tubular members but is preferably wound externally around the smaller diameter one of the first and second tubular members. By forming the thread in this manner, it is possible to start with first and second tubular members which are each plain tubular members of standard diameters chosen to interfit with one another to form a free-sliding fit. One may then cut a helical thread on one of the two tubular members and build up a corresponding helical thread on the other by attaching a said elongate member as described above.

The thread producing member may be received in a helical groove in said first or second tubular member, said groove being of a depth which is less than the thickness of said thread producing member. By this means, the thread producing member stands proud of the external diameter of the tubular member to form a thread.

The thread producing member may be adhesively secured to said first or second tubular member. Preferably it is adhesively secured over its length and is mechanically secured at at least one end, e.g. by a rivet or bolt passing through a bore through the thickness of the tubular member and either securing a clamp over the thread producing member or itself passing through the thread producing member so as to clamp it in position.

The thread producing member is preferably of elastomer material such as nitrile rubber. Preferably it is of 75 to 85 shore hardness or greater.

The first and second tubular members are preferably plastics pipes such as PVC pipes. Plastics pipes of substantial diameters, e.g. 8" to 12" (20cm to 30cm) generally have an ovality of several millimetres as manufactured. This is removable by lathing to facilitate the use of such pipes in the present invention.

Preferably, an O-ring seal or other form of seal is provided between the first and second tubular members below the threaded portions of the first and second tubular members. The seal may be provided by an annular member received in a groove in one of the two tubular members and making a slidable contact with the surface of the other tubular member. The annular member may be an O-ring or, for instance, a flat washer-like member of elastomer material.

Preferably, the first tubular member is provided with an internal thread and the second tubular member is received within the first tubular member and has an external thread.

The second tubular member may be provided with tool engaging formations for enabling said second tubular member to be engaged by an adjustment tool by means of which it may be rotated to adjust the height of the weir.

The tool engaging formations may be a plurality of lugs on the interior surface of said second tubular member.

These conveniently may be provided by securing by welding or adhesive a plurality of plate members on the interior of the second tubular member adjacent to the outlet end thereof. The height of the weir may then be adjusted by using an adjustment tool which is also used for adjusting other similar decanting columns in the plant.

Preferably, the bore of the second tubular member is unobstructed (apart from the presence of adjustment lugs of the kind described above) or at least has an unobstructed central region occupying a substantial part e.g. more than 80% or more than 90% of the cross-sectional area of the second tubular member. By avoiding the need for an apertured plate over the top of the outlet end of the second tubular member, one can achieve improved laminar flow of liquid out of the decanting column which makes it easier to compare the rate of flow between decanting columns and to adjust a number of columns to the same height and flow rate.

Preferably, to facilitate the adjustment of such columns, they are provided with a flow rate comparator in the form of a transversely extending measuring member which extends outwardly of the first tubular member or, less preferably, from the second tubular member and is provided with length graduations. The point at which a falling curtain of water originating from the weir outlet of the second tubular member cuts the line of the comparator provides a sufficiently accurate indication of the flow rate from the decanting column for use in setting different decanting columns to the same operating height or flow rate.

The present invention includes in a second aspect a method of joining interfitting, preferably tubular, members comprising forming a recessed helical thread on a portion of a first said member, forming a cooperating raised helical thread on a portion of a second said member by winding a thread producing elongate member therearound and attaching said elongate member thereto, and assembling said threaded portions together.

The tubular members may be lengths of pipe, e.g.

plastics pipe. The method enables a length adjustable joint to be produced between lengths of pipe of suitably chosen different standard external diameters.

The recessed thread is preferably formed by cutting material away from a pre-formed pipe and is preferably on the interior surface of the respective member.

The raised thread is preferably on the external surface of its respective member and the thread forming member is preferably laid into a helical groove cut on the surface of a pre-formed pipe.

This aspect of the invention further includes a joint assembly between interfitted members in which an end portion of a first said member has a recessed helical thread over a portion thereof and a second said member has a cooperating raised helical thread thereon formed by a thread producing elongate member wound about said second member and attached thereto.

The materials used, the manner of fixing the thread producing member and the use of seals may all be as described above.

The invention will be further described with reference to a preferred embodiment illustrated in the accompanying drawings in which: Figure 1 a side elevation of the interior of a flotation tank equipped with a decanting column according to the invention; and Figure 2 a partially sectioned side elevation of a decanting column according to the invention as shown in use in Figure 1.

As shown in Figure 1 a flotation tank 10 has an inlet 12 through which water containing impurities is continuously introduced. The water flows into the main body of the tank over a baffle 14 extending from the bottom of the tank. Treated water is removed from the lower part of the tank through an outlet pipe 16 which extends through the lower part of a side wall of the tank and is connected at an elbow joint to a riser column 18 at the top of which is positioned a decanting column 20 according to the invention. Water overflows from the decanting column and is removed for further treatment. The decanting column establishes a predetermined level 22 for liquid in the flotation tank 10 to enable a suitable scraper mechanism schematically illustrated at 24 to remove sludge from the flotation tank efficiently.

As shown in Figure 2, the decanting column comprises a first tubular member 26 having at its inlet end a mounting flange 28 by which it is connectable to the remainder of the water treatment apparatus and a groove 30 receiving an O-ring 32 in the end face of the first tubular member 26 for providing a water-tight connection.

At its upper outlet end, the first tubular member 26 has a female helical thread 34 cut therein and below the threaded portion the first tubular member 26 has an internal annular groove 36 receiving a second O-ring 38.

Received as a sliding fit within the first tubular member 26 is a second tubular member 40 which has a female helical thread 42 cut in an upper portion thereof in which is secured a length of circular cross-section nitrile rubber elastomeric material 44 so as to form a male thread on the second tubular member. At each of its ends, the thread forming material 44 is secured by a stainless steel stud bolt having a threaded end screwed into a retaining nut counter-sunk into the internal face of the second tubular member 40. Between these mechanical fixings, the thread forming material 44 is secured in the helical groove 42 by adhesive.

A bell mouth 45 is welded to the top of the second tubular member 40 to provide an increased length weir at its upper edge. A short way below the top of the second tubular member 40 there are secured by welding to the interior surface of the second tubular member three square plates 46. These enable a three-legged tool to be slid down the second tubular member from the top to engage the second tubular member by the square plates 46 which act as lugs to engage respective legs of the tool. By this means the second tubular member 40 may be rotated in the bore of the fixed first tubular member 26 so as to adjust the height of the weir provided by the bell mouth 45.

A measuring rod or plate 48 is provided extending laterally from a lower portion of the first tubular member 26 to act as a flow rate comparator. Typically, the length of this measuring rod or plate 48 will be somewhat greater than the diameter of the first tubular member 26. It may be provided with length graduations, preferably of high visibility, such as coloured bands. Means may alternatively or additionally be provided for measuring the height of the weir from a datum level. For instance, the adjustment tool may have a graduated stem readable against a datum above the weir or graduations may be provided on the exterior of the inner one of the two tubular members.

In use, water introduced into the flotation tank through the inlet 12 will after treatment exit from the bell mouth of the decanting column 20 and will overflow the weir constituted by the lip of the bell mouth in a mushroom-shaped curtain which will cut across the measuring rod or plate 48 further out along its length the faster the flow rate is. Typically, there will be a number of decanting columns 20 attached to respective riser columns 18 on the same flotation tank. These must all be adjusted to the same working height and this can conveniently be done by adjusting the height of the decanting columns so that a desired level 22 is achieved in the tank and the flow rate through each decanting column is the same as indicated on its respective measuring rod or plate 48.

Decanting columns of the kind described can be used in all applications in which decanting columns have been used previously in water treatment and may also be used in plant for treating other liquids.

A threaded joint as described above may be made between pipes other than in the context of a decanting column.

Although the invention has been described with reference to the characteristics of the specific embodiment illustrated, many modifications and variations thereof are possible within the scope of the invention.

Claims

1. A decanting column for use in liquid treatment apparatus, comprising a first tubular member having an inlet end for connection to said apparatus and an outlet end, and a second tubular member having an inlet end which is connected in a liquid tight manner to the outlet end of said first tubular member and a free outlet end forming a weir, wherein said connected ends of the first and second tubular members have co-operating internal and external threaded portions allowing length adjustment of the decanting column by rotation of said second tubular member.

2. A decanting column as claimed in Claim 1, wherein the thread on the threaded portion of one of said first and second tubular members is produced by winding a thread producing elongate member helically about an end portion of said first or second tubular member and attaching said elongate member thereto.

3. A decanting column as claimed in Claim 2, wherein the elongate member is wound externally around the smaller diameter one of the first and second tugular members.

4. A decanting column as claimed in Claim 2 or Claim 3, wherein the thread producing member is received in a helical groove in said first or second tubular member, said groove being of a depth which is less than the thickness of said thread producing member.

5. A decanting column as claimed in any one of Claims 2 to 4, wherein the thread producing member is adhesively secured to said first or second tubular member over its length and is mechanically secured at at least one end.

6. A decanting column as claimed in any one of Claims 2 to 5, wherein the thread producing member is of elastomer material.

7. A decanting column as claimed in Claim 6, wherein the thread producing member is of 75 to 85 shore hardness or greater.

8. A decanting column as claimed in any preceding claim, wherein the first and second tubular members are plastics pipes from which an as manufactured ovality of several millimetres has been removed by lathing.

9. A decanting column as claimed in any preceding claim, wherein the first tubular member is provided with an internal thread and the second tubular member is received within the first tubular member and has an external thread.

10. A decanting column as claimed in any preceding claim, wherein the second tubular member is provided with tool engaging formations for enabling said second tubular member to be engaged by an adjustment tool by means of which it may be rotated to ladjust the height of the weir.

11. A decanting column as claimed in Claim 10, wherein the tool engaging formations are a plurality of lugs on the interior surface of said second tubular member.

12. A decanting column as claimed in any preceding claim, wherein the bore of the second tubular member is unobstructed (apart from the optional presence of adjustment lugs) or at least has an unobstructed central region occupying more than 80% of the cross-sectional area of the second tubular member.

13. A decanting column as claimed in any preceding claim, provided with a flow rate comparator in the form of a transversely extending measuring member which extends outwardly of the first tubular member or from the second tubular member and is provided with length graduations.

14. A method of joining interfitting members comprising forming a recessed helical thread on a portion of a first said member, forming a cooperating raised helical thread on a portion of a second said member by winding a thread producing elongate member therearound and attaching said elongate member thereto, and assembling said threaded portions together.

15. A method as claimed in Claim 14, wherein the tubular members are lengths of pipe.

16. A method as claimed in Claim 14 or Claim 15, wherein the raised thread is on the external surface of its respective member and the thread forming member is laid into a helical groove cut on the surface thereof.

17. A joint assembly between interfitted members in which an end portion of a first said member has a recessed helical thread over a portion thereof and a second said member has a cooperating raised helical thread thereon formed by a thread producing elongate member wound about said second member and attached thereto.

18. A decanting column for use in liquid treatment apparatus, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

19. A method of joining interfitting members substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.