GB2515998A

GB2515998A - PFR bushing

Info

Publication number: GB2515998A
Application number: GB1307882.9A
Authority: GB
Inventors: Andrew Colverson; Stephen Martin Shaw
Original assignee: AES Engineering Ltd
Current assignee: AES Engineering Ltd
Priority date: 2013-05-01
Filing date: 2013-05-01
Publication date: 2015-01-14
Anticipated expiration: 2033-05-01
Also published as: US9423032B2; GB2515998B; GB2558161A; GB201311148D0; US20140325791A1; GB201307882D0

Abstract

An annular seal cavity throat bushing 6 is provided. The throat bushing 6 comprises: an inner annular surface 9; and an outer annular surface 8. The inner surface 9 comprises a substantially latitudinal channel 3 with the channel being provided with at least one orifice 12 to allow fluid communication between the inside of the bushing and the outside of the bushing. The bushing 6 is further provided with at least one groove 11 extending substantially longitudinally from one end of the bushing 6 to the channel 3. The groove 11 comprises at least one tapered edge, thereby increasing the width of the groove along its length.

Description

PFR BUSHING

Field of Invention

This invention is related to devices known as throat bushings, which are commonly used to improve the environment of seal packing positioned at the entrance to a seal cavity in rotating fluid equipment.

Background of Invention

Sealing equipment of various types is used in pumps in a variety of different industry for a variety of different purposes and applications. In order for the sealing equipment, which includes packing, bushing and mechanical seals, to operate continuously without premature failure its environment must be free from contaminants. In order for this to be the case a number of different techniques and accessories are used, however this patent is limited to accessories that are used with packing, called throat bushing.

Patent GB2007/001 674 teaches that one such solution for this issue is called the SpiralTrac seal which is an annular bushing which is placed at the entrance to a seal cavity of a pump, the cavity being defined by a portion of the pump housing, a shift that extends through the cavity, and a means for sealing a cavity itself. The sealing may take the form of a mechanical seal or packing material. The bushing includes a tapered central surface which has a spiral groove formed in its wall and which extends from adjacent to the outer surface of the bushing towards the cavity entrance. The spiral groove decreases in diameter down to the innermost diameter of the bushing, which defines a small angular gap around the shaft.

As the shaft rotates any particulate material that enters the seal cavity during operation of the pump will be centrifugally forced into the spiral groove and will flow towards the gap around the shaft. The particulate material is then forced outwardly through the gap to the exterior of the seal cavity.

In Patent GB20071001674 a design is described that overcomes the disadvantages of the SpiralTrac product by having more than one groove ensuring that should the contaminants build up in such a way that the groove is rendered impassable there is another that will ensure the flow of contaminants is maintained. The superior design also includes a groove which is rotated in clockwise direction and another which is in anticlockwise direction thereby allowing the product to operate irrespective of the direction of shaft rotation.

Through manufacturing trials it has be subsequently learnt that this design, although superior to the SpiralTrac design is very costly to manufacture. This is due to the nature of the grooves and vanes requiring complex geometry to be machined onto the inner surface of the product and so meaning that jigging must be manufactured for each size variant which allows the product to be secured on a machine post splitting.

Statements of Invention

Accordingly the present invention is directed to an annular seal cavity throat bushing comprising; an inner annular surface and an outer annular surface, the inner surface comprising a substantially latitudinal channel, the channel being provided with at least one orifice to allow fluid communication between the inside of the bushing and the outside of the bushing; the bushing being further provided with at least one groove extending substantially longitudinally from one end of the bushing to the channel, wherein the groove comprises at least one tapered edge, thereby increasing the width of the groove along its length.

It may be advantageous that the other edge of the groove is substantially perpendicular to the end of the bushing. Alternatively, it may also be tapered.

Having one of the sides of the groove tapered, or sloped, allows for easier machining of the groove. Additionally, as the edges are substantially longitudinal to the bushing, rather than spiralled, the fluid path is reduced, thereby reducing the time that debris and contaminates may be within the groove and thus reducing the likelihood of the debris and contaminants from building up and rendering the groove impassible. Any debris and contaminants are swiftly removed from within the bushing through the orifice.

Advantageously, the width of the, or each, groove increases as it approaches the channel. This creates a pressure differential that encourages the flow of fluid through the groove.

The seal cavity throat bushing may be used with rotating fluid equipment having a seal cavity which is defined by a rotary shaft having an axis, the shaft housing surrounding at least a portion of the shaft, and a sealing device engaging the shaft and said housing at one end of the cavity. In such a use, the said bushing may comprise: i) An outer annular surface divided into preferably three portions, the first being located at the exit of said cavity and the third being located at the entrance of said cavity and the third being located there between; wherein said first and third portions have minimal diametric clearance from said seal cavity and said second portion having a greater clearance; U) An inner annular surface divided into preferably three portions, the first being located at the exit of said cavity and the third being located at the entrance of said cavity and the second being located there between; wherein said first and third portions have minimal diametric clearance from said shaft and said second portion having a greater clearance; iU) One or more orifices longitudinally located in said second inner annular surface and extending radially outward thereby creating a passage between said second inner annular surface and said second outer annular surface; iv) One or more grooves longitudinally located on said third annular inner surface extending from the entrance of said cavity and extending longitudinally toward said second inner annular surface, the width of the said groove increases along its length with its widest point being located adjacent to the third portion of said inner annular surface.

The use of a tapered groove makes for a simplified manufacturing process and a more straight4orward construction. Additionally, the lack of a spiralled groove makes a more efficient device, especially with the introduction of the at least one tapered edge.

Preferably said grooves are radially located in line with at least one of said orifices.

Where the grooves lead fluid directly to the orifice, there is less distance to travel and so the device operates in an efficient manner.

More preferably the depths of said grooves increase along the longitudinal length with the deepest portion residing closest to said orifices. This creates a pressure differential, thereby encouraging the fluid flow along the groove.

More preferably the width of the grooves in opposing halves of the bushing are created in such a way that one groove creates a clockwise slope and the other creates an anticlockwise slope. Having grooves in different directions allows for the operation of the bushing regardless of the direction of rotation of the shaft around which it is positioned.

Preferably one or more annular grooves are located in said first and second outward annular surfaces allowing toroidal sealing members to reside therein creating a seal between said grooves and said cavity. The use of 0-ring seals provides for a simple and efficient sealing mechanism.

Preferably said throat bushing diameter is divided into two portions of equal size about said axis shaft axis thereby creating a split throat bushing. Creating a split throat bushing allows for easier transportation and installation of the bushing.

More preferably said split throat bushing is divided post machining and so when said halves are reassembled the annular surfaces are not circular.

More preferably said splits are located in a plane substantially perpendicular to a plane connecting the said grooves. Providing the split at what equates to a 12 o'clock and 6 o'clock position with the grooves at 3 o'clock and 9 o'clock, when viewed from one end, creates a bushing that is easy to orientate and install. Other dividing lines could be used, but it is more intuitive for the installer when the above dividing lines are used.

More preferably at least one hole capable of securely holding a pin is located on the split surface of one of the halves and the opposite half having holes located concentrically to said pins but with a larger diameter than said pin thereby allowing the halves to be assembled together. Location pins and holes make installation more precise and efficient.

Preferably a throat bushing has more than one threaded hole is located radially on said surface and adjacent to said cavity exit thereby allowing bolts to be fitted thereby aiding fitment of said bushing.

Preferably the material of construction is metallic and of a non-sparking nature.

Whilst other materials may be used, metallic and non-sparking materials are advantageous for the devices upon which the bushings are likely to be used.

Description of Drawings

The drawings forming part of this patent application are as follows:-Figure 1 is a longitudinal section of part of the rotary equipment including the throat bushing in accordance with the present invention; Figure 2 is an isometric view of half of a throat bushing in accordance with the present invention.

Figure 3 is an isometric view of the throat bushing of Figure 2 in its assembled state; Figure 4 is an end view from the cavity exit end of the bushing of Figure 3 showing the angling of the grooves.

Detailed Description of Invention

The present invention will now be described, by way of example only, and with reference to the accompanying drawings.

The rotary equipment shown in Figure 1 includes a shaft (1) which is free to rotate about its axis in operation and an equipment housing (2) which is stationary in operation. A sealing cavity (3) resides between the equipment housing (2) and the shaft (1) and located in this cavity (3) resides a sealing means in the form of packing rings (4) which are compressed by a gland ring (5) which is secured to the housing by bolts.

A throat bushing (6) is located between said packing rings (4) and the entrance of said cavity (7). The throat bushing comprises an outer annular surface (8), which is in close proximity to the inner diameter of the cavity (3), and an inner annular surface (9) which is in close proximity to the outer diameter of the shaft.

The outer annular surface (8) is divided into three portions; the first portion is located at the exit end of the cavity adjacent to the packing (4), the third portion is located adjacent to the entrance of the cavity, and the second portion is located between said first and third portions. In order for the bushing to seal against a cavity bore one or more 0-rings are located in grooves in the first and third annular portions thereby being in communication between the annular surface and the cavity bore ensuring that the bushing (6) is radially constrained in the cavity.

It is preferable that the second portion of the outer annular surface (8) is a smaller diameter than the first and third portions to allow the flow of fluid around the cavity allowing it to exit the cavity through one or more ports (10) in the cavity.

The inner annular surface (9) is also divided into three portions; the first portion is located at the exit end of the cavity adjacent to the packing (4), the third portion is located adjacent to the entrance of the cavity, and the second portion is located between said first and third portions. The second portion is has preferably a larger diameter than the first and third portions thereby allowing a greater clearance from the shaft (1). One or more grooves (11) are incorporated onto the third portion of the inner annular surface (9) providing a path for the fluid entering the cavity (3) to pass into the second portion. This groove (11) is preferably sloped in such a way that the deeper section is adjacent to the second portion thereby creating lower pressure at this end and so forcing the fluid to travel down this groove (11). One or more orifices (12) are created between the second portions of the inner (9) and outer annular surfaces (8) thereby allowing the fluid which travels down the groove (11) to exit the seal cavity (3) via the port (10). This ensures that any contaminants are removed prior to them entering the packing.

In Figure 2 it can be seen that the present invention has the groove (11) radially aligned with one or more of the orifices (12) thereby allowing the fluid to have the shortest route to exit the bushing. It also aids in the manufacture of the bushing as all the machining operations are done on the same plane as one another thereby reducing the complexity of the geometry and so the sophistication of the machine required. The groove (11) has varying width along one edge becoming wider as it passes from the end of the bushing (3) that is adjacent to the entrance of the cavity (7) and the second portion of the inner annular surface. This widening means that there is a pressure differential and so encouraging the fluid to flow down the groove and so carrying any contaminants with it. The orifice (12) in the present invention is the same width as the groove (11) aiding the fluid flow.

It can be seen in Figure 2 that the second portion of the inner annular surface (9) is elliptically shaped with the greater diameter being radially aligned with the orifice (12) and the groove (11) thereby encouraging the flow of fluid out of the orifice.

One or more orifices (13) are located on the planar surface of the bushing that is in direct communication with the packing (4) and provides a passageway between the orifice (12) and the packing (4) thereby allowing fluid to pass from the orifice (12) directly to the packing (4). Due to the sizing of these orifices (13) the contaminants cannot pass and so clean fluid is only passed into the packing (4). However, a gauze or filter may be positioned on or in the orifices (13).

One or more threaded orifices (14) are also located on the same surface as the passageway orifices (13) allowing threaded bolts to be fitted and so aiding removal of the bushing from the cavity (3).

Located on the split, or divided, surface (15) of each half of the bushing is one or more orifices (16) wherein pins can be located allowing the halves of the bushing to be assembled together creating the bushing assembly as shown in Figure 3.

The split line (17) as shown in Figure 3 is manufactured after all turning and milling operations are completed via wire eroding ensuring that the material removed is as small as possible meaning that the bushing does not need remachining after the splitting operation. The clearances between the inner annular surface (9) and the shaft (1) and the outer annular surface (8) and the cavity bore (2) are suitably large enough to allow the non circularity of the bushing post splitting to be fitted without interference with either of them. In order to aid the machining of the pin holes (16) slots (18) are also machined on the outer annular surfaces (8).

The end view of the present invention as shown in Figure 4 shows that the grooves (11) can be machined prior to the splitting operation using a I-cutter machining tool; thereby negating the need for jigging to be manufactured for each size variant. It can be seen in this view that in the present invention there are two grooves (11) one sloping in a clockwise direction and the other sloping in an anticlockwise direction thereby ensuring that the fluid flow is generated in both shaft directions.

Where the grooves and at least one wall thereof are described as being tapered or sloped, they may be stepped or otherwise graduated to result in a narrowing of the width of the groove along its length.

The grooves may be provided with vanes to assist with directing the fluid towards the orifices (12).

The bushing may have more than one groove in each half. For example, two grooves may be provided in each half, preferably equally spaced there. The two grooves in each half may be of the same or opposite (clockwise or counter-clockwise) direction.

The device may be split, or divided, into three or more parts to make transportation easier.

The substantially latitudinal channel on the internal annular surface may extend part or all of the way around the inside of the bushing. It might be desirable to align it slightly away from perfectly latitudinal, especially where the orifices are not position directly at the end of the groove.

Claims

Claims 1. An annular seal cavity throat bushing comprising; an inner annular surface and an outer annular surface, the inner surface comprising a substantially latitudinal channel, the channel being provided with at least one orifice to allow fluid communication between the inside of the bushing and the outside of the bushing; the bushing being further provided with at least one groove extending substantially longitudinally from one end of the bushing to the channel, wherein the groove comprises at least one tapered edge, thereby increasing the width of the groove along its length.
2. A throat bushing according to Claim 1, wherein the width of the, or each, groove increases as it approaches the channel.
3. A throat bushing according to Claim 1 or claim 2, wherein each groove is radially located substantially in line with at least one of the said orifices.
4. A throat bushing according to any preceding claim, wherein the depth of the, or each, groove increases along the longitudinal length as it approaches the channel.
5. A throat bushing according to any preceding claim, wherein the bushing is provided with a plurality of grooves and at least one groove creates a clockwise slope and at least one other creates an anticlockwise slope.
6. A throat bushing according to claim 5, wherein the clockwise sloped groove is positioned in one half of the bushing and the anticlockwise sloped grove is in the other half of the bushing.
7. A throat bushing according to any preceding claim, wherein at least one annular groove is located on one side of the orifice and at least one annular groove is located on the other side of the orifice, thereby allowing toroidal sealing members to reside therein creating a seal between said grooves and a seal cavity, when in use.
8. A throat bushing according to any preceding claim, wherein the annular structure is divided into two substantially equally sized portions, thereby creating a split throat bushing.
9. A throat bushing according to Claim 8, wherein the said divides are created post machining and such that when the said halves are reassembled the annular surfaces are not circular.
10.A throat bushing according to claim 8 or claim 9, wherein the said divides are located on a plane substantially perpendicular to a plane connecting the said grooves.
11.A throat bushing according to any one of claims 8 to 10, wherein at least one hole capable of securely holding a pin is located on the divide surface of one half and the opposite half is provided with holes located concentrically to said pins but with a larger diameter than said pin thereby allowing the halves to be assembled together.
12.A throat bushing according to any preceding claim, wherein the material of construction is metallic and of a non-sparking nature.
13.A throat bushing substantially as described herein with reference to any appropriate combination of text and/or drawings.Amendments to the claims have been filed as follows Claims 1. An annular seal cavity throat bushing comprising; an inner annular surface and an outer annular surface, the inner surface comprising a substantially latitudinal channel, the channel being provided with at least one orifice to allow fluid communication between the inside of the bushing and the outside of the bushing; the bushing being further provided with at least one groove extending substantially longitudinally from one end of the bushing to the channel, wherein the groove comprises at least one tapered edge, thereby increasing the width of the groove along its length.2. A throat bushing according to Claim 1, wherein the width of the, or each, groove increases as it approaches the channel. T 153. A throat bushing according to Claim 1 or claim 2, wherein each groove is (0 radially located substantially in line with at least one of the said orifices. (44. A throat bushing according to any preceding claim, wherein the depth of the, or each, groove increases along the longitudinal length as it approaches the channel.5. A throat bushing according to any preceding claim, wherein the bushing is provided with a plurality of grooves and at least one groove creates a clockwise slope and at least one other creates an anticlockwise slope.6. A throat bushing according to claim 5, wherein the clockwise sloped groove is positioned in one half of the bushing and the anticlockwise sloped grove is in the other half of the bushing.7. A throat bushing according to any preceding claim, wherein at least one annular groove is located on one side of the orifice and at least one annular groove is located on the other side of the orifice, thereby allowing toroidal sealing members to reside therein creating a seal between said grooves and a seal cavity, when in use.8. A throat bushing according to any preceding claim, wherein the annular structure is divided into two substantially equally sized portions, thereby creating a split throat bushing.9. A throat bushing according to Claim 8, wherein the said divides are created post machining and such that when the said halves are reassembled the annular surfaces are not circular.10. A throat bushing according to claim 8 or claim 9, wherein the said divides are located on a plane substantially perpendicular to a plane connecting the said grooves. r r11. A throat bushing according to any one of claims 8 to 10, wherein at least one (\,j20 hole capable of securely holding a pin is located on the divide surface of one half and the opposite half is provided with holes located concentrically to said pins but with a larger diameter than said pin thereby allowing the halves to be assembled together.12.A throat bushing according to any preceding claim, wherein the material of construction is metallic and of a non-sparking nature.13.A throat bushing substantially as described herein with reference to any appropriate combination of text and/or drawings.