CA2572362C - Pump wet end replacement procedure complete with an impeller fixing mechanism - Google Patents

Abstract

The pump comprises: one base, wet end and a rotating impeller connected to the drive shaft. The wet end has a casing formed by two bolted halves with faces or surfaces, inside the casing is the impeller screwed to the drive shaft. Wet end liner and impeller replacement is normally carried out by changing the complete pump or by dismantling the pump wet end in situ and removing the wet end liners and impeller component by component. To avoid vibration and prevent damage to the pump a precise re- alignment of the impeller and the drive shaft is necessary. Such a procedure during wet end liner and impeller replacement takes in excess of 8 hours. This long period of time is the technical problem that is resolved by the present invention which incorporates an impeller fixing device that allows removal of the pump wet end without disengaging the drive shaft from the coupling; therefore it does not require shaft re- alignment or wet end dismantling in situ. The impeller fixing mechanism is comprised of two elements concentric with the pump drive shaft, abutted against the casing faces. The elements are split-annular shaped, with a flexible elastomeric member and a stiff backing ring member where the clamping bolts fasten the mounting faces together. In addition, the backing ring member incorporates the mechanism for loosening the mounting bolts and nuts.

Description

DESCRIPTIVE MEMORANDUM

This invention relates generally to pumps such as for example centrifugal pumps including centrifugal slurry pumps and also to a method of handling components therefor.

Centrifugal slurry pumps are used in a large variety of industrial processes, especially in the grinding and grading stage of ore during mineral processing.

Ore slurries are highly abrasive causing great wear and tear to those parts of the pump in contact with the slurry, which requires slurry pumps to undergo frequent servicing.

In the processing of copper ore, a slurry pump typically processes approximately 2,000 tonnes of ore per hour, including about 20 tonnes of copper content.

Depending on the slurry pump size and weight, from 12 to 30 tonnes, its replacement takes from 8 to 16 hours and each replacement therefore causes a production loss of at least 150 to 300 tonnes of copper.

For this reason there have been advances in the design and development of slurry pumps to extend the pumps' operating time between services. One of the typical solutions is to protect the pump casing with metallic or elastomeric sacrificial internal liners.

However, in the state of the art there is no technical solution to reduce the period of time it takes to change out a slurry pump, this being the technical problem that the present invention solves.

Figure la is a cutaway elevation view of a slurry pump without a sacrificial liner, and Ib is the elevation view of the pump front face.

Figure 2a is a cutaway elevation view of a slurry pump with a sacrificial liner, and figure 2b is the elevation view of that same pump front face.

Figure 3a is a cutaway elevation view of a slurry pump in a preferred embodiment of the invention. Figure 3b is the elevation view of that same pump front face.
Figure 3c is a cutaway elevation view of a preferred embodiment of the impeller fixing mechanism which is the object of the present invention. Figure 3d is a cutaway axial elevation view of a preferred embodiment of the fixing mechanism corresponding to the pump frontal face, and figure 3d is the view corresponding to the pump rear face.

The description of the invention shall be based on these figures.

A slurry pump without liners, figures 1a and lb, comprising a base 2 that is connected to subbase I by means of bolts 17. Subbase 1 is anchored to the ground. Base 2 supports the slurry pump which consists of a casing, 3, or "wet end" according to the art and a rotating drive shaft 14, with a torque release mechanism, 27, where the shaft 14 is connected by means of coupling 15 to the impeller system of shaft 16. Wet end comprises a metallic casing formed by two members, the casing frontal face 4a and the casing rear face 4b. Both faces are connected to each other by bolts 10.
Frontal-face 4a is connected to the inlet or suction pipe 6 by means of bolts 8. The wet end is fixed to base 2 by bolts 13 that are located in the rear face 4b. On the inside of the wet end is impeller 5 which is screwed onto shaft 14. The slurry enters through inlet pipe 6 under the suction produced by the rotating impeller 5 and is propelled from the pump via outlet pipe 7 which is connected to the slurry pump by bolts 9.

A pump with a sacrificial liner differs from the preceding pump in that the inner surfaces of casing faces 4a and 4b have a covering or lining 18a and 18b as shown in figure 2a.

Because of the pump weight which, depending on the pump size, varies between 12 to 30 tonnes, including base 2, handling the pump requires the use of chain blocks or cranes, for which purpose the wet end comprises flanges 11 having orifices 12, such flanges are located at the outer side of casing faces 4a and 4b.

The pump high rotation speed demands the precise alignment between shafts 14, 16 and impeller 5.

Presently, the servicing of centrifugal slurry pumps is performed in two ways:
By Total Replacement of Pumpor Pump Liner and Impeller Replacement by Dismantling in situ.
Total Replacement of Pump Total replacement of pump requires the following procedure:

1. Disconnect suction pipe 6 and discharge pipe 7 from the pump by removing bolts 8 and 9, respectively.

2. Disconnect coupling 15 to disengage shaf114 from driveshaft 16.

3. Remove bolts 17 which connect the complete pump assembly to its subbase 1.

4. Remove the complete pump assembly from the pump location by means of a chain block or crane and transport the complete pump assembly to repair facility for maintenance.

5. Transport to the pump location a new complete pur.pp assembly by means of chain block or crane.

6. Connect the complete pump assembly to sub-base 1 by means of bolts 17.

7. Connect coupling 15 which joins pump shaft 14 and driveshaft 16.

8. Perform alignment of shafis 14 and 16.

9. Connect suction pipe 6 and discharge pipe 7 to pump by means of bolts 8 and 9, respectively.

Such procedure presents the following disadvantages:

1. The entire pump assembly 2, including the entire mechanical system, bearing housing, packing gland and lubrication, not shown in the figures, comprising shaft 14, implying a greater investment cost.

2. The weight to be handled, considering the complete pump assembly, is of about 12 to 30 tonnes, of which 4 to 10 tonnes corresponds to the weight of base.
3. Alignment of the pump drive shaft must be extremely accurate to avoid vibration and prevent equipment damage. This is an arduous task and requires much time.
4. Total pump replacement procedure takes over 8 hours.
Pump Liner and Impeller Replacement by Dismantling in situ.

Replacement of pump with elastomeric liners, by dismantling in situ, requires the following steps:

1. Disconnect pump from suction pipe 6 and discharge pipe 7 by removing bolts 8 and 9, respectively.
2. Place lifting slings on the pump casing front or suction section 4a.
3. Open wet end 3 by removing bolts 10.
4. Remove front section of pump casing 4a and store temporarily 5. Dis-engage torque release mechanism 27.
6. Secure impeller 5 with a special lifting device that maintains impeller in a vertical position, while allowing rotation of shaft 14 in reverse direction for disconnection and permit removal of the impeller 5.
7. Place lifting slings on the rear pump casing rear section 4b.
8. Remove bolts 13 which join the pump casing rear section 4b with the pump base 2.
9. Remove the rear pump casing section 4b and store temporarily. . to remove and replace liner.

10. Re-install the rear pump casing section 4b with a new liner in place to, pump base 2, by means of bolts 13.

11. Install the new impeller 5 by using the special device that keeps impeller in a centralised vertical position.

12. Re-engage the torque release mechanism.

13. Rotate shaft 14 in its normal rotation direction for connection to the impeller.

14. Install the front pump or suction casing section 4a with new liner installed and close the pump up by fastening bolts 10.

This procedure does not require the re-alignment of the shafts stage, however it presents the following disadvantages:

1. It requires many steps that take much working time, especially steps 3 and 11.
2. It requires using a special lifting device mounted on a chain block which keeps the impeller in a centralized vertical position for both disconnection and re-connection.
3. Total pump wet end liner and impeller replacement procedure takes over 8 hours.

The main common problem of such procedures is the time it takes for pump liner and impeller replacement purposes, which causes a production drop.

Due to the large mineral processing through-put, reduction in the amount of time the pump is off-line has a great impact in the plant productivity and profitability.

In the current state of the art there is no procedure to replace slurry pump liners in less than 8 hours. This is the technical problem that is solved by the present invention.
According to one aspect of the present invention there is provided a centrifugal pump in which a pump wet end comprises a casing with or without inner pump linings and one impeller which freely rotates inside the casing by means of a shaft, CHARACTERIZED
in that it has a fixing mechanism which immobilizes and fixes the impeller in a centralised position and a system for tightening and loosening the fixing mechanism.
Preferably, the fixing mechanism, comprises two elements concentric with the pump shaft, the first element attached to face and the second element attached to face.
Preferably the fixing elements are circular ring-shaped, having a diameter between 0.95D and ID, where D is the impeller diameter.

Preferably, the fixing elements comprise a flexible elastomeric member and a stiff backing part. Preferably, the elastomeric members thickness is about 10 mm to mm and each member can have a different thickness. Preferably, the diameter of stiff members is the same as that of members, and are formed by a flat base and ribs where the flat plate thickness is between 10 to 30 mm and the height of the ribs is between 20 to 50 mm.

Preferably, the fixing mechanism tightening system comprises two tightening bolts, which are screwed to the casing faces and abut against the rib of the fixing mechanism member, and the loosening system comprises loosening bolts, with nuts and washers, the bolts freely pass through the casing holes, bolts are jointly attached to stiff part on the same rib where bolts are fastened. Preferably, the tightening bolts and loosening bolts are inserted there between and evenly spaced apart in a circumference concentric to the shaft.

According to another aspect of the present invention there is provided a procedure for replacement of liners and impeller in a centrifugal pump, described above comprising the following steps:
a. Disconnect pump from suction pipe and discharge pipe by removing bolts, respectively.
b. Place lifting slings on the pump wet end.
c. Loosen nuts to allow axial displacement of members by tightening of bolts until members make contact and press on the impeller faces.
d. Remove bolts that join the casing rear face to the pump base.
e. Dis-engage the torque release mechanism.
f. Rotate shaft in its normal reverse rotation direction for disconnection from impeller.
g. Remove the complete wet end and take it to a repair facility.
h. Position the new wet end furnished with the impeller and assembled with the impeller fixing mechanism and fasten it to base by means of bolts.
i. Engage the torque release mechanism.
j. Rotate shaft in its normal rotating direction for connection to impeller.
k. Release bolts to allow movement of members, release impeller by rotating nuts, until members make contact with faces.

Reduction of slurry pump liner and impeller replacement time implies the reduction of the number of steps to be taken. In the case of total replacement of the slurry pump steps 2, 3, 6, 7 and particularly step 8 relating to alignment are eliminated;
and in the case of pump replacement by dismantling in situ, steps 3, 4, 6, 11 and 13 are eliminated.
A preferred embodiment of the present invention comprises a mechanism that temporarily fixes the impeller 5 to the faces of the casing sections 4a and 4b, in such a way that the impeller 5 remains immobilized and perfectly centered in the wet end 3, therefore it can be connected to shaft 14 without the need for re-alignment, that is to say, such special mechanism allows removal of the entire pump wet end assembly from the slurry pump without the impeller losing its position relative to shaft 14, therefore no re-alignment of impeller to pump shaft is required nor is the slurry pump required to be dismantled "in situ".

When impeller 5 is fixed and immobilized, the wet end 3 can be removed by removing bolts 13 only, without the need of disassembling shafts 14 and 16, in other words, disconnection of coupling 15 that connects the shafts is not required.
Consequently, no re-alignment is needed as in the case of total replacement of pump, nor is it necessary to open the slurry pump wet end 3, as required in the case of "dismantling in situ".

One of the preferred embodiments of the present invention involving the fixing mechanism is shown in figures 3a, 3b, 3c and 3e.

Figure 3a is a cutaway elevation view of the pump with fixing mechanism, which in this preferred embodiment comprises two elements concentric with the pump shaft, the first element 19a attached to the face of front pump casing section 4a and the second element 19b attached to the face of rear pump casing section 4b.

The fixing elements 19a, in figures 3c and 3d and 19b, in figure 3e are similar and are split-annular shaped, therefore there will be a simultaneous common description of them. Fixing elements 19a and 19b comprises a flexible clastomeric member 20a and 20b, respectively, and stiff backing parts 21a and 21b on which the tightening bolts 22a and 22b operate, being screwed to the casing faces 4a and 4b, respectively. In addition, in the stiff backing parts 21a and 21b is the loosening system consisting of loosening bolts 23a and 23b, nuts 24a and 24b, and washers 25a and 25b. Bolts 23a and 23b freely pass through the holes 26a and 26b in pump casing section faces 4a and 4b, respectively.

Figures 3b and 3d show the distribution of bolts 22a and 23a, which are inserted and evenly spaced apart in a concentric circumference with the shaft. Figure 3e shows a similar form for bolts 22b and 23b.

The elastomeric members 20a and 20b are split-annular shaped with a 0,95D to ID
diameter, where D is the impeller diameter with a 10 mm to 25 mm thickness depending on the pump size, the thickness of both members can be different but within the specified degree.

Stiff inembers 21a and 21b have the same diameter of members 20a and 20b, and are fonned by a flat base and ribs providing greater stiffhess and serving as support for tightening bolts 22 and as a base for the loosening bolts 23 where they are jointly positioned.

The thickness of the members' flat base 21 is ranked between 10 to 30 mm and the ribs height between 20 to 50 mm, which makes members 21 to have a total projected height of between 30 and 80 mm.

To fix the impeller, nuts 24a and 24b are firstly loosened, which allows free movement of loosening bolts 23a and 23b. When tightening bolts 22a and 22b, elements 19a and 19b move toward impeller 5 until making contact and pressing on the impeller surface immobilizing and keeping impeller fixed in a centered position with respect to shaft 14.
To unlock the impeller, bolts 22a and 22b are firstly loosened and nuts 24a and 24b of loosening bolts 23a and 23b are rotated.

By using this preferred fixing mechanism of the present invention the complete pump wet end replacement procedure comprises the following steps:

1. Disconnect pump from suction pipe 6 and discharge pipe 7 by removing bolts 8 and 9, respectively.
2. Place lifting slings on the entire pump wet end 3.
3. Loosen nuts 25a and 25b to allow displacement of members 19a and 19b by tightening bolts 22a and 22b until members 19a and 19b make contact and press on the impeller 5 front and rear faces.
4. Remove bolts 13 which fasten the casing rear face 4b to the pump base 2.
5. Dis-engage the torque release mechanism 27.
6. Rotate shaft 14 in its normal reverse rotation direction for disconnection from impeller 5.
7. Remove the wet end 3 and transport it to a repair facility.
8. Position the new wet end furnished with the impeller 5 assembled and restrained in the centralized position by the fixing mechanism and fasten it to base 2 by means of bolts 13.
9. Engage the torque release mechanism.
10. Rotate shaft 14 in its normal rotational direction for re-connection to impeller 5.
11. Release bolts 22a and 22b to allow movement of members 19a and 19b by rotating nuts 24a and 24b, until members 19a and 19b make contact with faces 4a and 4b.

The following are the advantages of this procedure that makes use of the impeller fixing mechanism, the object of the present invention:
= There is a maximum of plant operating down-time of less than 2 hours.
= It does not require disconnection of the pump shaft drive coupling..
= There is no need for re-alignment of the pump shafts.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is- not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the' field of endeavour to which this specification relates.

The reference numerals in the following claims do not in any way limit the scope of the respective claims.

Claims (5)

1. A method for handling a pump in a pump handling procedure, comprising:
providing a pump comprising: an outer casing having an inlet and a discharge outlet, a pumping chamber within the outer casing, an impeller mounted within the pumping chamber for rotation about an axis of rotation when in use, the impeller having a surface extending radially from an outer circumferential edge of the impeller toward the axis of rotation of the impeller, a fixing mechanism further comprising a fixing element having a radially-extending surface positioned to hold and engage said radially-extending surface of the impeller and having loosening bolts immovably secured to said fixing element and extending from the fixing element through holes formed in the outer casing, each loosening bolt having a tightening nut operatively associated therewith, and tightening bolts threadedly positioned through said outer casing and positioned to effect contact with said fixing element; and activating the fixing mechanism by operatively turning said tightening nut on each said loosening bolt to effect axial movement, by said loosening bolt, of said fixing element from either a holding position, where the radially-extending portion of the fixing element holds and engages the radially-extending surface of the impeller, or a release position, where the fixing element does not engage the impeller; and maintaining the fixing element in either a holding position or a release position by activating said tightening bolts to provide contact between each said tightening bolt and said fixing element to stabilize the fixing element.

2. A method according to claim 1 wherein, when in use, the pump casing is operatively mounted to a base and the impeller is operatively coupled to a drive shaft, and wherein the pump handling procedure comprises dismounting the pump casing and impeller from the base, the method further including activating the fixing mechanism so as to transfer the fixing mechanism from the release position to the holding position, decoupling at least a part of the drive shaft from the impeller and disconnecting the pump casing from the base.

3. A method according to claim 1 wherein, when in use, the pump casing is operatively connected to a base and the impeller is operatively coupled to a drive shaft, and wherein the pump handling procedure comprises mounting the pump casing and impeller to the base, the method further including positioning the impeller relative to the pump casing and activating the fixing mechanism so as to transfer the fixing mechanism from the release position to the holding position, mounting the pump casing to the base and operatively coupling at least part of the drive shaft to the impeller.

4. A method according to claim 1 wherein, when in use, the pump casing is operatively mounted to a base and the impeller is operatively coupled to a drive shaft, and wherein the pump handling procedure comprises replacing a first pump casing and first impeller with a second pump casing and second impeller, the method further comprising: activating the fixing mechanism of the first pump casing and first impeller so as to transfer the fixing mechanism from the release position to the holding position; decoupling at least a part of the drive shaft from the first impeller and disconnecting the first pump casing from the base; activating the fixing mechanism of the second pump casing and second impeller to axial fix the second impeller relative to the second pump casing; mounting the second pump casing to the base and operatively coupling at least part of the drive shaft to the second impeller.

5. A method according to claim 1 wherein said fixing mechanism is moved from said holding position to said release position by terminating contact between the tightening bolts and the fixing element by turning the tightening bolts until the tightening bolts are spaced apart from the fixing element, and turning said tightening nuts about said loosening bolts to effect axial movement by said loosening bolts of the fixing element.