Method And Apparatus For Use In The Transportation Of Solids

Abstract

A method and apparatus to increase the pressure of a mixture of liquid and solids in a pipeline for transportation of the mixture through the pipeline at a constant velocity. The mixture is pressurized in a series of chambers into which alternately flows low-pressure liquid and out of which alternately flows high-pressure liquid. The low-pressure liquid is continuously diverted from the pipeline into the chambers while an equal amount of the high-pressure liquid is diverted from the chambers back into the pipeline.

Description

The invention relates to the transportation of solids and more particularly is concerned with the transportation of solids mixed with a liquid through a pipeline.

Long distance transportation of petroleum and petroleum products through a pipeline is well known and is both economical and convenient. The petroleum transportation system generally includes one or more pumping stations interposed in the pipeline for raising the pressure of the petroleum liquid to a high level. The stations generally employ centrifugal pumps because of their lower first cost, their adaptability to varying pumping rates, and their adaptability to multistation systems brought about by their nonpositive displacement and nonpulsing characteristics.

Similar transportation of solids, such as coal, iron ore, sulfur, limestone, and wood chips, suspended in a liquid medium has long been considered as having attractive possibilities from the standpoint of convenience and reduced costs. Generally, the major obstacle which confronts long distance pipelining of solids is the development of an economical pump unit which will develop the high-pressure head required to transfer the slurry over long distances. The pump unit must also be adapted to raise the pressure head of the slurry while maintaining a constant velocity of slurry flow in the pipeline.

Success in part has been achieved in transporting slurry in a pipeline through the use of reciprocating-type pumps. However, these pumps have very high initial costs and high maintenance costs. Centrifugal pumps of the type used in petroleum pipelining are considered particularly desirable and have been used in some instances on short pipelines where the pressures involved are relatively low. However, in long distance pipelining where high pressure and high volume is required centrifugal pumps have proved unsuccessful because the abrasive action of the slurry causes damage to the pumps, creating considerable maintenance.

Therefore, the primary object of this invention is to provide a means for developing the pressure head necessary to transport slurry over long distances through a pipeline. In accordance with this object it is important that the pressure head of the slurry be raised without varying or reducing the velocity of the slurry flow in the pipeline.

A further object of this invention is to employ the use of centrifugal pumps without subjecting the pumps to the abrasive action of the slurry being pumped.

Another object of this invention is to transport solids over long distances through a pipeline by economical and practical means.

To accomplish these objects, the invention includes a pumping unit, of which there may be a plurality over the entire length of the pipeline, to raise the pressure level of the slurry being transported through the pipeline. The pumping unit includes a series of chambers, each up to several hundred feet in length. Each chamber is adapted to fill up with low-pressure slurry and then empty high-pressure slurry. Means are provided to continuously divert from the pipeline low-pressure slurry alternately into the chambers while continuously diverting alternately from the chambers high-pressure slurry back into the pipeline. A recirculating liquid which has been pressurized by one or more centrifugal pumps increases the pressure of the slurry in the chambers and means in the chambers are provided to maintain this liquid separate from the slurry. The filling and emptying of the slurry in the chambers is sequentially controlled in such a manner to provide continuous flow of slurry at all times into and out of the chambers and ensure that the amount of low-pressure slurry diverted continuously from the pipeline is equal to the amount of high-pressure slurry being diverted continuously back into the pipeline.

Other and further objects of this invention will be made readily apparent from the accompanying drawings and following detailed description.

IN THE DRAWINGS

FIG. 1 is a schematic view illustrating the emptying and filling of the chambers.

FIG. 2 is a schematic view illustrating the sequential operation of the valves when three chambers are employed.

FIG. 3 is a schematic view illustrating an alternative embodiment of the chamber.

FIG. 4 is a schematic view illustrating a still further alternative embodiment of the chamber.

Referring now in detail to the drawings, the pumping unit is generally designated 10. The pumping unit 10 as shown in FIG. 1 includes a series of three identical chambers 11, 12 and 13. From the following discussion it will be made evident that the invention in its preferred form includes at least three chambers, but is not necessarily limited to three chambers. However, for purposes of clarity the description will be directed to the three chamber unit as shown.

Each of the chambers 11, 12 and 13 are in communication with both the incoming or low-pressure slurry pipeline 14 and the outgoing or high-pressure slurry pipeline 15. Lines 16, 17 and 18 connect the chambers 11, 12, and 13, respectively, to the incoming slurry pipeline 14 and lines 19, 20 and 21 connect the chambers 11, 12 and 13, respectively, to the outgoing slurry pipeline 15. Check valves 22, 23 and 24 on the lines 16, 17, 18, respectively, are adapted to permit slurry to flow from the incoming slurry pipeline 14 into the chambers, as shown by the directional arrows 25, and check valves 26, 27 and 28, on the lines 19, 20 and 21, respectively, are adapted to permit slurry to flow from the chambers into the outgoing slurry pipeline 15, as shown by the directional arrows 29. The check valves operate according to the pressure differential in the respective lines.

The slurry is pressurized in each chamber by a liquid which is separately pressurized by a pump 30, preferably a centrifugal pump of the type used in petroleum pipelining systems. The pump is run by a motor 31. While only a single pump and motor are shown in FIG. 1, it is clear that a plurality of pumps and/or motors can be employed. The pressurized liquid is recirculated through a conduit 32. Lines 33 and 34 connect the pump 30 to the low liquid pressure and the high liquid pressure sides, 35 and 36, respectively, of the conduit 32. Valves 37 and 38 on the lines 33 and 34, respectively, are simply pump isolation valves.

Each of the chambers 11, 12 and 13 are in communication with both the low-pressure side 35 of the conduit 32 and the high-pressure side 36 of the conduit 32. Lines 39, 40 and 41 connect the chambers 11, 12 and 13, respectively, to the high-pressure side 36 and lines 42, 43 and 44 connect the chambers 11, 12 and 13, respectively, to the low-pressure side 35. Valves 1-D, 2-D and 3-D on the lines 39, 40 and 41, respectively, are adapted to permit the pressurized liquid to flow from the conduit 32 into the chambers, as shown by the directional arrows 45, and valves 1-S, 2-S and 3-S on the lines 42, 43 and 44, respectively, are adapted to permit the liquid to flow from the chambers back into the conduit 32, as shown by the directional arrows 46. These valves are sequentially operated by a timing system which is dependent on the movement of the slurry in the chambers and the sequencing of the valve operation is such that the slurry is both removed from the incoming slurry pipeline and reintroduced into the outgoing slurry pipeline in a pulsation-free manner which substantially prevents a variation in the velocity of the slurry flow through the pipeline. The timing system and the sequencing will be described more fully below.

Directing attention now to the individual chambers, the chambers in the pumping unit, as stated before, are all identical and each chamber includes a mechanical separator 47 which separates the slurry from the hydraulic liquid or medium in the chamber and prevents attenuation at the interface of the slurry and liquid and contamination of the liquid with slurry. The separator 47 moves in accordance with the movement of the slurry in the chamber as indicated by the directional arrows 47a. In the preferred embodiment shown in FIG. 1 the separator 47 moves slidably along the walls of the chamber and is in the form of a piston or other similar means such as an inflatable sealing ball. Means are provided to prevent leakage between the piston and the walls of the chamber. Preferably a pair of detector switches 48 and 49 are provided with each chamber, however, as will be seen later the pumping unit 10 can operate when only one detector switch is provided with each chamber. Detector switch 48 is activated when the chamber is nearly full of slurry and the separator has been moved to an actuating position by the slurry filling the chamber. Detector switch 49 is actuated when the chamber is nearly empty of slurry and the separator has been moved to an actuating position by the slurry emptying from the chamber. The separator 47 can actuate the detector switches 48 and 49 in various manners such as mechanical contacts or magnetic control. The detector switches in turn either directly initiate the operation of the valves or they can initiate the operation of a sequence timer (not shown) which in turn would control the valve operation.

In the alternative embodiment of the chamber, shown in FIG. 3 and designated generally 100, the separator 101 includes a cylindrical cup member 102 which is connected to the walls of the chamber 100 by a flexible member 103. Detector switches 104 and 105 are again actuated when the chamber is nearly full or empty of slurry, respectively, and actuated by the cup member 102 when it is moved into an actuating position by the movement of the slurry in the chamber.

In the other embodiment shown in FIG. 4 the chamber, generally designated 200, includes a flexible diaphragm member 201 which is connected to the inner walls of the chamber. Detector switches 202 and 203 are actuated when the chamber is nearly full or empty of slurry, respectively. A contact member 204, connected to the diaphragm 201 as shown diagrammatically in FIG. 3, extends beyond the chamber 200 and the switches 202 and 203 are actuated by the contact member 204 when it is moved to an actuating position by the diaphragm which is in turn moved by the movement of the slurry in the chamber. FIG. 4 also points out a further invention in the invention, that is, additional chambers may be placed in parallel operation with the other chamber 200, as shown by the phantom lines 205. This, of course, means that the same number of chambers will be placed in parallel with the other two chambers.

While not shown in the drawings, another variation of this invention would be to place the chambers in a more or less vertical position and to use a recirculating pressurized liquid with either a heavier or lighter specific gravity than the specific gravity of the slurry. In this instance, the mechanical separator 47 is not necessary as the difference in specific gravity between the slurry and the recirculating liquid would maintain a stable interface in the chambers. The recirculating liquid or slurry having the highest specific gravity would determine which end of the chamber the slurry or the liquid would be introduced, the heaviest one always being introduced at the bottom end. It should be noted that when the mechanical separator is not used other means of sensing and switching will need to be employed.

Before discussing the timing system and the sequence of the valves during operation of the pumping unit, certain other features of the unit should be noted. In order to provide for the dissipation of heat of the hydraulic medium or liquid generated by the inefficiency of the centrifugal pump or pumps 30, the pumping unit 10 includes a heat exchanger 50 which cools the hydraulic liquid by utilizing the temperature differential between the hydraulic liquid and the outgoing slurry. A solids separator 51 is also included on the recirculating conduit 35 to further prevent the inclusion of solids in the hydraulic liquid which might damage the centrifugal pump or pumps 30.

A further feature relates to the balance of slurry and liquid in the chambers. When three chambers are used, at any given instant, under normal operations, the total volume of hydraulic liquid in all three chambers will be approximately one-third the total volume of slurry in all three chambers. However, because of liquid or slurry slippage past the mechanical separator 47 or because of pump seal leakage, this balance can gradually go one way or the other. If allowed to be carried to the extreme, all the chambers at the same time would either become full of slurry or become full of hydraulic liquid which would result in a stoppage of the pump unit 10. To maintain this unbalancing of liquid volume versus slurry volume within certain predetermined tolerances, means 52 are provided for both the injection of liquid into and for the drainage of liquid from the recirculating system, depending on which way the unbalance has occurred. The unbalance is sensed by instrumentation (not shown) detecting predetermined extreme limits of travel of the mechanical separators. If the chambers are short on water, all mechanical separators 47 will fall short of reaching the slurry end of the chambers. If the chambers have too much water, all the mechanical separators 47 will fall short of reaching the liquid end of the chambers. The sensing instrumentation will detect these travel limits and depending on which end of the chambers the separator travel falls short, such instrumentation will determine whether liquid should be injected or drained from the recirculating system. Each injection or drainage will be controlled to a predetermined amount of volume. Sensing the location of the mechanical separators need only take place on one chamber, as the length and position of strokes will be identical in all the chambers.

FIG. 2 diagrammatically represents the sequence of the valve operation during operation of the pump unit 10. The darkened portion in the drawing represents an open valve. During a complete cycle in which all the chambers in a three chamber unit have first filled with low-pressure slurry and then emptied of high-pressure slurry, the sequence is as follows:

Beginning at a time in the cycle shown approximately in FIG. 1, slurry is emptying from chamber 11 and slurry is filling into chamber 13, this continues until the separator 47 in chamber 11 moves down with the slurry to a position to actuate switch 49 on chamber 11. The switch 49 on chamber 11 then opens valve 2-D which starts the emptying of slurry from chamber 12 and which when open begins the closing of valve 1-D. Valve 1-D when closed begins the opening of valve 1-S which starts the filling of slurry into chamber 11 and 1-S when open begins the closing of 3-S.

The valves then remain in this position until the separator 47 in chamber 12 moves down with the slurry to a position to actuate switch 49 on chamber 12. The switch 49 on chamber 12 then opens valve 3-D. which starts the emptying of slurry from chamber 13 and which when open begins the closing of valve 2-D. Valve 2-D when closed begins the opening of valve 2-S which starts the filling of slurry into chamber 12 and 2-S when open begins the closing of 1-S.

The valves then remain in this position until the separator 47 in chamber 13 moves down with the slurry to a position to actuate switch 49 on chamber 13 then opens valve 1-D which starts the emptying of chamber 11 and which when open begins the closing of valve 3-D. Valve 3-D when closed begins the opening of valve 3-S which starts the filling of slurry into chamber 13 and 3-S when open begins the closing of 2-S. The valves then remain in this position until the separator 47 in chamber 11 actuates switch 49 on chamber 11 and the cycle is repeated.

For the sake of clarity of description, only detector switches 49 on the chambers 11, 12 and 13 have been included in the description of the valve sequence. However, in actual operation the detector switches 48 on chambers 11, 12 and 13 play an important roll. For instance, when the amount of slurry in all three chambers is greater than two-thirds the total volume of all the chambers the mechanical separator 47 in chamber 13 would reach the position to actuate the switch 48 on chamber 13 before the separator 47 in chamber 11 reached the position to actuate the switch 49 on chamber 11. If this occurred, the switch 48 on chamber 13 would open valve 2-D to start the sequence described above. Similarly, switch 48 on chamber 11 will open valve 3-D and start that sequence and switch 48 on chamber 12 will open valve 1-D to begin that sequence. On the other hand, if the total volume of the slurry is less than two-thirds the total volume of the chambers, then switches 49 will start the valve sequence. Detector switches on either end of the separator stroke in this manner will thus prevent the pump unit from getting into a locked position. These additional detector switches 48 also provide for slippage of the mechanical separator 47 in the slurry or recirculating liquid and no matter how severe the slippage, the sequence of operation cannot get out of sequence, that is, the discharge of slurry from chamber 12 always follows the discharge of slurry from chamber 11, and the discharge of slurry from chamber 13 always follows the discharge of slurry from chamber 12, and the discharge of slurry from chamber 11 always follows the discharge of slurry from chamber 13.

The pump unit 10 with three or more chambers sequenced in this manner provides for the pressurizing of the slurry in a pulsation-free manner because there is a continuous flow of slurry at all times into and out of the pipeline which is uneffected by the valve switching. The pump unit is such that a centrifugal pump or pumps can be employed to raise the pressure head of the slurry without the pumps being subjected to the abrasiveness of the slurry.

Claims

I claim:

1. A pump unit to increase the pressure of slurry being transported through a pipeline, comprising: at least three chambers; pressurizing means adapted to alternately apply high and low pressure to each said chamber; means to provide for the flow of slurry from the pipeline into one end of each said chamber during the application of low pressure to fill each said chamber with slurry and to provide for the flow of slurry from said one end of each said chamber into the pipeline during the application of high pressure to empty each said chamber of slurry; and control means associated with the emptying and filling of slurry in each said chamber to cause the low pressure to be applied at all times to at least one of said chambers and the high pressure to be applied at all times to at least another one of said chambers and to cause the high and low pressure to be applied sequentially to said chambers with the application of either pressure to each chamber beginning before the end of the application of a corresponding like pressure to the preceding chamber in the sequence whereby at all times there is a continuous flow of slurry from the pipeline into at least one of said chambers and a continuous flow of slurry from at least another one of said chambers into the pipeline to provide the increased pressure to the slurry flow in the pipeline while avoiding undesirable pulsations.

2. The pump unit of claim 1, wherein said control means includes valve means associated with said other end of each said chamber which regulate the alternate application of the high and low pressure to each said chamber, switch means associated with each said chamber which sequentially operate said valve means, and actuating means in each said chamber associated with slurry flow therein operably contacting said switch means at predetermined intervals depending on the relative amounts of slurry in said chambers.

3. The pump unit of claim 2, wherein said actuating means comprises a separator in each said chamber, each said separator in contact with the slurry in each said chamber and moveable in each said chamber relative to the amount of slurry in each said chamber.

4. The pump unit of claim 2, wherein each said chamber comprises a sufficiently large volume which requires a substantial filling and emptying period thereby delaying the actuation of said switch means and reducing the operation time of said value means.

5. The pump unit of claim 4, wherein said chamber is cylindrical and the length of each said chamber exceeds 25 feet.

6. A pump unit to increase the pressure of slurry being transported through a pipeline, comprising: first, second and third chambers; pressurizing means adapted to alternately apply high and low pressure to each said chamber; means to provide for the flow of slurry from the pipeline into one end of each said chamber during the application of low pressure to fill each said chamber with slurry and to provide for the flow of slurry from said one end of each said chamber into the pipeline during the application of high pressure to empty each said chamber of slurry; control means associated with the emptying and filling of slurry in each said chamber to cause the high and low pressure to be applied sequentially to said chambers, said control means including valve means associated with each said chamber for regulating the alternate application of the high and low pressure to each said chamber, switch means associated with each said chamber which operate said valve means, and actuating means in each said chamber associated with slurry flow therein operably contacting said switch means at predetermined intervals to cause said valve means to operate according to a sequence whereby when slurry is flowing from said first chamber and into said third chamber and when said third chamber is near full, slurry begins to flow simultaneously from said second chamber, slurry flow from said first chamber is then stopped and slurry begins to flow into said first chamber simultaneously with slurry flow into said third chamber, slurry flow into said third chamber is then stopped, and when said first chamber is near full, slurry begins to flow simultaneously from said third chamber, slurry flow from said second chamber is then stopped and slurry begins to flow into said second chamber simultaneously with slurry flow into said first chamber, slurry flow into said first chamber is then stopped, and when said second chamber is near full, slurry begins to flow simultaneously from said first chamber, slurry flow from said third chamber is then stopped and slurry begins to flow into said third chamber simultaneously with slurry flow into second chamber, slurry flow into said second chamber is then stopped and the sequence begins again and is repeated.

7. The pump unit of claim 6, wherein second switch means associated with each said chamber are provided, said first switch means positioned to actuate and maintain said valve sequence when said chambers contain a first predetermined amount of slurry and said second switch means positioned to actuate and maintain said valve sequence when said chambers contain a second predetermined amount of slurry.

8. The pump unit of claim 7, wherein said first predetermined amount is equal to and greater than two-thirds the total volume of said chambers and said second predetermined amount is equal to and less than two-thirds the total volume of said chambers.

9. A pumping apparatus comprising: a plurality of at least three chambers; a pipeline transporting a first fluid, said pipeline in communication with one end of each said chamber to provide for flow of said first fluid from said pipeline through said one end into each said chamber and to provide for flow of said first fluid from each said chamber through said one end back into said pipeline; a conduit carrying a second fluid in a closed circuit; a pump assembly, in said closed circuit connected to said conduit and adapted to pressurize said second fluid; said conduit in communication with said other end of each said chamber to provide for flow of said second fluid when pressurized from said conduit into each said chamber through said other end and to provide for flow of said second fluid from each said chamber, said second fluid creating a high-pressure zone in said chambers when flowing into said chambers to cause said first fluid to flow from said chambers and creating a low-pressure zone in said chambers when flowing from said chambers to cause said first fluid to flow into said chambers; separator means in each said chamber to prevent communication of said first fluid with said pump assembly and to maintain said second fluid in said closed circuit; valve means in association with said other end to alternate flow of said second fluid into and from each said chamber; and control means to operate said valve means in a sequence which provides at all times a continuous flow of said first fluid into and a corresponding flow of said second fluid from at least one of said chambers and a continuous flow of said first fluid from and a corresponding continuous flow of said second fluid into at least another one of said chambers to provide a nonpulsating flow of said first fluid in said pipeline.

10. The pumping apparatus of claim 9, wherein said pump assembly includes at least one centrifugal pump.

11. The pumping apparatus of claim 9, wherein said second fluid is recirculated in said conduit from said pump assembly into said chambers and then from said chambers back to said pump assembly.

12. The pumping apparatus of claim 11, wherein a heat exchanger is provided in said closed circuit which utilizes the temperature difference between the second fluid flowing in said conduit from said chambers back to said pump assembly and the first fluid in said pipeline flowing from said chambers to cool said second fluid before said second fluid is recirculated back to said pump assembly.

13. The pumping apparatus of claim 11, wherein said conduit includes a solids separator in said closed circuit to remove solids from said second liquid before it passes to said pump assembly.

14. The pumping apparatus of claim 9, wherein said separator means includes a separator in each said chamber positioned between the interface of said first fluid and said second fluid in each said chamber and moveable relative to the movement of said first and second fluids in each said chamber.

15. The pumping apparatus of claim 14, wherein said separator comprises a moveable member slidably mounted to the walls of each said chamber and means to prevent leakage between said moveable member and the walls of each said chamber.

16. The pumping apparatus of claim 14, wherein said separator comprises a flexible diaphragm member sealably secured to the walls of each said chamber.

17. The pumping apparatus of claim 9, wherein said control means includes switch means in association with each said chamber, said switch means being actuated when each said chamber contains a predetermined amount of first fluid.

18. The pumping apparatus of claim 17, wherein said switch means is actuated by said separator means.

19. The pumping apparatus of claim 9, wherein said first fluid comprises a mixture of liquid and solid particles.

20. A pumping apparatus of claim 9, wherein first, second and third chambers are employed.

21. The pumping apparatus of claim 20, wherein said valve means includes first, second and third inlet and outlet valves, said first, second and third inlet valves regulate the flow of said second fluid into said first, second and third chambers, respectively, and said first, second and third outlet valves regulate the flow of said second fluid from said first, second and third chambers, respectively; and said control means includes first, second and third switches associated with said first, second and third chambers, respectively, whereby, while said first fluid is flowing from said first chamber and said second fluid is flowing from said third chamber and said second chamber is full of said first fluid, said first switch is actuated and operates and begins the opening of said second inlet valve to begin the flow of said second fluid into said second chamber, said second inlet valve when open then begins the closing of said first inlet valve, said first inlet valve when closed then begins the opening of said first outlet valve to begin the flow of said first fluid into said first chamber, said first outlet valve when open then begins the closing of said third outlet valve, subsequently said second switch is actuated and operates and begins the opening of said third inlet valve to begin the flow of said second fluid into said third chamber, said third inlet valve when open then begins the closing of said second inlet valve, said second inlet valve when closed then begins the opening of said second outlet valve to begin the flow of said first fluid into said second chamber, said second outlet valve when open then begins the closing of said first outlet valve, subsequently said third switch is actuated and operates and begins the opening of said first inlet valve to begin the flow of said second fluid into said first chamber, said first inlet valve when open then begins the closing of said third inlet valve, said third inlet valve when closed then begins the opening of said third outlet valve to begin the flow of said first fluid into said third chamber, said third outlet valve when open then begins the closing of said second outlet valve, subsequently said first switch is actuated and the cycle is repeated.

22. A pumping method to increase the pressure of a first fluid flowing through a pipeline, the steps comprising:

applying for a period of time low pressure to each chamber of a group of at least three chambers to cause said first fluid to pass into said chambers from the pipeline and alternately applying for a substantially equal period of time high pressure to cause said first fluid to pass from said chambers and back into the pipeline;

passing at a controlled rate a volume of said first fluid from the pipeline into at least one of said chambers while applying low pressure;

simultaneously passing at an equal rate an equal volume of said first fluid from at least another one of said chambers while applying high pressure; and

sequentially applying said high and low pressure to said group of chambers to provide at all times a continuous flow of said first fluid from said pipeline into said group of chambers and a continuous flow of said first fluid from said group of chambers back into said pipeline to provide the increased pressure to said first fluid without creating pulsations in the flow of the first fluid through the pipeline.

23. The method of claim 22, wherein a second fluid when pressurized is passed alternately into said chambers to apply high pressure to said chambers and is withdrawn alternately from said chambers to apply low pressure to said chambers.

24. The method of claim 23, wherein at least one centrifugal pump is employed to pressurize said second fluid.

25. The method of claim 24, wherein each said chamber is provided with a separator to separate said second fluid from said first fluid in said chambers to prevent communication of said first fluid with said centrifugal pump.

26. The method of claim 23, wherein valve means are provided to control the flow of said second fluid into and from said chambers.

27. The method of claim 26, wherein said valve means are sequentially operated by switch means which are associated with predetermined amounts of said first fluid in each said chamber.

28. A pumping method to increase the pressure of a slurry flowing through a pipeline, the steps comprising:

providing a group of at least three pressure chambers, each of which is in communication with the pipeline;

alternately applying first a low pressure and then a high pressure to each chamber to cause the slurry to first flow from the pipeline into a chamber and then flow from the chamber back into the pipeline;

applying to each chamber the low pressure until the chamber is filled with slurry and applying to each filled chamber the alternate high pressure until the chamber is empty of the slurry;

applying low pressure at all times to at least one of the chambers to provide a continuous flow of slurry into the group of chambers and simultaneously applying high pressure to at least another one of the chambers to provide a continuous flow of slurry from the group of chambers back to the pipeline; and

applying the low pressure to the chambers in sequence to begin the filling of another chamber before the preceding chamber in the sequence is filled and applying the high pressure to the chambers in a similar sequence to begin the discharge of another chamber before the preceding chamber in the sequence is empty whereby pulsations in the incoming and outgoing slurry are avoided.

29. The method of claim 28, wherein a fluid in a closed circuit is communicated to each chamber to provide for the application of high pressure and communicated from each chamber to provide for the application of low pressure.

30. The method of claim 29, wherein centrifugal pump means in the closed circuit pressurize the fluid in the circuit.