SE467839B - HYDRAULIC DRIVE DEPLACEMENT PUMP - Google Patents

Description

467 839 10 'other displacement pumps are the pulsating mode of operation. with plunge pumps, you can avoid some of the difficulties that characterize piston pumps. However, plunge pumps are not without problems either.

This applies in particular to plunge pumps that work in highly contaminated or abrasive media, such as slurries of various kinds, for example cement. This is basically related to the plunger being driven into the pump housing chamber during the pump stroke. During the return stroke, the pumping medium must be prevented from passing by and / or damaging the sealing devices in the cylinder wall. These difficulties have not been satisfactorily solved in known devices.

Another problem that characterizes not only plunge pumps but also Like them. In most other pumps, it is desirable that the pump does not operate in a pulse-like manner but as evenly as possible. By allowing two pump units (pump cylinders) to work alternately in an integrated pump unit, the pulsations can be greatly reduced. In the case of mechanically driven displacement pumps, there are definite geometric relationships between the number of pump cylinders and the degree of non-uniformity of the pump, ie variations in the pump flow during a pump cycle. Although these variations can be reduced quite significantly by a larger number of cylinders, one is always bound by said geometric conditions and corresponding pulsations in the pump flow. In the case of hydraulically driven pumps, these fixed connections can be broken, the cylinders can be driven independently of each other, but the problem of pulsations has not been solved satisfactorily in hydraulically driven displacement pumps according to known technology. THE INVENTION The object of the invention is to bring about improvements in displacement pumps and in particular in plunge pumps. In particular, the invention aims to solve the above-mentioned problems. These and other objects can be achieved in that the invention is characterized by what is stated in the appended claims.

The most important improvement in this context relates to the arrangement of sealing devices for the plunger in order to substantially reduce the wear of the plunger and its seals in connection with pumping liquids containing solid particles or other abrasive media. In addition, it is intended to provide a pump unit with very small flow pulsations, despite the fact that the unit in principle only consists of a single-acting pair of cylinders, ie two cylinders.

Additional objects and features and aspects of the invention will become apparent from the following description of some preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS In the following description of preferred embodiments, reference will be made to the accompanying drawing figures, of which Figs. 1A-1C schematically illustrate how two pump units or cylinders in a two-cylinder plunge pump assembly according to the invention are constructed and arranged to cooperate during the workflow, Figs. Fig. 2B is a diagram illustrating the flow of pump medium in the two pump units of the integrated two-cylinder plunge pump assembly during a working cycle; Fig. 3 schematically shows how a pump housing chamber with pump housing cylinder and associated sealing devices can be cleaned, after completion of work, and Fig. 4 shows a portion of a pump unit comprising a sealing housing according to an alternative embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS According to a first preferred embodiment, the plunge pump unit consists of two pump units or cylinders A, B, the shifts of which are controlled by a common, specially designed slide valve V. The equipment also includes a hydraulic unit, both commonly referred to as H. units A and B are identically designed and equipped. In the following, therefore, only one of the pump units, the A-unit, will be described in more detail. When required for understanding the job description, _.

Numerical references to details attributable to the A-unit have been given the appendix A, while corresponding details in the B-unit have been given the appendix B in the drawing figures and / or in the text.

The A-unit includes a pump housing 1A and a drive unit 2A. In the pump housing 1A there is a pump housing chamber 5A with an inlet line with a non-return valve 3A and an outlet line with a non-return valve 4A. Connected to the pump housing 1A is a sealing housing 6A, which forms a continuation of the cylindrical pump housing chamber 5A, albeit with narrower inner dimensions. Connected to the sealing housing 6A is a flushing water housing 7A and a drainage housing 8A.

A sleeve or spacer between the drive unit 2A and the pump housing with its sealing housing 6A has been designated 9A. A plunge has been designated IOÄ.

The drive unit 2A consists of the following main parts: a hydraulic cylinder 11A, a drive piston 12A, a drive rod 13A, which connects the drive piston 12A to the plunger 10A, an end block 14A, and a cylinder head 15A. The details 1A, 6A, 7A, 8A, 9A, 11A, 14A, 15A are connected to each other by screw connections to a unit. In this fixed unit, the unit constituted by the plunger 10A, the drive piston 12A and the drive rod 13A is movable between two end positions.

The plunger 10A has a smooth, cylindrical exterior. This is arranged to cooperate with a number of ring- or cuff-shaped seals in the sealing housing 6A, which also forms part of the pump housing cylinder. Closest to the pump housing chamber 5A is a first sealing sleeve 17, which constitutes a combined main seal and wiper. A secondary sealing sleeve has been designated 18, and a third seal has been designated 19. The latter seals against the ambient air which fills the space 58 inside the intermediate piece 9A. A lower guide between the sealing sleeves 17 and 18 has been designated 20 and an upper guide outside the seal 19 has been designated 21.

Details 17-21 are arranged in annular grooves in the sealing housing 6A; Furthermore, the inner wall of the sealing housing 6A in cross section has been given a profile, where an annular, slit-shaped space 22 is found inside and also over the combined main seal of the wiper 17, an annular recess 23 inside and below the secondary seal 18 and an annular space 24 between the secondary seal 18 and the third ambient seal 19.

From the flushing water housing 7A a line 26 goes to the annular space 24 and from there a line 25 which branches in a line 26 up to the drain housing 8A and a line 27 down to a non-return valve 28, on the downstream side of which there is a line 29, which via a connecting line 30 opens into the annular spaces 22 and 23.

An inlet line 32 for flushing water extends via a non-return valve 33 into a flushing water chamber 34, which communicates with the above-mentioned line 26, which extends into the annular space 24 in the sealing housing 6A. In the flushing water chamber 34 there is a flushing plunger 35 with a helically wound spring 36 on the inside, which strives to move the plunger 35 upwards towards a hydraulic, small operating plunger 37 operating in a hydraulic operating cylinder 38.

The discharge housing 8A consists of a cylinder containing a hydraulic piston 40 with a piston rod 41, which presses against a non-return valve ball 48, which in Fig. 1A blocks the passage between the line 26 and a drainage line 39. A return spring for the piston 40 has been designated 49.

The hydraulic cylinder 11A in the drive unit 2A has on one side of the piston 12A a drive or plus chamber 42A and on the other side a return or minus chamber 43A. Inside the cylinder head 15A and inside the end portion of the end block 14A, respectively, there is an annular slot 44A and 45A, respectively, which communicates with the drive chamber 42A and with the return chamber 43A, respectively, through a number of openings 46 and 47, respectively, which extend along a certain length of the hydraulic cylinder 11A. ends. The piston 12A has an axial cavity 50A which also extends a distance into the drive rod 13A. The cavity 50A communicates via channels 51A with an annular gap 52A in the middle of the piston 12A. A channel that -. extending through the hydraulic cylinder 11A of the drive unit a distance from the outer gap 45A of the return chamber has been designated 53A. In the cylinder head 15A 467 839 10 there is a central opening, into which is screwed a tube 54A, which has the same length as and extends into the axial cavity SOA in the drive piston 12A and the drive rod 13A. A seal between the outside of the tube 54A and the outer end of the space SOA has been designated 55.

J; A strong aeration channel 57 connects the space 58 inside the sleeve 9A to the surroundings.

In the control valve V there is a slide 60, which has a first, a second, a third and a fourth flange 61-64 arranged to slide against the inside of the valve housing. Between the said flanges there is a left, annular recess 65, a middle, annular recess 66 and a right, annular recess 67.

According to the embodiment, the hydraulic unit H contains a sump 70, a first hydraulic pump 71, which constitutes the main pump in the system, and an auxiliary pump 72.

The system includes a number of hydraulic lines. The lines that are primarily connected to the A-unit have been given the addition A, and those that are primarily connected to the B-unit have been assigned the designation B.

A main line 80 leads to the control valve V, and the hydraulic oil, transported through the line 80, can be distributed via the central recess 66 in the SOYU slide 60 to either a drive line 82A to the slot 44A or to a drive line 82B to a corresponding slot 44B in the B unit. or via the two drive lines 82A and 82B to the two units A and B depending on the position of the slide 60. The drive chambers 42A and 42B can also be drained of hydraulic oil through the lines 82A and 828 via said right recess 67 and a drain line 83A and via the left recess 65 and a drain line 83B, respectively. The heat chambers 43A and 43B can be filled with hydraulic oil at the return stroke by means of the auxiliary pump 72 via a line 81 and a line 84A leading to the gap _A, respectively via the line 81 and a line 84B leading to -. column 45B. At the pump stroke, the return chambers 43A and 43B can be emptied of oil the same way, however, the oil from line 81 is led to the sump 70 via a line 85 past an overflow valve 96. As can be seen from the figures, slots 45A and 45B communicate directly with each other via lines 84A and 84B, which are part of the common, pressurized return system, where a constant pressure is maintained by the pump 72 and the overflow valve 96.

From the gap 44A in the rear end portion of the hydraulic cylinder 11A, a line 86A goes to the operating cylinder 38 in the flushing water housing 7A. From line 82A (or from the same gap 44A) a line 87A goes to the cylinder of the lead housing 8A. From line 83B, line 88A goes to center tube 54A. Finally, there is an operating line 89A and 89B, respectively, which extends from the channel 53A in the end block 14A and from the corresponding channel in the B-unit to the control valve V and the ends, respectively. In the control lines 89A and 898 there is a throttle 68A and 68B, respectively.

The operation of the equipment described will now be explained.

The initial position is assumed to be the moment immediately preceding the situation shown in Fig. IA. The slide 60 is in its higher position, and hydraulic oil is driven by the pump 71 through the line 80, the gap 66 and the line 82A to the drive chamber 42A and pushes the drive piston 12A_forward, so that the plunger 10A is driven forward (downward in Fig. 1A) in the pump housing chamber 5A. The non-return valve 3A is closed, and the pumped medium is forced out of the pump housing chamber 5A via the valve 4A. Line 89A is blocked by piston 12A.

The drive piston 12B in the B-unit is on return and begins to approach its rear end position. The return chamber 43B is supplied with hydraulic oil from the return chamber 43A of the A unit, from which the hydraulic oil is forced out via the line 84A.

The auxiliary pump 72 helps to maintain the pressure in the return system 43A-43B. A certain amount of oil is recycled through line 85.

The drive chamber 428 of the B unit is drained on hydraulic oil through line 82B, column 65 and drain line 83B. The oil in the volume 50B and in the pipe 54Ä is drained through the lines 88B, 83A. This phase is represented by the solid horizontal curve of the A unit and the dashed, inclined curve of the B unit to the left of position I in Fig. 2A. The inclination of the curve is due to the fact that the drive piston 12B moves within the area of the openings 45B within the gap 44B, so that a successive restriction of the hydraulic oil flow is obtained. (Position I is the position in which the drive piston 12B reaches its upper / rear end position, which occurs when the plunger 10B abuts the end block 14B.) When the drive piston 12A with its annular gap 52A reaches and begins to communicate with the conduit 53A, which roughly corresponds to position In the diagram in Fig. 2A, the following happens. The pressure on the left side of the slide 60 in the control valve V is relieved by the fact that the hydraulic medium to the left of the slide 60 can be drained through the lines and channels 89A, 53A, 51A, 54A, 88A, 83B to the sump 70. At the same time a pressure remains on the right side of the slide 00 via the control line 89B, which causes the slide 60 to begin to move to the left. However, the movement is relatively slow due to the throttles 68A and 68B.

During the movement of the slide 60 to the left, the following sequence is obtained: Position I - II In position I, the drive piston 12B reaches its upper end position and remains in this position until position II, while the drive piston 12A continues to move forward a further distance at a reduced speed up to position II. The flange 62 closes the connection between the conduit 82B and the drainage conduit 83B.

Position II - III The flange 62 passes the line 823, whereby hydraulic oil from the main line 80 can be distributed to the two lines 82A and 828 via the central gap 66 in the valve V. The B-unit thus receives pressure in the drive chamber 428, which means that the drive piston 12B begins its movement forward (downward, Fig. 1). Since the main pump 71 feeds a constant flow of hydraulic medium through the line 80, the supply to the drive chamber 42A will decrease as much as is now supplied to the drive chamber 423 in the B unit, which corresponds to the inclined portions and curves in Pig. 2A between positions II and III, and means that the drive piston 128 accelerates, while the drive piston 12A decelerates correspondingly. - - 10 15 20 25 30 35 467 839 Position III - IV During this phase, during which the slide 60 passes the position shown in Fig. 1B, the hydraulic flow from the line 80 is distributed practically equally between the drive chamber 42A of the A-unit and the B-unit drive chamber 42B, which is represented by the coincident horizontal part of the curves between positions III and IV in Fig. 2A. This idealized situation is also shown in Fig. 1B. The return chambers 43A and 43B are drained through lines 84A, 84B, 81 and 85. The hydraulic oil is forced out of the return chambers 43A and 43B through lines 84A, 84B, 81 and through the overflow valve 96.

Position IV - V Between positions IV and V, the flange 63 begins to close to the conduit 82A of the drive unit 42A of the A-unit, and in position V the connection 82A is completely closed, which means that the drive piston 12A and the plunger 10A remain in their front end positions, while the drive piston 12B and the plunger 1OB in the B unit have accelerated to full speed during its pump stroke.

During the entire work process described so far, i.e. from the moment before position I and between positions I and V, there has been a hydraulic overpressure Ph in the drive chamber 42A and thus also in the control line 86A. The same pressure Ph also prevails in line 87A. The pressure Ph thus partly affects the control plunger 37 in the control cylinder 38 in the flushing water housing 7A and partly the piston 40 in the discharge housing 8A. The cross-sectional areas of the operating plunger 37, the flush chamber plunger 35, the drive piston 12A and the main plunger 10A are designated Y37, Y35, Y122 and Y10A, respectively. According to one aspect of the invention, the area ratios are such that Y37: Y35> Y12A: Y10A. More specifically, the Y ratio Y37: Y35 is so much larger than the ratio Y122: Y10A that the pressure Pv on the rinsing water in the rinsing water housing 7A (also taking into account the force exerted by the spring 36 by several factors) is slightly greater than the pressure Pp on the pump medium in pump housing chamber 5A. At the same time, the pressure Ph is large enough to compress the spring 44 in the diverter housing BA via the line 87A and the piston 40 and close the non-return valve 42. Under the influence of the pressure in the control cylinder 38, the control plunger 37 will thus press the coil plunger 35 against the spring 36. The non-return valve 33 closes. The resulting pressure in the flush water chamber 34 propagates through the conduit 26 in the sealing housing 6A into the gap 24 and thence further through the channels 10 and 25, past the check valve 28 and through the channel 29 into the gap 22 inside and behind the combined primary seal and the wiper 17.

If the pressure difference between the rinsing water pressure in the column 22 and the pump medium pressure in the pump housing chamber 5A were greater than the contact force of the wiper lip on the primary seal 17, rinsing water will be forced past the seal into the pump chamber until equilibrium is reached between rinsing water pressure and pressure. in such a case, the flushing plunger 35 will move downwards in step with the flushing water flow past the primary seal 17.

As already indicated initially, one of the most important aspects of this invention is to arrange the plunger seals in such a way as to obtain a substantially reduced wear of the plunger and its seals when pumping liquids containing solid and / or abrasive particles. This is achieved mainly by using a wiper operating in the manner described above as a primary seal against the pump medium.

Since wipers with a configuration as shown in the figures are not normally suitable for working at pressure differences corresponding to the working pressure of the pump, the invention has provided a pressure balancing of the combined primary seal / wiper 17 by means of the rinsing water pressure acting in the gap 22, therefore largely the same pressure prevails on both sides of the wiper during the pump stroke. As an additional safety, the flushing water on the back of the primary seal / wiper 17 has a slightly higher pressure than the pressure prevailing in the pump housing 5A, which prevents the pump medium from penetrating into spaces above the primary seal in the event of damage to it. Similarly, the secondary seal 18 is also pressure-balanced, as rinsing water of substantially the same pressure acts both on the front of the seal in the space 23 and on the back thereof in the gap 24.

The purpose of pressure balancing of the secondary seal 18 is partly to reduce the wear of the secondary seal and partly to minimize frictional forces from the secondary seal. Through Pv> Pp, flushing water can also be forced past the primary seal / wiper 17 into the pump housing at least initially during the pump stroke. If it is desired that this flushing action should take place substantially during the entire pump stroke, this can be achieved by regulating the oil supply to the control cylinder 38 by a suitably dimensioned throttle in the line 86A.

Position V - VI During the last phase of the movement of the slide 60 to the left, the recess 67 in the slide 60 will open connection between the lines 82A and 83A, so that the drive piston 12A in the A-unit can begin its return stroke, position V. Since no working pressure develops on the drive piston 12A in the drive chamber 42A, the pressure from the line 84A, which is substantially obtained from the return chamber 43B in the B unit, will be sufficient to drive the drive piston 12A back, the hydraulic medium from the drive chamber 42A being diverted to the sump 70 via the line 82A, recess 67 and drain line 83A. .

After the slide 60 has reached its left end position, it remains in this position under the influence of the return pressure in the line 89B until the drive piston 128 in the B-unit has moved so far forward that hydraulic medium can be drained from the right side of the slide 60 through the line 89B in the same way as described above with reference to the A-unit (positions VI-VIII).

Position VI - VIII The drive piston 12B moves forward at a steady speed in the same way as the drive piston 12A did at the beginning of the function description. This phase of the B-piston 12B drive piston is represented by the dashed upper, flat curve in the diagram in Fig. 2A. At the same time, the drive piston 12A is driven back and pulls the plunger out of the pump housing chamber 5A by means of the drive rod 13A. The valve 4A is now closed, and new pumped medium is sucked into the pump housing chamber SA via the valve 3A. This phase lasts until the drive piston 12B has advanced so far that the gap 52B has begun to communicate with the line 898 and the drive piston 12A has reached its upper end position, whereby the slide o 60 can begin to be displaced to the right, position VIII. 467 839 10 15 20 25 30 35 12 During the return movement of the plunger 10A, the drive chamber 42A is of course not pressurized. Therefore, the flush chamber plunger can be returned to the initial position by means of the return spring 36, whereby the operating plunger 37 is also returned to its rear (upper) end position. Flush water is forced in under pressure through the line 32 past the non-return valve 33, Fig. 10 »°° h Further through the flush water chamber 34, the channel 26, the gap 24, the lines 25 and 26, past the valve 42 and out through the drainage line 43. In this case the flush water chamber 34 is filled with flush water , at the same time as the gap 24 between the sealing sleeves 18 and 19 is flushed, so that any contaminants which accompany the plunger 10A past the sealing sleeves 17 and 18 are flushed out of the system. However, substantially all of the contaminants are removed by means of the main seal 17, which in this phase acts as a scraper against the smooth, cylindrical outside 16 of the plunger 10A.

Therefore, only insignificant amounts of contaminants pass the main seal 17 as long as the sleeve 17 is undamaged.

Should the primary seal / wiper 17 be severely damaged, the spaces 22, 30, 29 and 23 closest to the wiper are isolated from the rest of the flushing water system by the secondary seal 18 and the non-return valve 28, which is kept closed during In addition, as already mentioned, a flushing takes place of spaces and ducts above the secondary seal 18. suction stroke of the pump.

In the above description of the function of the pump units A and B, it has not been mentioned in detail how the series of openings 44A, 44B, 45A, 45B in the hydraulic cylinders 11A and 11B affect the pump characteristics of the units. movements are damped in the end positions, which corresponds to the inclined portions in Fig. 2A. Fig. 2A otherwise shows idealized characteristics for the two pump units. In Fig. 2B, the pressure strokes for A- have been summed in the upper curve. and the B-units In the idealized case, the result is a completely even flow of the pumped medium from the integrated two-cylinder pump unit, something which is essentially achieved in practice as well. The lower curve in Fig. 23 illustrates corresponding conditions in the suction line of the integrated pump assembly. The '- discontinuous course of the suction line is considerably simpler that The effect with these openings is that the drive pistons 12A and 12B 10 control and do not affect the even outflow from the pump. In practice, the pump characteristics do not have the shape of completely straight lines.

Between position III and IV, however, there is a substantially horizontal curve, where the middle position of the slide, Fig. 1B, defines an inflection point on the curve. I - Although the sealing housing 6A is flushed with rinsing water during two phases at each work cycle, it may be desirable to clean the sealing housing 6A and also the pump housing IAÄ more thoroughly after completion of work. out of the pump so as not to damage it, such as cement or other substances that can harden and eventually make the pump inoperable. Fig. 3 illustrates how such a flushing can be performed. For this purpose, there are a further pair of conduits 90 and 91, which extend through the flush water housing wall to the annular space 23 in front of the secondary sealing sleeve 18 and from the annular gap 22 behind the main sealing and scraping sleeve 17. Flush water is introduced through the conduit 90 to the annular the space 23 and flows through this space on both sides of the plunger 10A to its opposite side, from where the water flows through the passage 30 on the back of the guide 20 into the annular gap 22. The water continues through the gap 22 and passes again on both sides of the plunger 10A to be finally evacuated through the drainage line 91. This effectively removes all possible contaminants in the spaces 22 and 23. If desired, flushing water can also be introduced through the line 32 in the stationary pump to also clean via the flushing water chamber 34 and the line 26 gap 24, which is drained through line 43 in the manner explained in connection to the description of the return stroke of the plunger 10A. Finally, the pump housing chamber 5A can be flushed with rinsing water which is started through a line 92 (possibly through the same line as the outlet line for the pump medium). A bottom plug 93 has been removed so that the rinsing water can be drained through the bottom opening 94. In the embodiment according to Fig. 4 there is a rinsing water housing 107 with the same embodiment as in the previous embodiment and a modified sealing housing 106. Diversion housings and associated diversion means are missing in this embodiment. In the sealing housing there is a combined primary seal and wiper 117, a second, rear seal 119 and guides 120 and 121. In the sealing housing 106 there is a non-return valve 100, the countercurrent side of which communicates with a gap 122 on the primary seal / wiper. 117 rear and with a circumferential recess 124 between the rear seal 119 and the first guide 120.

During the return stroke, the rinsing water chamber 134 is filled with rinsing water, which during the pump stroke is forced out past the valve 100 into the space 124 and the gap 122, whereby in the same manner as in the previous embodiment, contaminants are substantially prevented from being forced past the primary seal / wiper 117 during the pump stroke. During the return stroke, according to this embodiment, no flushing takes place. During the return stroke, the non-return valve 100 prevents any contaminants from passing into the rinsing water chamber 134 as it communicates with the rinsing water filling line.

Claims (8)

_10 15 20 25 30 35 467 839 15 PATENT REQUIREMENTS A displacement pump arranged to be operated hydraulically, comprising at least one pump housing chamber (5A), a pump housing cylinder and a plunger (10A) arranged therein, which at the pump stroke is driven into the pump housing chamber (SA), a drive unit (2A) belonging to each plunge comprising a hydraulic cylinder (11A) with a drive piston (12A) arranged therein, and a drive rod (13A) arranged between the drive piston and the plunger, characterized in that in the pump housing cylinder there is at least one sealing element acting against the cylindrical surface (16) of the plunger on the back of which there is a space (22, 122), which during the pump stroke of the plunger (10A) is filled with flushing water, the pressure of which is always slightly above the pressure of the pumped medium in the pump housing chamber, which is achieved by the pump comprising a hydraulic propellant operating piston (37) and a flushing chamber piston ( 35) for rinsing water, and in that the area ratio between the control piston (37) and the rinsing chamber piston (35) is greater than the area ratio between the drive unit (2A) d shredder piston (12A) and the plunger (10A) in the pump housing (1A). Pump according to claim 1, characterized by means, comprising said operating piston (37) and flushing chamber piston (35) for supplying said space (22, 122) with clean and pressurized flushing water during each pump stroke. Pump according to claim 1, characterized by at least two sealing elements, of which the first-mentioned sealing element (17, 117) is designed so that it acts as a wiper against the pump medium at the return stroke. A pump according to claims 2 and 3, characterized by a non-return valve (28, 100) between said means for forcing pure purge water into said space during each pump stroke, and that the purge water during the pump stroke of the plunger is arranged to be introduced into said space past said non-return valve. Pump according to claim 4, characterized by at least three sealing elements, and that the rinsing water during the pump stroke of the plunger is arranged to be inserted into an annular space (24) between two rear sealing elements (18, 19). ) for being conveyed via said non-return valve (28) past one of said seals to said space (22) behind the first-mentioned sealing element (17). A pump according to any one of claims 1-5, characterized by a rinsing water chamber (34, 134) containing a certain amount of rinsing water, which during the pump stroke is kept at a pressure related to and preferably slightly lower than the pump pressure. Pump according to claim 6, characterized in that the rinsing water from the rinsing water chamber (34) during the pump stroke is fed to said space behind the first-mentioned sleeve (17) by means of a piston (35) arranged in the rinsing water chamber, which is actuated by said operating piston ( 37). Pump according to any one of the preceding claims, characterized in that rinsing water is arranged to flow through at least one annular gap or recess behind the first-mentioned sealing sleeve (17), preferably the annular recess or gap between said second and third sealing sleeves (18, 19 ).