EP2728190B1

EP2728190B1 - A hydraulic piston pump

Info

Publication number: EP2728190B1
Application number: EP13175582.9A
Authority: EP
Inventors: Fulvio Montipo'
Original assignee: Interpump Engineering SRL
Current assignee: Interpump Group SpA
Priority date: 2012-11-02
Filing date: 2013-07-08
Publication date: 2016-01-13
Anticipated expiration: 2033-07-08
Also published as: EP2728190A1; EP2728190B8; ITRE20120078A1

Description

The present invention relates to a hydraulic piston pump, in particular a high-pressure hydraulic piston pump for industrial applications.
As is known e.g. from document EP-2466138-A1 , a hydraulic piston pump generally comprises a casing in which a drive shaft is rotatably supported, which drive shaft is able to activate at least a crank mechanism of the con-rod-shaft type giving a respective piston an alternating motion.
A head is fixed to the casing, internally of which a blind cylindrical seating is fashioned in which the piston is slidably housed, such as to define a variable-volume pump chamber. Also housed in the cylindrical seating is at least an annular seal, which is suitable for inserting substantially snugly on the piston skirt, such as to delimit and sealingly close the pump chamber.
The pump chamber is also delimited by an aspirating valve and a delivery valve, by means of which the chamber can be placed in communication respectively with an aspirating conduit and a delivery conduit that are both fashioned in the head.
Owing to the alternating piston movement, the fluid to be pumped is aspirated at low pressure through the aspirating valve, is compressed internally of the pump chamber, and lastly is made to exit at high pressure through the delivery valve.
During this functioning, the seal gaskets interposed between the cylindrical seating and the piston are however subjected to normal phenomena of wear which make the gaskets progressively less effective and which thus require periodical replacement.
A drawback of these hydraulic pumps consists in the fact that each time it is necessary to replace the seal gaskets the hydraulic pump operation has to be halted, the delivery and aspiration conduits evacuated, the connections with the hydraulic circuit in which the hydraulic pump is inserted disconnected, and lastly the head of the casing removed and the pistons extracted.
After replacing the seals it is then necessary to repeat the above operations in reverse up to completely remounting and connecting-up the hydraulic pump.
These operations are clearly very costly, in terms of both the time required for the intervention and the physical work for the operators carrying out the task, especially when concerning hydraulic pumps which are significantly voluminous and very heavy.
In fact, in some of these hydraulic pumps which function at high pressure, the weight of only the head can be tens of kilograms, and therefore the maintenance interventions, apart from taking up a lot of time for the number of intervention steps as mentioned above, are decidedly difficult and laborious for the personnel involved.
With the aim of mitigating the above-described drawbacks, in a known solution the cylindrical piston seatings are defined by a plurality of cylindrical bushings removably associated to the head, and extractable in the sliding direction of the pistons from the opposite side with respect to the casing. In particular, the cylindrical bushings are all associated to a single support plate, which is fixed to the front part of the head by means of a plurality of screws. By removing the screws, the support plate can be distanced from the head, extracting the cylindrical bushings from the respective pistons together with the gaskets.
The above process is however not sufficient to guarantee the total elimination of the above-described drawbacks. In fact, in this case too the seal-gasket replacement operations require the demounting of a support plate which can be rather heavy. Further, the removal together of all the cylindrical bushings means that the bushings whose seals do not require replacing might also be removed.
Lastly, the cylindrical bushing extracting operation can be rather tricky, as it can require considerable effort on the part of the operator to overcome the adhesion force that the worn gaskets exert against the walls and against the piston skirt.
An aim of the present invention is to obviate the above-mentioned drawbacks in the prior art, with a solution that is simple, rational and relatively inexpensive.
These aims are attained by the characteristics of the invention reported in the independent claim. The dependent claims delineate preferred and/or particularly advantageous aspects of the invention.
In particular, the invention discloses a hydraulic piston pump comprising a head in which an aspiration conduit, a delivery conduit, and at least a pump chamber in which an alternating piston is partially housed are fashioned, wherein the pump chamber is separated from the aspirating conduit and from the delivery conduit respectively by an automatic aspirating valve and an automatic delivery valve, which are housed in respective seatings realised in the head, and wherein the piston is slidably housed internally of a cylindrical bushing, which is housed internally of the head and bears at least a first annular seal able to be coaxially interposed between the piston and the bushing, such as to sealingly close the pump chamber. The pump further comprises a cap which is coupled to the bushing by connecting means which constrain the bushing to the cap in an axial direction and enable reciprocal free rotations about the axis of the bushing, the cap being rotatably coupled to the head by threaded means which define a screw axis of the cap coinciding with the axis of the bushing.
Thanks to this solution, the seal replacement operations are simpler and more rapid and the aid of special apparatus or specialised personnel is not required, as for removing the bushing and replacing the annular seal it is sufficient to unscrew the cap.
The cap is further only associated to the respective bushing, so it is possible to proceed to mounting a single bushing at a time, leaving the ones having still-efficient seals in their housings.
Lastly, by exploiting the coefficient of multiplication defined by the threaded means of the cap, it is advantageously possible to reduce the effort required to overcome the adhesion forces of the worn seals on the piston and on the head seating, during extraction of the bushing.
In an aspect of the invention, the connecting means between the bushing and the cap can comprise a plurality of axial tabs projecting from a first end of the cylindrical bushing and arranged circumferentially about the axis of the bushing, angularly distanced from one another, which tabs snap-fit to a cylindrical shank realised at an end of the cap.
In this way, the engaging tabs facilitate the operations of mounting and demounting the bushing from the cap.
In a further aspect of the invention, the cylindrical bushing (30) further bears a second annular seal (low-pressure) able to be coaxially interposed between the piston and the bushing, which is positioned at a certain axial distance from the first annular seal (high pressure).
In this way, the second annular seal prevents small quantities of fluid, possibly leaking from the first seal, from exiting the pump.
In a further aspect of the invention, the lateral wall of the cylindrical bushing can be provided with at least a discharge through-hole, which is interposed between the first and second annular seal and is in communication with the aspirating conduit via a scavenger conduit afforded in the head.
In this way, the above-mentioned small quantities of fluid that may have leaked from the first seal (high-pressure) can be advantageously recycled by aspiration.
In a further aspect of the invention, the cylindrical bushing bears a third annular seal (high-pressure) able to be coaxially interposed between the cylindrical bushing and a relative cylindrical seating of the head in which the bushing is housed.
The advantage of this solution is to prevent the fluid to be pumped from exiting from the pump chamber by leaking between the cylindrical bushing and the respective housing seating of the head.
In relation to this, the cylindrical bushing can also bear a fourth annular seal (low pressure) able to be coaxially interposed between the cylindrical bushing and the relative cylindrical seating, which is positioned such that the discharge hole (for recycling the leakage) is also located between the third and fourth annular seal.
In this way, any small quantities of fluid which might leak from the third annular seal (high-pressure between the bushing and the head) can be blocked by the fourth annular seal (low-pressure between the bushing and the head) and recycled by aspiration through the scavenger channels.
In an aspect of the invention, the cylindrical bushing comprises a first cylindrical portion and a second cylindrical portion which are coaxial and reciprocally coupled by means of further connecting means able to constrain them reciprocally at least in an axial direction, for example using further snap-fit means.
This solution has the advantage of providing a cylindrical bushing which is separable into two easily-demountable and re-mountable components, thus simplifying the replacement of the various seals associated to the bushing.
In a further aspect of the invention, the second cylindrical portion is at least partly inserted internally of the first cylindrical portion, such that the first annular seal (high-pressure between the piston and the bushing)is axially interposed and blocked between the second cylindrical portion and an abutment of the first cylindrical portion.
In this way, the replacement of the first annular seal can be done simply by separating the two cylindrical portions of the bushing.
In other preferred aspects of the invention, the second annular seal (low-pressure between the piston and the bushing) is borne by the second cylindrical portion of the bushing, the third seal (high-pressure between the bushing and the head) is borne by the first cylindrical portion of the bushing, and the fourth annular seal (low-pressure between the bushing and the head) is borne by the second cylindrical portion of the bushing.
In a further aspect of the invention, the cylindrical bushing is at least partly made of a plastic material, for example only the first cylindrical portion, only the second cylindrical portion, or both.
In this way a very economical component is obtained, which can be replaced in a block together with the seals, as a single-use disposable exchange part. Further characteristics and advantages of the invention will emerge from a reading of the following description provided by way of non-limiting example, with the aid of the figures illustrated in the appended tables of drawings.

Figure 1 is an axial section of a pump of the present invention.
Figure 2 is an axial section of a cylindrical seal-bearing bushing and the relative seal.
Figure 3 is an axial section of the cylindrical bushing and the cap, decoupled.
Figure 4 is an axial section of the cylindrical bushing in which the first and second cylindrical portions are decoupled.

With particular reference to the figures, 21 denotes in its entirety a hydraulic piston pump comprising a head 10 (i.e. an external body) in which the following are fashioned: an aspirating conduit 12, a delivery conduit 13 and at least a pump chamber 11, which communicates with the aspiration conduit 12 and delivery conduit 13 via corresponding aspiration and delivery valves 121 and 131.
The valves 121 and 131 are housed in special seatings fashioned in the head 10 and fixed thereto with the aid of relative caps 122 and 132 screwed to the head 10. The valves 121 and 131 are automatic valves of known type and are therefore not described in further detail.
An alternating piston 14 is partially housed in the pump chamber 11, which piston 14 is pivoted to a thrust mechanism 20 activated by a motor (not shown in the figures) and contained in a casing 21 fixed to the head 10.
The piston 14 is coaxially housed internally of a substantially cylindrical bushing 30, in such a way as to be slidable alternatingly in the direction defined by the longitudinal axis A of the bushing 30.
The bushing 30 is in turn housed in a cylindrical seating 16 afforded internally of the head 10, so that the internal volume of the bushing 30 is able to at least partially define the pump chamber 11.
The bushing 30 is coaxially coupled to a cap 31, which can be removably fixed to the head 10. In particular, the cap 31 comprises a cylindrical shank 311, the external lateral surface of which is provided with a thread. The cap 31 is screwed via the thread to an opening afforded in the head 10 in the opposite side to the casing 21, such as to obstruct it.
The screwing/unscrewing axis of the cap 31 coincides with the longitudinal axis of the bushing 30, which is coupled to the cap 31 by connecting means which constrain it in the axial direction but allow free rotations about the longitudinal axis A. In this way, by unscrewing/screwing the cap 31 the bushing 30 can be slid extractingly/insertingly internally of the cylindrical seating 16.
Observing the detail of figures 2, 3 and 4, the internal surface of the cylindrical shank 311 of the cap 31 exhibits a coaxial annular gully 312, which defines a circumferential tooth 313 projecting radially internally with respect to the longitudinal axis A of the bushing 30. The bushing 30 comprises a first and a second cylindrical portion 32 and 33, coaxially coupled to one another. The first cylindrical portion 32 exhibits an end edge 321 from which a plurality of axially-developing tabs 322 project. The tabs 322 are arranged circumferentially about the longitudinal axis A and are angularly distanced from one another in such a way as to place the internal volume of the bushing 30 in communication with the remaining part of the pump chamber 11 when the bushing 30 is inserted in the cylindrical seating 16.
Each tab 322 comprises a tooth 323 projecting radially externally with respect to the longitudinal axis A of the bushing 30. In this way the first cylindrical portion 32 can be snap-fitted to the cap 31, by partially inserting the tabs 322 internally of the cylindrical shank 311 and enabling the teeth 323 to snap-fit in the annular gully 312.
The contact between the teeth 323 and the circumferential tooth 313 thus realises an axial constraint to reciprocal motion of the first cylindrical portion 32 and the cap 31, while allowing reciprocal rotations.
A perimeter gully is fashioned coaxially in the external surface of the cylindrical portion, for housing a high-pressure seal 34, which will be coaxially interposed between the bushing 30 and the relative cylindrical seating 16 of the head (see figure 1), such as to prevent leakage of fluid from the pump chamber 11 towards the casing 21.
The first cylindrical portion 32 of the bushing 30 also bears a further high-pressure annular seal 35, which will be coaxially interposed between the bushing 30 and the piston 15 (see figure 1). This further high-pressure seal 35 is placed in contact with an abutment 324 of the cylindrical portion 32, which defines an annular surface perpendicular to the longitudinal axis A. In this way, the abutment 324 prevents the axial sliding of the high-pressure seal 35 in the direction of the cap 31. On the opposite side the high-pressure seal 35 is axially blocked by the second cylindrical portion 33 of the bushing 30.
In particular, the second cylindrical portion 33 is suitable for partial insertion coaxially internally of the first cylindrical portion 32. In this way, the end edge 331 of the second cylindrical portion 33 enters into contact with the high-pressure seal 35 (with a possible interposing of a spacer ring), compressing it and preventing it from sliding in an axial direction towards the casing 21. The blocking of the first and second cylindrical portion 32 and 33 is obtained by snap-fitting means, which comprise a circumferential tooth 325, coaxially afforded in the first cylindrical portion 32, and a further circumferential tooth 335, coaxially afforded in the second cylindrical portion 33.
The circumferential tooth 325 projects radially towards the inside of the bushing 30 with respect to the longitudinal axis A, and is localised at an end edge 327 of the first cylindrical portion 32, opposite the end edge 321 from which the tabs 322 project.
The second circumferential tooth 335 projects radially towards the outside of the bushing 30 with respect to the longitudinal axis A, and is localised in an intermediate position of the second cylindrical portion 33, such as to enable the end edge 331 to come into contact with the high-pressure seal 35.
In this way, when the second cylindrical portion 33 is inserted in the first cylindrical portion 32, the circumferential teeth 325 and 335 enter into contact with and snap-fit to one another, creating a constraint to reciprocal axial sliding between the first and the second cylindrical portion 32 and 33.
The second cylindrical portion 33 in turn bears a low-pressure annular seal which will be coaxially interposed between the bushing 30 and the relative cylindrical seating 16 of the head 10 (see figure 1). This low-pressure seal 36 is axially blocked between the end edge 327 of the first cylindrical portion 32 and an abutment 332 of the second cylindrical portion 33, which extends radially externally with respect to the longitudinal axis A and is localised at the opposite end with respect to the end edge 331.
Further afforded in the internal surface of the second cylindrical portion 33 is a perimeter gully for housing a further low-pressure annular seal 37 able to be coaxially interposed between the bushing 30 and the piston 14.
In this way, collection spaces for the fluid which might leak from the pump chamber 11 are defined between the high-pressure seals 34, 35 and the low-pressure seals 36, 37, (this fluid may seep from the high-pressure seals 34 and 35). These collection spaces communicate with the aspirating conduit 12 via scavenger channels 15 afforded in the head 10 and are in communication with one another through passages fashioned in the lateral wall of the bushing 30, between the high-pressure seals and low-pressure seals.
In particular, these passages are defined by a plurality of lateral openings 326 (see figure 2) realised in the first cylindrical portion 32, and the circumferential tooth 325, and by through-holes 336 afforded in the second cylindrical portion 33, between the end edge 331 and the second tooth 335. In this way, the through-holes 336 are positioned at the lateral openings 326 when the first and the second cylindrical portions 32 and 33 are reciprocally coupled.
In the light of the above, the hydraulic piston pump 1 operates as follows.
A motor (not illustrated) activates the thrust mechanism 20 and at the same time the piston 14, which slides internally of the bushing 30. When the piston 14 slides in the direction of the casing 21 it generates a depression in the pump chamber 11 which causes the opening of the aspirating valve 121 and, consequently, the passage of the fluid from the aspirating conduit 12 to the pump chamber 11.
When the piston 14 slides towards the cap 31, the pressure in the pump chamber 11 increases, the aspirating vale 121 closes and, on exceeding a predetermined pressure level, the delivery valve 131 opens and the high-pressure liquid exits into the delivery conduit 13. The fluid is retained in the pump chamber 11 by the high-pressure seals 34 and 35.
If the wear on the high-pressure seals 34 35 causes small leakages of the fluid, these losses will not however reach the casing 21 thanks to the presence of the low-pressure seals 36 and 37, and will be scavenged by aspiration through the scavenger channels 15.
To replace the high- and/or low-pressure seals, the cap 31 is unscrewed from the head 10, causing a simultaneous extraction of the bushing 30. This operation is very simple as the multiplication ratio defined by the thread of the cap 31 enables the bushing 30 coupled thereto to be extracted progressively, also reducing the effort the operator has to apply to overcome any adhesion forces of the worn seals on the piston 14 and on the cylindrical seating 16 of the head 10.
Once the bushing 30 is extracted one or more of the high- or low-pressure seals 34, 35, 36, 37 can be replaced. This replacement can be done by the removal of the seals from the bushing or by completely substituting the bushing 30 together with the seals. In the last case the bushing 30 (i.e. one or both the cylindrical portions 32,33) is preferably made of a plastic material, for example by moulding, such as to realise a low-cost component of the single-use disposable type.
As the bushing 30 is realised in two cylindrical portions 32 and 33 it is also possible to replace only of the portions, or briefly separate the first cylindrical portion 32 from the second cylindrical portion 33 such as to facilitate the removal of the seals.
It is however stressed that the bushing 30 might also be realised in a single piece, instead of with the two cylindrical portions 32 and 33 described above. The invention as it is conceived herein is susceptible to numerous modifications and variants, all falling within the scope of the inventive concept. Furthermore, all the details can be replaced by other technically-equivalent elements. In practice the materials used, as well as the contingent shapes and dimensions, can be of any type according to requirements, without forsaking the scope of protection of the following claims.

Claims

A hydraulic piston pump (1) comprising a head (10) in which an aspiration conduit (12), a delivery conduit (13), and at least a pump chamber (11) in which an alternating piston (14) is partially housed are fashioned, wherein the pump chamber (11) is separated from the aspirating conduit (12) and from the delivery conduit (13) respectively by an automatic aspirating valve (121) and an automatic delivery valve (131), which are housed in respective seatings realised in the head (10), and wherein the piston (14) is slidably housed internally of a cylindrical bushing (30), which is housed internally of the head (10) and bears at least a first annular seal (35) able to be coaxially interposed between the piston (14) and the bushing (30), such as to sealingly close the pump chamber (11), characterised in that it comprises a cap (31) which is coupled to the bushing (30) by connecting means (312, 322) which constrain the bushing (30) to the cap (31) in an axial direction and enable reciprocal free rotations about the axis of the bushing (30), the cap (31) being rotatably coupled to the head (10) by threaded means which define a screw axis of the cap (31) coinciding with the axis (A) of the bushing (30).
The pump (1) of claim 1, wherein the connecting means comprise a plurality of axial tabs (322) projecting from a first end (321) of the cylindrical bushing (30) and arranged circumferentially about the axis (A) of the bushing (30), angularly distanced from one another, which snap-fit to a cylindrical shank (311) realised at an end of the cap (31).
The pump (1) of claim 1 or 2, wherein the cylindrical bushing (30) bears a second annular seal (37) able to be coaxially interposed between the piston (14) and the bushing (30), which is positioned at a certain axial distance from the first annular seal (35).
The pump (1) of claim 3, wherein the lateral wall of the cylindrical bushing (30) is provided with at least a discharge through-hole (336), which is interposed between the first and second annular seal (35, 37) and is in communication with the aspirating conduit (12) via a scavenger conduit (15) afforded in the head (10).
The pump (1) of any one of the preceding claims, wherein the cylindrical bushing (30) bears a third annular seal (34) able to be coaxially interposed between the cylindrical bushing (30) and a relative cylindrical seating (16) of the head (10) in which the bushing (30) is housed.
The pump (1) of claims 4 and 5, wherein the cylindrical bushing (30) bears a fourth annular seal (36) able to be coaxially interposed between the cylindrical bushing (30) and the relative cylindrical seating (16), which is positioned such that the discharge hole (336) is located also between the third and fourth annular seal (34, 36).
The pump (1) of any one of the preceding claims, wherein the cylindrical bushing (30) comprises a first cylindrical portion (32) and a second cylindrical portion (33) which are coaxial and which are reciprocally coupled by means of further connecting means (335, 325) able to constrain them reciprocally at least in an axial direction.
The pump (1) of claim 7, wherein the further connecting means (335, 325) are snap-fitting means.
The pump (1) of any one of claims 7 and 8, wherein the second cylindrical portion (33) is at least partly inserted internally of the first cylindrical portion (32), such that the first annular seal (35) is axially interposed and blocked between the second cylindrical portion (33) and an abutment (324) of the first cylindrical portion.
The pump (1) of claim 3 and any one of claims from 7 to 9, wherein the second annular seal (37) is borne by the second cylindrical portion (33) of the bushing (30).
The pump (1) of claim 5 and any one of claims from 7 to 10, wherein the third seal (34) is borne by the first cylindrical portion (32) of the bushing (30).
The pump (1) of claim 6 and any one of claims from 7 to 11, wherein the fourth annular seal (36) is borne by the second cylindrical portion (33) of the bushing (30).
The pump (1) of any one of the preceding claims, wherein the cylindrical bushing (30) is at least partly made of plastic material.