EP1903217A1

EP1903217A1 - Hydropneumatic damper for damping pressure pulsations in fluid pumping plants

Info

Publication number: EP1903217A1
Application number: EP20060425648
Authority: EP
Inventors: Giovanni Zanardi
Original assignee: SAIP Srl
Current assignee: SAIP Srl
Priority date: 2006-09-22
Filing date: 2006-09-22
Publication date: 2008-03-26

Abstract

A hydropneumatic damper (1) for damping pressure pulsations in a fluid pumping plant comprises one or more hollow containers (5) each of which defines in its inside a chamber (6) hermetically closed by a substantially flat elastic membrane (7) which separates the chamber (6) from a fluid flowing in a main piping of the plant, the chamber (6) containing an inert gas, as well as a duct (2) which is suitable to allow the mounting thereof in line with the plant main piping, the duct (2) being provided with openings (4) which are suitable for fluid-tight connection of the hollow containers (5). Thanks to the arrangement in line with the main piping and to the particular structure of the membrane (7), the damper (1) according to the present invention allows to achieve output pulsation values down to 0,05% of the input pulsations and high velocity of response to the input pulsations, and is also easier to be cleaned.

Description

The present invention relates to a hydropneumatic damper for damping pressure pulsations in fluid pumping plants, and in particular to a damper to be mounted in line with the main piping.
Hydropneumatic dampers, which are hydropneumatic accumulators being used for damping pulsations, are devices which are capable of storing and releasing pressure energy in hydraulic circuits by utilizing the compressibility of a gas contained therein. They are widely used, for instance, in the food industry, chemical industry and pharmaceutical industry and are also used for hydraulic applications such as, for example, in the hydraulic circuits of machine tools.
A hydropneumatic damper generally comprises a metallic chamber arranged in fluid communication with the plant piping. In the chamber there is mounted a membrane separating the plant fluid from an inert gas, usually nitrogen, which is in the chamber of the damper at a suitable pressure and occupies the whole internal volume thereof.
When the pressure in the plant exceeds the pressure of the gas contained in the damper, the membrane is displaced thus reducing the volume which is occupied by the gas and consequently the gas pressure increases until it balances the pressure of the fluid. When the pressure in the plant decreases, the membrane is displaced in the opposite direction and the gas expands until it balances the new pressure of the fluid. The membrane displacement thus allows to accumulate fluid when the pressure in the plant increases and to release fluid when the pressure in the plant decreases.
In the plants where the fluid is fed by means of reciprocating displacement pumps, the pressure increases and decreases cyclically due to the reciprocating motion of the piston. The pressure pulsations mechanically stress the piping and other mechanical members such as, for instance, valves and sealing devices, thus causing considerable fatigue problems in the structures and failure problems, as well as noise problems.
The use of hydropneumatic dampers allows to damp pressure pulsations by utilizing the compressibility of the gas contained in the chamber of the damper. Dampers are generally immediately downstream of the pumps on the main piping line of the plant and are usually mounted perpendicularly to the main piping, on a secondary piping which is in fluid communication with the main one.
An example of a known damper can be found in the patent application US 2005/0139277 , which discloses a membrane hydropneumatic damper for damping pulsations in hydraulic circuits, comprising a chamber provided with inlet and outlet ducts for the fluid. In the damper chamber there is a membrane separation element dividing a gas reservoir from the chamber for the fluid. The membrane is made of a material containing PTFE.
Similarly, patent EP 0078721 discloses a hydropneumatic damper consisting of a container divided into two chambers which are isolated one from the other by means of a diaphragm. One chamber is connected to a hydraulic plant through a duct, while the other chamber is connected to a gas reservoir.
Independently of the different designs, known hydropneumatic dampers do not allow to completely damp the pressure pulsations in the plants, and in particular to obtain pulsation values at the output from the damper which are lower than 0,5% of the input pulsations.
Another drawback of known dampers is that the velocity of the response to the pressure pulsations is rather low. This is mainly due to the shapes of the membranes being used, which do not allow them to quickly adapt to the pressure variations. Furthermore, in the secondary piping connecting the damper to the main piping line of the plant, eddies and pressure drops, which alter and further delay the pressure signal reaching the membrane, are generated.
Finally, known hydropneumatic dampers are easily subject to fouling, especially in case of pumping food and pharmaceutical products, as the material being transported tends to accumulate in the interstices between the elastic membrane and the duct communicating with the main piping. The deposits of material are hardly removable and require long and costly cleaning and maintenance operations.
Object of the present invention is thus to provide a hydropneumatic damper which is free from such drawbacks. Said object is achieved by means of a hydropneumatic damper arranged in line with the main piping and provided with one or more membranes having a substantially flat shape.
A first important advantage of this damper is that it allows to obtain output pulsation values down to 0,05% of the input pulsation.
A second significant advantage of this damper is that it allows to obtain high velocities of response to the input pulsations.
Another advantage of the present damper is that it allows a remarkable ease of cleaning and maintenance without the need to be disassembled, thanks to the flat shape of the elastic membranes being used and to the type of fixing of the latter to the damper chamber.
Further advantages and features of the hydropneumatic damper according to the present invention will be evident to those skilled in the art from the following detailed description of some embodiments thereof with reference to the annexed drawings, wherein:

Figure 1 shows a partially sectioned front view of a first embodiment of a hydropneumatic damper according to the present invention;
Figure 2 shows a top plan view of the damper of Fig. 1;
Figure 3 shows a partially sectioned front view of a second embodiment of the damper; and
Figure 4 shows a partially sectioned side view of a third embodiment of the damper.

Figures 1 and 2 show a first embodiment of a pneumatic damper 1 according to the present invention, which comprises a duct 2 provided at each of its ends with a flange 3 suitable for fluid-tight connection of damper 1 to the piping (not shown) of the pumping plant line. The duct 2 of damper 1 is further provided in its mantle with one or more openings 4 around which one or more corresponding hollow containers 5 are hermetically fixed. In the embodiment illustrated in Figures 1 and 2, damper 1 is provided with two openings 4 and two corresponding hollow containers 5, diametrically opposite with respect to the axis of duct 2.
In other embodiments, not shown, duct 2 may have more than two ends suitable to receive or distribute the fluid of the plant in more directions.
Each container 5 defines in its inside a chamber 6 hermetically closed by an elastic membrane 7 which separates chamber 6 from the central part of duct 2. The elastic membrane 7 has a substantially flat disc shape and is secured along its perimeter to container 5 at the zone of connection of container 5 to duct 2. Each chamber 6 contains an inert gas, usually nitrogen, as well as a dividing baffle 8 limiting the deformation of membrane 7 towards the inside of chamber 6.
During the operation of damper 1, the fluid being pumped in the plant goes through duct 2 thus applying on each membrane 7 a pressure which is equal to the pumping pressure. When the pumping pressure exceeds the pressure of the gas contained in chamber 6, membrane 7 is deformed thus reducing the volume which is occupied by the gas and consequently increasing the volume of the central part of duct 2, and as a consequence the pressure of the gas in chamber 6 increases until it balances the pressure of the fluid.
Also the deformation of membrane 7 contributes to balancing the pressure of the fluid, in fact, because of the effect of the deformation, internal stresses arise in the membrane which oppose the deformation by trying to bring the membrane back to the non-deformed condition, that is by contrasting the increase in pressure of the fluid in duct 2. On the contrary, when the pumping pressure decreases, membrane 7 is deformed in the opposite direction and the gas expands until it balances the new pressure of the fluid, thus reducing the internal volume of the central part of duct 2. The deformation of membrane 7 thus allows to vary the volume of the central part of duct 2 according to the pumping pressure of the fluid, that is to accumulate fluid as the plant pressure increases and to release fluid as the plant pressure decreases.
The deformation of membrane 7 is limited in the direction of gas compression, that is from the axis of duct 2 towards chamber 6, by means of the dividing baffle 8. The dividing baffle 8 is provided with a central hole 9 wherein a perforated element may be fixed, such as for example a grid, a net or a perforated sheet, which allows the gas contained in chamber 6 to go through it and to apply a pressure on membrane 7. Further, the deformation of membrane 7 is limited in the direction of gas expansion, that is from chamber 6 towards the axis of duct 2, by means of a second perforated baffle 10 having a convex shape facing the axis of duct 2.
The baffle 10 is perforated in order to allow the fluid pumped in duct 2 to easily flow therethrough and to apply a pressure on membrane 7, and the size of the holes in baffle 10 is suitable for preventing the stagnation of fluid between baffle 10 and membrane 7 especially in case of very dense fluids such as, for example, greases, paints, rubbers in the fluid state, etc. In this way, the duct 2 of damper 1 according to the present invention can be cleaned, for example after each cycle, directly in line without disassembling any component thereof. Furthermore, the size of the holes of baffle 10 has to be suitable for preventing excessive deformations of membrane 7 as it pushes on baffle 10 due to the effect of the pressure of the gas contained in chamber 6, i.e. when the pressure in duct 2 decreases. The baffle 10 may be a grid, a net or a perforated sheet, made e.g. of a metallic material, a polymeric material, PTFE, PVDF and other materials compatible with the pumped fluid.
In addition, baffle 10 has to be firmly fixed so as to not be damaged when membrane 7 pushes thereon, for example when the plant internal pressure is low and membrane 7 is pushed towards duct 2 by the gas contained in chamber 6. Thus, baffle 10 can be fixed to the perimeter of opening 4 by welding and/or stiffened by means of a suitable frame connecting baffles 10 one to another and keeping fixed the mutual distances.
The damper 1 according to the present invention is arranged in line with the plant piping. Thus, the entire surface of membrane 7 is arranged directly in contact with the fluid flowing in duct 2 and in the main line piping during the operation, and in this way it is possible to achieve high damping velocities of the pressure pulsations. In fact, mounting the membrane dampers in branch configuration with respect to the line piping, which is typical of the prior-art dampers, involves the use of side ducts and fittings which generate eddies and pressure drops thus altering and delaying the pressure signal reaching the membrane or bag.
Also the shape and the type of mounting of membrane 7 contribute to increase the damping velocity of damper 1; in fact, as membrane 7 is substantially flat and is firmly fixed to the damper along the perimeter of container 5, a variation in the pressure of the fluid flow induces on membrane 7 a displacement which involves immediately the whole surface of the membrane itself and which is immediately transmitted to the gas contained in chamber 6. Thus, the flatness of membrane 7 makes the response of damper 1 very sensitive and quick to high-frequency, small-amplitude pulsations.
In other embodiments it is possible to use membranes 7 having a slightly wavy, sinusoidal or concave section, whereby it is possible to achieve a higher volume of fluid accumulation. Therefore, slightly wavy or differently shaped membranes are particularly suitable for damping large amplitude pulsations.
Moreover, membrane 7 exhibits a damping characteristic which can be suitably selected by adjusting the mounting tension thereof and using suitable materials, such as e.g. PTFE.
The membrane 7 can be entirely made of PTFE, however, as this material does not have optimal gas barrier properties, it is preferred to use a membrane consisting of a PTFE layer suitable for the contact with fluids which is coupled, e.g. in a vulcanization step, with a layer of butyl rubber or other elastomers.
Other materials suitable for manufacturing membrane 7 can be fluororubbers, EPDM, NBR, depending on the fluid being worked.
The pulsations transmitted by the membrane are mainly damped by suitably adjusting the pressure of the gas which is contained in each chamber 6. In fact, thanks to its compressibility, the pressurized gas in chamber 6 behaves as a hydraulic damper activated by the action of membrane 7. Suitable values of gas pressure in chamber 6 are comprised between 80% and 97% of the pumping pressure of the fluid, and preferably between 90% and 95%.
As mentioned above, damper 1 according to the present invention may be provided with a number of containers 5 and respective membranes 7, whereby in this case it is possible to obtain a higher damping action. Furthermore, by connecting the chambers 6 one to another by means of channels 11, which are for example formed in the thickness of duct 2, the gas pressure in chambers 6 is homogeneous and it is thus possible to achieve a uniform behaviour of membranes 7.
The damper 1 according to the present invention allows to achieve extremely low output pulsation values, which are equal to e.g. 0,05% of the input pulsation.
Figure 3 shows a second embodiment of the above illustrated double-chamber damper 1, which comprises a second membrane 12 within each chamber 6, which is fluid-tightly fixed to the hollow container 5 in a way similar to the first membrane 7. This embodiment is particularly suitable for plants in which no accumulation of the fluid being worked must occur, e.g. for food and pharmaceutical plants. In fact, in the damper 1 shown in the figure no dividing baffle 10 is present between the flat membrane 7 and duct 2 so that there are no cavities or recesses where the fluid being worked may stop. Furthermore, the internal surfaces of duct 2 usually have a very low roughness, e.g. lower than 0,2 µm, in order to avoid the adhesion of the fluid being worked.
As it can be seen in the figure, the volume comprised between the second membrane 12 and the first membrane 7 contains an incompressible fluid 13, which is suitable for contacting the fluid passing through duct 2 in case of failure of the first membrane 7. In fact, in case of failure of membrane 7, the gas contained in chamber 6 would be mixed with the fluid being transported in duct 2 and this could be detrimental to the quality of the fluid itself and also to the main line piping. In the hole of the dividing baffle 8 it is not necessary to arrange a perforated element, since when membrane 7 is pressed towards the dividing baffle 8, it cannot be pushed through the hole because it is supported by the incompressible fluid contained between the two membranes 7, 12.
In addition to the dividing baffle 8 which is useful for limiting the displacement of membrane 7 towards chamber 6 and the displacement of membrane 12 towards duct 2, in order to prevent an excessive deformation of membrane 12 in the direction away from duct 2, chamber 6 is provided with a second dividing baffle 14 which is arranged between membrane 12 and container 5, and which is provided with a hole for the passage of the gas contained in chamber 6. The membrane 12 may be provided with an anti-extrusion element (12a) which is suitable to engage the edge of the hole of the dividing baffle 14 thus preventing membrane 12 from exiting through said hole. In this last case, it is not necessary that the hole is provided with a perforated element for limiting the displacement of membrane 12.
Materials suitable for manufacturing membrane 12 are e.g. elastomers such as EPDM, fluororubbers and/or NBR.
The chamber 6 may also have shapes which are different from the dome shape shown in Figure 3, such as for example a dome shape with one or more cylindrical expansions. Further, it is possible to replace or combine chamber 6 with one or more accumulators of the prior art.
Figure 4 shows a third embodiment of damper 1 according to the present invention, which comprises a heating and/or cooling system. Such a system can for example allow to maintain a desired viscosity value in the fluid being transported in duct 2, and thus allows to keep in the fluid state substances which can solidify inside duct 2, such as e.g. waxes. The heating and/or cooling system may for example consist of a hydraulic circuit which is provided with a delivery pipe 15 and a return pipe 16, and with passageways 17 formed in the structure of damper 1 wherein a suitable heating/cooling fluid circulates.
The heating system may be carried out in other ways, e.g. by means of electrical resistances.
It is clear that the above disclosed and illustrated embodiments of the pneumatic damper according to the present invention are only examples which can be varied in numerous ways. In particular, when the processing temperatures are particularly high, membranes 7, 12 may, for example, be metallic membranes. Furthermore, damper 1 may be provided with manometers or pressure sensors being mounted, for example, on container 5 in order to keep the operating state of the device under control and to detect possible failures of membranes 7, 12.
In addition, the sizes of dampers 1 according to the present invention, and thus their volumetric capacity, may vary depending on the application they are intended for. The volumetric capacities of the single chambers 6 of a single damper 1 may be different from each other in order to obtain an optimal pulsation damping response.
Finally, it is possible to apply to damper 1 according to the present invention a pressure control system capable of keeping constant the ratio between the pressure in each chamber 6 and the plant internal pressure, which may undergo variations during the operation.

Claims

Hydropneumatic damper (1) comprising one or more hollow containers (5) each of which defines in its inside a chamber (6) hermetically closed by an elastic membrane (7) which separates said chamber (6) from a fluid flowing in a main piping of a fluid pumping plant, said chamber (6) containing an inert gas, characterized in that said damper (1) further comprises a duct (2) which is suitable to allow the mounting thereof in line with the plant main piping, said duct (2) being provided, in its mantle, with one or more openings (4) which are suitable for the fluid-tight connection of one or more of said corresponding hollow containers (5).
Hydropneumatic damper (1) according to the previous claim, characterized in that said duct (2) comprises two openings (4) diametrically opposite with respect to the axis of the duct (2).
Hydropneumatic damper (1) according to claim 1 or 2, characterized in that said membrane (7) is substantially flat.
Hydropneumatic damper (1) according to one of the previous claims, characterized in that said membrane (7) is made of an elastomeric material.
Hydropneumatic damper (1) according to one of claims 1 to 3, characterized in that said membrane (7) is made of PTFE.
Hydropneumatic damper (1) according to one of claims 1 to 3, characterized in that said membrane (7) consists of a layer of PTFE coupled with a layer of butyl rubber.
Hydropneumatic damper (1) according to one of claims 1 to 3, characterized in that said membrane (7) is made of a metallic material.
Hydropneumatic damper (1) according to one of the previous claims, characterized by comprising in each chamber (6) a dividing baffle (8), provided with a central hole (9), which is suitable to limit the deformation of each membrane (7) towards the inside of the respective chamber (6).
Hydropneumatic damper (1) according to the previous claim, characterized in that a perforated element is fixed in the hole of the dividing baffle (8).
Hydropneumatic damper (1) according to one of the previous claims,
characterized by comprising in the duct (2) in correspondence to each opening (4) a perforated baffle (10), which is suitable to limit the deformation of each membrane (7) towards the axis of the duct (2).
Hydropneumatic damper (1) according to the previous claim, characterized in that said baffle (10) has a convex shape facing the axis of the duct (2).
Hydropneumatic damper (1) according to claim 10 or 11, characterized in that said baffle (10) is a grid, a net or a perforated sheet.
Hydropneumatic damper (1) according to claim 10 or 11 or 12, characterized in that said baffle (10) is made of a metallic material.
Hydropneumatic damper (1) according to claim 10 or 11 or 12, characterized in that said baffle (10) is made of a polymeric material.
Hydropneumatic damper (1) according to claim 14, characterized in that said baffle (10) is made of PTFE.
Hydropneumatic damper (1) according to claim 14, characterized in that said baffle (10) is made of PVDF.
Hydropneumatic damper (1) according to any claim from 10 to 16, characterized in that said baffle (10) is firmly fixed to the perimeter of the opening (4).
Hydropneumatic damper (1) according to any claim from 10 to 17, characterized by comprising at least two baffles (10) which are stiffened by means of a frame which connects the baffles (10) one to another and is suitable to keep fixed the mutual distances.
Hydropneumatic damper (1) according to one of the previous claims, characterized in that the gas pressure in the chamber (6) is comprised between 80% and 97% of the pumping pressure of the fluid in the main piping, preferably between 90% and 95%.
Hydropneumatic damper (1) according to one of the previous claims, characterized in that the chambers (6) are in communication through channels (11) formed in the thickness of the duct (2).
Hydropneumatic damper (1) according to one of the previous claims,
characterized in that each chamber (6) contains a second membrane (12) fluid-tightly fixed to the hollow container (5) and arranged between the latter and the first membrane (7), the volume comprised between the second membrane (12) and the first membrane (7) being filled with an incompressible fluid (13).
Hydropneumatic damper (1) according to the previous claim, characterized in that each chamber (6) is provided with a further perforated dividing baffle (14) arranged between the second membrane (12) and the hollow container (5).
Hydropneumatic damper (1) according to one of claims 21 or 22, characterized in that said membrane (12) is made of an elastomeric material selected among EPDM, fluororubbers and NBR.
Hydropneumatic damper (1) according to one of the previous claims, characterized in that the internal surfaces of the duct (2) have a roughness which is lower than 0,2 µm.
Hydropneumatic damper (1) according to one of claims from 21 to 24, characterized in that the second membrane (12) is provided with an anti-extrusion element (12a) suitable to engage the edge of the hole of said dividing baffle (14).
Hydropneumatic damper (1) according to one of the previous claims, characterized by comprising a heating and/or cooling system.
Hydropneumatic damper (1) according to the previous claim, characterized in that said heating and/or cooling system comprises a hydraulic circuit provided with a delivery pipe (15), a return pipe (16) and passageways (17) which are formed in the structure of the damper (1).
Hydropneumatic damper (1) according to one of the previous claims, characterized by being provided with manometers or pressure sensors which are suitable to keep the operating state of the device under control and to detect possible failures of the membranes (7, 12).
Hydropneumatic damper (1) according to one of the previous claims, characterized by being provided with a pressure control system which is suitable to keep constant the ratio between the pressure in each chamber (6) and the plant internal pressure.