GB2494681A - A low compressibility and high tightness, high performance piston seal - Google Patents

Abstract

A seal 200 for sealing in a piston chamber 202 of a piston pump 204 of a fluid separation device 10 is provided. The seal comprises a seal body 206 having a central through bore 208 for receiving a piston 216 and having a circumferential recess 210 between the central through bore 208 and an outer circumferential surface 291 of the seal body 206. A clamping force generating element 214 is accommodated in the circumferential recess 210 and is configured for generating a radial clamping force acting along an entire circumference of the circumferential recess 210.

Description

DESCRIPTION

LOW COMPRESSIBILITY AND HIGH TIGHTNESS, HIGH PERFORMANCE

PISTON SEAL

BACKGROUND ART

[0001] The present invention relates to a piston seal, a piston pump, a fluid separation device, and methods.

[0002] In liquid chromatography, a fluidic sample and an eluent (liquid mobile phase) may be pumped, by a piston pump, through conduits and a column in which separation of sample components takes place. In a sample loop, the sample may be injected into a fluidic path by a mechanically drivable needle. The drivable needle is controllable to be moved out of a seat of the sample loop into a vial to receive a fluid and back from the vial into the seat. The column may comprise a material which is capable of separating different components of the fluidic analyte. Such a material, so-called beads which may comprise silica gel, may be filled into a column tube which may be connected downstream to other components, such as a detector, a fractioner, a waste, etc., by conduits.

[0003] Within the piston pump, a piston reciprocates in a pumping charnber.Aseal cooperating with the piston is provided to prevent leakage of pumped fluid into undesired areas.

[0004] However, conventional piston pumps may suffer from an insufficient sealing.

DISCLOSURE

[0005] It is an object of the invention to provide a fluid-tight seal for a piston pump.

The object is solved by the independent claims. Further embodiments are shown by the dependent claims.

[0006] According to an exemplary embodiment of the present invention, a seal for sealing in a piston chamber of a piston pump of a fluid separation device is provided, the seal comprising a seal body having a central through bore for receiving a piston and having a circumferential recess between the central through bore and an outer circumferential surface (i.e. a surface of the seal body directly facing the piston chamber or sealing at the piston chamber) of the seal body, and a clamping force generating element accommodated in the circumferential recess and being configured for generating a radial clamping force acting along an entire circumference of the circumferential recess or along basically an entire circumference of the circumferential recess.

[0007J Accordfrig to another exemp'ary embodiment, a piston pump for a fluid separation device is provided, the piston pump comprising a piston chamber, a piston configured for reciprocating within the piston chamber, and a seal having the above mentioned features and being arranged for sealing between the piston chamber and the piston.

[0008] According to still another exemplary embodiment, a fluid separation device for separating compounds of a fluid in a mobile phase is provided, the fluid separation device comprising a piston pump having the above mentioned features and being configured to drive the mobile phase through the fluid separation device, and a separation unit, particularly a chromatographic column, configured for separating compounds of the fluid in the mobile phase.

[0009] According to yet another exemplary embodiment, a method of manufacturing a seal for sealing in a piston chamber of a piston pump of a fluid separation device is provided, wherein the method comprises providing a seal body having a central through bore for receiving a piston and having a circumferential recess between the central through bore and an outer circumferential surface of the seal body, and accommodating a clamping force generating element in the circumferential recess for generating a radial clamping force acting along an entire circumference of the circumferential recess or along basically an entire circumference of the circumferential recess.

[0010] According to yet another exemplary embodiment, a method of sealing in a piston chamber of a piston pump of a fluid separation device is provided, wherein the method comprises arranging a seal body in the piston chamber, the seal body having a central through bore receiving a piston and having a circumferential recess between the central through bore and an outer circumferential surface of the seal body, and accommodating a clamping force generating element in the circumferential recess for generating a radial clamping force acting along an entire circumference of the circumferential recess or along basically an entire circumference of the circumferential recess.

[0011] In the context of this application, the term "acting along basically the entire circumference of the circumferential recess" may particularly denote that the clamping force generated by the clamping force generating element is not provided only at certain individual contacting points between the clamping force generating element on the one hand and a wall of the seal body delimiting the recess on the other hand. In contrast to this, the term "basically" means that one or more long continuous contacting lines is/are provided along said wall (particularly along an inner bounding surface and/or along an outer bounding surface of said wall delimiting the circumferential recess) along which contacting line(s) the clamping force is applied uninterruptedly to the wall of the seal body and from there inwardly to the piston and/or outwardly to the piston chamber. However, one or more short interruptions of the continuous force transmission still fall under the term "basically", as long as this does not disturb the comprehensive sealing force exerted around a full perimeter of the central through bore to the piston and/or around a full perimeter of the outer circumferential surface of the seal body to the piston chamber. For instance, a direct contact and thus a transmission of a clamping force along at least 80% of the entire circumference of the circumferential recess is still covered by the term "basically".

[0012] According to an exemplary embodiment of the invention, a seal for a piston pump is provided which allows to provide for a continuous clamping force around at least basically the whole perimeter of the piston in an interior of the seal body and/or of the surrounding piston chamber at an exterior of the seal body. By such a basically uninterrupted clamping force transmission trajectory which fully surrounds the piston or which is fully surrounded by pumping chamber, the reliability and reproducibility of the sealing function is significantly improved. This particularly holds in comparison to conventional approaches in which a clamping spring is accommodated in a circumferential recess of a seal body in such a manner that only spaced, individual contacting points are provided at which the spring force presses the corresponding part of the seal body against the element to be sealed thereto.

[0013] In the following, further exemplary embodiments of the seal will be explained.

However, these embodiments also apply to the piston pump, the fluid separation device, and the methods.

[0014] In an embodiment, the clamping force generating element is configured for generating a radially inward clamping force acting to clamp the seal body towards the piston. "Radially inward" may denote a force vector oriented towards the central through hole. Such a force may act along basically an entire inner circumference of the circumferential recess. In such an embodiment, the inner circumferential surface of the recess in the seal body is made subject of a clamping force in a continuous uninterrupted way so as to significantly improve the sealing performance between reciprocating piston and seal.

[0015] In an embodiment, the clamping force generating element is configured for generating a radially outward clamping force acting to clamp the seal body towards the piston chamber. "Radially outward" may denote a force vector oriented away from the central through hole. Such a force may act along basically an entire outer circumference of the circumferential recess. In this embodiment, the continuous circumferential uninterrupted sealing is provided into a radially outward direction (i.e. away from the central axis of the seal body) so as to clamp an exterior surface of the seal body onto a wall of the piston chamber.

[0016] In an embodiment, the clamping force generating element is configured for generating both a radially inward clamping force acting to clamp the seal body towards the piston and a radially outward clamping force acting to clamp the seal body towards the piston chamber. This embodiment combines the performances of the previously described two embodiments and impacts the piston as well as the pumping chamber with at least almost continuous clamping force lines around the respective circumference.

[0017] In an embodiment, the clamping force generating element provides for a direct (i.e. without any other element in between) continuous (i.e. uninterrupted) contact along basically said entire circumference of the circumferential recess with a wall, particularly with an inner circumferential wall and/or with an outer circumferential wall, of the seal body delimiting the circumferential recess.

[0018] In an embodiment, the clamping force generating element comprises a first spring having a first diameter (for instance in case of a coil spring, the first diameter is a diameter of the coil windings of the first spring) and being configured for generating a radially inward clamping force acting to clamp an inner section of the seal body towards the piston. The clamping force generating element may further comprise a second spring having a second diameter (for instance in case of a coil spring, the second diameter is a diameter of the coil windings of the second spring) being larger than the first diameter and being configured for generating a radially outward clamping force acting to clamp an outer section of the seal body towards the piston chamber. In an embodiment, the first diameter is so that the first spring can be inserted under slight spring expanding pressure into the circumferential recess to contact the inner circumferential surface of the recess while applying an inwardly oriented clamping force to this inner circumferential surface. This is achievable if the first diameter is, in a force free state, slightly smaller (for instance between 1% and 10% smaller) than the inner diameter assigned to the inner circumferential surface of the recess. In an embodiment, the second diameter is so that the second spring can be inserted under slight spring compressing pressure into the circumferential recess to contact the outer circumferential surface of the recess while applying an outwardly oriented clamping force to this outer circumferential surface. This is achievable if the second diameter is, in a force free state, slightly larger (for instance between 1% and 10% larger) than the outer diameter assigned to the outer circumferential surface of the recess.

[0019] In an embodiment, the first spring and the second spring are integrally formed as one common spring structure having windings of different diameter. Such an embodiment may allow for a particularly compact construction of the device, since a single spring body may be sufficient in which for instance alternating windings have a smaller and a larger diameter. The smaller diameter windings may then clamp the seal body towards the piston, whereas the outer diameter windings of the single spring may press the outer surface of the seal body towards the piston chamber. Such a single spring body configuration is also advantageous in terms of mounting it in the recess.

[0020] In another embodiment, the first spring and the second spring are formed as two separate spring structures. In such an embodiment, two separate spring structures may be foreseen, one for providing the inner clamping force and the other one for providing the outer clamping force. Therefore, the clamping performance of the respective spring may be optimized individually with regard to the requirements forthe inner and for the outer clamping, respectively.

[0021] In an embodiment, a central axis (or symmetry axis) of the first spring, a central axis (or symmetry axis) of the second spring, and a central axis (or symmetry axis) of the through bore coincide. This provides for a highly symmetrical structure in terms of force transmission and, in turn, of sealing performance. By co-ahgning the axes of the two springs with the central axis of the seal body, each spring winding of the respective spring may contact a closed line or loop of the recess in the seal body.

In other words, each winding of the inner spring contacts one whole circular surface line of the inner cylindrical delimiting wall of the seal body recess, and each winding of the outer spring contacts one whole circular surface line of the outer cylindrical delimiting wall of the seal body recess.

[0022] In an embodiment, at least one of the first spring and the second spring comprises a helical spring or coil spring. A helical spring is a standard memberwhich can be manufactured with low cost and in which each winding on its own may provide for the clamping along a closed loop so that a multiple redundant clamping loops can be achieved.

[0023] In an embodiment, the first spring and/or the second spring comprises a biasing ring (in case of only one biasing ring, the other spring may be of another type such as a helical spring). For example, such a biasing ring may be configured as an 0-ring. Also an 0-ring is a very simple member which can be manufactured at low cost and which can be used to impact an inwardly or outwardly directed force. One or more 0-ring may be arranged along a radial direction and/or along a longitudinal direction of the circumferential recess.

[0024] In an embodiment, the circumferential recess is configured as a blind hole in fluid communication with an interior of the piston chamber. Thus, the blind hole is freely accessible from an exterior direction and is for instance also in fluid communication with the fluid to be pumped by the piston pump during operation. This has the advantage of a simple mounting of the clamping force generating element in the circumferential recess which is freely accessible from an external position. For instance, a spring only has to be pressed inside the recess with a biasing force.

[00251 In an embodiment, the seal body has a first disc-like section and has a second disc-like section, the second disc-like section having a larger diameter and a smaller longitudinal extension than the first disc-like section. It has turned out to be highly appropriate for piston seals to have this rotationally symmetric arrangement of two concentric and longitudinally connected seal parts for providing both a sealing with regard to a piston and a sealing with regard to a sealing chamber. Relaflve to a fluid flow or pumping direction, the section with the smaller external diameter may be arranged downstream relative to the section with the larger external diameter.

[0026] In an embodiment, the recess is formed (partly or completely) within the first disc-like section. Forming the recess in the long thin disc-like section allows to obtain a proper impact of the clamping force generating material along a long longitudinal section.

[0027] In an embodiment, the seal body comprises at least one of the group consisting of polytetrafluoroethylene, polyethylene, and perfluoroalkoxy. More generally, the seal body may be made of a material which can withstand high pressure values as typical in chromatographic pumps, such as several hundreds or even more than thousand bar. Furthermore, the seal body should be made ofa material which has some flexibility and elasticity to thereby allow to perform the sealing function underthe high present environmental pressure. Moreover, it may be appropriate that the seal body is made of a material which is not prone to deterioration under the influence of biological fluids, or chemically aggressive solvents such as organic solvents. The mentioned materials allow to achieve these effects. Generally, polymer materials may be used. The seal body may be an integrally formed body, for instance a body made of exactly one material.

[0028] In an embodiment, the clamping force generating element is made of a metal or a plastic. Hence, the clamping force generating element may be made of many different materials which however should be pressure-resistant, compatible with aggressive chemicals such as organic solvents or biological fluids, and they should maintain their clamping force capabilities over a long time.

[0029] In an embodiment, the clamping force generating element contacts the seal body along at least about 80% of said entire circumference of the circumferential recess, particularly along at least about 90% of said entire circumference of the circumferential recess.

[0030] In the following, further exemplary embodiments of the piston pump will be explained. However, these embodiments also apply to the seal, the fluid separation device, and the method.

[0031] In an embodiment, the piston pump is configured as a mobile phase drive for a chromatographic separation system and to be located upstream of a chromatographic separation column. Such a mobile phase drive is configured for intaking fluid from different containers, for example a mixture of water and an organic solvent such as acetonitrile, in order to conduct a chromatographic gradient run. In such a pumping chamber, the intaken fluid is compressed from a low pressure to a high pressure of for instance 1000 bar in which sealing is vital.

[0032] In another embodiment, the piston pump is configured as a metering pump for a sample injector of a chromatographic separation system. A fluid injector of a chromatographic separation system comprises a needle which can intake fluid from a vial or the like and may then be driven into a seat. After switching a fluidic valve, the intaken sample may be injected into a chromatographic path between a mobile phase drive (as the one described above) and a separation device such as a chromatographic separation column. For the purpose of metering the injected fluid, a metering pump has to be provided for sucking fluid from the vial through the needle into a sample loop. This metering device operates also under high pressure so that the provision of a reliable seal is of importance here as well.

[0033J In an embodiment, the piston pump is configured for pressurizing the fluid to a pressure in a range between about 400 bar and about 1500 bar, particularly in a range between about 800 bar and about 1200 bar.

[0034] In the following, further exemplary embodiments of the fluid separation device will be explained. However, these embodiments also apply to the seal, the piston pump, and the methods.

[0035] In an embodiment, the fluid separation device is configured as at least one of the group consisting of an autosampler device, a fractioner device, a measurement device for performing a measurement in a coupled measurement environment, a measurement device for measuring at least one physical, chemical or biological parameter, a measurement device for performing a measurement of a fluidic sample, a sensor device, a device for chemical, biological and/or pharmaceutical analysis, and a chromatography device (such as a liquid chromatography device or a gas chromatography device).

[0036] The fluid separation device may comprise a pump configured for pumping fluid through the system. The fluid may be sucked from a vial into the needle and from there to a capillary. As a pump, a piston pump, a peristaltic pump, etc., may be implemented.

[0037] The fluid separation device may comprise a sample loop for handling a fluidic sample. Such a sample loop may be pad of a liquid chromatography apparatus and may allow to inject a sample into the sample loop via the needle at an end portion of a capillary. After having taken up the fluid, the needle can be moved back into the seat so that the injected fluid can be introduced via the sample loop onto a chromatographic column for fluid separation. Such a fluid separation may then be performed by separately releasing different fractions of a sample trapped on the chromatographic column by running a gradient during which a solvent with varying composition may be conducted through the chromatographic column. Exemplary embodiments may hence be implemented in a sample injector module of a liquid chromatography apparatus which sample injector module may take up a sample from a fluid container and may inject such a sample in a conduit for supply to a separation column. During this procedure, the sample may be compressed from, for instance, normal pressure to a higher pressure of, for instance several hundred bars or even 1000 bar and more. An autosampler may automatically inject a sample from the vial into a sample loop. A tip or needle of the autosampler may dip into a fluid container, may suck fluid into the capillary and may then drive back into a seat of a sample loop to then, for instance via a switchable fluidic valve, inject the fluid towards a sample separation section of the liquid chromatography apparatus.

[0038] In an embodiment, the above mentioned apparatus served by the autosampler may be a chromatographic column. Therefore, the autosampler may take up a sample and may inject the sample towards a chromatographic column for sample separation.

[0039] The fluid separation device may thus include or cooperate with a processing element (such as a chromatographic column) filled with a separating material. Such a separating material which may also be denoted as a stationary phase may be any material which allows an adjustable degree of interaction with a sample so as to be capable of separating different components of such a sample. The separating material may be a liquid chromatography column filling material or packing material comprising at least one of the group consisting of polystyrene, zeolite, polyvinylalcohol, polytetrafluorethylene, glass, polymeric powder, silicon dioxide, and silica gel, or any of above with chemically modified (coated, capped etc) surface. However, any packing material can be used which has material properties allowing an analyte passing through this material to be separated into different components, for instance due to different kinds of interactions or affinities between the packing material and fractions of the analyte.

[0040] Atleasta part of the processing element may be filled with a fluid separating material, wherein the fluid separating material may comprise beads having a size in the range of essentially 1 pm to essentially 50 pm. Thus, these beads may be small particles which may be filled inside the separation section of the microfluidic device.

The beads may have pores having a size in the range of essentially 0.01 pm to essentially 0.2 pm. The fluidic sample may be passed through the pores, wherein an interaction may occur between the fluidic sample and the pores.

[0041] The fluid separation device may be configured for separating components of the sample. When a mobile phase including a fluidic sample passes through the fluidic device, for instance with a high pressure, the interaction between a filling of the column and the fluidic sample may allow for separating different components of the sample, as performed in a liquid chromatography device.

j0042] However, the analysis system may also be configured as a fluid purification system for purifying the fluidic sample. By spatially separating different fractions of the fluidic sample, a multi-component sample may be purified, for instance a protein solution. When a protein solution has been prepared in a biochemical lab, it may still comprise a plurality of components. If, for instance, only a single protein of this multi-component liquid is of interest, the sample may be forced to pass the columns. Due to the different interaction of the different protein fractions with the filling of the column, the different samples may be distinguished, and one sample or band of material may be selectively isolated as a purified sample.

[0043] As an alternative to a liquid mobile phase, a gaseous mobile phase or a mobile phase including solid particles may be processed using the fluid separation device. Also materials being mixtures of different phases (solid, liquid, gaseous) may be processed using exemplary embodiments. The fluid separation device may be configured to conduct the mobile phase through the system with a high pressure, particularly of at least 600 bar, more particularly of at least 1200 bar.

[0044] The analysis system may be configured as a microfluidic device. The term "microfluidic device" may particularly denote a fluidic device as described herein which allows to convey fluid through microchannels having a dimension in the order of magnitude of less than 500 pm, particularly less than 200 pm, more particularly less than 100 pm or less than 50 pm or less. The analysis system may also be configured as a nanofluidic device. The term "nanofluidic device" may particularly denote a fluidic device as described herein which allows to convey fluid through nanochannels with a flow rate of less than 100 nI/mm, particularly of less than 10 nI/mm.

[0045] A multi-way switching valve may be provided for selectively routing a fluid input flow to the valve to one of more alternate output flows from the valve. Such a rotary valve may direct fluid flow by rotating a valve rotor element to discrete angular positions relative to a stationary valve stator element. A dual rotary valve provides two valves in one valve body, both simultaneously operated by the positioning of the valve rotor. Such rotary switching valves may be used, for example, in HPLC and other analytical methods to selectively direct a flow stream of one or more fluids along alternate paths to an analytical device or containment vessel.

BRIEF DESCRIPTION OF DRAWINGS

[0046] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawings. Features that are substantially or functionally equal or similar will be referred to by the same reference signs.

[0047] Figure 1 shows a liquid separation device, in accordance with embodiments of the present nverition, e.g. used in high performance Iiqud chromatography (HPLC).

[0048] Figure 2 to Figure 5 show piston pumps having a seal according to an exemplary embodiment of the invention.

[0049] Figure 6 shows two separate springs cooperating as clamping force generating elements for a seal according to an exemplary embodiment of the invention.

[0050] Figure 7 shows a seal body for a seal according to an exemplary embodiment of the invention.

[0051] Figure 8 shows how the springs of Figure 6 are mounted within a recess of the seal body of Figure 7 so as to manufacture a seal according to an exemplary embodiment of the invention.

[0052] Figure 9 shows a cross-section of the seal of Figure 8.

[0053] Figure 10 and Figure 11 show cross-sections of conventional seals.

[0054] The illustration in the drawing is schematically.

[0055] In liquid chromatography (LC) systems with very low dead volume and/or very low flow (down to p1/mm or nI/mm), leakage or high compressibility of components in the flow path is an issue in terms of retention time fluctuation and analysis speed. A high dead volume is primarily a challenge with regard to analysis speed, whereas a high compressibility of components and leakage in the flow path may contribute strongly to retention time jitter. Embodiments of the invention may reduce dead volume, compressibility and seal leakage by a novel piston seal design. The seal body itself may reduce the dead volume and allows for less empty space surrounding the -12-seal. Compressibility can be reduced through eliminating spring design seal lips to a certain degree. Retainer springs embedded in the recess are closely together and allow for a small void and hence compressible space within the piston seal. The seal design of an embodiment of the invention uses two connected or separate tightly wound springs as retainer rings. The inner spring inherits the function of ensuring a tight fit to the piston, while the outer spring takes the function of keeping the outer wall at its position as the pressure varies in the pressurized zone.

[0056] Referring now in greater detail to the drawings, Fig. I depicts a general schematic of a liquid separation system 10. A pump 20 receives a fluid or mobile phase from a solvent supply 25, typically via a degasser 27, which degases and thus reduces the amount of dissolved gases in the mobile phase. The pump 20 -as a mobile phase drive -drives the mobile phase through a separating device 30 (such as a chromatographic column) comprising a stationary phase. A sampling unit 40 (having a needle/seat arrangement depicted in Fig. 1 schematically) is provided between the pump 20 and the separating device 30 in order to subject or add (often referred to as sample introduction) a sample fluid into the mobile phase. The stationary phase of the separating device 30 is configured for separating compounds of the sample liquid. A detector 50 is provided for detecting separated compounds of the sample fluid. A fractionating unit 60 can be provided for outputting separated compounds of sample fluid.

[0057J While the mobile phase can be comprised of one solvent only, it may also be mixed from plural solvents. Such mixing might be a low pressure mixing and provided upstream of the pump 20, so that the pump 20 already receives and pumps the mixed solvents as the mobile phase. Alternatively, the pump 20 might be comprised of plural individual pumping units, with plural of the pumping units each receiving and pumping a different solvent or mixture, so that the mixing of the mobile phase (as received by the separating device 30) occurs at high pressure und downstream of the pump 20 (or as part thereof). The composition (mixture) of the mobile phase may be kept constant over time, the so called isocratic mode, or varied over time, the so called gradient mode.

[0058] A data processing unit 70, which can be a conventional PC or workstation, might be coupled (as indicated by the dotted arrows) to one or more of the devices in the liquid separation system lOin order to receive information and/or control operation.

For example, the data processing unit 70 might control operation of the pump 20 (e.g. setting control parameters) and receive therefrom information regarding the actual working conditions (such as output pressure, flow rate, etc. at an outlet of the pump).

The data processing unit 70 might also control operation of the solvent supply 25 (e.g. setting the solvent/s or solvent mixture to be supplied) and/or the degasser 27 (e.g. setting control parameters such as vacuum level) and might receive therefrom information regarding the actual working conditions (such as solvent composition supplied overtime, flow rate, vacuum level, etc.). The data processing unit 70 might further control operation of the sampling unit 40 (e.g. controlling sample injection or synchronization sample injection with operating conditions of the pump 20). The separating device 30 might also be controlled by the data processing unit 70 (e.g. selecting a specific flow path or column, setting operation temperature, etc.), and send -in return -information (e.g. operating conditions) to the data processing unit 70.

Accordingly, the detector 50 might be controlled by the data processing unit 70 (e.g. with respect to spectral or wavelength settings, setting time constants, start/stop data acquisition), and send information (e.g. about the detected sample compounds) to the data processing unit 70. The data processing unit 70 might also control operation of the fractionating unit 60 (e.g. in conjunction with data received from the detector 50) and provides data back.

[0059] In the following, referring to Fig. 2, a piston pump 204 according to an exemplary embodiment of the invention will be described. The piston pump 204 shown in a cross-sectional view in Fig. 2 (and any of the piston pumps 204 shown in Fig. 3to Fig. 5 as well) can for instance be implemented in the mobile phase drive 20 or in a metering pump of the fluid injector or sampling unit 40 shown in Fig. 1.

[0060] The piston pump 204 shown in Fig. 2 comprises a piston chamber 202 or housing body. In the interior thereof, a hollow space 251 is defined within which a piston 216 and a seal 200 may be accommodated. The piston chamber 202 denotes the chamber within which the piston 216 is reciprocating in a forward direction (i.e. from left to right referring to Fig. 2, which equals to a pumping direction 285) and subsequently in a rearward direction (i.e. from right to left referring to Fig. 2). In -14-operation, the piston 216 reciprocates in the piston chamber 202 thereby displacing fluid from the left-hand side through orifice or fluid outlet 295 on the right-hand side of the piston pump 204. The piston chamber 202 is delimited by walls to form the hollow space 251 in which the piston 216 as well as the seal 200 according to an exemplary embodiment of the invention are arranged. The seal 200 and the piston 216 on the one hand and the piston chamber 202 on the other hand are shaped to correspond to one another forming the basis of a cooperating sealing performance described below in more detail.

[0061] In order to provide for a sealing of the piston 216, the seal 200 is provided with a seal body 206 made of a polymeric material having a central through bore 208 into which the piston 216 may engage. Thus, the first sealing performance of the seal is to provide a sealing between the seal body 206 on the one hand and the piston 216 on the other hand. Apart from that, the seal 200 fulfills a second sealing performance, i.e. to provide a sealing between an exterior surface of the seal 200 on the one hand and an interior surface or wall of the piston chamber 202 on the other hand.

[0062] The central through-bore 208 is formed in a rotationally symmetrical way around a central symmetry axis 287 of the rotationally symmetrical seal 200. The central through-bore 208 tapers from the left-hand side of Fig. 1 towards the right-hand side, i.e. continuously reduces the diameter. Furthermore, the seal body 206 has a circumferential recess 210 located between the central through-bore 208 on the one hand and an outer circumferential surface 291 of the seal body 206 facing or opposingthe wall of the piston chamber 202 (i.e. being arranged parallel thereto, or alternatively having a continuously increasing outer diameter, i.e. being arranged not parallel, but slanting with respect to the wall of the piston chamber 202). Central through-bore 208 which is slightly tapering towards fluid outlet 295 of the piston pump is configured to receive the piston 216 in a sealing manner. The outer circumferential surface 291 of the seal body 206 and an outer circumferential surface 212 of the recess 210 are maintaining a constant distance from a central axis 287 of the seal 200, or can be alternatively arranged slanting with respect to the central axis 287.

[0063] The piston pump 204 has to operate under harsh conditions such as the presence of chemicals like organic fluids. For chromatographic gradient applications, a composition of for instance water and acetonitrile (ACN) has to be prepared, metered precisely and pressurized so that the components shown in Fig. 2 have to be compatible with such chemicals. Further requirements of the piston pump 204 are that they are capable of withstanding a pumping pressure of 1200 bar or more. Therefore, the mechanical load acting on the components of the seal 200 is very high. The seal body 206 is hence made of a pressure resistant, biocompatible and elastic polymeric material.

[0064] As can further be taken from Fig. 2, the circumferential recess 210 is not a closed or hermetically sealed cavity, but is configured as an externally accessible annular recess (in Fig. 2 access to recess 210 is possible from the right hand side when the recess 210 is open). This simplifies insertion or mounting of two clamping springs 232, 230, as will be described in the following in more detail. It should however be said that, in an alternative embodiment, the recess 210 may be also closed or even hermetically sealed which can shield the springs 230, 232 with regard to the fluids processed to within the pumping chamber 202 and which may further reduce the dead volume.

[0065] The inner spring 230 is mounted in the recess 210 in such a manner that itis tightly fit around an inner cylindrical ring 223 of the seal body 206. In other words, when the inner spring 230 is inserted into the recess 210, it will automatically exert a radially inward clamping force, as shown by the arrows drawn close to spring 230 in Fig. 2. Thus, the inner spring 230 has the function of an inner clamping force generating element and generates a radially inward clamping force acting uninterruptedly along the entire inner circumferential surface of the recess 210 and, in turn, along the entire inner circumferential surface of the seal body 206 facing or contacting the piston 216.

[0066] In an inverse way, the outer spring 232 is mounted in the recess 210 in such a manner that it is tightly fit to the outer cylindrical ring 221 of the seal body 206. In other words, when the outer spring 232 is inserted into the recess 210, it will automatically exert a radially outward clamping force, as shown by the arrows drawn -16-close to spring 232 in Fig. 2. Thus, the outer spring 232 has the function of an outer clamping force generating element and generates a radially outward clamping force acting uninterruptedly along the entire outer circumferential surface 212 of the recess 210 and, in turn, along the entire outer circumferential surface 291 of the seal body 206 facing or contacting the piston chamber 202.

[0067] As can furthermore be taken from Fig. 2, the two springs 230 and 232 are provided as two completely separate spring bodies. Therefore, they can be mounted individually and separately within the circumferential recess 210 and can be optimized individually with regard to their respective clamping performance. The springs 230, 232 are both helical springs having a symmetry axis which coincides with the symmetry axis of the seal body 206 and of the entire piston pump 204, as indicated by reference numeral 297.

[0068] As can furthermore be taken particularly from detailed drawing 250 in Fig. 2, the seal body 206 is constituted of a first disc-like section 220 and a second disc-like section 222. The second disc-like section 222 has a larger diameter D as compared to a smaller diameter d of the first disc-like section 220. Furthermore, the second disc-like section 222 has a smaller longitudinal extension I as compared to a larger longitudinal extension L of the first disc-like section 220. The circumferential recess 210 as well as the springs 230, 232 are integrated in and form part of the first disc-like section 220.

[0069] Another detailed drawing 270 in Fig. 2 shows a plan view (from a right hand side) of the seal 200 and shows particularly as to how the inner and outer rings of the first disc-like section 220, as well as the springs 230, 232 and the second disc-like section 222 are concentrically arranged around one and the same symmetry axis 287.

Clamping force generating element 214 is formed by the springs 230, 232 being tightly fit into the circumferential recess 210.

[0070] Fig. 3 shows a piston pump 204 with a seal 200 according to another exemplary embodiment of the invention. The seal 200 of Fig. 3 differs from the seal in Fig. 2 in that the access to the longitudinal recess 210 is not via the first disc-like section 220 in Fig. 3, but rather via the second disc-like section 222.

[0071] Furthermore, a front face (in terms of a fluid flow or pumping direction 285 of the piston pump 204) of the seal body 206 has a circumferential indentation or concave portion 299. This can be advantageous for the sealing performance particularly between this front face and a corresponding opposing surface of the pumping chamber 202.

[0072] Fig. 4 shows a piston pump 204 having a seal 200 according to yet another exemplary embodiment of the invention which differs from the embodiment of Fig. 2 in that the inner helical spring 230 is replaced by an inner biasing sealing ring 400. The sealing ring 400 extends basically along the entire length of the circumferential recess 210, but can even be shorter or can be separated into two or more separate structures.

The biasing ring 400 applies in an inwardly directed clamping force and therefore functionally substitutes the inner spring 230.

[0073] Fig. 5 shows a piston pump 204 having a seal 200 according to yet another exemplary embodiment of the invention and differs from Fig. 2 in that the two separate spring bodies 230, 232 of Fig. 2 are substituted by one integral helical spring having an alternating sequence of windings with a smaller inner diameter b and a larger outer diameter B. The windings with the smaller inner diameter b exert the radially inward clamping force for clamping the seal body 206 against the piston 216, whereas the windings with the larger diameter B exert a radially outwardly oriented force pressing an exterior surface of the seal body 206 against the piston chamber 202.

[0074] Fig. 6 shows the two separate springs 230 and 232 as implemented in the embodiment of Fig. 2. They may be arranged, for mounting purposes, concentrically around one another, as also shown in another image in Fig. 6.

[0075] The springs 230, 232, which may be made of stainless steel, titanium or coated parts (for instance of steel), can then be combined together with the seal body 206 shown in a three-dimensional view in Fig. 7 to form a seal 200 according to an exemplary embodiment of the invention. For this purpose, the springs 230, 232 are pressed against a back driving counterforce of the springs 230, 232 into the circumferential recess 210 of the seal body 206. More precisely, the inner spring 230 is forced to align around the inner ring of the seal body 206 so as to exert an inwardly oriented biasing force. In contrast to this, the second spring 232 is forced inwardly during the mounting so as to exert a radially outwardly oriented force on the exterior ring of the seal body 206.

[0076] Fig. 8 shows the springs 230, 232 mounted within the circumferential recess 210 of the seal body 206.

[0077] Fig. 9 shows a cross-sectional view of the seal 200 of Fig. 8.

[0078] Fig. 10 shows a cross-sectional view of a conventional seal 1100. In the conventional seal 1100, an externally accessible gap between an outer cylindrical part 1102 and an inner cylindrical part 1104 of a seal body is filled with a biased spring 1106. The biased spring 1106 alone, as shown in Fig. 10, is only capable of applying clamping forces and therefore providing sealing effects at the contact points or dots 1108 shown in Fig. 10. This however does not allow for a circumferentially reliable sealing.

[0079] Fig. 11 shows another conventional seal 1200 which is similar to the conventional seal 1100 of Fig. 10 with the exception that a spirally wound spring 1202 is used here. However, also in this embodiment only at individual contact points ordots 1108 clamping forces are provided which is not appropriate for a reliable and long-term usable seal.

[0080] It should be noted that the term "comprising" does not exclude other elements or features and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims (1)

1. <claim-text>CLAIMS1. A seal (200) for sealing in a piston chamber (202) of a piston pump (204) of a fluid separation device (10), the seal (200) comprising a seal body (206) having a central through bore (208) for receiving a piston (216) and having a circumferential recess (210) between the central through bore (208) and an outer circumferential surface (291) of the seal body (206); a clamping force generating element (214) accommodated in the circumferential recess (210) and being configured for generating a radial clamping force acting along basically an entire circumference of the circumferential recess (210).</claim-text> <claim-text>2. The seal (200) according to claim 1, wherein the clamping force generating element (214) is configured for generating a radially inward clamping force acting to clamp the seal body (206) towards the piston (216).</claim-text> <claim-text>3. The seal (200) according to claim 1 or 2, wherein the clamping force generating element (214) is configured for generating a radially outward clamping force acting to clamp the seal body (206) towards the piston chamber (202).</claim-text> <claim-text>4. The seal (200) according to any of claims 1 to 3, wherein the clamping force generating element (214) is configured for generating both a radially inward clamping force acting to clamp the seal body (206) towards the piston (216) and a radially outward clamping force acting to clamp the seal body (206) towards the piston chamber (202).</claim-text> <claim-text>5. The seal (200) according to any of claims 1 to 4, wherein the clamping force generating element (214) provides for a direct continuous contact along basically said entire circumference of the circumferential recess (210) with a wall, particularly with an inner circumferential wall and/or with an outer circumferential wall, of the seal body (206) delimiting the circumferential recess (210).</claim-text> <claim-text>6. The seal (200) according to any of claims 1 to 5, wherein the clamping farce generating element (214) comprises a first spring (230) having a first diameter (b) and being configured for generating a radially inward clamping force acting to -20 -clamp an inner section of the seal body (206) towards the piston (216), and the clamping force generating element (214) comprises a second spring (232) having a second diameter (B) being larger than the first diameter (b) and being configured for generating a radially outward clamping force acting to clamp an outer section of the seal body (206) towards the piston chamber (202).</claim-text> <claim-text>7. The seal (200) according to claim 6, wherein the first spring and the second spring are integrally formed as one common sphng structure (500) having windings of different diameters (b, B), particularly having alternating windings of two different diameters (b, B).</claim-text> <claim-text>8. The seal (200) according to claim 6, wherein the first spring (230) and the second spring (232) are formed as two separate spring structures.</claim-text> <claim-text>9. The seal (200) according to any of claims 6 to 8, wherein a central axis (287) of the first spring (230), a central axis (287) of the second spring (232), and a central axis (287) of the through bore (208) coincide.</claim-text> <claim-text>10. The seal (200) according to any of claims 6 to 9, wherein at least one of the first spring (230) and the second spring (232) comprises a helical spring.</claim-text> <claim-text>11. The seal (200) according to any of claims 6 to 10, wherein at least one of the first spring and the second spring comprises at least one biasing ring (1000, 1002, 1004).</claim-text> <claim-text>12. The seal (200) according to any of claims ito 11, wherein the circumferential recess (210) is configured as an annular blind hole in fluid communication with an interior of the piston chamber (202).</claim-text> <claim-text>13. The seal (200) according to any of claims 1 to 12, wherein the seal body (206) has a first disc-like section (220) and has a second disc-like section (222), the second disc-like section (222) having a larger diameter (D, d) and a smaller longitudinal extension (I, L) than the first disc-like section (220).</claim-text> <claim-text>14. The seal (200) according to claim 13, wherein the circumferential recess (21 0) is formed at least partly within the first disc-like section (220). -21 -</claim-text> <claim-text>15. The seal (200) according to any of claims ito 14, wherein the seal body (206) comprises a pressure robust polymer, particularly at least one of the group consisting of polytetrafluoroethylene, polyethylene, and perfluoroal koxy.</claim-text> <claim-text>16. The seal (200) according to any of claims 1 to 15, wherein the clamping force generating element (214) comprises at least one of the group consisting of a metal, a plastic, and a coated material.</claim-text> <claim-text>17. The seal (200) according to any of claims ito 16, wherein the clamping force generating element (214) contacts the seal body (206) along at least 80% of said entire circumference of the circumferential recess (210), particularly along at least 90% of said entire circumference of the circumferential recess (210).</claim-text> <claim-text>18. A piston pump (204) for a fluid separation device (10), the piston pump (204) comprising a piston chamber (202); a piston (216) configured for reciprocating within the piston chamber (202); a seal (200) according to any of claims 1 to 17 arranged for sealing between the piston chamber (202) and the piston (216).</claim-text> <claim-text>19. The piston pump (204) according to claim 18, configured as a mobile phase drive (20) for a chromatographic separation system (10) and to be located upstream of a chromatographic separation column (30).</claim-text> <claim-text>20. The piston pump (204) according to claim 18, configured as a metering pump for a fluid injector (40) of a chromatographic separation system (10).</claim-text> <claim-text>21. The piston pump (204) according to any of claims 18 to 20, configured for pressurizing the fluid to a pressure in a range between 400 bar and 1500 bar, particularly in a range between 800 bar and 1200 bar.</claim-text> <claim-text>22. A fluid separation device (10) for separating compounds of a fluid in a mobile phase, the fluid separation device (10) comprising: a piston pump (204) according to any of claims 18 to 21 configured to drive the -22 -mobile phase through the fluid separation device (10); a separation unit (30), particularly a chromatographic column, configured for separating compounds of the fluid in the mobile phase.</claim-text> <claim-text>23. The fluid separation device (10) of claim 22, further comprising at least one of: a fluid injector (40) for introducing the fluid into the mobile phase, wherein the fluid injector (40) comprises an injection needle and a seat, wherein the injection needle is selectively insertable into the seat for conducting the fluid between the needle and the seat, and wherein the injection needle is selectively movable out of the seat; a detector (50) configured to detect separated compounds of the fluid; a collection unit (60) configured to collect separated compounds of the fluid; a data processing unit (70) configured to process data received from the fluid separation device; a degassing apparatus (27) for degassing the mobile phase.</claim-text> <claim-text>24. A method of manufacturing a seal (200) for sealing in a piston chamber (202) ofa piston pump (204) of a fluid separation device (10), the method comprising providing a seal body (206) having a central through bore (208) for receiving a piston (216) and having a circumferential recess (210) between the central through bore (208) and an outer circumferential surface (291) of the seal body (206); and accommodating a clamping force generating element (214) in the circumferential recess (210) for generating a radial clamping force acting along basically an entire circumference of the circumferential recess (210).-23 -</claim-text>