System and method for minimizing force change in a solenoid in a pressurized flow system

Abstract

Pressure regulator (57), comprising: a body section (74); a head section (72) comprising a needle (86) and a seat (82) defining a bore (84), wherein the needle (86) and the seat (82) are positioned such that the movement of the needle (86) within the bore (84) of the seat (82) creates a pressure differential through the seat (82) when a flow of fluid is directed to the head section (72); an actuator section (76) which is at least partially arranged and positioned within the body section (74) to communicate with the needle (86) in order to move the needle (86) within the bore (84) of the seat (82), wherein the actuator section (76) has a shaft (94) driven in a first direction by a solenoid (90) and a compensating spring (96), wherein the solenoid (90) applies a negative spring constant to the shaft (94) in the first direction and the compensating spring (96) is configured to apply a positive spring constant to the shaft (94) in the first direction, wherein the value of the positive spring constant is greater than the value of the negative spring constant in order to provide an overall positive spring constant at the shaft (94) in the first direction; and a calibration collar (110) detachably attached to the shaft (94), which is designed in such a way as to prevent movement of the shaft (94) relative to the shaft lining when the latter is in a locked position.

Description

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 61 / 607943, filed March 7, 2012, which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] This disclosure relates to systems and methods that minimize force change in a solenoid, and more particularly to systems and methods that produce a nearly constant or substantially constant force for a solenoid through a power stroke for pressure control in a pressurized flow application, such as CO2-based chromatography. BACKGROUND

[0003] Chromatographic techniques are important tools for identifying and separating complex samples. The basic principle underlying chromatographic techniques is the separation of a mixture into individual components by transporting the mixture into a moving liquid through a retentive medium. The moving liquid is commonly referred to as the mobile phase, and the retentive medium is commonly referred to as the stationary phase. The separation of the various components of the mixture is based on differential partitioning between the mobile and stationary phases. Differences in the partition coefficient of the components result in different retention at the stationary phase and lead to separation.

[0004] The traditional methods of choice for chromatographic separations have been gas chromatography (GC) and liquid chromatography (LC). A key difference between GC and LC is that the mobile phase in GC is a gas, whereas in LC the mobile phase is a liquid. For example, in GC, a supply of inert carrier gas (mobile phase) is continuously passed as a stream through a heated column containing porous bibulous media (stationary phase). A sample of the mixture of interest is injected into the mobile phase stream and passed through the column, where separation of the mixture occurs primarily due to differences in the volatile characteristics of each sample component at the column temperature. A detector positioned at the exit end of the column detects each separated component as it exits the column.Although GC is normally a sensitive analytical technique, the high temperatures required by GC make it unsuitable for biopolymers or high molecular weight proteins commonly found in biochemistry (heat denatures them).

[0005] LC, on the other hand, is a separation technique in which the mobile phase is a liquid and does not require sample volatilization. Liquid chromatography that generally uses small packing particles and moderately high pressure is called high-performance liquid chromatography (HPLC); whereas liquid chromatography that generally uses very small packing particles and high pressure is called ultrahigh-performance liquid chromatography (UHPLC). In HPLC and UHPLC, the sample is passed through a column filled with a stationary phase composed of irregularly or spherically shaped particles, a porous monolithic layer, or a porous membrane by a liquid under high pressure (mobile phase).

[0006] Because LC uses liquid as the mobile phase, LC methods can analyze compounds with higher molecular weights, and in some cases, LC can be used to prepare large batches of purified proteins. GC methods, however, are usually more sensitive and easily allow the separation of individual chiral materials. Therefore, GC has conventionally been used to isolate and determine the relative purity of a chiral compound, e.g., via the determination of the enantiomeric excess (% ee) or diastereomeric excess (% de) of a given sample. As with most chromatographic techniques, the limiting factor for both GC and LC has been the ability to obtain and / or reproduce pure sample separations, which are typically dependent on the equipment, procedures, and conditions used, e.g.,Flow rate, column size, column packing material, solvent gradient, etc.

[0007] Supercritical fluid chromatography (SFC) is another chromatographic technique typically used in preparative applications. For every liquid substance, there is a temperature above which it can no longer exist as a liquid, regardless of the applied pressure. Analogously, there is a pressure above which the substance can no longer exist as a gas, regardless of the extent of the temperature increase. These points are called the supercritical temperature and supercritical pressure, respectively, and they define the boundaries of a phase diagram for a pure substance ( Fig. 1). At this point, the liquid and vapor have the same density, and the liquid cannot be liquefied by increasing the pressure. Above this point, where no phase change occurs, the liquid acts as a supercritical fluid (SF). An SF can therefore be described as a liquid obtained by heating above the critical temperature and compressing above the critical pressure. There is a continuous transition from liquid to SF by increasing the temperature at constant pressure, or from gas to SF by increasing the pressure at constant temperature.

[0008] The term SFC, normally used for supercritical fluid chromatography, does not require or imply that supercritical conditions are achieved or maintained during the separation. This means that columns do not always have to be operated in the critical range of the mobile phase. For example, if the mobile phase has a modifier (e.g., CO2 and methanol as modifiers), the mobile phase is often in its subcritical range (e.g., a highly compressed gas or a compressible liquid rather than a supercritical fluid). For example, Guiochon et al. state in section 2.3 of their review article entitled "Fundamental challenges and opportunities for preparative supercritical fluid chromatography", Journal of Chromatography A, 1218 (2011) 1037-1114: "It is clear that SFC has often been and still is carried out under subcritical conditions.“ The term SFC is therefore not limited to processes that require supercritical conditions.

[0009] Because SFC typically uses CO2, SFC processes are cost-effective, non-toxic, environmentally friendly, and non-toxic. The use of volatile solvents (e.g., hexane) is typically not required. Furthermore, the mobile phase in SFC processes (e.g., CO2 together with any modifiers / additives such as SF, highly compressed gas, or compressible liquid) typically exhibits higher diffusion constants and lower viscosities compared to liquid solvents. The low viscosity means that pressure drops across the column are significantly reduced for a given flow rate. The greater diffusivity means that longer column lengths can be used. SUMMARY

[0010] Example embodiments of this technology address systems and methods for generating a nearly or substantially constant force from a solenoid over its operating stroke. Generally, commercially available solenoids generate a non-linear force that varies along the stroke, making commercially available solenoids undesirable for use as an actuator in a power-driven system, such as a pressure regulator in a pressurized flow system. In embodiments of this technology, systems and methods are provided for establishing a nearly or substantially constant force from a solenoid over its operating stroke. Embodiments include characterizing the solenoid over its stroke and employing an assembly of counterbalance springs and shims to space or separate the solenoid in the power-driven system. The counterbalance springs can be linear (e.g., compression springs) or non-linear (e.g.,Belleville springs). Example embodiments of a method for minimizing force variation in a solenoid include: (a) characterizing force, current, and stroke for a given solenoid; (b) identifying a linear region within the stroke with sufficient load for force applications at desired currents; (c) applying rings or shims to create a gap to achieve an initial position of the identified linear region; and (d) applying a spring to flatten a load profile in an operating region to minimize force variation within the solenoid stroke.While embodiments do not ensure constant force from a standard commercial solenoid, they do provide minimization of force variation within the stroke of the operating range so that the commercial solenoid, with the modifications provided by the systems and methods described herein, can be used in a pressure regulator of a flow system, such as a CO2-based chromatography system.

[0011] According to one aspect of this disclosure, pressure regulators are disclosed that include a body portion, a head portion, and an actuator portion. The head portion of the pressure regulator includes a needle and a seat defining a bore. The needle and seat are positioned such that movement of the needle within the bore of the seat creates a pressure differential across the seat when flow of fluid is directed to the head portion. The actuator portion is at least partially disposed within the body portion and is positioned to communicate with the needle for moving the needle within the bore of the seat. The actuator portion includes a shaft moved in a first direction by a solenoid and a counterbalance spring.The solenoid applies a negative spring constant to the shaft in the first direction, and the balance spring applies a positive spring constant to the shaft in the first direction. The positive spring constant is greater than the negative spring constant of the solenoid to provide an overall positive spring constant on the shaft in the first direction.

[0012] Embodiments of the above exemplary pressure regulator may include one or more of the following features. In embodiments, the pressure regulator is used to control pressure in a CO2-based chromatography system. In other embodiments, the pressure regulator is used to control pressure in other pressurized flow systems, such as supercritical fluid extraction systems or HPLC systems. In embodiments, the actuator portion is positioned a distance from the body portion (e.g., 0.01 inches) such that a distal end of the needle is disposed within the body portion. In some embodiments, a disk made of plastic or other non-magnetic material is used to position the solenoid within the device. In particular, the disk is used to create a gap within an operating range of the solenoid stroke. Generally, the gap is equal to or greater than the maximum gap width of the solenoid.substantially equal to a stroke distance that marks the beginning of the linear range identified by the solenoid characterization. In embodiments, the gap created by the disc is less than about 0.2 inches. Embodiments also include a compression bead to preload the balance spring to impart the positive spring rate. In some embodiments, the balance spring is a linear spring, such as a compression coil spring. Generally, linear springs change force at a constant ratio with respect to the change in relative displacement. In other embodiments, the balance spring is a non-linear spring, such as a Belleville spring. Generally, non-linear springs have a more complex force-displacement relationship.The behavior of pressure regulators using this technology generally depends on the additional effects of the solenoid spring constant and the balance spring constant. Therefore, the use of different types of balance springs can be employed to provide different balance spring constants and solenoid nonlinearities along one or more segments of a force versus displacement curve. One advantage of using a nonlinear spring is that, in addition to applying a positive spring constant, nonlinear springs can be designed to counteract specific solenoid nonlinearities. It is noted that any combinations or variations of embodiments are contemplated.

[0013] According to another aspect of this technology, exemplary methods for minimizing force change in a solenoid-driven pressure regulator are disclosed.The exemplary methods include the steps of: (a) obtaining data relating to solenoid force as a function of current when the solenoid is actuated over a solenoid stroke distance; (b) using the data, determining a first stroke distance to define a range of linear force for a range of desired current application; (c) determining a spring constant of the solenoid in an operating range; (d) applying a spring constant having a value opposite and greater than the spring constant of the solenoid in the operating range to a device such that a stem of the solenoid is biased to extend in a first direction in a non-operative state of the solenoid; and (e) positioning the solenoid within the body portion of the pressure regulator such that a gap is created in solenoid stroke operation that is equal to (or substantially equal to) the distance to the first stroke distance.

[0014] Embodiments of the above example methods may include one or more of the following features. In embodiments, the method is used to modify a commercially available solenoid for use in a CO2-based chromatography system. In other embodiments, the method is used to modify a commercially available solenoid for use in other pressurized flow systems, such as supercritical fluid extraction systems or HPLC systems. In some embodiments, the pressure regulator includes a body portion in which the solenoid is disposed. The pressure regulator may further include a head portion with a needle valve, wherein the solenoid physically communicates with a needle of the needle valve during pressure regulation. In some embodiments, the gap is between about 0.02 inches and about 0.2 inches.In other embodiments, the gap is between about 0.005 inches and about 0.3 inches. Generally, the method of this technology is performed once at the time the solenoid is placed in the system. However, in some embodiments, the methods may be performed again during maintenance events or reconfiguration events (e.g., introducing new components into the pressure regulator to change operating conditions). It is noted that any combinations or variations of embodiments are contemplated.

[0015] According to another aspect of this disclosure, pressure regulators are disclosed that include an actuator portion that communicates with a variable throttle assembly. The actuator portion includes a stem that is moved in a first direction by a solenoid and a balance spring. The solenoid applies a negative spring constant to the stem in the first direction, and the balance spring applies a positive spring constant to the stem in the first direction. The value of the positive spring constant is greater than the negative spring constant of the solenoid to provide an overall positive spring constant on the stem in the first direction.

[0016] Embodiments of the above exemplary pressure regulator may include one or more of the following features. In some embodiments, the pressure regulator is used to control pressure in a CO2-based chromatography system. In other embodiments, the pressure regulator is used to control pressure in other pressurized flow systems, such as supercritical fluid extraction systems or HPLC systems. In some embodiments, a disk made of plastic or other non-magnetic material is used to position the solenoid within the device. In particular, the disk is used to create a gap within an operating range of the solenoid stroke. Generally, the gap is equal to or substantially equal to a stroke distance that marks the beginning of the linear region identified by the characterization of the solenoid.In embodiments, the gap created by the disc is less than about 0.2 inches. Embodiments also include a compression bead to preload the balance spring to provide the positive spring rate. In some embodiments, the balance spring is a linear spring, such as a compression coil spring. In other embodiments, the balance spring is a non-linear spring, such as a Belleville spring. In some embodiments, the variable throttle assembly includes a needle valve. In other embodiments, the variable throttle assembly includes a poppet valve. In still other embodiments, the variable throttle assembly includes a diaphragm valve. Any combinations or variations of embodiments are contemplated.

[0017] The exemplary systems and methods according to this disclosure provide numerous advantages. For example, if one or more exemplary systems and / or methods of this disclosure are incorporated into a force-driven device in a pressurized flow system, the device can be accurately controlled. For example, if one or more systems and / or methods of this disclosure are incorporated into a pressure regulator using a solenoid as the actuator, the pressure can be accurately controlled during the operating stroke. As a result, solenoids can be used to drive pressure regulators in pressurized flow systems, such as CO2-based chromatography systems, where the pressure of the mobile phase has a strong influence on its ability to elute samples from a chromatography column.The solenoids and their systems and assemblies used to minimize force change are generally inexpensive to manufacture and operate (e.g., requiring minimal power to generate the desired force), thus providing significant cost savings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The foregoing and other features and advantages provided by this disclosure will be more fully understood from the following description of exemplary embodiments when read with the accompanying drawings, in which: Fig. Figure 1 is an exemplary representation of the state of aggregation of a substance in relation to the values ​​of temperature and pressure assigned to the substance. Fig. Figure 2 is a block diagram of an example pressurized flow system. Fig. 3 is a block diagram of an exemplary arrangement of an embodiment of the system of Fig. 2. Fig. 4 is a block diagram of another exemplary arrangement of an embodiment of the system of Fig. 2. Fig. 5 is a flow diagram of a mobile phase through a system management portion of an exemplary embodiment of the pressurized flow system. Fig. 6 is a cross-sectional view of a valve assembly for an exemplary dynamic pressure regulator in an exemplary embodiment of the pressurized system. Fig. 7 is a flowchart illustrating an exemplary method for minimizing pressure change in a solenoid-driven pressure regulator. Fig. Figure 8 is a graph showing force, current, and stroke position data used to characterize a solenoid. Fig. 9 is the diagram from Fig. 8 indicating the operating range. Fig. 10 is a graph using the characterization data from Fig. 8 when the solenoid is acted upon by a device with opposing force, such as a spring; and Fig. 11(a) and Fig. 11(b) show the graph from Fig. 10 again with specified operating range. DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0019] SFC can be set up as a hybrid between HPLC and GC devices, with the predominant modification being the replacement of either a liquid or gas in the mobile phase with a supercritical fluid (or a near-supercritical fluid) in the mobile phase, such as CO2. In SFC, the mobile phase is first pumped as a liquid or gas and brought into the supercritical region by heating or pressurizing the mobile phase above its supercritical temperature / pressure before entering a column. As the mobile phase passes through an injection valve, the sample is introduced into the supercritical stream, and the mixture is subsequently transferred to a column. The mixture passes through the column (in the supercritical or liquid state) and reaches the detector.

[0020] In general, the mobile phases in SFC processes have the ability to act both as substance carriers (like the mobile phases in GC) and to dissolve substances easily (like the solvents used in LC). In addition to generally lower viscosities and better diffusion profiles similar to those of certain gases, the mobile phases in SFC processes also generally have higher densities and greater dissolving capabilities similar to those of certain liquids. For example, the high densities (0.2-0.5 g / cm 3) of SF its remarkable ability to dissolve large, non-volatile molecules; for example, supercritical or near-supercritical CO2 can readily dissolve n-alkanes, di-n-alkyl phthalates, and polycyclic and aromatic compounds. Since the diffusion of solutions in a mobile phase in SFC is about ten times greater than for liquids (about three times lower than for gases), this leads to a decrease in mass transfer resistance in the column and enables rapid, high-resolution separation. Furthermore, the dissolving power of the mobile phase in SFC processes is directly related to the liquid density. Thus, the solubility of solids can be easily influenced by making minor changes in temperatures and pressures.

[0021] Another important property of the mobile phase in SFC processes is that it provides high-resolution chromatography at significantly lower temperatures. For example, an analyte dissolved in supercritical CO2 can be recovered if the pressure is reduced and the sample is allowed to evaporate under ambient laboratory conditions. This property is useful when dealing with thermally unstable analytes such as biopolymers or high-molecular-weight proteins. The combination of one or more mechanical or column modifications to an SFC instrument (e.g., a CO2-based chromatography instrument) coupled with the inherent properties of SFC itself enables the separation of both chiral and achiral components and is increasingly dominating the field of preparative separations for drug discovery and development.Despite significant advances in SFC technology, there is a need to develop novel methods and devices that improve the use of SFC. Controlling and stabilizing the pressure in an SFC instrument through one or more processes and / or improving one or more instrument properties of the system can lead to, among other things, improved connection separation and efficiency.

[0022] For example, better resolution and higher flow rate would reduce cycle times (i.e., result in shorter cycle times) and enable improved separation of both chiral and achiral compounds, leading to an overall increase in laboratory efficiency; an increase in speed and throughput would reduce the solvent load and costs associated with SFC; and the ability to further integrate SFC with other detection techniques such as mass spectrometry (MS), flame ionization detectors (FID), and ultraviolet / visible light detectors would enhance the primary application of SFC using a mobile phase containing CO2 as an environmentally friendly, yet effective, alternative method for rapid, complete, and sensitive analysis of analytes.

[0023] Example embodiments of this disclosure address the creation of a nearly or substantially constant force solenoid assembly for use in a pressure regulator in a flow system. Example embodiments may implement one or more systems and / or methods for creating a constant or substantially constant force solenoid assembly (i.e., minimizing force variation) to provide a substantially linear force over a range of operating stroke, such that the solenoids, when modified according to this technology, may be used in a pressurized flow system for accurate pressure control. For example, in one embodiment, force, current, and stroke of a solenoid are characterized; a linear (e.g.,A substantially linear (substantially linear) range with sufficient loads for actuator operation at desired currents is identified, and shims or other spacers are used to position the solenoid within a device such as a pressure regulator to accommodate a non-linear stroke range prior to the specified linear stroke range; and the solenoid is biased with one or more springs to minimize a force-load profile over an operating range.

[0024] As used herein, the terms "downstream" and "upstream" refer to corresponding positions in a system flow, where "upstream" refers to an assignment to a previous section of the system flow compared to a subsequent section of the system flow, and "downstream" refers to an assignment to a subsequent section of the system flow compared to a previous section of the system flow.

[0025] Fig. Figure 2 is a block diagram of an exemplary pressurized flow system implemented in this disclosure as a CO2-based chromatography system 10 (hereinafter referred to as "system 10"). While this embodiment exemplifies a CO2-based chromatography system operating under supercritical or near-supercritical conditions, those skilled in the art will recognize that exemplary embodiments of this disclosure may be implemented as other pressurized flow systems and that one or more system components of this disclosure may be implemented as components of other pressurized systems. System 10 may be configured to detect sample components of a sample using chromatographic separation, wherein the sample is introduced into a mobile phase that passes through a stationary phase.The system 10 may include one or more system components to manage and / or control the state of the mobile phase, pressure control of the system 10, introduction of the sample into the mobile phase, separation of the sample into components and / or detection of the sample components, and venting of the sample and / or mobile phase from the system 10.

[0026] In this embodiment, the system 10 may include a solvent delivery system 12, a sample delivery system 14, a sample separation system 16, a detection system 18 (e.g., a PDA detector), and a system / convergence manager 20. In some embodiments, the system components may be arranged in one or more stacks. As another example, in one embodiment, the system components of the system 10 may be arranged in a single vertical stack ( Fig. 3). The system components of the system 10 can be arranged in several stacks ( Fig. 4). Those skilled in the art will recognize that other arrangements of the components of system 10 are possible. While embodiments of system 10 are illustrated as including system components 12, 14, 16, 18, and 20, those skilled in the art will further recognize that embodiments of system 10 may be implemented as a single, integrated unit, one or more components may be combined, and / or other configurations are possible.

[0027] The solvent delivery system 12 may include one or more pumps 22a and 22b configured to pump one or more solvents 24, such as mobile phase media 23 (e.g., carbon dioxide) and / or modifying media 25 (i.e., a co-solvent such as methanol, ethanol, 2-methoxyethanol, isopropyl alcohol, or dioxane), through the system 10 at a predetermined flow rate. For example, pump 22a may be in pumping communication with modifying media 25 to pump modifying media 25 through the system 10, and pump 22b may be in pumping communication with mobile phase media 23 to pump mobile phase media 23 through the system 10. An output of pump 22a may be monitored by a transducer 26a, and an output of pump 22b may be monitored by a transducer 26b.Transducers 26a and 26b may be configured to determine the pressure and / or flow rate associated with the output of solvent 24 from pumps 22a and 22b, respectively. In some embodiments, pump 22a and / or 22b further includes a pump control valve configured to be placed, for example, in a flow position, a blocking position, a venting position, and the like.

[0028] The outputs of pumps 22a and 22b may be operatively coupled to an input of accumulators 28a and 28b, respectively. Accumulators 28a and 28b are replenished by the outputs of pumps 22a and 22b, respectively, and may include an algorithm for reducing undesirable fluctuations in flow rate and / or pressure downstream of pumps 22a and 22b that may introduce noise levels and / or analysis errors to system 10. An output of accumulator 28a may be monitored by a transducer 30a, and an output of accumulator 28b may be monitored by a transducer 30b. Transducers 30a and 30b may be configured to determine the pressure and / or flow rate at an output of accumulators 28a and 28b, respectively. The outputs of the accumulators 28a and 28b may be coupled in operation to a multiport valve 32 which may be controlled to control the solvent 24 (e.g.Mobile phase media 23 and modifying media 25) and / or to dispense the solvent 24 to a mixer 34. The mixer 34 may mix the output of the modifying media 25 and the mobile phase media 23 from the pumps 22a and 22b, respectively (e.g., after the initial pass through the accumulators 28a and 28b) and dispense a mixture of the mobile phase media 23 and the modifying media 25 to form a solvent stream (i.e., a mobile phase) flowing through the system 10. The output of the mixer 34 may be operatively coupled to the system / convergence manager 20, as described in detail below.

[0029] In exemplary embodiments, the solvent delivery system 12 may include a multi-port solvent selection valve 36 and / or a degasser 38. The solvent selection valve 36 and / or the degasser 38 may be operatively disposed between an inlet of the pump 22a and solvent reservoirs 40, such that the solvent selection valve 36 and / or the degasser 38 are disposed upstream of the pump 22a. The solvent selection valve 36 may be controlled to select the modifying media 23 to be used by the system 10 from one or more solvent reservoirs 40, and the degasser 38 may be configured to remove dissolved gases from the media modifier 23 before the media modifier 23 is pumped through the system 10.

[0030] In exemplary embodiments, the solvent delivery system 12 may include a pre-cooler 42 disposed between an inlet of the pump 22b and a solvent reservoir 41 such that the pre-cooler is disposed before the inlet of the pump 22b and after the solution reservoir 41. The pre-cooler 42 may reduce the temperature of the mobile phase media 23 before it is pumped through the system 10 via the pump 22b. In this embodiment, the mobile phase media 23 may be carbon dioxide. The pre-cooler may lower the temperature of the carbon dioxide such that the carbon dioxide is maintained in a liquid state (i.e., not in a gaseous state) as it is pumped through at least a portion of the system 10. Maintaining the carbon dioxide in a liquid state may enable the efficient measurement of the carbon dioxide by the system 10 at the specified flow rate.

[0031] Pumps 22a and 22b can pump solvent 24 through system 10 to pressurize system 10 to a predetermined pressure, which can be controlled at least in part by system / convergence manager 20. In exemplary embodiments, system 10 can be pressurized between about 700 psi and about 18,000 psi, and between about 1,400 psi and about 8,000 psi, respectively. In one embodiment, system 10 can be pressurized to about 6,000 psi. By pressurizing the system 10 to these pressure levels (such as the pressure levels described above), the solvent stream (i.e., the mobile phase) can be maintained in a liquid state before transitioning to a supercritical or near-supercritical liquid state for chromatographic separation in a column, which can be accomplished by elevating the temperature of the pressurized solvent stream (e.g.,highly compressed gas or compressible liquid).

[0032] The sample introduction system 14 can select one or more samples to be passed through the system 10 for chromatographic separation and detection. The sample introduction system 14 can include a sample selection and injection element 44 and a multiport valve 45. The sample selection and injection element 44 can include a needle through which the sample can be injected into the system 10. The multiport valve 45 can be configured to couple the sample selection and injection element 44, during operation, to an input port of the system / convergence manager 20.

[0033] The sample separation system 16 can receive the sample to be separated and detected from the sample delivery system 14, as well as the pressurized solvent stream from the solvent delivery system 12, and it can separate components of the sample passing through the system 10 to enable detection of the samples using the detection system 18. The sample separation system 16 can include one or more columns 46 disposed between an inlet valve 48 and an outlet valve 50. The one or more columns 46 can have a generally cylindrical shape forming a cavity, although those skilled in the art will recognize that other shapes and configurations of the one or more columns are possible. The cavity of the columns 46 can include a volume at least partially filled with retention medium, such as hydrolyzed silica such as C8 or C 18or with any hydrocarbon to form the stationary phase of the system 10 and promote the separation of the components of the sample. The inlet valve 48 may be disposed upstream of the one or more columns and configured to select which, if any, of the one or more columns receive the sample. The outlet valve 50 may be disposed downstream of the one or more columns 46 to selectively receive an output from the one or more columns 46 and to pass the output of the selected one or more of the one or more columns 46 to the detection system 18. The columns 46 may be removably disposed between the valves 48 and 50 to allow replacement of the one or more columns 46 with new columns after use. In some embodiments, the system 10 may include multiple sample separation systems 16 to accommodate an expanded set of columns 46 supplied from the system 10 ( Fig. 4) can be used.

[0034] In exemplary embodiments, the sample separation system 16 may include a heating element 49 for heating the pressurized solvent stream 24 prior to and / or during passage of the solvent stream 24 through the one or more columns 46. The heating element 49 may heat the pressurized solvent stream to a temperature at which the pressurized solvent transitions from a liquid state to a supercritical fluid state, such that the pressurized solvent stream passes through the one or more columns 46 as a supercritical fluid.

[0035] With reference again to Fig. 2, the detection system 18 may be configured to receive components separated from a sample by the one or more columns 46 and detect a composition of the components for subsequent analysis. In an exemplary embodiment, the detection system 18 may include one or more detectors 51 configured to detect one or more properties of the sample components. For example, in one embodiment, the detectors 51 may be implemented as one or more photodiode arrays.

[0036] The system / convergence manager 20 may be configured to introduce a sample from the sample introduction system 14 into the pressurized solvent stream flowing from the solvent introduction system 12 and to direct the solvent stream and sample to the sample separation system 16. In this embodiment, the system / convergence manager 20 may include a multiport auxiliary valve 52 that receives the sample injected by the sample introduction system 14 through a first input port and the pressurized solvent stream injected by the solvent introduction system 12 through a second input port. The auxiliary valve 52 may mix the sample and the solvent stream and discharge the sample and solvent stream via an output port of the multiport auxiliary valve 52 to an input port of the inlet valve 48 of the sample separation system 16.

[0037] The system / convergence manager 20 may also be configured to regulate the pressure of the system 10 and enable cooling, heating, and / or venting of the solvent from the system 10, and may include a vent valve 54, a shutoff valve 56, a backpressure regulator 58, and a transducer 59. The vent valve 54 may be located downstream of the detection system 18 and may be configured to decompress the system 10 via venting the solvent from the system 10 after the solvent has passed through the system 10. The shutoff valve 56 may be configured to isolate the solvent supply from the inlet of the pump 22b of the solvent supply system to prevent solvent from being pumped through the system 10. An exemplary vent valve 54 is described in more detail below.

[0038] The backpressure regulator 58 can regulate the backpressure of the CO2-based chromatography system 10 to control the flow of the mobile phase and sample through the column, to maintain the mobile phase in a supercritical fluid state (or, in some embodiments, a near-supercritical state, such as that of a highly compressed gas or compressible liquid) as the mobile phase passes through the one or more columns 46 of the sample separation system 16, and / or to prevent the backpressure from causing the mobile phase to reverse its flow direction through the one or more columns 46. Embodiments of the backpressure regulator 58 can be configured to regulate the pressure of the system 10 so that the state of the solvent stream (i.e., the mobile phase) does not uncontrollably change prior to and / or within the backpressure regulator(s) 58.The transducer 59 may be a pressure sensor arranged upstream of the backpressure regulator 58 to sense a pressure of the system 10. The transducer 59 may output a feedback signal to a processing device, which may process the signal to control an output of an actuator control signal from the processing device.

[0039] In exemplary embodiments as shown in Fig. 5, the backpressure regulator 58 may include a dynamic pressure regulator 57, a static pressure regulator 61, and a heating element 63. The static pressure regulator 61 may be configured to maintain a predetermined pressure upstream of the backpressure regulator 58. The dynamic pressure regulator 57 may be located upstream of the static pressure regulator 61 and may be configured to adjust the system pressure above the predetermined pressure maintained by the static pressure regulator 61. The heating element 63 may be located downstream of the dynamic pressure regulator 57 and may be located very close to the static pressure regulator 61 to heat the solvent stream as it passes through the static pressure regulator 61 to assist in controlling the state of the solvent as it passes through the static pressure regulator.

[0040] In summary, an exemplary operation of the CO2-based chromatography system 10 may pump mobile phase media 23 and modifying media 25 through the system 10 at a specified flow rate as a solvent stream (i.e., as the mobile phase), and may pressurize the system 10 to a specified pressure such that the solvent stream maintains a liquid state before entering the sample separation system 16. A sample may be injected into the pressurized solvent stream through the sample introduction system 14, and the sample passed through the pressurized solvent stream may pass through the sample separation system 16, which may heat the pressurized solvent stream for the transition of the pressurized solvent stream from a liquid state to a supercritical fluid state.The sample and the solvent stream as a supercritical fluid can pass through at least one or more columns 46 in the sample separation system 16, and the columns 46 can separate components of the sample from each other. The separated components can be fed to the detection system 18, which can detect one or more properties of the sample for subsequent analysis. After the separated sample and solvent have passed through the detection system 18, the solvent and sample can be vented from the system 10 by the system / convergence manager 20.

[0041] In other embodiments, the system 10 described herein can also be used for preparative processes and separations. Typical parameters such as those described above can be manipulated to achieve effective preparative separations. For example, the system 10 described herein offers the advantage of using higher flow rates, larger columns, and column packing sizes, each contributing to achieving preparative separation and functionality, while maintaining little or no variability in overall peak shape, peak size, and / or retention times compared to corresponding analytical processes and related separations. Thus, in one embodiment, this disclosure provides CO2-based chromatography systems 10 adaptable to preparative processes and separations with high efficiency and correlation to analytical runs.

[0042] Fig. 6 is a cross-sectional view of an exemplary embodiment of a dynamic pressure regulator 57 taken along a longitudinal axis L of the dynamic pressure regulator. The dynamic pressure regulator 57 may be implemented as a valve assembly having a proximal head portion 72, a distal actuator portion 76, and an intermediate body portion 74. The head portion 72 of the valve assembly may have an inlet 78 for receiving the pressurized solvent stream and an outlet 80 through which the pressurized solvent stream is discharged, such that the solvent stream flows through the head portion from the inlet 78 to the outlet 80. A seat 82 may be disposed within the head portion 72 and have a bore 84 through which the solvent stream can flow from the inlet 78 to the outlet 80 of the head.

[0043] A needle 86 extends from the body portion 74 of the valve assembly through a seal 88 into the head portion 72. A position of the needle 86 can be controlled relative to the seat 82 to selectively control a flow of the solvent stream from the inlet 78 to the outlet 80. In exemplary embodiments, the position of the needle 86 can be used to restrict flow through the bore 84 of the seat 82 and increase the pressure of the system 10, and it can selectively close the valve by fully engaging the seat 82 to interrupt flow between the inlet 78 and the outlet 80. By controlling the flow of the solvent stream through the head portion based on the position of the needle 86, the pressure of the system 10 can be increased or decreased.For example, the pressure of system 10 may generally increase as needle 86 moves toward seat 82 along longitudinal axis L, and may generally decrease as needle 86 moves away from seat 82 along longitudinal axis L.

[0044] The actuator portion 76 may include an actuator 90, such as a solenoid, a voice coil, and / or any other suitable electromechanical actuation device. In the present embodiment, the actuator 90 may be implemented using a solenoid having a main body 92 and a shaft 94. The shaft 94 may extend along the longitudinal axis L and may engage a distal end of the needle 86 such that the needle 86 and the shaft may form a valve element. A position of the shaft 94 may be adjustable relative to the main body 92 along the longitudinal axis L and may be controlled by a voice coil (not shown) of the main body 92, which generates a magnetic field proportional to an electrical current passing through the coil and a load applied to the shaft.The electrical current flowing through the coil may be controlled in response to an actuator control signal received from actuator 90. In some embodiments, the actuator control signal may be a pulse-width modulated (PWM) signal, and / or the actuator control signal may be determined at least in part by the feedback signal from pressure transducer 59.

[0045] The position of the shaft 94 can be used to move the needle 86 toward or away from the seat 82 to increase or decrease the pressure, respectively. In exemplary embodiments, a position of the shaft 94, and therefore a position of the needle 86 relative to the seat 82, can be controlled and / or determined based on an amount of electrical current flowing through the solenoid. For example, the higher the electrical current, the closer the needle 86 and shaft 94 are to the seat and the lower the pressure in the system 10. The relationship between a position of the shaft 94 and the electrical current flowing through the coil can be determined via the characterization of the actuator 90. The force exerted by the load on the solenoid can be proportional to the magnetic field. Accordingly, the magnetic field can be proportional to the electrical current flowing through the solenoid coil.In embodiments where the actuator control signal is implemented as a PWM control signal, the pressure through the pressure regulator 57 (e.g., the pressure balance between needle 86 and shaft 94) can be adjusted via a correlation with the switching duration of the PWM control signal, e.g., as a percentage of the switching duration corresponding to an "on" state.

[0046] The force provided by actuator 90 for pressure adjustment by pressure regulator 57 can be varied for the purpose of force control through the inclusion of a compression spring 96. Spring 96 is compressed by bead 98 to apply a normalizing force to actuator 90 through an external stem chuck 100. This normalizing force assists in providing a linear load force over the cycle of actuator 90. Generally, commercially available solenoids (i.e., solenoids not appropriately modified as described herein, e.g., without spring 96) provide a non-linear force along their operating stroke, so their use for control purposes is not desirable. In addition, actuator / solenoid 90 has a negative spring constant, so that when actuator 90 is in an inactive state, stem 94 is forced in a direction opposite to outlet 80 (i.e.,toward the end of the device labeled B on axis L), so that the force decreases with increasing solenoid stroke. To compensate for this force, the compressed spring 96 applies pressure to the shaft 94 to balance the negative spring constant of the actuator 90. In some embodiments, the spring constant selected for the compression spring 96 has a value that not only balances, but also applies a positive spring constant, so that the shaft 94 moves toward the end of the device labeled A. Additionally, a disc (e.g., a non-magnetic disc such as a plastic disc, a non-magnetic metal disc, or a blank) is positioned within the main body 92 to create a distance or gap 95 for the purpose of minimizing force changes (e.g., to subsequently produce a nearly constant force from the solenoid).That is, gap 95 prevents actuator 90 from reaching a fully closed state. Gap 95 is designed to accommodate an initially higher nonlinear force region within the solenoid stroke (i.e., a portion of the stroke adjacent to the fully closed state, where the generated force is far from linear). Gap 95 eliminates the effects of the highly nonlinear region (e.g., the region adjacent to the fully closed state) from the solenoid stroke for control purposes. Methods for selecting the bias conditions of spring 96 and the spacing of gap 95 to minimize force variation along the solenoid's operating stroke are discussed further below.

[0047] For pressure regulation by device 57 from inlet 78 to outlet 80, needle 86 and seat 82 are carefully positioned relative to each other. A calibrated position between needle 86 and seat 82 is set at the position where needle 86 first engages bore 84 of seat 82 to stop solvent flow. Generally, this calibrated position is carefully adjusted so that needle 86 does not bind in bore 84 during operation of pressure regulator 57. It can be seen that preventing, or at least minimizing, needle binding in the bore will increase the life of the pressure regulator and / or extend the period of use before maintenance.

[0048] During the service life of the pressure regulator 57, components such as the needle 86 or the seat 82 may wear out. These components must be replaced during maintenance. After maintenance, the needle and seat must be returned to the calibration position.

[0049] Example embodiments of the pressure regulator 57 include a calibration collar 110 attached to the shaft 94 to automatically (e.g., mechanically) reset the calibration position. That is, the calibration collar 110 applies a force to the shaft 94 to lock further extension of the shaft 94. With the calibration collar 110 attached to the shaft 94, a service person or user need only bring the shaft 94 into physical contact with the distal end of the needle and lock the calibration collar to mechanically adjust the needle 86 relative to the seat 82 in the calibrated position.

[0050] To apply the force, the calibration collar 110 has a spring 112 and two locking mechanisms 114 and 116. The locking mechanism 114 holds the calibration collar 110 to the external chuck 100 of the shaft 94, while the locking mechanism 116 engages the distal end 118 of the shaft 94 to clamp or lock the extended position of the shaft 94 to prevent the needle 86 from becoming jammed in the seat 82. Fig. 6, the locking mechanisms include fasteners 120 and 122 for securing a housing 124 that binds the calibration collar 110 to the actuator 90.

[0051] The housing 124 of the calibration collar 110 is typically formed from a metal such as stainless steel or aluminum. The locking mechanisms 114 and 116 may be integrally formed in at least a portion of the housing 124.

[0052] During a maintenance procedure, the actuator 90 is deactivated (i.e., no signal is applied to drive the solenoid), and the solvent flow is stopped. The needle 86 and the seat 82 are in the calibrated position at the beginning of the maintenance event. This means that the needle 86 is engaged with the seat 82 to block the bore 84. The calibration collar 110 attached to the shaft 94 maintains the calibrated position as shown in Fig. 6 the needle and seat in this calibrated position. To access the distal end of the needle 86 and potentially the seat, the shaft 94 must be pulled back toward end B. When configuring the calibration collar with both fasteners 120 and 122 in place, the alignment of the needle 86, the seat 82, and the shaft 94 is maintained. However, to release this fastening position, the user only needs to loosen the fastener 120 to release the handle of the locking mechanism 116 from the distal end 118 of the shaft 94. The fastener 122 remains firmly tightened or closed, so that the locking mechanism 114 continues to hold the housing 124 of the calibration collar 110 to the external chuck 100. The distal end 118 of the shaft 94 is free to move to allow access to the needle / seat for maintenance.At the end of the maintenance procedure, the user places the proximal end 126 of the shaft 94 in contact with the needle 86 and tightens the fastener 120 to reposition the needle 86 relative to the seat in the calibrated position.

[0053] The spring 112 of the calibration collar 110 has a spring constant that is lower (e.g., much smaller) than a constant of the compression or balance spring 96. Consequently, the compression spring 96 dominates with respect to force balance and positioning of the shaft 94 in an inactive solenoid 90 (e.g., with no applied signal). To provide minimization of force change over an operating stroke of the solenoid 90, the spring constant of an opposing balance force (e.g., the spring 96 compressed by the bead 98) and the gap spacing (e.g., the disk thickness) 95 are determined by characterizing the force, current, and stroke of the solenoid.

[0054] Fig. Figure 7 shows an exemplary method 200 for minimizing the pressure change in a solenoid for use as an actuator in a pressure regulator. As described above, commercially available solenoids generate a non-linear force along their stroke, making them undesirable for use as force control devices in pressure regulators. Fig. The method illustrated in Figure 7 modifies a solenoid to produce a nearly constant or substantially constant force over the entire intended operating stroke of the solenoid. Fig. The method illustrated in Figure 7 produces a substantially constant force by minimizing the force variation within the operating stroke of a modified solenoid to minimize or eliminate undesirable force control characteristics that have prevented or limited the use of solenoids for this purpose.

[0055] The Fig. The method 200 illustrated in Figure 7 has five steps and is generally performed only once, at the time of manufacture of the solenoid-force-driven device (e.g., pressure regulator 57). However, in certain embodiments, the method 200 may be performed after a maintenance intervention or during a reconfiguration event (e.g., replacing the needle and / or seat for a configuration with a different cross-sectional design). The first step 210 of the method 200 includes obtaining data regarding solenoid force versus current when the solenoid is energized over a solenoid stroke distance. In step 210, the performance of the solenoid at a particular temperature is characterized. Fig. Figure 8 shows a representative graph 300 depicting such a characterization for a commercially available solenoid, part number 191016-023, from Ledex, Ohio, USA. Plots 320-410 plot force versus shaft position for various percentages of applied current. From the characterization information, a first stroke distance is determined in step 220 that defines a linear force range for a desired energized range. That is, step 220 identifies a range where the force changes linearly or substantially linearly using a subset of the plots corresponding to the desired applied current (e.g., 30% to 70%, plots 340 to 380).

[0056] Fig. 9 illustrates one embodiment of an exemplary process 500 showing how the first stroke distance is determined to define a linear force range or operating range 530. That is, using representations 340-380 for an energized range of 30% to 70% maximum current, a linear force range is identified as a function of stroke distance. The range is defined by a first position 510 and an end position 520 that define the operating range 530. In other embodiments (not shown), an energized range of 10% to 80% maximum current is used. In still other embodiments, 25% to 75% maximum current is used. In still other embodiments, 35% to 65% maximum current is used. Each of these different embodiments may result in the determination of a different operating range.

[0057] From the characterization data, information regarding a spring constant of the solenoid in the operating range 530 can also be determined - see step 230 in the Fig. 7. For example, using plots 340-380, the spring constant (force per distance) in the operating range 530 may be determined. In step 240, a device having a spring constant with a value opposite and greater than the spring constant determined in the operating range is applied to the solenoid to counteract the spring constant of the commercially available solenoid. For example, if the spring constant of the characterized solenoid is -620 pounds per inch (lbf), a device (e.g., a compressed coil or Belleville spring) having a spring constant of approximately 650 pounds per inch or greater is applied to the solenoid. The spring 96 may be compressed by the bead 98, if desired, to apply a preload condition.Other factors used to select the spring constant for spring 96 include checking all force requirements for the applied currents so that a spring with the lowest stiffness is used for a force increase with displacement (e.g., stable force requirement).

[0058] Fig. Figure 10 illustrates the effect of adding the compensating spring to the solenoid. Plots 320' to 410' show the force as a function of the solenoid position with the compression spring 96 attached. Fig. 10 also shows the force generated at a needle at different flow rates 610-660 corresponding to 0.5 ml / min to 5 ml / min. Fig. 10 further shows the maximum upper force state 670 and lower force state 680 expected via the pressure regulator 57.

[0059] To minimize the force change along the operating stroke in a pressure control device such as the pressure regulator 57, the method 200 comprises Fig. 7 includes step 250, in which the solenoid is positioned within the body portion such that the gap 95 is created at the same distance as the first stroke distance 510 in the solenoid's operating stroke. As a result of creating this gap, the non-linear operating region of the solenoid is avoided, and the counterbalanced solenoid produces a substantially constant force throughout the operating range. To create the gap 95, a disc or spacer made of non-magnetic material with a thickness corresponding to the distance in front of the operating range may be used to correctly position the solenoid within the main body 92. (See, for example, the Fig. 6 shown gap 95 created in the main body 92.)

[0060] With reference to Fig. 11a and Fig. Figure 11b illustrates the result of applying spring 96 to the characterized solenoid; and also shown is the operating region 530 created by incorporating gap 95 formed, for example, by placing a disk for positioning solenoid 90 in regulator 57. Fig. 11a shows the result over a distance of 0.2 inches (e.g. 0 to 0.2 inches), while Fig. Figure 11b shows the stroke over an operating position from 0.06 inches to 0.085 inches. The operating stroke distance is 0.025 inches and the gap distance is 0.06. Fig. Figure 11b shows that the force is essentially linear over the operating range for the pressure regulator.

[0061] The above method provides numerous advantages. For example, the method provides cost savings in the manufacture and operation of pressure regulators in flow systems. Embodiments of the method enable low-cost solenoids, when modified with the inexpensive assemblies specified herein (e.g., springs and gap positioning spacers), to be used for pressure control in CO2-based chromatography systems. The method provides not only cost savings due to the manufacturing costs of the force-driven devices, but also in operating costs, since solenoids require minimal current to generate force compared to more expensive actuators such as voice coils.

[0062] In addition to the embodiments shown and described above, other embodiments are also possible. For example, different solenoids have different properties, resulting in the acquisition of different characterization data. Since the acquired data is used to determine the gap positioning, operating range, and spring constant of the compression spring 96 applied to the solenoid, different assemblies / solenoid modifications are possible. Furthermore, while some of the pressure regulator embodiments described herein have the actuator (e.g., the solenoid) positioned in communication with a needle of a needle valve, other types of variable throttle assemblies may be used in addition to a needle valve. For example, in some embodiments, the needle valve may be replaced with a diaphragm valve, wherein the solenoid would communicate with the diaphragm disposed therein.

[0063] While exemplary embodiments have been described herein, it is expressly understood that these embodiments are not to be construed as limiting, but that additions and modifications to the explicit description given herein are also within the scope of the invention. It is further understood that the features of the various embodiments described herein are not mutually exclusive and may be present in various combinations and variations, even if such combinations and variations are not expressly mentioned herein, without departing from the spirit and scope of the technology.

Claims

[1] Pressure regulator (57), comprising: a body portion (74); a head portion (72) having a needle (86) and a seat (82) defining a bore (84), the needle (86) and seat (82) being positioned such that movement of the needle (86) within the bore (84) of the seat (82) creates a pressure differential across the seat (82) when a flow of fluid is directed to the head portion (72); an actuator portion (76) disposed at least partially within the body portion (74) and positioned to communicate with the needle (86) to move the needle (86) within the bore (84) of the seat (82), the actuator portion (76) including a shaft (94) driven in a first direction by a solenoid (90) and a counterbalance spring (96), the solenoid (90) applying a negative spring constant to the shaft (94) in the first direction, and the counterbalance spring (96) being adapted to apply a positive spring constant to the shaft (94) in the first direction, the value of the positive spring constant being greater than the value of the negative spring constant to provide an overall positive spring constant on the shaft (94) in the first direction; and a calibration collar (110) releasably attached to the shaft (94) and adapted to prevent movement of the shaft (94) relative to the shaft chuck when the latter is in a locked position. [2] The pressure regulator of claim 1, further comprising a disc of non-magnetic material disposed within the actuator portion (76) to create a gap (95) within an actuating region of the solenoid (90). [3] Pressure regulator according to claim 1, wherein the compensating spring (96) is a linear spring. [4] Pressure regulator according to claim 3, wherein the linear spring is a compression coil spring. [5] Pressure regulator according to claim 1, wherein the compensating spring (96) is a non-linear spring. [6] Pressure regulator according to claim 5, wherein the non-linear spring is a disc spring. [7] A method (200) for minimizing force variation in a solenoid-driven pressure regulator (57), the method comprising: Obtaining data from the solenoid force as a function of the current applied to the solenoid (90) over a solenoid stroke distance; Using the data to determine a first stroke distance that defines a range of linear force for a range of desired current application; Determining a spring constant of the solenoid (90) in an operating range; Using a device (96) having a spring constant having a value opposite to and greater than the spring constant of the solenoid (90) in the operating range, so that a shaft (94) of the solenoid (90) is biased to extend in a first direction in a non-operative state of the solenoid (90); Positioning the solenoid (90) within the body portion (74) of the pressure regulator so that a gap (95) is created in the solenoid stroke operation that is substantially equal to the distance to the first stroke distance; and releasably securing a calibration collar (110) to the shaft (94) to prevent movement of the shaft (94) relative to the shaft chuck when the latter is in a locked position. [8] The method of claim 7, wherein the gap (95) is between about 0.02 inches and about 0.2 inches. [9] The method of claim 7, wherein positioning the solenoid (90) within the body portion (74) comprises placing a spacer sized to accommodate the gap within an operating stroke of the solenoid. [10] Pressure regulator comprising: an actuator section (76) communicating with a variable throttle assembly, the actuator section (76) having a shaft (94) driven in a first direction by a solenoid (90) and a balance spring (96), the solenoid (90) applying a negative spring constant to the shaft (94) in the first direction, and the balance spring (96) being adapted to apply a positive spring constant to the shaft (94) in the first direction, the value of the positive spring constant being greater than the value of the negative spring constant to provide an overall positive spring constant on the shaft (94) in the first direction; and a calibration collar (110) releasably attached to the shaft (94) and configured to prevent movement of the shaft (94) relative to the shaft chuck when the latter is in a locked position. [11] The pressure regulator of claim 10, further comprising a disc of non-magnetic material disposed within the actuator portion (76) to create a gap (95) within an actuating region of the solenoid (90). [12] Pressure regulator according to claim 10, wherein the compensating spring (96) is a linear spring. [13] Pressure regulator according to claim 12, wherein the linear spring is a compression coil spring. [14] Pressure regulator according to claim 10, wherein the compensating spring (96) is a non-linear spring. [15] Pressure regulator according to claim 14, wherein the non-linear spring is a disc spring. [16] The pressure regulator of claim 10, wherein the variable throttle assembly comprises a needle valve. [17] A pressure regulator according to claim 10, wherein the variable throttle assembly comprises a diaphragm valve.

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