Release of pressure in critical and subcritical flow regimes under backpressure conditions

Abstract

The pressure relief valve includes the following features. The housing defines an inlet and an outlet. The housing defines a flow passage between the inlet and the outlet. A seat may be defined by the housing. The seat defines a throat flow area. The plunger is configured to rest on the seat. The plunger blocks the flow passage when in the closed position. The plunger is configured to actuate between a fully open position and a closed position. The plunger and seat may at least partially define a curtain flow area. A biasing member guides the plunger toward the seat. The ratio of the throat flow area to the curtain flow area is sized for acoustic velocity or supersonic velocity during critical flow conditions and subacoustic velocity during subcritical flow conditions.

Description

Technical Field

[0001] The present disclosure relates to the flow geometry through a pressure relief valve. Background Art

[0002] In gas processing, pressurized gas is directed through various infrastructure components such as pressure vessels, conduits, and storage tanks. In the event of a gas process upset, the pressure within such infrastructure components may exceed a safety threshold. If not mitigated, such pressure buildup can lead to rupture and / or explosion of the infrastructure components. To mitigate this situation, pressure relief valves are strategically placed throughout the infrastructure components. In some processing facilities such as hydrocarbon gas processing facilities, the released gas cannot or should not be released directly to the external environment. In such facilities, the pressure relief valve directs the released gas to a common header for proper disposal and / or venting. The size of the pressure relief valve that releases pressure into the header is typically designed to accommodate the backpressure within the header.

[0003] Various regulatory bodies provide sizing rules for the capacity of pressure relief valves in the presence of backpressure. Such rules are for the flow capacity of the pressure relief valve. The flow capacity can be adjusted through various internal and external valve geometries to ensure that the valve is "large enough", i.e., capable of providing a sufficient flow rate in the event the valve is triggered. The flow through a pressure relief valve is idealized as the flow through a converging-diverging nozzle. In the critical flow regime, the mass flow through the pressure relief valve is considered choked (or at critical flow) when the mass flow rate does not vary with changes in backpressure and is independent of backpressure. There is a transition point when the mass flow rate depends on backpressure, and as the backpressure increases, the mass flow rate decreases. When the mass flow rate depends on backpressure, this flow regime is referred to as the subcritical flow regime. The transition point from critical flow to subcritical flow is a function of the specific heat ratio between the inlet and the outlet of the valve. In practice, this specific heat difference can be observed through the pressure differential. For air, the transition from critical flow to subcritical flow is 55%. For air, this means that the flow through the pressure relief valve will be the same at a backpressure up to 55% of the inlet pressure as it is at atmospheric backpressure. For a pressure relief valve set to release a compressible fluid flow, a calculated correction factor (Kb) is applied when the flow regime is subcritical. In compressible fluids, several standards such as the American Petroleum Institute (API) and the International Organization for Standardization (ISO) state that the backpressure correction factor is one (1.00) in the critical flow regime. API 526 and ISO 4126 provide theoretical formulas for calculating the correction factor (Kb) in the subcritical flow regime. This assumes that the flow through the safety pressure relief valve is idealized as the flow through a converging-diverging nozzle. For an idealized nozzle, the Mach number at the nozzle outlet is equal to or greater than 1.0 as long as the outlet area is equal to or greater than the throat area in the critical flow regime. Summary of the Invention

[0004] The present disclosure relates to techniques for releasing pressure in critical and subcritical flow regimes under backpressure conditions.

[0005] One embodiment described within the present disclosure is a pressure reducing valve having the following characteristics. A housing defines an inlet and an outlet. The housing defines a flow passage between the inlet and the outlet. A seat may be defined by the housing. The seat defines a throat flow area. A plunger is configured to rest on the seat. The plunger blocks the flow passage when in the closed position. The plunger is configured to be actuated between a fully open position and the closed position. The plunger and the seat may at least partially define a curtain flow area. A biasing member biases the plunger towards the seat. The ratio of the throat flow area to the curtain flow area is sized for sonic or supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions.

[0006] In some embodiments, a guide may surround the plunger. The guide may be arranged to maintain the alignment of the plunger during operation. Such alignment assistance is useful for shorter plungers. For example, in some embodiments, the plunger may include a mandrel having a length-to-diameter ratio greater than or equal to 0.75. In some embodiments, the guide defines a flow passage that further defines the curtain flow area. In some embodiments, the curtain flow area depends on the stroke length of the plunger.

[0007] In some embodiments, the ratio of the throat flow area to the curtain flow area may be 0.484 or less. In some embodiments, the biasing member includes a spring.

[0008] One embodiment described within the present disclosure is a method having the following characteristics. A pressurized fluid flow is received through an inlet of a pressure reducing valve. In response to receiving the pressurized fluid flow, a plunger may be lifted from a valve seat within the pressure reducing valve. The throat of the pressure reducing valve reduces the pressure of the fluid and increases the velocity of the fluid. The throat defines a throat flow area. The departure of the plunger increases the pressure of the fluid flow within the pressure reducing valve and reduces the velocity of the fluid flow. The plunger at least partially defines a curtain flow area. The fluid flow may be directed through the pressure reducing valve to a pressure reducing header. The pressure reducing header may have a backpressure. The ratio of the throat flow area to the curtain flow area of the fluid flow may be 0.428 or less.

[0009] After a period of time, in response to lifting the plunger from the valve seat, the pressure within the pressurized environment is reduced. Once the pressure is sufficiently reduced, the plunger abuts the valve seat in response to the reduced pressure.

[0010] In some cases, the backpressure may be substantially less than 55% of the pressure at the inlet of the pressure reducing valve. In such cases, a shock wave may be formed within the pressure reducing valve. Increasing the velocity of the fluid flow may then involve increasing the velocity of the fluid flow to supersonic velocities.

[0011] In some cases, the outlet pressure of the pressure reducing valve is substantially at least 55% of the pressure at the inlet of the pressure reducing valve. In such cases, a flow rate substantially equal to the back pressure correction factor curve is maintained.

[0012] In some embodiments, alignment of the plunger is maintained by a guide surrounding the plunger. In some cases, the guide may include an opening. In such cases, fluid flow is received through the opening within the guide.

[0013] One embodiment described within the present disclosure is a pressure reducing system having the following features. A pressure reducing valve may couple a pressurized system to a pressure reducing manifold. The pressure reducing valve may be configured to direct fluid flow from the pressurized system to the pressure reducing manifold when the pressure within the pressurized system exceeds a specified threshold. The pressure reducing valve includes a housing defining an inlet and an outlet. The housing defines a flow passage between the inlet and the outlet. A seat may be defined by the housing. The seat defines a throat flow area. A plunger is configured to rest on the seat. The plunger may block the flow passage when in a closed position. The plunger may be configured to be actuated between a fully open position and the closed position. The plunger and the seat may at least partially define a curtain flow area. A biasing member biases the plunger toward the seat. The magnitude of the ratio of the throat flow area to the curtain flow area may be designed for supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions.

[0014] In some embodiments, the guide may surround the plunger. The guide may be arranged to maintain alignment of the plunger during operation. Such embodiments are particularly useful in embodiments having a shorter plunger. For example, in some embodiments, the plunger may include a mandrel having a length to diameter ratio greater than or equal to 0.75. In some embodiments, a shorter plunger is useful because the curtain flow area may depend on the stroke length of the plunger. In some embodiments, the guide may define a flow passage that further defines the curtain flow area. In some embodiments, the ratio of the throat flow area to the curtain flow area is 0.428 or less. In some embodiments, the biasing member includes a pilot system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] These and other features will be more readily understood from the following detailed description in conjunction with the accompanying drawings, in which:

[0016] Figure 1 is a perspective view of an example pressure reducing system;

[0017] Figure 2A is a side cross-sectional view of an example pressure reducing valve;

[0018] Figure 2B is a side cross-sectional view of an example pressure reducing valve;

[0019] Figure 3is a schematic view of the cross-sectional flow area within an exemplary pressure reducing valve;

[0020] Figures 4A to 4C is an example of a skirt that can be used within an exemplary pressure reducing valve;

[0021] Figure 5 is a computational fluid dynamics simulation showing the flow velocity through an exemplary pressure reducing valve;

[0022] Figure 6 is a graph of an exemplary ideal backpressure curve; and

[0023] Figure 7 is a flowchart of a method that can be used in conjunction with aspects of the present disclosure. Detailed Description

[0024] Certain embodiments will now be described to provide a thorough understanding of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described and illustrated herein are non-limiting embodiments, and the scope of the present invention is defined only by the claims. Features shown or described in connection with one embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

[0025] In addition, in the present disclosure, similarly named components of the embodiments generally have similar features, and thus, within a particular embodiment, not every feature of every similarly named component is necessarily fully elaborated. Additionally, insofar as linear or circular dimensions are used in the description of the disclosed systems, devices, and methods, such dimensions are not intended to limit the types of shapes that can be used in conjunction with such systems, devices, and methods. Those skilled in the art will recognize that for any geometry, equivalent forms of such linear and circular dimensions can be readily determined. The size and shape of the systems and devices and their components can depend at least on the anatomical structure of the object in which the systems and devices will be used, the size and shape of the components in which the systems and devices will be used, and the methods and procedures in which the systems and devices will be used.

[0026] Compared to a simple ideal 2D nozzle, the flow through a pressure reducing valve is relatively complex. This results in a deviation from the flow regime of the idealized 2D nozzle envisioned by the API and ISO standards. The flow through a safety pressure reducing valve involves a converging-diverging nozzle, the nozzle exit area, as well as a 90-degree bend, an expansion volume, and the valve exit area. As a result, the performance of many safety pressure reducing valves is much worse than that of the ideal nozzles used in the calculations according to API 526 and ISO 4126. Consequently, many safety pressure reducing valves are deliberately oversized, resulting in valves that are bulkier and more expensive to use in a facility than the calculations indicate.

[0027] The present disclosure relates to a pressure reducing valve having performance similar to an ideal nozzle used in API 526 and ISO 4126. The pressure reducing valve includes a housing defining an inlet and an outlet. The housing defines a flow passage between the inlet and the outlet. A seat defines a throat flow area. A plunger is configured to rest on the seat. The plunger blocks the flow passage when in a closed position. The plunger is configured to be actuated between a fully open position and the closed position. The plunger and the seat at least partially define a curtain flow area. The magnitude of the ratio of the throat flow area to the curtain flow area is designed for sonic or supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions. Such characteristics allow the valve to behave as an ideal nozzle. Since a valve having such characteristics behaves as an ideal nozzle, a smaller (and thus less expensive) valve can be used compared to valves having conventional flow characteristics.

[0028] Figure 1 is a perspective view of an exemplary pressure relief system 100. As shown, the pressure relief system 100 includes a pressurization system 102 for processing and delivering a pressurized fluid (such as a pressurized gas). The pressurization system 102 may include a pressure vessel, fluid conduits, or similar pressurized fluid infrastructure. In some embodiments, the pressure relief system 100 further includes a pressure relief header 104. The pressure relief header 104 is typically used in embodiments where the pressurized fluid within the pressurization system 102 cannot or should not be directly discharged to the atmosphere. For example, in some embodiments, the pressurized fluid includes hydrocarbon gas, and the pressure relief header 104 is a flare header that directs the discharged hydrocarbons to a flare for safe disposal. In some embodiments, the pressure relief header is arranged to receive fluid from multiple sources in the event that the pressurization system 102 becomes overpressurized and pressure must be released from the pressurization system.

[0029] A pressure reducing valve 106 couples the pressurization system 102 to the pressure relief header 104. The pressure reducing valve is configured to direct a fluid flow from the pressurization system 102 to the pressure relief header 104 when the pressure within the pressurization system 102 exceeds a specified threshold. In some embodiments, the specified threshold is determined by a pressure reading of the pressurization system. In some embodiments, the specified threshold is determined based on regulatory requirements and / or expected operating parameters of the pressurization system. In the illustrated embodiment, a pilot-operated pressure reducing valve is shown; however, the subject matter of the present disclosure is applicable to other pressure reducing valves, e.g., lift-type pressure reducing valves or other spring-biased pressure reducing valves.

[0030] Figures 2A to 2BIt is a side cross-sectional view of an exemplary pressure reducing valve. The pressure reducing valve 106 includes a housing 202 that defines an inlet 204 and an outlet 206. The housing defines a flow passage 208 between the inlet 204 and the outlet 206. The inlet 204 is fluidly coupled to a pressurization system 102. Within the housing 202 is a seat 210 that defines a throat flow area, which is the cross-sectional area of a portion of the flow passage defined by the seat 210. In some embodiments, the seat 210 is at least partially defined by the housing 202. In some embodiments, the seat 210 is a separate insert supported and held by the housing 202. Such embodiments allow a single housing to be used for different "sizes" of valves.

[0031] The plunger 212 is configured to rest on the seat when the valve is in the closed position. When in the closed position, the plunger blocks the flow passage. The plunger is configured to be actuated between a fully open position (as Figure 2A shown) and the closed position. The plunger 212 and the seat 210 at least partially define a curtain flow area. That is, the plunger 212 and the seat define the flow passage. In other words, the curtain flow area depends on the stroke length (travel distance) of the plunger 212. As Figure 2B shown, the plunger 212 may include two pieces coupled to each other. The top plunger 212A may be configured to receive a force from a biasing member , and the bottom plunger 212B may be configured to seal against the seat in the closed position. In some embodiments, the plunger includes a mandrel 214. In some embodiments, the mandrel 214 has a length-to-diameter ratio greater than or equal to 0.75. Such a ratio can increase the curtain flow area by providing a shorter mandrel length, which allows for a greater stroke length during operation.

[0032] In some embodiments, the pressure reducing valve 106 includes a guide 216 that surrounds the plunger 212. The guide is arranged to maintain the alignment of the plunger throughout its stroke length during operation. Examples of such guides are discussed in more detail later in this disclosure.

[0033] The biasing member 218 biases the plunger 212 toward the seat 210. The strength of the biasing member 218 determines the opening (opening) pressure of the valve 106. In some embodiments, the biasing member is field adjustable, which means that the set pressure of the valve can be adjusted by a technician at the installation site. As previously discussed, in some embodiments, the biasing member 218 includes a pilot system 108 ( Figure 1 ). Alternatively or additionally, in some embodiments, the biasing member includes a spring 220.

[0034] The flow capacity through the valve can be at least partially a function of the geometry of the flow passage defined by the valve. Generally, such geometry can be simplified to a 2D representation of the various flow areas through the flow passage 208.Figure 3 It is a schematic diagram of the cross-sectional flow area of the flow passage 208 defined by the exemplary pressure reducing valve 106. The flow passage 208 has a variable cross-section along the length of the flow passage 208. The first cross-sectional area is the inlet cross-sectional area 302 defined by the housing 202. The next cross-sectional area is the throat cross-sectional area 304 defined by the seat 210. Just downstream of the throat cross-sectional area is the curtain cross-sectional flow area 306 defined by both the seat 210 and the plunger 212. Next is the valve body cross-sectional area 308. This is the largest cross-sectional area and is defined by the valve housing 202. Finally, the fluid flow exits through the outlet cross-sectional area 310 defined by the outlet 206.

[0035] In some embodiments, the flow passage 208 is configured to allow pressurized fluid to leave the pressurized system under various conditions. For example, in the case where there is backpressure in the pressure reducing manifold. The presence and amount of backpressure affect the flow rate of the fluid flow. Generally, the greater the backpressure present in the pressure reducing manifold, the lower the flow rate. When the backpressure has an insignificant (e.g., less than 10%) effect on the flow rate through the pressure reducing valve, the flow is said to be in a critical flow state. In cases where the backpressure has a more significant effect, the flow is said to be in a subcritical flow state. In some embodiments, when the backpressure within the pressure reducing manifold is substantially 55% (plus or minus 5%) of the pressure reducing valve opening pressure, the fluid transitions from critical flow to subcritical flow. The backpressure required to change the flow regime between critical flow and subcritical flow depends to some extent on the gas, temperature, and other factors in the fluid flow.

[0036] Return Figure 3 , in some embodiments, the magnitude of the ratio of the throat flow area 304 to the curtain flow area 306 is designed for sonic or supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions. That is, during critical flow conditions, the fluid flow reaches a velocity greater than or equal to 1 Mach. To achieve such velocities, the ratio of the throat area 304 to the curtain area 306 is set, for example, to 0.484 or less. In some embodiments, the ratio of the throat area 304 to the curtain area 306 is set to 0.428 or less. This ratio depends on the opening pressure of the pressure reducing valve, the composition of the fluid, and the temperature of the fluid, and thus, the ratios provided are only provided as examples.

[0037] In some embodiments, the stroke length of the plunger 212 (Figure 2) is of sufficient length so as to lift the lower end of the plunger 212 (configured to abut the end of the seat 210) above the lower end of the guide 216. In such embodiments, the guide 216 partially defines the curtain flow area 306. Figures 4A to 4Cis an example of a guide that can be used within the exemplary pressure reducing valve 106. In such an embodiment, the guide 216 can define flow channels (216a, 216b, 216c). In such an embodiment, the flow channels (216a, 216b, 216c) of the guide further define a curtain flow area 306.

[0038] Now that the importance of the ratio of the throat area 304 to the curtain area 306 within the exemplary valve 106 has been discussed, Figure 5 a computational fluid dynamics simulation 500 is shown that depicts the flow velocity through the exemplary pressure reducing valve 106 during the critical flow stage. As can be seen from the simulation 500, the flow velocity reaches the sonic velocity 502 within the throat area 304. For the depicted embodiment, the throat area to curtain area ratio is 0.484.

[0039] Figure 6 is a graph 600 of an exemplary ISO / API backpressure curve 602. The graph 600 shows a correction factor 604 for the backpressure 606. The first curve 608 shows the typical correction factor for the valve design, while the ISO / API curve 602 is an ideal curve developed by ISO and API. As can be seen, the typical valve curve 608 is offset from the ISO / API curve 602. A valve designed with the typical valve curve 608 will require more to accommodate the necessary flow rate during subcritical flow conditions.

[0040] The benefit of having a ratio of the throat area 304 to the curtain area 306 that is configured to accelerate the fluid flow to sonic velocity during critical flow conditions is that the flow rate decreases at an ideal rate, i.e., the correction factor (kb) matches a calculated curve such as the ISO / API curve 602. In other words, a pressure reducing valve configured to provide sonic or supersonic flow velocity can provide a greater flow rate (i.e., mass flow rate) during subcritical conditions. This can be seen from the third curve 610 based on the computational fluid dynamics simulation 500 and the fourth curve 612 based on testing of the exemplary pressure reducing valve 106.

[0041] In a practical environment, a valve can be classified as undergoing several discreet steps during operation. Figure 7 Such steps are shown in the flowchart of the method 700. At 702, a pressurized fluid flow is received through the inlet 204 (FIG. 2) of the pressure reducing valve 106. At 704, in response to receiving the pressurized fluid flow, the plunger 212 is lifted from the valve seat 210. For example, this event occurs when the pressurized fluid exceeds the set point of the pressure reducing valve 106. In some embodiments, the alignment of the plunger is maintained by a guide or skirt surrounding the plunger 212. In some embodiments, the guide defines openings (216a, 216b, 216c) through which the fluid flows.

[0042] At 706, the fluid flow pressure is reduced and the fluid flow velocity is increased by the seat 210 of the pressure reducing valve 106. The seat 210 defines a throat flow area 304. At 708, the fluid flow pressure increases and the velocity decreases with the departure of the plunger 212. The plunger 212 at least partially defines a curtain flow area. At 710, the fluid flow is directed by the pressure reducing valve 106 to the pressure reducing manifold 104. The pressure reducing manifold has a back pressure. In some embodiments, the ratio of the throat flow area to the curtain flow area is 0.484 or less. In some embodiments, the ratio is 0.428 or less.

[0043] When the back pressure (outlet pressure) is substantially less than 55% (plus or minus 5%) of the pressure at the inlet of the pressure reducing valve, a shock wave is formed within the pressure reducing valve. In this case, the velocity of the fluid flow increases to sonic or supersonic velocity.

[0044] When the back pressure (outlet pressure) of the pressure reducing valve is substantially at least 55% (plus or minus 5%) of the pressure at the inlet of the pressure reducing valve, a flow rate substantially equal to the back pressure correction factor curve (such as Figure 6 those shown therein) is maintained.

[0045] Regardless of the flow rate, after a period of time, the pressure within the pressurized environment decreases in response to lifting the plunger from the valve seat. Once the pressure has decreased by more than a specified threshold, such as 95% of the lift pressure of the plunger 212, the plunger abuts the valve seat in response to the decreased pressure.

[0046] Although this disclosure includes many specific implementation details, these should not be construed as limitations on the scope of the claimed subject matter, but rather as descriptions of features specific to particular embodiments of a particular invention. Certain features described in the context of separate embodiments of this disclosure may also be implemented in combination within a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments. Additionally, although features may have been described above as acting in certain combinations and even initially claimed as such, one or more features from the claimed combination may in some cases be removed from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0047] Similarly, although the operations are depicted in the drawings in a particular order, this should not be construed as requiring that the operations be performed in the particular order shown or in sequential order, or that all of the illustrated operations be performed to achieve the desired result. Additionally, the separation of various system components in the above-described embodiments should not be construed as requiring such separation in all embodiments, and it should be understood that the described components and systems can generally be integrated together in a single product or packaged in multiple products. Accordingly, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the acts recited in the claims can be performed in a different order and still achieve the desired result. Additionally, the processes depicted in the drawings do not necessarily require the particular order or sequence shown to achieve the required result.

Claims

1. A pressure reducing valve, the pressure reducing valve comprising: a housing defining an inlet and an outlet, the housing defining a flow passage between the inlet and the outlet; a seat defined by the housing, the seat defining a throat flow area; a plunger configured to rest on the seat, the plunger blocking the flow passage when in a closed position, the plunger being configured to be actuated between a fully open position and the closed position, the plunger and the seat at least partially defining a curtain flow area; and a biasing member that biases the plunger towards the seat, wherein the magnitude of the ratio of the throat flow area to the curtain flow area is designed for sonic or supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions.

2. The pressure reducing valve according to claim 1, the pressure reducing valve further comprising a guide surrounding the plunger, the guide being arranged to maintain the alignment of the plunger during operation.

3. The pressure reducing valve according to claim 2, wherein the guide defines a flow passage, the flow passage further defining the curtain flow area.

4. The pressure reducing valve according to claim 1, wherein the curtain flow area depends on the stroke length of the plunger.

5. The pressure reducing valve according to claim 1, wherein the ratio of the throat flow area to the curtain flow area is 0.484 or less.

6. The pressure reducing valve according to claim 1, wherein the plunger comprises a mandrel, wherein the mandrel has a length to diameter ratio greater than or equal to 0.

75.

7. The pressure reducing valve according to claim 1, wherein the biasing member comprises a spring.

8. A method, the method comprising: receiving a pressurized fluid flow through an inlet of a pressure reducing valve; lifting a plunger from a valve seat within the pressure reducing valve in response to receiving the pressurized fluid flow; reducing the pressure of the fluid flow and increasing the velocity of the fluid flow through a throat of the pressure reducing valve, the throat defining a throat flow area; increasing the pressure of the fluid flow and reducing the velocity of the fluid flow by the departure of the plunger within the pressure reducing valve, the plunger at least partially defining a curtain flow area; and directing the fluid flow through the pressure reducing valve to a pressure reducing header having a back pressure, wherein the flow area ratio of the throat flow area to the curtain flow area is 0.428 or less.

9. The method according to claim 8, wherein the back pressure is substantially less than 55% of the pressure at the inlet of the pressure reducing valve, the method further comprising: forming a shock wave within the pressure reducing valve, wherein increasing the velocity of the fluid flow comprises increasing the velocity of the fluid flow to a supersonic velocity.

10. The method according to claim 8, wherein the outlet pressure of the pressure reducing valve is substantially at least 55% of the pressure at the inlet of the pressure reducing valve, the method further comprising: maintaining a flow rate substantially equal to a back pressure correction factor curve.

11. The method according to claim 8, the method further comprising: maintaining the alignment of the plunger by a guide surrounding the plunger.

12. The method according to claim 11, the method further comprising: Receive the fluid flow through an opening within the guide.

13. The method of claim 8, the method further comprising: Reducing the pressure within the pressurized environment in response to lifting the plunger from the valve seat; And Adjacent the plunger to the valve seat in response to reducing the pressure.

14. A pressure relief system, the pressure relief system comprising: A pressurization system; A pressure relief manifold; And A pressure relief valve that couples the pressurization system to the pressure relief manifold, the pressure relief valve being configured to direct a fluid flow from the pressurization system to the pressure relief manifold when the pressure within the pressurization system exceeds a specified threshold, the pressure relief valve comprising: A housing that defines an inlet and an outlet, the housing defining a flow passage between the inlet and the outlet; A seat defined by the housing, the seat defining a throat flow area; A plunger configured to rest on the seat, the plunger blocking the flow passage when in a closed position, the plunger being configured to actuate between a fully open position and the closed position, the plunger and the seat at least partially defining a curtain flow area; and A biasing member that directs the plunger toward the seat, Wherein the magnitude of the ratio of the throat flow area to the curtain flow area is designed for supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions.

15. The pressure relief system of claim 14, the pressure relief system further comprising a guide surrounding the plunger, the guide being arranged to maintain alignment of the plunger during operation.

16. The pressure relief system of claim 15, wherein the guide defines a flow passage that further defines a curtain flow area.

17. The pressure relief system of claim 14, wherein the curtain flow area depends on the stroke length of the plunger.

18. The pressure relief system of claim 14, wherein the ratio of the throat flow area to the curtain flow area is 0.428 or less.

19. The pressure relief system of claim 14, wherein the plunger includes a mandrel, wherein the mandrel includes a length-to-diameter ratio greater than or equal to 0.

75.

20. The pressure relief system of claim 14, wherein the biasing member includes a pilot system.

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