Pressure release in critical and subcritical flow regimes under backpressure conditions.

Abstract

The pressure relief valve includes the following features: A housing defines an inlet and an outlet. The housing defines a flow path between the inlet and the outlet. A seat can 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 path when in a closed position. The plunger is configured to operate between a fully open position and a closed position. The plunger and seat can at least partially define a curtain flow area. A bias directs the plunger toward 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.

Description

[Technical Field]

[0001] The present disclosure relates to flow geometry through pressure relief valves. [Background technology]

[0002] In gas processing, pressurized gas is directed through various infrastructure components, such as pressure vessels, conduits, and storage tanks. If a gas processing anomaly occurs, the pressure within such infrastructure components may exceed safety thresholds. If such pressure buildup is not mitigated, it may lead to rupture and / or explosion of the infrastructure components. To mitigate such scenarios, pressure relief valves are strategically placed throughout the infrastructure components. In some processing facilities, such as hydrocarbon gas processing facilities, released gas cannot or should not be released directly to the external environment. In such facilities, pressure relief valves direct released gas to a common header for proper disposal and / or venting. Pressure relief valves that release pressure to the header are often sized to accommodate the backpressure within the header.

[0003] Various regulatory agencies provide sizing rules for the capacity of pressure relief valves in the presence of backpressure. These rules address the flow capacity of pressure relief valves. Flow capacity can be adjusted through various internal and external valve geometries to ensure the valve is "large enough," i.e., capable of providing sufficient flow rate when the valve is actuated. Flow through a pressure relief valve is idealized as flow through a convergent-divergent nozzle. In the critical flow regime, mass flow through a safety valve is considered choked (or critical flow) when the mass flow rate does not change with and is independent of backpressure. A transition point exists when the mass flow rate is dependent on backpressure, and as backpressure increases, the mass flow rate decreases. This flow regime, when the mass flow rate is dependent on backpressure, is called the subcritical flow regime. The transition point from critical flow to subcritical flow is a function of the specific heat ratio between the valve inlet and the valve outlet. In practice, this specific heat difference is observable through a pressure differential. For air, the transition from critical to subcritical flow is 55%. For air, this means that flow through a safety valve at backpressures up to 55% of the inlet pressure is the same as flow when the backpressure is atmospheric. For pressure relief valves configured to release compressible fluid flow, a calculated correction factor (Kb) is applied when the flow regime is subcritical. For compressible fluids, some standards, such as the American Petroleum Institute (API) and the International Standards Organization (ISO), indicate that the backpressure correction factor in the critical flow regime is 1 (1.00). 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 a pressure relief valve is idealized as flow through a convergent-convergent nozzle. For an idealized nozzle, in the critical flow regime, if the exit area is equal to or greater than the throat area, the Mach number at the nozzle exit is 1.0 or greater. Summary of the Invention

[0004] The present disclosure relates to techniques involving pressure relief in critical and subcritical flow regimes under back pressure conditions.

[0005] One embodiment described in this disclosure is a pressure relief valve having the following features: A housing defines an inlet and an outlet. The housing defines a flow path between the inlet and the outlet. A seat can 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 path when in a closed position. The plunger is configured to operate between a fully open position and a closed position. The plunger and the seat can at least partially define a curtain flow area. A bias directs the plunger toward 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, the guide can surround the plunger. The guide can be arranged to maintain alignment of the plunger during operation. Such alignment assistance is useful for shorter plungers; for example, in some embodiments, the plunger can include a mandrel having a length-to-diameter ratio of 0.75 or greater. In some embodiments, the guide defines a flow channel that further defines a curtain flow area. In some embodiments, the curtain flow area is dependent 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 less than or equal to 0.484.In some embodiments, the bias includes a spring.

[0008] One embodiment described in this disclosure is a method having the following features: A flow of pressurized fluid is received by an inlet of a pressure relief valve. In response to receiving the flow of pressurized fluid, a plunger can be lifted from a valve seat in the pressure relief valve. A throat of the pressure relief valve reduces the pressure and increases the velocity of the fluid. The throat defines a throat flow area. An outlet of the plunger increases the pressure and decreases the velocity of the fluid flow in the pressure relief valve. The plunger at least partially defines a curtain flow area. The fluid flow can be directed by the pressure relief valve to a relief header. The relief header can have a back pressure. A flow area ratio between the throat flow area and the curtain flow area can be less than or equal to 0.428.

[0009] After a period of time, the pressure in the pressurized environment decreases in response to lifting the plunger off the valve seat, and once the pressure has dropped sufficiently, the plunger abuts against the valve seat in response to the pressure reduction.

[0010] In some cases, the back pressure may be substantially less than 55% of the pressure at the inlet of the pressure relief valve. In such cases, shock waves may form within the pressure relief valve. Increasing the velocity of the fluid flow may then involve increasing the velocity of the fluid flow to supersonic speeds.

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

[0012] In some embodiments, the alignment of the plunger is maintained by a guide that surrounds the plunger. In some cases, the guide can include an opening. In such cases, the fluid flow is received through the opening in the guide.

[0013] One embodiment described in this disclosure is a pressure relief system having the following features: A pressure relief valve can couple a pressurized system to a relief header. The pressure relief valve can be configured to direct fluid flow from the pressurized system to the relief header when pressure in the pressurized system exceeds a specified threshold. The pressure relief valve includes a housing defining an inlet and an outlet. The housing defines a flow path between the inlet and the outlet. A seat can be defined by the housing. The seat defines a throat flow area. A plunger is configured to rest on the seat. The plunger can block the flow path when in a closed position. The plunger can be configured to operate between a fully open position and a closed position. The plunger and the seat can at least partially define a curtain flow area. A bias directs the plunger toward the seat. A ratio of the throat flow area to the curtain flow area can be sized for supersonic flow velocities during critical flow conditions and subsonic flow velocities during subcritical flow conditions.

[0014] In some embodiments, the guide can surround the plunger. The guide can be arranged to maintain alignment of the plunger during operation. Such embodiments are particularly useful for embodiments having short plungers; for example, in some embodiments, the plunger can include a mandrel having a length-to-diameter ratio of 0.75 or greater. In some embodiments, shorter plungers are useful because the curtain flow area can depend on the stroke length of the plunger. In some embodiments, the guide can 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 bias includes a pilot system. [Brief explanation of the drawings]

[0015] These and other features will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a perspective view of an exemplary pressure relief system. [Figure 2A] FIG. 1 is a cross-sectional side view of an exemplary pressure relief valve. [Figure 2B] FIG. 1 is a cross-sectional side view of an exemplary pressure relief valve. [Figure 3] 1 is a schematic diagram of a cross-sectional flow area within an exemplary pressure relief valve. [Figure 4A] 1 is an example of a skirt that may be used in an exemplary pressure relief valve. [Figure 4B] 1 is an example of a skirt that may be used in an exemplary pressure relief valve. [Figure 4C] 1 is an example of a skirt that may be used in an exemplary pressure relief valve. [Figure 5] 1 is a computational fluid dynamics simulation illustrating flow rates through an exemplary pressure relief valve. [Figure 6] 1 is a plot of an exemplary ideal backpressure curve. [Figure 7] 1 is a flowchart of a method that can be used with aspects of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] Certain embodiments will now be described to provide a thorough understanding of the principles 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 herein and illustrated in the accompanying drawings are non-limiting embodiments, and that the scope of the invention is defined only by the claims. Features illustrated or described in connection with one embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be within the scope of the present invention.

[0017] Furthermore, in this disclosure, like-named components of embodiments generally have similar characteristics, and therefore, every feature of each like-named component within a particular embodiment is not necessarily described in full detail. Additionally, to the extent that linear or circular dimensions are used in describing the disclosed systems, devices, and methods, such dimensions are not intended to limit the types of shapes that may be used with such systems, devices, and methods. Those skilled in the art will recognize that the equivalents of such linear and circular dimensions can be readily determined for any geometric shape. The size and shape of the systems and devices and their components may depend, at least, on the anatomical structure of the subject with whom the systems and devices are to be used, the size and shape of the components with which the systems and devices are to be used, and the method and procedure with which the systems and devices are to be used.

[0018] The flow through a pressure relief valve is relatively complex compared to a simple, ideal 2D nozzle. This results in a flow regime that deviates from the idealized 2D nozzle assumed by API and ISO standards. The flow through a safety relief valve involves a convergent-divergent nozzle, a nozzle exit area with a 90-degree bend, an expansion volume, and a valve exit area. As a result, many safety relief valves perform substantially worse than the ideal nozzle used in calculations according to API 526 and ISO 4126. For this reason, many safety relief valves are intentionally oversized, resulting in facilities using bulkier and more expensive valves than the calculations would indicate.

[0019] The present disclosure relates to a pressure relief valve that functions similarly to an ideal nozzle used in API 526 and ISO 4126. The pressure relief valve includes a housing defining an inlet and an outlet. The housing defines a flow path 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 path when in a closed position. The plunger is configured to operate between a fully open position and a closed position. The plunger and the seat at least partially define a curtain flow area. 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 flow velocities during subcritical flow conditions. Such characteristics enable the valve to behave as an ideal nozzle. Because a valve having such characteristics behaves as an ideal nozzle, a smaller (and therefore less expensive) valve can be used compared to valves having conventional flow characteristics.

[0020] FIG. 1 is a perspective view of an exemplary pressure relief system 100. As shown, the pressure relief system 100 includes a pressurized system 102 used in the processing and transportation of pressurized fluids, such as pressurized gases. The pressurized system 102 may include a pressure vessel, a flow conduit, or similar pressurized fluid infrastructure. In some embodiments, the pressure relief system 100 also includes a relief header 104. The relief header 104 is often used in embodiments where the pressurized fluid in the pressurized system 102 cannot or should not be vented directly to the atmosphere. For example, in some embodiments, the pressurized fluid includes hydrocarbon gases, and the relief header 104 is a flare header that directs the vented hydrocarbons to a flare for safe disposal. In some embodiments, the relief header is arranged to receive fluid from multiple sources in the event that the pressurized system 102 becomes over-pressurized and pressure must be relieved from the pressurized system.

[0021] A pressure relief valve 106 couples the pressurized system 102 to the relief header 104. The pressure relief valve is configured to direct fluid flow from the pressurized system 102 to the relief header 104 when the pressure in the pressurized system 102 exceeds a specified threshold. In some embodiments, the specified threshold is determined by a pressure indication of the pressurized system. In some embodiments, the specified threshold is determined according to regulatory requirements and / or expected operating parameters of the pressurized system. In the illustrated embodiment, a pilot-style pressure relief valve is illustrated. However, the subject matter of the present disclosure is applicable to other pressure relief style valves, such as poppet-style pressure relief valves or other spring-biased pressure relief valves.

[0022] 2A-2B are side cross-sectional views of an exemplary pressure relief valve. Pressure relief valve 106 includes a housing 202 defining an inlet 204 and an outlet 206. The housing defines a flow path 208 between inlet 204 and outlet 206. Inlet 204 is fluidly coupled to pressurized system 102. Within housing 202 is a seat 210 that defines a throat flow area, which is the cross-sectional area of ​​a portion of the flow path defined by seat 210. In some embodiments, seat 210 is at least partially defined by housing 202. In some embodiments, seat 210 is a separate insert that is supported and retained by housing 202. Such embodiments allow a single housing to be used in different "sized" valves.

[0023] The plunger 212 is configured to rest against the seat when the valve is in the closed position. The plunger blocks the flow path when in the closed position. The plunger is configured to operate between a fully open position (shown in FIG. 2A ) and a closed position. The plunger 212 and the seat 210 at least partially define the curtain flow area. That is, the plunger 212 and the seat bound the flow path. In other words, the curtain flow area depends on the stroke length (travel distance) of the plunger 212. As shown in FIG. 2B , the plunger 212 can include two parts coupled to each other. The top plunger 212A can be configured to receive force from a bias ###, and the bottom plunger 212B can 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 of 0.75 or greater. Such a ratio can increase the curtain flow area by providing a shorter mandrel length, which allows for a longer stroke length during operation.

[0024] In some embodiments, the pressure relief valve 106 includes a guide 216 that surrounds the plunger 212. The guide is arranged to maintain alignment of the plunger throughout the stroke length of the plunger 212 during operation. Examples of such guides are discussed in more detail later in this disclosure.

[0025] Bias 218 directs plunger 212 toward seat 210. The strength of bias 218 determines the cracking (opening) pressure of valve 106. In some embodiments, bias is field adjustable, meaning that a technician can adjust the set pressure of the valve at the installation site. As discussed above, in some embodiments, bias 218 includes pilot system 108 ( FIG. 1 ). Alternatively, or in addition, in some embodiments, bias includes spring 220.

[0026] The flow capacity through a valve can be, at least in part, a function of the geometry of the flow path defined by the valve. Generally, such geometry can be simplified to a 2D representation of the various flow areas through the flow path 208. FIG. 3 is a schematic diagram of the cross-sectional flow area of ​​the flow path 208 defined by the exemplary pressure relief valve 106. The flow path 208 has a variable cross-section over the length of the flow path 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. Immediately downstream from 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, which 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.

[0027] In some embodiments, the flow path 208 is configured to allow pressurized fluid to exit the pressurized system under various conditions, such as when backpressure exists in the relief header. The presence and amount of backpressure affects the flow rate of the fluid stream. Generally, the more backpressure exists in the relief header, the lower the flow rate. When the backpressure has only a small effect (e.g., less than 10%) on the flow rate through the pressure relief valve, the flow is said to be in a critical flow regime. When the backpressure has a greater effect, the flow is said to be in a subcritical flow regime. In some embodiments, when the backpressure in the relief header is substantially 55% (±5%) of the cracking pressure of the pressure relief valve, the flow transitions from critical to subcritical flow. The backpressure required to change the flow regime between critical and subcritical flow depends somewhat on the gases in the fluid stream, temperature, and other factors.

[0028] Returning to FIG. 3 , in some embodiments, the ratio of throat flow area 304 to curtain flow area 306 is sized 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 speeds of Mach 1 or greater. To achieve such velocities, the ratio of throat area 304 to curtain area 306 is set to be, for example, 0.484 or less. In some embodiments, the ratio of throat area 304 to curtain area 306 is set to be 0.428 or less. This ratio depends on the pressure of the pressure relief valve, the composition of the fluid, and the temperature of the fluid; therefore, the ratio provided is provided merely as an example.

[0029] In some embodiments, the stroke length of plunger 212 (FIG. 2) is long enough to lift the lower end of plunger 212 (the end configured to abut seat 210) beyond the lower end of guide 216. In such embodiments, guide 216 partially defines curtain flow area 306. FIGS. 4A-4C are examples of guides that may be used in exemplary pressure relief valve 106. In such embodiments, guide 216 may define flow paths (216a, 216b, 216c). In such embodiments, the guide flow paths (216a, 216b, 216c) further define curtain flow area 306.

[0030] Having discussed the importance of the ratio of throat area 304 to curtain area 306 in the exemplary valve 106, Figure 5 shows a computational fluid dynamics simulation 500 illustrating the flow velocity through the exemplary pressure relief valve 106 during the critical flow stage. As can be seen from the simulation 500, the flow velocity reaches the speed of sound 502 within the throat area 304. For the illustrated embodiment, the throat area to curtain area ratio is 0.484.

[0031] 6 is a plot 600 of an exemplary ISO / API backpressure curve 602. Plot 600 illustrates a correction factor 604 over backpressure 606. A first curve 608 illustrates the correction factor specific to the valve design, while ISO / API curve 602 is an idealized curve generated by ISO and API. As such, typical valve curve 608 is offset from ISO / API curve 602. A valve designed according to typical valve curve 608 would need to be oversized to accommodate the flow rate required during a subcritical flow scenario.

[0032] An advantage of having a throat area 304 to curtain area 306 ratio configured to accelerate the fluid flow to sonic speeds during critical flow conditions is that the flow rate decreases at an ideal ratio, i.e., the correction factor (kb) matches a calculated curve, such as ISO / API curve 602. In other words, a relief valve configured to provide sonic or supersonic flow velocities can provide a higher flow rate (i.e., mass flow rate) during subcritical conditions. This can be seen by a third curve 610, based on computational fluid dynamics simulation 500, and a fourth curve 612, based on testing of the exemplary pressure relief valve 106.

[0033] In the field, a valve can be classified as undergoing several distinct steps during operation. FIG. 7 illustrates such steps in a flowchart of a method 700. At 702, a flow of pressurized fluid is received by the inlet 204 (FIG. 2) of the pressure relief valve 106. At 704, in response to receiving the flow of pressurized fluid, the plunger 212 is lifted from the valve seat 210. Such an event occurs, for example, when the pressurized fluid exceeds a set point of the pressure relief valve 106. In some embodiments, the alignment of the plunger is maintained by a guide or skirt that surrounds the plunger 212. In some embodiments, the guide defines openings (216a, 216b, 216c) through which the fluid flows.

[0034] At 706, the pressure of the fluid flow is reduced and the velocity is increased by the seat 210 of the pressure relief valve 106. The seat 210 defines the throat flow area 304. At 708, the pressure of the fluid flow is increased and the velocity is decreased by the outlet of the plunger 212. The plunger 212 at least partially defines the curtain flow area. At 710, the pressure relief valve 106 directs the fluid flow to the relief header 104. The relief header has a back pressure. In some embodiments, the flow area ratio of the throat flow area to the curtain flow area is 0.484 or less. In some embodiments, this ratio is 0.428 or less.

[0035] If the back pressure (outlet pressure) is substantially less than 55% (±5%) of the pressure at the inlet of the pressure relief valve, shock waves will form within the pressure relief valve. In such a situation, the velocity of the fluid flow will increase to sonic or supersonic speeds.

[0036] When the back pressure (outlet pressure) of the pressure relief valve is substantially at least 55% (±5%) of the pressure at the inlet of the pressure relief valve, a flow rate substantially equal to the back pressure correction factor curve as illustrated in FIG. 6 is maintained.

[0037] Regardless of the flow rate, after a certain duration, the pressure in the pressurized environment decreases in response to lifting the plunger off the valve seat. When the pressure decreases beyond a specified threshold, e.g., 95% of the lift pressure of plunger 212, the plunger abuts against the valve seat in response to the decreased pressure.

[0038] While this disclosure includes details of many specific embodiments, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular embodiments of a particular invention. Certain features described in this disclosure in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as working in a particular combination and initially claimed as such, one or more features from a claimed combination may, in some cases, be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination.

[0039] Similarly, although operations are depicted in the figures in a particular order, this should not be understood as requiring such operations to be performed in the particular order shown, or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Furthermore, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described components and systems may generally be integrated together in a single product or packaged in multiple products. Accordingly, specific embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the operations recited in the claims can be performed in a different order and still achieve desirable results. Additionally, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results.

Claims

1. A pressure relief valve, a housing defining an inlet and an outlet, the housing defining a flow path 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 path when in a closed position, the plunger configured for actuation between a fully open position and the closed position, the plunger and the seat at least partially defining a curtain flow area; a bias that directs the plunger toward the seat; A pressure relief valve in which the ratio of throat flow area to curtain flow area is sized for sonic or supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions.

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

3. The pressure relief valve of claim 2 , wherein the guide defines a flow path that further defines the curtain flow area.

4. 2. The pressure relief valve of claim 1, wherein the curtain flow area is dependent on the stroke length of the plunger.

5. 2. The pressure relief valve of claim 1, wherein the ratio of the throat flow area to the curtain flow area is less than or equal to 0.

484.

6. 10. The pressure relief valve of claim 1, wherein the plunger comprises a mandrel, the mandrel having a length to diameter ratio of 0.75 or greater.

7. The pressure relief valve of claim 1 , wherein the bias comprises a spring.

8. 1. A method comprising: receiving a flow of pressurized fluid through an inlet of a pressure relief valve; lifting a plunger off a valve seat within the pressure relief valve in response to receiving the flow of pressurized fluid; reducing the pressure and increasing the velocity of the fluid flow through a throat of the pressure relief valve, the throat defining a throat flow area; increasing the pressure and decreasing the velocity of the fluid flow through the outlet of a plunger in the pressure relief valve, the plunger at least partially defining a curtain flow area; directing the fluid flow with the pressure relief valve to a relief header, the relief header having a back pressure and a flow area ratio of the throat flow area to the curtain flow area being less than or equal to 0.

428.

9. the back pressure is substantially less than 55% of the pressure at the inlet of the pressure relief valve, and the method comprises:

10. The method of claim 8, further comprising forming a shock wave within the pressure relief valve, and wherein increasing the velocity of the fluid flow comprises increasing the velocity of the fluid flow to supersonic speed.

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

11. The method of claim 8 further comprising maintaining alignment of the plunger with a guide surrounding the plunger.

12. The method of claim 11 , further comprising receiving the fluid flow through an opening in the guide.

13. reducing pressure within the pressurized environment in response to lifting the plunger from the valve seat; 9. The method of claim 8, further comprising: abutting the valve seat against the plunger in response to reducing the pressure.

14. 1. A pressure relief system comprising: A pressurizing system; Relief header and a pressure relief valve coupling the pressurized system to the relief header, the pressure relief valve configured to direct fluid flow from the pressurized system to the relief header when pressure in the pressurized system exceeds a designated threshold, the pressure relief valve comprising: a housing defining an inlet and an outlet, the housing defining a flow path 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 path when in a closed position, the plunger configured for actuation between a fully open position and the closed position, the plunger and the seat at least partially defining a curtain flow area; a bias that directs the plunger toward the seat; a pressure relief valve, the ratio of throat flow area to curtain flow area being sized for supersonic flow velocities during critical flow conditions and subsonic velocities during subcritical flow conditions.

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

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

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

18. 15. The pressure relief system of claim 14, wherein the ratio of the throat flow area to the curtain flow area is less than or equal to 0.

428.

19. 15. The pressure relief system of claim 14, wherein the plunger comprises a mandrel, the mandrel having a length to diameter ratio of 0.75 or greater.

20. The pressure relief system of claim 14 , wherein the bias comprises a pilot system.

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