An ultra-low pressure safety valve for air tightness test of aircraft fuel tank and its use method

Abstract

The present application belongs to the technical field of ultra-low pressure safety valves, and particularly relates to an ultra-low pressure safety valve for air tightness test of aircraft fuel tanks and a method for using the same. The ultra-low pressure safety valve for air tightness test of aircraft fuel tanks of the present application has the following working principle: when the ultra-low pressure safety valve is closed, the steel ball enters the shell annular groove of the shell, clamps the piston and the shell, and keeps the piston and the shell stationary. When the pressure of the aircraft fuel tank gradually increases, the piston rod moves downward, and the steel ball tends to move inward due to the thrust spring pushing the shell downward. When the piston rod annular groove of the piston rod enters the horizontal plane where the steel ball is located, the steel ball enters the piston rod annular groove. At this time, the piston is disengaged from the shell, the ultra-low pressure safety valve is opened, and the steel ball clamps the piston and the piston rod. When resetting, the ultra-low pressure safety valve can be returned to the closed state by directly pushing the regulating port cover and the handle. The present application adopts a ball lock structure, and the opening pressure is accurate and reliable, the sealing is good, the service life is high, and the flow rate is large after opening.

Description

Technical Field

[0001] The present application belongs to the technical field of ultra-low pressure safety valves, and in particular relates to an ultra-low pressure safety valve for air tightness testing of aircraft fuel tanks and a method of using the same. Background Art

[0002] The air tightness test of aircraft fuel tanks is generally 35KPa-40KPa, and the opening pressure of the installed safety valve cannot be greater than 45KPa. The test time is 1 hour, and the accuracy of the safety valve is very high. The commonly used safety valve is generally composed of an adjusting nut, a locking nut, a valve seat, a rubber pad, a valve core, a spring, etc. The rubber pad is fixed to the valve core by vulcanization. The commonly used safety valve uses spring force to hold the valve core to seal the valve port. This safety valve changes the clamping force on the valve core by adjusting the compression of the spring, and then adjusts the opening pressure of the safety valve. When the gas pressure is higher than the spring force, the valve core moves upward and the safety valve opens, but after opening, the flow is very small, and it is difficult to discharge the air in time to ensure that the fuel tank is not damaged by high pressure. In addition, the commonly used safety valve seal uses soft materials such as rubber pads. Since the contact between the rubber pad on the valve core and the valve seat needs to be ground to ensure air tightness, the accuracy after grinding is extremely high. Moreover, the spring force is adjusted to make the commonly used safety valve open at 43KPa. Since the test pressure is 35KPa-40KPa, the opening pressure and the test pressure are very close. It is difficult to ensure that there is no leakage at the contact between the valve core and the valve seat after repeated use.

[0003] Therefore, it is desired to have a technical solution to overcome or at least alleviate at least one of the above-mentioned defects of the prior art. Summary of the invention

[0004] The purpose of the present application is to provide an ultra-low pressure safety valve for an aircraft fuel tank air tightness test and a method of using the same, so as to solve at least one problem existing in the prior art.

[0005] The technical solution of this application is:

[0006] The first aspect of the present application provides an ultra-low pressure safety valve for an aircraft fuel tank air tightness test, comprising:

[0007] Piston assembly, comprising:

[0008] The piston is cylindrical, and the piston comprises an upper piston section and a lower piston section, wherein the radial dimension of the lower piston section is larger than the radial dimension of the upper piston section, wherein the upper piston section comprises an external thread section and a polished rod section, wherein the upper end of the external thread section is fixedly connected to the aircraft fuel tank adapter, and the upper end side wall of the lower piston section is provided with a guide groove and a square hole, and the lower end side wall of the lower piston section is provided with a plurality of circular holes along the circumferential direction, and a steel ball is installed in each of the circular holes;

[0009] A first cover, wherein the upper end of the first cover is threadedly mounted on the external thread section of the upper piston section, and an annular accommodating cavity is formed between the first cover and the upper piston section;

[0010] A thrust spring, wherein the thrust spring is arranged in the annular accommodating cavity, and an upper end of the thrust spring abuts against an upper end surface of the first cover;

[0011] a first adjusting nut, wherein the first adjusting nut is threadedly mounted on the external threaded section of the upper piston section;

[0012] A valve seat, the valve seat being sleeved on the polished rod section of the upper piston section;

[0013] A first compression spring, wherein the first compression spring is sleeved on the upper piston section, and an upper end of the first compression spring abuts against the first adjusting nut, and a lower end of the first compression spring abuts against the valve seat;

[0014] The housing assembly comprises:

[0015] The housing is cylindrical, and includes an upper housing and a lower housing. The radial dimension of the upper housing is greater than that of the lower housing. An annular boss is formed at the connection between the upper housing and the lower housing, and the annular boss abuts against the lower end of the thrust spring. The housing is sleeved on the piston, and the upper housing is clearance-matched with the first cover. A square hole is provided on the upper housing, and the lower housing is clearance-matched with the lower piston section. A threaded hole is provided on the upper end side wall of the lower housing, and a housing annular groove for matching with the steel ball is provided on the middle side wall, and an external thread is provided on the lower end side wall;

[0016] A guide member, wherein the guide member is threadedly mounted in a threaded hole of the lower housing;

[0017] A second cover, wherein the upper end of the second cover is threadedly mounted on the lower end of the lower shell, and the lower end surface of the second cover is provided with an opening;

[0018] Piston rod assembly, comprising:

[0019] The piston rod is cylindrical, and the piston rod comprises an upper piston rod section, a middle piston rod section and a lower piston rod section, wherein the upper piston rod section is nested in the piston and has a clearance fit with the lower piston section, a closed surface A is provided inside the piston rod, and the upper end of the closed surface A forms a cavity connected to the piston, the upper piston rod section is provided with a guide groove and a square hole, and is also provided with a piston rod annular groove for matching with the steel ball, the middle piston rod section has a clearance fit with the lower shell of the shell, and the lower piston rod section is provided with an external thread;

[0020] A sealing ring, wherein the sealing ring is sleeved on the upper end of the lower piston rod section, the inner side of the sealing ring abuts against the outer wall surface of the lower piston rod section, and the outer side abuts against the inner wall surface of the lower shell body;

[0021] a second adjusting nut, wherein the second adjusting nut is threadedly mounted on the lower piston rod section;

[0022] A second compression spring, wherein the second compression spring is sleeved on the lower piston rod section, and the upper end of the second compression spring abuts against the sealing ring, and the lower end of the second compression spring abuts against the second adjusting nut;

[0023] A calibration spring, wherein the calibration spring is sleeved on the lower piston rod section, and the upper end of the calibration spring abuts against the second adjusting nut, and the lower end of the calibration spring abuts against the lower end surface of the second cover;

[0024] A handle is provided, wherein the handle passes through the opening on the lower end surface of the second cover and cooperates with the adapter to be connected with the lower end of the lower piston rod section.

[0025] Optionally, surfaces of the piston, the housing and the piston rod are all nickel-plated.

[0026] Optionally, the first port cover is mounted on the external threaded section of the upper piston section in cooperation with a first locking nut, and a first lead seal is provided between the first locking nut and the first port cover.

[0027] Optionally,

[0028] A first valve seat annular groove is provided on the inner wall surface of the valve seat, and a first O-ring is provided in the first valve seat annular groove;

[0029] A second valve seat annular groove is formed on the lower end surface of the valve seat, and a rubber pad is arranged in the second valve seat annular groove.

[0030] Optionally,

[0031] Both ends of the first compression spring are provided with first washers;

[0032] Second washers are provided at both ends of the second compression spring.

[0033] Optionally, the guide member is installed in a threaded hole of the lower shell in cooperation with a sealing gasket.

[0034] Optionally, the second cover is mounted on the lower shell in cooperation with a second locking nut, and a second lead seal is provided between the second locking nut and the guide member.

[0035] Optionally, both the upper end surface and the lower end surface of the sealing ring are provided with sealing ring annular grooves, and a second O-ring is installed in both of the sealing ring annular grooves.

[0036] Optionally, the process of determining whether the calibration spring meets the use requirements includes:

[0037] The gas in the aircraft fuel tank enters the ultra-low pressure safety valve through the piston. The thrust F generated by the gas on the closed surface A is calculated as:

[0038] ;

[0039] Wherein, P is the pressure when the ultra-low pressure safety valve opens, and S is the area of ​​the closed surface A;

[0040] Calculate the calibration spring winding ratio C as:

[0041] ;

[0042] Calculate the calibration spring stress correction factor K as:

[0043] ;

[0044] Calculate the maximum permissible load P of the calibration spring as:

[0045] ;

[0046] Where D0 is the spring median diameter, d is the spring wire diameter, and t2 is the working stress of the spring material;

[0047] When the maximum allowable load P of the calibration spring is greater than the thrust F, it is determined that the calibration spring meets the use requirements.

[0048] A second aspect of the present application provides a method for using an ultra-low pressure safety valve for an aircraft fuel tank air tightness test, based on the ultra-low pressure safety valve for an aircraft fuel tank air tightness test as described above, comprising:

[0049] Step 1: Check whether the working performance of the ultra-low pressure safety valve is normal, including:

[0050] The upper end of the piston is fixedly connected to the connecting pipe of the airtight test bench, and the pressure of the airtight test bench is gradually increased from 0KPa until the ultra-low pressure safety valve opens;

[0051] If the pressure when the ultra-low pressure safety valve opens is lower than the preset pressure value, rotate the second cover clockwise to increase the pressure when the ultra-low pressure safety valve opens;

[0052] If the pressure when the ultra-low pressure safety valve is opened is greater than the preset pressure value, rotate the second cover counterclockwise to reduce the pressure when the ultra-low pressure safety valve is opened;

[0053] Until the pressure when the ultra-low pressure safety valve opens is equal to the preset pressure value;

[0054] Step 2: When the working performance of the ultra-low pressure safety valve is normal, install the second lead seal and put on the insurance;

[0055] Step 3: Use the ultra-low pressure safety valve on the machine, including:

[0056] The upper end of the piston is fixedly connected to the aircraft fuel tank adapter, and the inflation nozzle on the aircraft fuel tank is connected to the inflation device to pressurize the aircraft fuel tank;

[0057] When the aircraft fuel tank pressure reaches the preset pressure value, the ultra-low pressure safety valve opens to release the gas in the aircraft fuel tank;

[0058] When resetting, push the second cover and the handle upward to return the ultra-low pressure safety valve to the closed state.

[0059] The invention has at least the following beneficial technical effects:

[0060] The ultra-low pressure safety valve for the air tightness test of the aircraft fuel tank of the present application adopts a ball lock structure, has accurate and reliable opening pressure, good sealing, long service life, large flow after opening, meets the requirements of salt spray test and mold test, and can be used between minus 50 degrees and plus 60 degrees. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a schematic diagram of an ultra-low pressure safety valve for an aircraft fuel tank air tightness test in a closed state according to an embodiment of the present application;

[0062] Figure 2 It is a schematic diagram of an ultra-low pressure safety valve for an aircraft fuel tank air tightness test in an open state according to an embodiment of the present application;

[0063] Figure 3 is a schematic diagram of a piston according to one embodiment of the present application;

[0064] Figure 4 is a schematic diagram of a first cover of an embodiment of the present application;

[0065] Figure 5 is a schematic diagram of a valve seat according to an embodiment of the present application;

[0066] Figure 6 is a schematic diagram of a housing according to an embodiment of the present application;

[0067] Figure 7 is a schematic diagram of a guide member according to an embodiment of the present application;

[0068] Figure 8 is a schematic diagram of a second cover of an embodiment of the present application;

[0069] Fig. 9 is a schematic diagram of a piston rod according to an embodiment of the present application;

[0070] Fig.10 It is a schematic diagram of a sealing ring according to an embodiment of the present application. DETAILED DESCRIPTION

[0071] In order to make the purpose, technical scheme and advantages of the implementation of this application clearer, the technical scheme in the embodiment of this application will be described in more detail below in conjunction with the drawings in the embodiment of this application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of this application, not all of them. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain this application, and should not be construed as limitations on this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The embodiments of this application are described in detail below in conjunction with the drawings.

[0072] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the scope of protection of the present application.

[0073] The following is combined with Figures 1 to 10 This application is described in further detail.

[0074] A first aspect of the present application provides an ultra-low pressure safety valve for an aircraft fuel tank air tightness test, comprising: a piston assembly, a housing assembly, and a piston rod assembly.

[0075] Specifically, the piston assembly includes: a piston 1, a thrust spring 4, a first cover 5, a first compression spring 7, a valve seat 8, a steel ball 14, an adjusting nut 25, etc.

[0076] like Figure 3As shown, the piston 1 is a cylindrical steel part with a nickel-plated surface. The piston 1 includes an upper piston section and a lower piston section. The radial dimension of the lower piston section is larger than the radial dimension of the upper piston section. In this embodiment, the inner cavity of the upper piston section is a cylindrical cavity with a diameter of Φ33mm; the outer wall surface of the lower piston section is a cylindrical surface with a diameter of Φ50mm and a tolerance of f8; the inner cavity of the lower piston section is a cylindrical surface with a diameter of Φ44.6mm and a tolerance of H9. The upper piston section includes an external thread section and a polished rod section. The outer wall of the external thread section is provided with an external thread M39×1.5. The upper end of the external thread section is connected with the internal thread of the aircraft fuel tank adapter through the external thread to perform an airtight test. The upper side wall of the lower piston section is provided with a guide groove and a square hole. In this embodiment, a guide groove with a width of 3.5mm is provided on the left side wall at 8.5mm to 38mm from the lower end of the lower piston section. A plurality of square holes evenly distributed along the circumferential direction are provided on the side wall at 8.5mm to 38mm from the lower end of the lower piston section, which are used to release gas when the ultra-low pressure safety valve is opened. The lower side wall of the lower piston section is provided with a plurality of circular holes along the circumferential direction, and a steel ball 14 is installed in each circular hole. In this embodiment, four Φ3mm circular holes for installing the steel ball 14 are provided on the side wall of the lower piston section at a distribution of 90°. The number of the steel balls 14 is 4 and the diameter is 3mm.

[0077] like Figure 4 As shown, the upper end surface of the first cover 5 is provided with a threaded hole, which is installed on the external thread section of the upper piston section through a thread. The first cover 5 is a cylindrical structure, and an annular accommodating chamber is formed between the first cover 5 and the upper piston section. In the preferred embodiment of the present application, the first locking nut 2 is installed on the external thread section of the upper piston section and is located above the first cover 5, and the position of the first cover 5 is locked by double threads. Advantageously, in this embodiment, a first lead seal 3 is provided between the first locking nut 2 and the first cover 5, and the first lead seal 3 locks the first cover 5 and the first locking nut 2 through the safety holes on the first cover 5 and the first locking nut 2, which plays a safety role.

[0078] The thrust spring 4 is arranged in the annular accommodation cavity, and the upper end abuts against the upper end surface of the first cover 5, and the lower end abuts against the annular boss of the housing 11. One end of the thrust spring 4 elastically acts on the first cover 5, and the other end elastically acts on the housing 11, which can exert a downward thrust on the housing 11, and is used to provide thrust when the ultra-low pressure safety valve is opened. In addition, the elastic force of the thrust spring 4 is adjusted by rotating the first cover 5.

[0079] The first adjusting nut 25 is threadedly mounted on the external threaded section of the upper piston section. The valve seat 8 is an annular structural steel part. The valve seat 8 is sleeved on the smooth rod section of the upper piston section. The first clamping spring 7 is sleeved on the upper piston section, and the upper end abuts against the first adjusting nut 25, and the lower end abuts against the valve seat 8. The valve seat 8 moves downward under the elastic force of the first clamping spring 7. The elastic force of the first clamping spring 7 can be adjusted by rotating the first adjusting nut 25. The force should be adjusted to not affect the opening and closing of the debugging ultra-low pressure safety valve. At the same time, when the ultra-low pressure safety valve is in the closed state, the contact between the lower end face of the valve seat 8 and the annular protrusion of the shell 11 is ensured to be sealed. In a preferred embodiment of the present application, Figure 5 As shown, a first valve seat annular groove is provided on the inner wall surface of the valve seat 8, and a first O-ring 9 is provided in the first valve seat annular groove to ensure the sealing of the contact between the valve seat 8 and the outer wall surface of the piston 1; a second valve seat annular groove is provided on the lower end surface of the valve seat 8, and a rubber pad 10 is provided in the second valve seat annular groove to contact the annular protrusion of the housing 11. In this embodiment, first washers 6 are provided at both ends of the first compression spring 7, and the first compression spring 7 cooperates with the first washers 6 to contact and connect with the first adjusting nut 25 and the valve seat 8 respectively.

[0080] The housing assembly includes: a housing 11, a guide member 12, a second cover 21, etc.

[0081] like Figure 6 As shown, the housing 11 is a cylindrical steel part, and the surface is nickel-plated. The housing 11 includes an upper housing and a lower housing. The radial dimension of the upper housing is larger than the radial dimension of the lower housing. An annular boss is formed at the connection between the upper housing and the lower housing, and the annular boss abuts against the lower end of the thrust spring 4, so that the thrust generated by the thrust spring 4 can act on the housing 11. The housing 11 is sleeved on the piston 1, and the upper housing is clearance-matched with the first cover 5. The upper housing is provided with square holes evenly distributed along the circumference. The inner cavity of the lower housing is a cylindrical cavity with a diameter of Φ50mm and a tolerance of H9. The lower housing and the lower piston section form a clearance fit according to the tolerance of H9 / f8. A threaded hole is provided in the horizontal direction on the left side of the upper end side wall 12mm away from the upper end for installing the guide member 12. The middle side wall of the lower housing is provided with a housing annular groove for matching with the steel ball 14, and the lower side wall is provided with an external thread M56×1.5.

[0082] like Figure 7 As shown, the guide member 12 is in the form of a bolt, which is threadedly installed in the threaded hole of the lower housing. The head of the guide member 12 passes through the guide grooves of the piston 1 and the piston rod 15 in sequence. Since the piston 1 is connected to the aircraft fuel tank adapter and is in a static state, the guide member 12 guides and restricts the housing assembly and the piston rod assembly during the opening and closing process of the ultra-low pressure safety valve. Advantageously, the sealing gasket 13 is installed at the contact point between the guide member 12 and the left end surface of the housing 11 to ensure sealing.

[0083] like Figure 8 As shown, the upper end of the second cover 21 has a threaded hole M56×1.5, which is threadedly mounted on the lower end of the lower shell, and a Φ13mm opening is provided on the lower end surface of the second cover 21. In a preferred embodiment of the present application, the second locking nut 17 is mounted on the lower shell and is located above the second cover 21, which has a locking effect on the second cover 21. The second lead seal 16 is installed through the second locking nut 17 and the safety hole on the guide member 12, and the second lead seal 16 plays a safety role.

[0084] Furthermore, the piston rod assembly includes: a piston rod 15, a sealing ring 19, a second adjusting nut 27, a second compression spring 20, a calibration spring 23, a handle 24 and the like.

[0085] like Fig. 9 As shown, the piston rod 15 is a cylindrical steel part with a nickel-plated surface. The piston rod 15 includes an upper piston rod section, a middle piston rod section and a lower piston rod section. Among them, the outer diameter of the upper piston rod section is Φ44.6mm, the tolerance is f8, the upper piston rod section is nested in the piston 1, and the clearance with the lower piston section is H9 / f8. The interior of the piston rod 15 is provided with a closed surface A, and the upper end of the closed surface A forms a cavity connected to the piston 1, and the gas entering from the piston 1 can generate pressure on the closed surface A. The upper piston rod section is provided with a guide groove and a square hole, and is also provided with a piston rod annular groove for matching with the steel ball 14. In this embodiment, a guide groove with a width of 3.5 mm is provided on the left wall surface at 1.5 mm to 29 mm from the upper end of the upper piston rod section; square holes evenly distributed along the circumferential direction are provided on the side wall surface at 1.5 mm to 29 mm from the upper end of the upper piston rod section, which are used to release gas when the ultra-low pressure safety valve is opened; a piston rod annular groove is provided on the outer wall surface at 35 mm from the upper end of the upper piston rod section, which is used to clamp the steel ball 14. The outer diameter of the middle piston rod section is Φ50m, with a tolerance of f8, and forms a H9 / f8 clearance fit with the lower shell of the shell 11. The lower piston rod section is provided with an external thread M39×1.5 for assembling the second adjusting nut 27, and is also provided with an internal thread M33×2 for assembling the adapter 22.

[0086] like Fig.10 As shown, the sealing ring 19 is made of fluoroplastic and is an annular member. The sealing ring 19 is sleeved on the upper end of the lower piston rod section, and its inner side abuts against the outer wall of the lower piston rod section, and its outer side abuts against the inner wall of the lower shell. Advantageously, in this embodiment, the upper end face and the lower end face of the sealing ring 19 are both provided with sealing ring annular grooves, and the second O-ring 18 is installed in both sealing ring annular grooves.

[0087] The second adjusting nut 27 is threadedly mounted on the lower piston rod section; the second compression spring 20 is sleeved on the lower piston rod section, and the upper end abuts against the sealing ring 19, and the lower end abuts against the second adjusting nut 27. Preferably, a second washer 26 is provided at both ends of the second compression spring 20. The second compression spring 20 elastically acts on the second O-ring 18 installed on the lower end surface of the sealing ring 19 at one end through the second washer 26, and elastically acts on the second adjusting nut 27 threadedly mounted on the lower end of the piston rod 15 at the other end.

[0088] It is understood that by rotating the second adjusting nut 27, the compression amount of the second compression spring 20 is adjusted, thereby compressing the second O-ring 18, so that the inner side of the sealing ring 19 is closely attached to the outer wall surface of the piston rod 15, and the outer side is closely attached to the inner wall surface of the housing 11, thereby ensuring the sealing of the contact point. In order to ensure the sliding property, grease is applied to the outer side of the sealing ring 19.

[0089] The calibration spring 23 is sleeved on the lower piston rod section and is located inside the second cover 21. The upper end of the calibration spring 23 abuts against the second adjustment nut 27, and the lower end abuts against the lower end surface of the second cover 21. The calibration spring 23 has an upward thrust on the piston rod 15. By rotating the second cover 21, the compression amount of the calibration spring 23 can be controlled, thereby controlling the pressure when the ultra-low pressure safety valve is opened.

[0090] The upper end of the adapter 22 is threadedly mounted on the internal thread of the lower end of the lower piston rod. The handle 24 passes through the opening on the lower end surface of the second cover 21 and is threadedly connected with the lower end of the adapter 22.

[0091] The ultra-low pressure safety valve for the aircraft fuel tank air tightness test of the present application, the calibration spring 23 needs to meet certain use requirements when designing, and the process of judging whether the calibration spring 23 meets the use requirements includes:

[0092] The gas in the aircraft fuel tank enters the ultra-low pressure safety valve through piston 1. The thrust F generated by the gas on the closed surface A is calculated as:

[0093] ;

[0094] Wherein, P is the pressure when the ultra-low pressure safety valve opens, and S is the area of ​​the closed surface A;

[0095] The winding ratio C of the calibration spring 23 is calculated as:

[0096] ;

[0097] Calculate the stress correction coefficient K of the calibration spring 23 as:

[0098] ;

[0099] The maximum permissible load P of the calibration spring 23 is calculated as:

[0100] ;

[0101] Where D0 is the spring median diameter, d is the spring wire diameter, and t2 is the working stress of the spring material;

[0102] When the maximum allowable load P of the calibration spring 23 is greater than the thrust F, it is determined that the calibration spring 23 meets the use requirements.

[0103] In one embodiment of the present application, it is assumed that the pressure when the ultra-low pressure safety valve is opened is 43 KPa.

[0104] Then the gas in the aircraft fuel tank enters the ultra-low pressure safety valve through piston 1, and the thrust F generated by the gas on the closed surface A is calculated as:

[0105] ;

[0106] The calibration spring 23 is designed by selecting a spring pitch of t=14 mm, a height of h=50 mm, a spring wire diameter of d=3 mm, and a spring material of 50CrVA with a working stress of t2=607 MPa;

[0107] Then the winding ratio C of the calibration spring 23 is:

[0108] ;

[0109] The stress correction coefficient K of the calibration spring 23 is:

[0110] ;

[0111] The maximum permissible load P of the calibration spring 23 is:

[0112] ;

[0113] Since the maximum allowable load is greater than the thrust of the gas, the calibration spring 23 meets the use requirements.

[0114] The ultra-low pressure safety valve for the air tightness test of the aircraft fuel tank of the present application is connected to the aircraft fuel tank adapter through the piston 1, and the housing 11, the piston 1, and the piston rod 15 are connected together through the guide 12. At the same time, the piston 1, the housing 11, and the piston rod 15 are all in contact with each other with clearance fit to ensure that the ultra-low pressure safety valve can slide freely during the opening and closing process. The first O-ring 9, the rubber pad 10, the sealing pad 13, the second O-ring 18 and the sealing ring 19 on the valve seat 8 ensure the sealing of the ultra-low pressure safety valve in the closed state. The opening and closing of the ultra-low pressure safety valve are completed by moving and locking the steel ball 14. There are 4 steel balls in total, which are distributed at 90 degrees to ensure uniform force during sliding.

[0115] The ultra-low pressure safety valve for the air tightness test of the aircraft fuel tank of the present application has the following working principle: when the ultra-low pressure safety valve is closed, the steel ball 14 enters the shell annular groove of the shell 11, clamps the piston 1 and the shell 11, and keeps the piston 1 and the shell 11 stationary. When the pressure of the aircraft fuel tank gradually increases, the piston rod 15 moves downward, and the thrust spring 4 pushes the shell 11 downward, so that the steel ball 14 has a tendency to move inward. When the piston rod annular groove of the piston rod 15 enters the horizontal plane where the steel ball 14 is located, the steel ball 14 enters the piston rod annular groove. At this time, the piston 1 is disengaged from the shell 11, the ultra-low pressure safety valve is opened, and the steel ball 14 clamps the piston 1 and the piston rod 15. When resetting, the ultra-low pressure safety valve can be returned to the closed state by directly pushing the second cover 21 and the handle 24.

[0116] The second aspect of the present application provides a method for using an ultra-low pressure safety valve for an aircraft fuel tank air tightness test, comprising:

[0117] Step 1: Check whether the working performance of the ultra-low pressure safety valve is normal, including:

[0118] The upper end of the piston 1 is fixedly connected to the connecting pipe of the airtight test bench, and the pressure of the airtight test bench is gradually increased from 0 KPa until the ultra-low pressure safety valve opens;

[0119] If the pressure when the ultra-low pressure safety valve is opened is lower than the preset pressure value, the second cover 21 is rotated clockwise to increase the pressure when the ultra-low pressure safety valve is opened;

[0120] If the pressure when the ultra-low pressure safety valve is opened is greater than the preset pressure value, the second cover 21 is rotated counterclockwise to reduce the pressure when the ultra-low pressure safety valve is opened;

[0121] Until the pressure when the ultra-low pressure safety valve opens is equal to the preset pressure value;

[0122] Step 2: When the working performance of the ultra-low pressure safety valve is normal, install the second lead seal 16 and put on insurance;

[0123] Step 3: Use the ultra-low pressure safety valve on the machine, including:

[0124] The upper end of the piston 1 is fixedly connected to the aircraft fuel tank adapter, and the inflation nozzle on the aircraft fuel tank is connected to the inflation device to pressurize the aircraft fuel tank;

[0125] When the aircraft fuel tank pressure reaches the preset pressure value, the ultra-low pressure safety valve opens to release the gas in the aircraft fuel tank;

[0126] When resetting, the second cover 21 and the handle 24 are pushed upwards to return the ultra-low pressure safety valve to the closed state.

[0127] The method for using the ultra-low pressure safety valve for the air tightness test of the aircraft fuel tank of the present application adjusts the second cover 21 so that the pressure when the ultra-low pressure safety valve is opened is equal to the preset pressure value, such as 43KPa. When using the ultra-low pressure safety valve, when the pressure of the aircraft fuel tank is less than 43KPa, the ultra-low pressure safety valve is closed, and when the pressure of the aircraft fuel tank is greater than 43KPa, the ultra-low pressure safety valve is opened to release the gas in the aircraft fuel tank, protect the aircraft fuel tank from being damaged by high pressure, and the ultra-low pressure safety valve works normally.

[0128] The ultra-low pressure safety valve for the air tightness test of aircraft fuel tanks and the method of use of the same solve the problem of the air tightness test of aircraft fuel tanks. The opening pressure of the ultra-low pressure safety valve is accurate and reliable, the sealing is good, the service life is long, the flow rate is large after opening, and the requirements of salt spray test and mold test are met. It can be used between -50 degrees and +60 degrees to protect the aircraft fuel tank from being damaged by high pressure. The present application can also be applied to the air tightness test of other air low-pressure containers.

[0129] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. An ultra-low pressure safety valve for air tightness test of aircraft fuel tank, characterized in that: include: Piston assembly, comprising: The piston (1) is cylindrical, the piston (1) comprising an upper piston section and a lower piston section, the radial dimension of the lower piston section being larger than the radial dimension of the upper piston section, wherein the upper piston section comprises an external thread section and a bare rod section, the upper end of the external thread section being fixedly connected to the aircraft fuel tank adapter, the upper end side wall of the lower piston section being provided with a guide groove and a square hole, the lower end side wall of the lower piston section being provided with a plurality of circular holes along the circumferential direction, each of the circular holes being provided with a steel ball (14); A first port cover (5), the upper end of the first port cover (5) being threadedly mounted on the external thread section of the upper piston section, and an annular accommodating cavity being formed between the first port cover (5) and the upper piston section; a thrust spring (4), the thrust spring (4) being arranged in the annular accommodating cavity, and the upper end of the thrust spring being in contact with the upper end surface of the first cover (5); a first adjusting nut (25), the first adjusting nut (25) being threadedly mounted on the external threaded section of the upper piston section; A valve seat (8), the valve seat (8) being sleeved on the polished rod section of the upper piston section; a first compression spring (7), the first compression spring (7) being sleeved on the upper piston section, with an upper end abutting against the first adjusting nut (25) and a lower end abutting against the valve seat (8); The housing assembly comprises: The housing (11) is cylindrical, and comprises an upper housing and a lower housing. The radial dimension of the upper housing is greater than the radial dimension of the lower housing. An annular boss is formed at the connection between the upper housing and the lower housing, and the annular boss abuts against the lower end of the thrust spring (4). The housing (11) is sleeved on the piston (1). The upper housing is clearance-matched with the first cover (5). A square hole is provided on the upper housing, and the lower housing is clearance-matched with the lower piston section. A threaded hole is provided on the upper side wall of the lower housing, and a housing annular groove for matching with the steel ball (14) is provided on the middle side wall. An external thread is provided on the lower side wall. A guide member (12), the guide member (12) being threadedly mounted in a threaded hole of the lower shell; a second cover (21), the upper end of the second cover (21) being threadedly mounted on the lower end of the lower shell, and the lower end surface of the second cover (21) being provided with an opening; Piston rod assembly, comprising: The piston rod (15) is cylindrical in shape, and comprises an upper piston rod section, a middle piston rod section and a lower piston rod section, wherein the upper piston rod section is nested in the piston (1) and is loosely matched with the lower piston section, a closed surface A is provided inside the piston rod (15), and the upper end of the closed surface A forms a cavity connected to the piston (1), the upper piston rod section is provided with a guide groove and a square hole, and is also provided with a piston rod annular groove for matching with the steel ball (14), the middle piston rod section is loosely matched with the lower shell of the shell (11), and the lower piston rod section is provided with an external thread; A sealing ring (19), the sealing ring (19) being sleeved on the upper end of the lower piston rod section, the inner side of the sealing ring (19) abutting against the outer wall surface of the lower piston rod section, and the outer side abutting against the inner wall surface of the lower shell body; a second adjusting nut (27), the second adjusting nut (27) being threadedly mounted on the lower piston rod section; a second compression spring (20), the second compression spring (20) being sleeved on the lower piston rod section, with an upper end abutting against the sealing ring (19) and a lower end abutting against the second adjusting nut (27); a calibration spring (23), the calibration spring (23) being sleeved on the lower piston rod section, with an upper end abutting against the second adjustment nut (27) and a lower end abutting against a lower end surface of the second cover (21); A handle (24), the handle (24) passing through the opening on the lower end surface of the second cover (21) and fitting into the adapter (22) to be connected to the lower end of the lower piston rod section.

2. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 1, characterized in that: The surfaces of the piston (1), the housing (11) and the piston rod (15) are all nickel-plated.

3. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 2, characterized in that: The first cover (5) is mounted on the external threaded section of the upper piston section in cooperation with the first locking nut (2); a first lead seal (3) is provided between the first locking nut (2) and the first cover (5).

4. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 3, characterized in that: A first valve seat annular groove is formed on the inner wall surface of the valve seat (8), and a first O-ring (9) is arranged in the first valve seat annular groove; A second valve seat annular groove is provided on the lower end surface of the valve seat (8), and a rubber pad (10) is provided in the second valve seat annular groove.

5. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 4, characterized in that: Both ends of the first compression spring (7) are provided with first washers (6); Second washers (26) are provided at both ends of the second compression spring (20).

6. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 5, characterized in that: The guide member (12) is installed in cooperation with the sealing gasket (13) in the threaded hole of the lower shell.

7. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 6, characterized in that: The second opening cover (21) is mounted on the lower shell in cooperation with a second locking nut (17); a second lead seal (16) is provided between the second locking nut (17) and the guide member (12).

8. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 7, characterized in that: The upper end surface and the lower end surface of the sealing ring (19) are both provided with sealing ring annular grooves, and a second O-ring (18) is installed in both of the sealing ring annular grooves.

9. The ultra-low pressure safety valve for the air tightness test of an aircraft fuel tank according to claim 8, characterized in that: The process of judging whether the calibration spring (23) meets the use requirements comprises: The gas in the aircraft fuel tank enters the ultra-low pressure safety valve through piston (1). The thrust F generated by the gas on the closed surface A is calculated as: ； Wherein, P is the pressure when the ultra-low pressure safety valve opens, and S is the area of ​​the closed surface A; The winding ratio C of the calibration spring (23) is calculated as: ； Calculate the stress correction factor K of the calibration spring (23) as: ； Calculate the maximum permissible load P of the calibration spring (23) as: ； Where D0 is the spring median diameter, d is the spring wire diameter, and t2 is the working stress of the spring material; When the maximum allowable load P of the calibration spring (23) is greater than the thrust F, it is determined that the calibration spring (23) meets the use requirements.

10. A method for using an ultra-low pressure safety valve for an aircraft fuel tank air tightness test, based on the ultra-low pressure safety valve for an aircraft fuel tank air tightness test according to claim 9, characterized in that: include: Step 1: Check whether the working performance of the ultra-low pressure safety valve is normal, including: The upper end of the piston (1) is fixedly connected to the connecting pipe of the airtight test bench, and the pressure of the airtight test bench is gradually increased from 0 KPa until the ultra-low pressure safety valve opens; If the pressure when the ultra-low pressure safety valve is opened is lower than the preset pressure value, the second cover (21) is rotated clockwise to increase the pressure when the ultra-low pressure safety valve is opened; If the pressure when the ultra-low pressure safety valve is opened is greater than the preset pressure value, the second cover (21) is rotated counterclockwise to reduce the pressure when the ultra-low pressure safety valve is opened; Until the pressure when the ultra-low pressure safety valve opens is equal to the preset pressure value; Step 2: When the ultra-low pressure safety valve is operating normally, install the second lead seal (16) and activate the safety valve; Step 3: Use the ultra-low pressure safety valve on the machine, including: The upper end of the piston (1) is fixedly connected to the aircraft fuel tank adapter, and the inflation nozzle on the aircraft fuel tank is connected to the inflation device to pressurize the aircraft fuel tank; When the aircraft fuel tank pressure reaches the preset pressure value, the ultra-low pressure safety valve opens to release the gas in the aircraft fuel tank; When resetting, the second cover (21) and the handle (24) are pushed upwards, so that the ultra-low pressure safety valve returns to the closed state.

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