Emergency pressure relief valve with enhanced reset

[0001] 1. Field of the Invention

[0002] This invention relates in general to valves and in particular to an improved pressure relief valve that relieves a pressure of a system fluid by entering an open position and then by returning to the normally-closed position following a delay period.

[0003] 2. Description of Related Art

[0004] In a fluid transport system having a system fluid with a pressure that varies, it is often desirable to relieve or lower the pressure of the system fluid if the pressure reaches an unacceptably high level. The most common way of relieving these high pressures is by use of a pressure relief valve. The pressure relief valve, which is in fluid communication with the system fluid, is designed to detect an unacceptable pressure level and relieve the pressure by opening the valve and allowing the system fluid to escape the system line.

[0005] A problem sometimes develops in the use of these valves in systems that experience rapidly varying pressures. For example, in certain oil and gas well treatments, high pressure liquid is pumped down the well to fracture the earth formation. Large high pressure reciprocating pumps at the surface pump the liquid through flow lines leading into the well. In these systems, the pressure in the system lines can become cyclical, with the pressure of the system fluid exceeding and dropping below an acceptable level.

[0006] A typical pressure relief valve for use in one of these systems includes a housing having an inlet port and an outlet port. The inlet port is connected to the system line. A valve member is located within the housing that is capable of moving between an open position and a closed position. In the open position, fluid communication is allowed between the inlet port and the outlet port. In the closed position, the valve member sealingly engages a portion of the housing, thereby preventing fluid communication between the inlet port and the outlet port. The valve member is biased such that it remains in the closed position when the pressure of the system fluid is at an acceptable level. As the pressure rises above an acceptable level, the valve member moves to the open position, thereby relieving the pressure by allowing the fluid to flow out of the outlet port of the valve.

[0007] A standard pressure relief valve includes a spring which provides a force to bias the valve member into the closed position. The size and type of spring is chosen based on the desired acceptable level of pressure of the system fluid. As the pressure of the system fluid rises above the acceptable level, the force exerted on the valve member by the fluid exceeds the force exerted by the spring, causing the valve member to move to an open position. As soon as the pressure of the system fluid returns to an acceptable level, the force exerted by the fluid becomes less than that exerted by the spring, and the valve member immediately returns to the closed position.

[0008] The spring may be mechanical or it may be a compressed gas chamber. A gas cushion spring includes a piston that is connected to one end of the valve member. The piston is disposed within a pressure chamber in the housing, and the piston and the valve member are adapted to move together from the open position to the closed position. A bias or control fluid, which is usually nitrogen gas, is introduced into the pressure chamber above the piston. The pressure of the control fluid exerts a biasing force on the piston, which pushes the piston and the valve member into the closed position. The valve member and piston move to the open position when the force exerted on the valve member by the system fluid exceeds the force exerted on the piston by the control fluid.

[0009] Both the mechanical spring and gas spring valves described above provide adequate ventilation of the system fluid when it reaches an unacceptably high pressure. However, both of these valves return immediately to the closed position when the pressure of the system fluid returns to an acceptable level. This method of operation is undesirable when the pressure of the system fluid varies rapidly. A rapid variation of the system fluid pressure causes these standard valves to “chatter,” as they rapidly open and close. The rapid movement of the valve member within the housing causes excessive valve wear and excessive heat to be generated, both of which are undesirable features.

[0010] One solution to the “chatter” problem is currently employed in some pressure relief valves. These valves incorporate a manual reset feature that requires an operator to reset the valve once the valve has moved to an open position. Valves of this type typically use a valve member which is biased into the closed position by a mechanical spring. As the pressure of the system fluid rises to an unacceptable level, the valve member moves to an open position. Once it reaches the open position, the valve member is locked until an operator manually resets the valve, allowing the valve member to return the closed position. The problem with this type of valve is that it requires extensive operator monitoring and involvement when the pressure of the system fluid varies rapidly. Additionally, because the valve will not return to a closed position until manually reset, once the valve is opened the system fluid will be expelled from the valve even if the pressure returns to an acceptable level.

[0011] U.S. Pat. No. 6,209,561 solved the chatter problem by introducing a pressurized fluid, or delay fluid, beneath the piston to slow the return of the piston and valve member to the closed position. A one-way check valve extends through the piston from the lower portion to the upper portion of the pressure chamber. While returning to the closed position, the fluid in the lower chamber would flow through to the check valve to the upper chamber. While solving the “chatter” problem due to quick returns to the closed position, sometimes pressurized gas would remain in the lower portion of the pressure chamber and prevent the piston and check valve from fully returning to the closed position.

[0012] The pressure relief valve according to the present invention solves the problems associated with the prior art. The pressure relief valve of the present invention includes a piston that is connected to one end of the valve member. The piston is disposed within a pressure chamber in the housing, the piston defining an upper chamber and a lower chamber within the pressure chamber. The piston and the valve member are adapted to move together from the open position to the closed position. Like the gas spring valve described above, the valve according to the present invention uses a control fluid such as nitrogen gas, which is introduced into the upper chamber. The pressure of the control fluid exerts a biasing force on the piston, which pushes the piston and the valve member into the closed position. The valve member and piston move to the open position when the force exerted on the valve member by the system fluid exceeds the force exerted on the piston by the control fluid.

[0013] The pressure relief valve according to the present invention uses a delay fluid to delay a return of the valve member from the open position to the closed position. As the valve is exposed to a system fluid with an unacceptably high pressure, the valve moves from the closed position to the open position. Between the closed and open positions is an intermediate position, at which point a control fluid is introduced into the chamber beneath the piston. A fluid injector stab injects pressurized fluid into the portion of the chamber beneath the piston after the valve moves from the closed position to the open position. The pressure of the control fluid beneath the piston provides a delay force to the piston which is opposite in direction to the biasing force provided by the control fluid above the piston. As the pressure of the system fluid returns to an acceptable level, the fluid beneath the piston acts against the piston to delay the return of the piston to the closed position.

[0014] As the piston and valve member initially return to the closed position, the fluid flows from the portion of the chamber below the piston. Preferably, the fluid beneath the piston travels from below the piston into the chamber above the piston by way of a check valve carried by the piston. As the piston and valve member continue to return to the closed position, the fluid below the piston is exposed to a port that allows the fluid to vent from the area below the piston. Venting the fluid helps the piston and valve member fully return or land in a valve seat of the pressure relief valve.

[0019] Referring to FIG. 1–4 in the drawings, the preferred embodiment of a pressure relief valve 11 according to the present invention is illustrated. Valve 11 includes a housing 13 having a wall and a relief passage with an inlet 15 and an outlet 17. Inlet 15 is situated such that its longitudinal axis intersects and forms a right angle to the longitudinal axis of outlet 17. A system line 19 is fluidly connected to inlet 15, system line 19 carrying a system fluid 21 which is introduced to valve 11 through inlet 15. A valve seat 23 is disposed within housing 13 between inlet 15 and outlet 17.

[0020] A valve member 25 having an upper end and a lower end is slidingly disposed within housing 13 so that the longitudinal axis of valve member 25 is coaxial to the axis of inlet 15. Valve member 25 passes through a partition 27. A seal 29 provides a sealing engagement between partition 27 and valve member 25. Toward its upper end, valve member 25 is engaged by a guide 31 which is disposed within a counterbore 33. Guide 31 is used to control the translational movement of valve member 25 within housing 13 so that it moves in a direction parallel to the longitudinal axis of valve member 25. A sealing area 35 is located at the lower end of valve member 25.

[0021] Valve member 25 is adapted to move within housing 13 between a closed position shown in FIG. 1 and an open position shown in FIG. 4. In the closed position, sealing area 35 fully engages valve seat 23 to block flow of system fluid 21 through the relief passage. In the open position, sealing area 35 no longer engages valve seat 23, thereby allowing flow of system fluid 21 through the relief passage.

[0022] Referring now to FIG. 2 in the drawings, the components associated with valve seat 23 and sealing area 35 are illustrated. The components of valve seat 23 work cooperatively with the components of sealing area 35 to block flow of system fluid 21 through the relief passage when valve member 25 is in the closed position. Valve seat 23 includes a seal 37 secured by an upper and a lower retainer 39. Retainers 39 sealingly engage an interior wall of housing 13 to prevent leakage of system fluid 21 when valve member 25 is in the closed position.

[0023] The primary component associated with sealing area 35 is a bushing 41 which is releasably connected to valve member 25. Bushing 41 is sealingly disposed in a circumferential depression milled in the lower end of valve member 25. Bushing 41 forms a sealing engagement with seal 37 when valve member 25 is in the closed position. The sealing engagement between seal 37 and bushing 41 provides the primary method of sealing the relief passage when valve member 25 is in the closed position.

[0024] Referring again to FIGS. 1, 3, and 4, a pressure chamber 43 is formed within housing 13, the pressure chamber being annular in shape with an inner annular surface. A pressure barrier or piston 45 is connected to the upper end of valve member 25. Piston 45 is annular in shape and has an upper, or first side and a lower, or second side. Piston 45 sealingly and slidingly engages the inner annular surface of pressure chamber 43. Piston 45 moves within chamber 43 in conjunction with valve member 25 between the open and closed positions.

[0025] Piston 45 divides pressure chamber 43 into an upper portion 47 and a lower portion 49. A delay passage 51 extends through piston 45 and carries a check valve 53. Together, delay passage 51 and check valve 53 make up a delay fluid outlet port, providing unidirectional fluid communication between lower portion 49 below piston 45 and upper portion 47 above piston 45. In the preferred embodiment, fluid communication through check valve 53 is possible only when fluid flow is from lower portion 49 to upper portion 47. Check valve 53 prevents fluid flow from upper portion 47 to lower portion 49.

[0026] Referring to FIGS. 1, 3, and 4, an axial bore 55 is formed in an upper portion of valve member 25. A fluid injector stab 57 extends through a side of pressure chamber 43 and stabs into bore 55. Fluid injector stab 57 remains stationary when piston 45 and valve member 25 move between the open and closed positions. A seal 59 located toward the end of injector stab extending into bore 55 sealingly engages the interior surface of valve member 25. Fluid injector stab 57 is preferably tubular, and is connected to a pressurized fluid source 61 through a fluid line 63. In the preferred embodiment, a lower stab port 65 is located adjacent seal 59, and extends from the interior of tubular injector stab 57 to an annulus 67 defined by bore 55 and injector stab 57. Annulus 67 extends away from seal 59 to upper portion 47 of pressure chamber 43. An upper stab port 69 located on a portion of injector stab 57 that is not received within bore 55 extends through a sidewall of injector stab 57 into upper portion 47 of pressure chamber 43. A control fluid 71, preferably nitrogen gas, communicates from fluid source 61, through fluid line 63 and the interior of injector stab 57 to ports 65, 69. When valve member 25 and piston 45 are in the closed position, as shown in FIG. 1, both ports 65, 69 transmit control fluid 71 into upper portion 47.

[0027] A valve member port 73 extends from bore 55 through a sidewall of valve member 25. In the preferred embodiment, valve member port 73 is positioned so that seal 59 sealingly engages bore 55 between valve member port 73 and lower stab port 65 when piston 45 and valve member 25 are in the closed or lower position. Valve member port 73 is in fluid communication with lower portion 49 of pressure chamber 43. Valve member port 73 moves relative to seal 59 and lower stab port 65 when piston 45 and valve member 25 are in the intermediate position (FIG. 3) or the open position (FIG. 4). In both the intermediate and open positions, lower stab port 65 is in fluid communication with valve member port 73, thereby allowing fluid source 61 to transmit control fluid 71 into lower portion 49 of pressure chamber 43. Control fluid 71 continues to communicate from fluid source 61 to upper portion 47 of pressure chamber through upper stab port 69.

[0028] A venting port 75 extends from bore 55 through a sidewall of valve member 25. Venting port 75 transmits control fluid 71 within bore 55 below seal 59 to either atmosphere or to a control fluid collection assembly (not shown). Venting port 75 does not communicate with lower portion 49 of pressure chamber when valve member port 73 is above seal 59, as shown in FIGS. 3 and 4 of the intermediate and open positions. Therefore, seal 59 helps to prevent control fluid 71 from exiting lower portion 49 of pressure chamber 43 while valve member port 73 is above seal 59. Control fluid 71 flows through check valve 53 of piston 45 and valve member 25 moves from the open position shown in FIG. 4 to the intermediate position shown in FIG. 3 while valve member port 73 is substantially at or above seal 59, thereby delaying the return of piston 45 and valve member 25 to the closed position shown in FIG. 1. Control fluid 71 vents through valve chamber port 73 and venting port 75 when valve chamber port 73 is below seal 59, thereby allowing the full return to the closed position. Control fluid 71 typically vents from lower portion 49 of pressure chamber 43 while piston 45 and valve member 25 are returning to the closed position shown in FIG. 1.

[0029] The upper side of piston 45 has a pressure area proportional to the squared value of the diameter of pressure chamber 43. The lower side of piston 45 has a pressure area proportional to the squared value of the diameter of chamber 43 minus the diameter of guide 31. The result is that the upper pressure area of piston 45 is greater than the lower pressure area. If the pressure on both upper and lower sides of piston 45 is the same, the net pressure force is downward. The significance of the difference in the pressure areas is explained below in relation to the operation of valve 11.

[0030] Referring now primarily to FIGS. 1, 3, and 4, the operation of valve 11 is illustrated. Relief passage inlet 15 is connected to system line 19 to regulate the pressure of system fluid 21. During a low pressure operation, when the pressure of system fluid 21 is below or at an acceptable level, valve member 25 remains in the closed position (see FIG. 1). During a high pressure operation, when the pressure of system fluid 21 is above the acceptable level, valve member 25 moves to the open position (see FIG. 4). In the open position, system fluid 21 is allowed to flow through the relief passage, exiting the valve through outlet 17.

[0031] In the preferred embodiment, the acceptable level of pressure of system fluid 21 is determined and set by the pressure of control fluid 71. During normal operations, when in the closed position of FIG. 1, control fluid is introduced into upper portion 47 of pressure chamber 43 through stab ports 65, 69 on injector stab 57. Control fluid flows directly into upper portion 47 from stab port 69. Control fluid communicates through annulus 67, above seal 59, from stab port 65. The presence of pressurized control fluid 71 in upper portion 47 causes a biasing force to be exerted on the upper side of piston 45. The biasing force pushes piston 45 and valve member 25 toward into the closed position (see FIG. 1). Piston 45 and valve member 25 remain in the closed position while system fluid 21 is below the maximum pressure level. When the pressure of system fluid 21 exceeds the acceptable level, the force exerted by system fluid 21 on the lower end of valve member 25 exceeds the biasing force exerted on the upper side of piston 45, thereby causing valve member 25 and piston 45 to move into the open position (see FIG. 4). Valve member 25 will stay in the open position during high pressure operation of valve 11. System fluid 21 flows through relief passage outlet 17.

[0032] As the pressure of system fluid 21 exceeds the predetermined level necessary to overcome the biasing force due to control fluid 71 in upper portion 47 of chamber 43, piston 45 and valve member 25 move through the intermediate position shown in FIG. 3 to the open position shown in FIG. 4. Stab port 65 begins injecting control fluid 71 into lower portion 49 of pressure chamber 43 after valve member port 73 moves passed seal 59. Control fluid 71 applies the same pressure on both sides of piston 45. Therefore, control fluid 71 in lower portion 49 of chamber 43 creates a force on the lower side of piston 45 that delays a quick return of piston 45 and valve member 25 to the closed position shown in FIG. 1.

[0033] As mentioned above, because the surface area of the upper side of piston 45 is larger than the surface area of the lower side of piston 45, the biasing force from control fluid 71 in upper portion 47 is larger than the delay force from control fluid in lower chamber 49 even though the pressure is the same. Therefore, piston 45 and valve member 25 begin returning to the closed position of FIG. 1 when the pressure of system fluid 21 returns to below the predetermined level. Control fluid 71 passes through check valve 53 from lower portion 49 to upper portion 47 of pressure chamber 43 while valve member port 73 is on the same side of seal 59 as stab port 65. After valve member 25 returns toward the closed position far enough for valve member port 73 to be on the opposite side of seal 59 from stab port 65, control fluid 71 vents from lower portion 49 into bore 55 and through venting port 75.

[0034] Venting the gas from lower portion 47 of chamber 43 advantageously discontinues the delay forces experienced by piston 45. The biasing force on the upper side of piston 45 can more easily force piston 45 and valve member 25 to return fully, or land completely in valve seat 23, after the pressure of system fluid 21 returns to below the predetermined value. The problem involving chattering is still reduced because control fluid 71 prevents valve member 25 from rapidly closing after each opening while valve member port 73 is above seal 59 and transmitting control fluid 71 into lower portion 49.

[0035] It should be apparent from the foregoing that an invention having significant advantages has been provided. While the invention is shown in only one of its forms, it is not just limited but is susceptible to various changes and modifications without departing from the spirit thereof.