Abstract:
A pressure relief valve has a hollow valve body with one or more vent ports in the side wall and a small pilot opening in a first end. A lightweight sleeve, closed at one end, telescopes over the first end of the valve body to close the vent ports. A pressure actuatable element is positioned on the outer surface of the valve body end so as to block the pilot opening therein until the pressure in the valve body exceeds a predetermined value. When the pressure actuatable element unblocks the pilot opening, the interior of the closed end of the sleeve is exposed to the pressure in the valve body, causing the lightweight sleeve to move relative to the valve body to open the vent ports. Suitable pressure actuated elements include a rolling ball or a spring biased closure plate.

Description:
FIELD OF THE INVENTION 
     This invention relates to pressure relief valves. In one aspect, the invention relates to a light-weight pressure relief valve. In another aspect, the invention relates to a light-weight relief valve actuated by a high pressure pilot valve. 
     BACKGROUND OF THE INVENTION 
     Pressure relief valves, utilizing a variable number of control weights to determine the relief pressure at which the valve is actuated, are employed commercially. However, for large size valves such design has a severe disadvantage, the amount of weight required. For example, a weighted relief valve with a 12&#34; diameter would require a total of 1131 pounds of weight (movable cap plus control weights) for a relief pressure of only 10 psig. Such high total weights make these valves very expensive to manufacture, to support in their installation, and to maintain. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved pressure relief valve. Another object of the invention is to provide a light-weight pressure relief valve which is inexpensive to manufacture and install. A further object of the invention is to provide an improved pressure relief valve which can be readily maintained. 
     The present invention provides a light-weight pressure relief valve which avoids the foregoing difficulties of the weighted pressure relief valve. A relief valve in accordance with the present invention comprises a hollow valve body having one or more large vent ports in its side wall and a small pilot orifice in a first end wall. Fluid communication is provided between the interior of the valve body and the pressurized container to be protected against excessive pressure. A light-weight sleeve, closed at one end, telescopes over the first end of the valve body to close the vent ports under normal pressure conditions in the pressurized container. A pressure actuatable element is positioned on the outlet of the pilot orifice to permit fluid communication between the valve body interior and the interior chamber formed in the sleeve between the closed end of the sleeve and the first end of the valve body. The ratio of (a) the inside surface of the sleeve which is effectively perpendicular to the direction of movement of the sleeve and is exposed to fluid pressure in the interior chamber to (b) the area of the pilot orifice, and the ratio of (c) the weight of the sleeve to (d) the effective weight of the resistance of the pressure actuatable element are such that the pressure in the pressurized container necessary to move the pressure actuatable element to unblock the pilot orifice is substantially more than the pressure in the interior chamber necessary to move the sleeve to open the vent ports. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, FIG. 1 is a diagrammatic representation of a pressurized fluid vessel provided with a pressure relief valve; 
     FIG. 2 is a vertical cross-sectional view of a prior commercial pressure relief valve; 
     FIG. 3 is a vertical cross-sectional view of a pressure relief valve in accordance with a first embodiment of the invention; 
     FIG. 4 is a cross-sectional view taken along line 4--4 in FIG. 3; and 
     FIG. 5 is a fragmentary vertical cross-sectional view of a pressure relief valve in accordance with a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1, a pressurized fluid container 11 is provided with an inlet conduit 12 and an outlet conduit 13. In order to protect container 11 against excessive internal pressures, a pressure relief valve 14 is mounted on the flange of an access conduit 15. 
     A prior art commercial weighted pressure relief valve 16 is represented by the illustration in FIG. 2. The valve 16 comprises a valve body 17, cap 18 and control weights 19 and 21. Valve body 17 comprises an annular flange 22 surrounding and connected to the base of an annular side wall 23. The opposite end of the annular side wall 23 is joined to end wall 24. The inner surfaces of annular side wall 23 and end wall 24 form a chamber 25. Fluid communication can be provided from the interior of container 11 through access conduit 15 to chamber 25 so that the fluid pressure in chamber 25 is the same as in container 11. A plurality of vent ports 26 are provided in the annular side wall 23 so that when the cap 18 is the raised position shown in FIG. 2, the fluid from container 11 can be vented through ports 26. 
     Cap 18 comprises an annular wall 27 and an end wall 28. The interior surface 29 of wall 27 mates with the exterior surface 31 of the valve body sidewall 23 so that cap 18 can telescope over end 24 of valve body 17. A passageway 32 in end wall 24 provides for fluid communication between chamber 25 and chamber 33 formed by the interior of cap 18 between valve body end wall 24 and cap end wall 28. A bleed opening 34 in the sidewall 27 of cap 18 is provided with a bleed valve 35 to permit release of fluid from chamber 33 at a very slow rate. A solid rod 36 is secured to end wall 28 of the cap 18 to provide a secure retention of weights 19 and 21 which have central openings therethrough to accommodate rod 36. 
     When the pressure in container 11 is below the predetermined value at which the relief valve is to be actuated, cap 18 rests with the lower edge of sidewall 27 sitting on flange 17, thereby closing vent ports 26. The shoulder 37 is spaced from end wall 24 in this closed position. The pressure in each of chambers 25 and 33 is essentially the same as the pressure in container 11. To the extent that bleed valve 35 is partially or fully open, there will be a constant bleeding of fluid through chambers 25 and 33 and valve 35. 
     The pressure at which relief valve 16 is actuated is determined by (a) the area of end wall 28, including shoulder 37, which is effectively perpendicular to the line of movement of the cap 18 and (b) the total weight of cap 18 and weights 19 and 21. Weights 19 and 21 can be of different size and more than two weights can be positioned on the cap 18 to achieve the desired total weight. Where the external diameter of end wall 24 is 12&#34; and the actuation pressure in chamber 33 is to be 10 psig, the weight of cap 18 and weights 19 and 21 must be 1131 pounds. Fine tuning of the activation pressure can be achieved by the position of bleed valve 35. 
     Referring now to FIG. 3 and 4, the inventive pressure relief valve 41 comprises a valve body 42 and a cap sleeve 43. The valve body 42 comprises an annular flange 44, containing bolt holes 45, an annular sidewall 46 containing vent ports 47, and an end wall 48 containing a pilot passageway 49. Flange 44 is connected to the lower end of sidewall 46 while end wall 48 is connected to the upper end of sidewall 46. The inner surfaces of annular sidewall 46 and end wall 48 form a pressurizable chamber 51 in valve body 42 which can be in fluid communication with the interior of container 11 through access conduit 15 so that the pressure in chamber 51 is essentially the same as in container 11. 
     Cap sleeve 43 comprises an annular sidewall 52 and an end wall 53. The inner surface 54 of cap sleeve sidewall 52 mates with the outer surface 55 of valve body sidewall 46 so that cap sleeve 43 telescopes over the end wall 48 and side wall 46 of the valve body 42. The length of cap sleeve side wall 52 is substantially longer than the length of valve body sidewall 46 so that in the closed position shown in FIG. 3, the lower end of cap sleeve sidewall 52 rests on flange 44, leaving a pressurizable chamber 56 within cap sleeve 43 between end wall 53 and valve body end wall 48. A bleed valve 57 can be positioned in bleed opening 58 in the portion of side wall 52 which forms chamber 56. If desired, an annular seal 59 can be provided between the mating portions of the sidewalls 46 and 52 to provide greater protection against fluid communication between chambers 51 and 56 via any annular space between the outer surface 55 of sidewall 46 and the inner surface 54 of sidewall 52. 
     A pressure actuatable element is positioned on the outlet end of pilot passageway 49 to block passageway 49 whenever the pressure in chamber 51 is less than the predetermined value at which the pressure relief valve is to be actuated, and to unblock the passageway 49 whenever the fluid pressure in chamber 51 is above that predetermined value. The transverse cross-sectional area of passageway 49 is very small compared to the area of the interior surface of end wall 48 which forms part of chamber 51. In the embodiment of FIG. 3, passageway 49 has a circular outlet opening and the pressure actuatable element is a spherical body 61 which has a diameter greater than the diameter of the outlet of passageway 49, but less than the distance between end walls 48 and 53 when sleeve 43 is in the closed position. Thus, when the upward force represented by the fluid pressure in chamber 51 acting upwardly on the transverse surface of sphere 61 represented by the transverse cross sectional area of the outlet opening of passageway 49 exceeds the sum of the weight of sphere 61 and the force represented by the fluid pressure in chamber 56 acting downwardly on the transverse surface area of sphere 61 represented by the transverse cross-sectional area of the outlet opening of passageway 49, the sphere 61 is moved aside, permitting passage of fluid from chamber 51 into chamber 56. When the upward force is less than the downward force, sphere 61 is sealing secured in the outlet opening of passageway 49, blocking fluid communication between chambers 51 and 56. The outer surface of end wall 48 can be curved so that it diverges upwardly and outwardly from the outlet end of passageway 49. This facilitates the return of sphere 61 to its closed position, blocking passageway 49. 
     When the pressure in container 11 has been below the predetermined actuation pressure long enough, the fluid in chamber 56 has been reduced to atmospheric pressure (or other desired reference pressure) by excess fluid having been bled off through bleed valve 57. With atmospheric pressure in chamber 56, the force required to move the weight of sphere 61 off passageway 49 is a function of the diameter of passageway 49 and the gage pressure in chamber 51. Where side wall 46 of valve body 42 has an external diameter of 12&#34; and passageway 49 has a diameter of 0.5&#34;, the weight of ball 61 required to close passageway 49 up to 10 psig in chamber 51 is only 1.96 pounds, compared to the 1131 pounds for the valve of FIG. 2. The side wall 52 of cap sleeve 43 has to have sufficient strength to resist the radially outwardly directed pressures through vent ports 47 when cap sleeve 43 is in the closed position, but cap sleeve 43 does not have to provide the weight to resist all pressures below the predetermined value applied against the transverse cross-sectional area of the inner surface of end wall 53. A cap sleeve 43 with an internal diameter of 12&#34; and formed of 1/2&#34; thick cast iron might weigh approximately 50 pounds in contrast to the 1131 pounds for the weighted cap of FIG. 2. 
     Referring now to FIG. 5, an alternate embodiment of the pressure actuable element for blocking or unblocking passageway 49 in end wall 48 comprises a plate 71, spring 72 and bracket 73. The dimensions of plate 71 are larger than the corresponding dimensions of the outlet of passageway 49 so as to completely block the outlet when biased against end wall 48 by spring 72. Bracket 73 surmounts the outlet opening of passageway 49 and plate 71, with the ends of bracket 73 being secured by suitable means to the outer surface of wall 48. Where sufficient height in chamber 56 is available, other spring and support configurations can be employed. Plate 71 can be a disc where the outlet opening of passageway 49 is circular. 
     While the side wall 46 of valve body 42 and the side wall 52 of valve sleeve 43 have been illustrated as having mating cylindrical surfaces, other configurations can be employed so long as sleeve 43 is telescopically slidable over valve body 42 along a direction parallel to the longitudinal axis 62 of the effective portion of valve body 42. In general, it is preferable that each of the outer surface 55 of valve body side wall 46 and the corresponding inner surface 54 of sleeve side wall 52 be representable as a surface at least generally defined as the revolution of a line about the longitudinal axis 62, with the line preferably being parallel to the axis 62. While surface 55 extends completely about the periphery of valve body 42, it is recognized that it can be interrupted, for example, by one or more longitudinal keyways to receive keys to prevent rotation of sleeve 43, as well as circumferential grooves for seals such as 59. Similarly, inner surface 54 of sleeve 43 extends completely about the inner periphery of sleeve 43, but can be interrupted for keyways and seal grooves. 
     The mating surface 55 does not have to extend completely from one to the other of the spaced apart ends of valve body 42; and the mating surface 54 does not have to extend the full length of sleeve 43; so long as the surfaces 54 and 55 mate at and between the open and closed positions of the pressure relief valve. Thus, a seat for the lower end of sleeve side wall 52 could be provided on valve body 42 at a position above flange 44. Similarly, the upper end of sleeve 43 could have one or more stages of reduced interior diameter, as provided by shoulder 37 in FIG. 2, or even a hemispherical configuration. In such multi-surface configurations, it is recognized that the effective pressure surface is represented by the cross-sectional area of the valve body end wall 48 measured in a plane perpendicular to the longitudinal axis 62. 
     In the embodiment employing a rotatable pressure actuatable member, the outer surface of end wall 48 can be contoured as a frustoconical surface, a parabolic surface or any other curved surface suitable for aiding the return of the rotatable element to its blocking position over passageway 49. Instead of a spherical configuration, such rotatable element can have a cylindrical shape, a barrel shape or any other curved shape which permits it to rotate and yet block a suitable correspondingly shaped outlet of passageway 49. The pressure actuatable member can be placed in a cage which would minimize, if not eliminate, its sidewise movement but permit it to clear the passageway 49 sufficiently for the fluid pressure in chamber 51 to cause sleeve 43 to be moved from its closed position, blocking vent ports 47, to its open position, at least substantially clearing vent ports 47. 
     Other reasonable variations and modifications of the invention are possible within the scope of the foregoing disclosure and the appended claims to the invention.