Patent Publication Number: US-2013233407-A1

Title: Relief valve

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is related to the field of valves, and more particularly, to a relief valve. 
     2. Description of the Prior Art 
     Relief valves are used to prevent a build-up of excessive pressure in a fluid system. A relief valve can prevent an overpressure situation that could damage components of the fluid system. A relief valve can prevent an overpressure situation that could cause leakage and/or failure of components. A relief valve can prevent an overpressure situation that could present safety issues. A relief valve can prevent undesired pressure fluctuations. 
       FIG. 1  shows a prior art relief valve. Prior art relief valves typically use a spring and piston to counter a fluid force. The spring is selected to be compressed and therefore to allow the piston move to an open position when the pressure exceeds a threshold. The prior art relief valve includes a face seal on the face of the piston. The face seal contacts (and seals) against an end of the piston chamber. The strength of the seal therefore depends on the force applied to the piston by the spring, wherein the prior art piston compresses the face seal against the interior of the piston chamber. The face seal may sealingly contact the end of the piston chamber radially outward from the input port, as shown, or may directly block the input port. The input pressure will move the piston and compress the spring when the fluid pressure exceeds a threshold. 
     The prior art relief valve has drawbacks. The prior art relief valve is designed to have a single, specific position when closed. The prior art relief valve desirably should not move from a fully closed position until a threshold pressure has been exceeded, but this is practically impossible. The fluid pressure counters the closing/sealing force provided by the spring. Therefore, as soon as significant pressure is applied to the prior art relief valve, the piston will move and weaken the sealing force provided by the spring. 
     The prior art relief valve may stick. This is due to stiction, the force needed to overcome static cohesion between two objects pressing against each other. Stiction therefore increases the force that is needed in order to cause the two contacting objects to slide. 
     This tendency to have undesirably large levels of stiction in the prior art pressure relief valve results in the need for opening forces that are higher than just the pressure threshold. Stiction in the prior art relief valve therefore may result in a delayed opening, may result in erratic opening forces and erratic opening times, and may result in inaccurate and variable resulting pressure levels. 
     Further, because the prior art piston may not move for long periods of time, the prior art face seal may at least partially bond to the piston chamber. This tendency to have undesirably large levels of stiction in the prior art pressure relief valve may damage the prior art face seal. 
     ASPECTS OF THE INVENTION 
     In some aspects of the invention, a relief valve comprises:
         a floating piston configured to move reciprocally in a piston chamber in response to fluid pressure, with the piston chamber including a fluid inlet;   a circumferential seal located on the floating piston and configured to substantially seal the floating piston to the piston chamber;   a biasing device configured to keep the floating piston within a piston float movement range, wherein the fluid is held when the floating piston is within the piston float movement range and the fluid is exhausted when the floating piston exceeds the piston float movement range; and   one or more relief grooves formed in a sidewall of the piston chamber, with the one or more relief grooves being configured to conduct fluid around the floating piston and the circumferential seal when the floating piston is compressed past a predetermined relief location in the piston chamber.       

     Preferably, the floating piston includes a circumferential groove that receives and retains the circumferential seal. 
     Preferably, the one or more relief grooves comprises two or more relief grooves spaced around the sidewall. 
     Preferably, the one or more relief grooves are substantially constant in cross-sectional area along a groove length. 
     Preferably, the one or more relief grooves vary in cross-sectional area along a groove length. 
     Preferably, the circumferential seal maintains a substantially constant seal contact with the piston chamber at any point in an actuation span of the floating piston. 
     Preferably, a sealing force between the circumferential seal and the piston chamber is substantially constant even where the fluid pressure varies. 
     Preferably, the one or more relief grooves extend from a predetermined release threshold over at least a portion of a piston release movement range. 
     Preferably, the one or more relief grooves extend from a predetermined release threshold over at least a portion of a piston release movement range, wherein the predetermined release threshold substantially corresponds to an end of the piston float movement range. 
     In some aspects of the invention, a method of making a relief valve comprises:
         providing a floating piston configured to move reciprocally in a piston chamber in response to fluid pressure, with the piston chamber including a fluid inlet;   providing a circumferential seal located on the floating piston and configured to substantially seal the floating piston to the piston chamber;   providing a biasing device configured to keep the floating piston within a piston float movement range, wherein the fluid is held when the floating piston is within the piston float movement range and the fluid is exhausted when the floating piston exceeds the piston float movement range; and   providing one or more relief grooves formed in a sidewall of the piston chamber, with the one or more relief grooves being configured to conduct fluid around the floating piston and the circumferential seal when the floating piston is compressed past a predetermined relief location in the piston chamber.       

     Preferably, the floating piston includes a circumferential groove that receives and retains the circumferential seal. 
     Preferably, the one or more relief grooves comprises two or more relief grooves spaced around the sidewall. 
     Preferably, the one or more relief grooves are substantially constant in cross-sectional area along a groove length. 
     Preferably, the one or more relief grooves vary in cross-sectional area along a groove length. 
     Preferably, the circumferential seal maintains a substantially constant seal contact with the piston chamber at any point in an actuation span of the floating piston. 
     Preferably, a sealing force between the circumferential seal and the piston chamber is substantially constant even where the fluid pressure varies. 
     Preferably, the one or more relief grooves extend from a predetermined release threshold over at least a portion of a piston release movement range. 
     Preferably, the one or more relief grooves extend from a predetermined release threshold over at least a portion of a piston release movement range, wherein the predetermined release threshold substantially corresponds to an end of the piston float movement range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The same reference number represents the same element on all drawings. It should be understood that the drawings are not necessarily to scale. 
         FIG. 1  shows a prior art relief valve. 
         FIG. 2  shows a relief valve according to the invention. 
         FIG. 3  shows detail of one or more relief grooves inside the relief valve according to the invention. 
         FIG. 4  shows the relief valve when in a relief state. 
         FIG. 5  shows the relief valve according to another embodiment of the invention. 
         FIG. 6  shows the relief valve according to another embodiment of the invention. 
         FIG. 7  shows the relief valve according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-7  and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
       FIG. 2  shows a relief valve  100  according to the invention. The relief valve  100  includes a valve body  101  including a piston chamber  103  formed therein, and a fluid inlet  112  that is in fluidic communication with the piston chamber  103 . The piston chamber  103  is substantially elongate. A floating piston  120  is configured to move reciprocally in the piston chamber  103  in response to fluid pressure. Pressurized fluid can be introduced into the piston chamber  103  through the fluid inlet  112 . The valve body  101  includes one or more exhaust ports  114  that exhaust any fluid that has passed by the floating piston  120 . The one or more exhaust ports  114  are on an opposing side of the floating piston  120  from the fluid inlet  112 . The one or more exhaust ports  114  may be of any cross-sectional area with respect to the cross-sectional area of the fluid inlet  112 . Further, the one or more exhaust ports  114  may comprise multiple passages, as shown. 
     During normal operation with normal fluid pressures, the floating piston  120  may move within the piston float movement range. When the fluid pressure exceeds a predetermined pressure threshold, however, then the excessive pressure will move the floating piston  120  past a predetermined release threshold and into a piston release movement range. The predetermined release threshold substantially corresponds to a predetermined release pressure of the fluid. The predetermined release threshold substantially corresponds to an end of the piston float movement range and a beginning of the piston release movement range. Consequently, the relief valve  100  operates by compressing the floating piston  120 , wherein fluid is exhausted from the relief valve  100  when the floating piston  120  is compressed to (or past) the predetermined release threshold. When the fluid pressure provided by the fluid inlet  112  exceeds this predetermined release pressure, the floating piston  120  reaches or passes the predetermined release threshold and fluid is vented around the floating piston  120  and out of the relief valve  100 . 
     In some embodiments, the piston chamber  103  and the floating piston  120  are substantially cylindrical in shape. However, other cross-sectional shapes are contemplated and are within the scope of the description and claims. 
     The piston chamber  103  includes a sidewall  106 . One or more relief grooves  107  are formed in the sidewall  106 . The one or more relief grooves  107  are configured to conduct fluid around the floating piston  120  and the circumferential seal  124  when the floating piston  120  is compressed to a predetermined relief location in the piston chamber  103 . The one or more relief grooves  107  extend only partially along the sidewall  106  and are configured to conduct fluid around the floating piston  120  when the floating piston  120  is compressed to a predetermined relief location in the piston chamber  103  (i.e., moved due to pressure greater than a predetermined relief threshold). 
     The one or more relief grooves  107  are of a length and position to conduct fluid around the floating piston  120  and the circumferential seal  124  when the floating piston  120  reaches and/or passes a predetermined point in the piston chamber  103 . This point coincides with a beginning of a groove (or grooves) of the one or more relief grooves  107  and comprises the predetermined release threshold. The one or more relief grooves  107  may extend partially or fully from this opening point to the end of the piston chamber  103 , which is the left end in the figure. The one or more relief grooves  107  comprise two or more relief grooves  107  spaced around the sidewall  106  of the piston chamber  103 . In some embodiments, the two or more relief grooves  107  may be equidistantly spaced around the sidewall  106 . 
     It should be understood that the one or more relief grooves  107  do not have to extend from the threshold point to the end of the piston chamber  103 . Instead, the one or more relief grooves  107  only have to extend far enough to relieve excess pressure on the inlet side of the floating piston  120 . For example, the one or more relief grooves  107  may extend only a predetermined distance from the threshold point, allowing the floating piston  120  to move and relive pressure, but not constructed to necessarily enable the floating piston  120  to be completely compressed within the piston chamber  103 . 
     The one or more relief grooves  107  may feature any desired cross-sectional shape and any desired cross-sectional area. The groove cross-sectional area may be chosen according to the expected fluid and according to the expected fluid pressure, wherein the cross sectional groove area will control how rapidly excess fluid pressure is relieved. The one or more relief grooves  107  are substantially constant in cross-sectional area along a groove length in some embodiments. The one or more relief grooves  107  vary in cross-sectional area along a groove length in some embodiments. 
     The one or more relief grooves  107  are substantially aligned with the axis of the piston chamber  103  in the embodiment shown. However, it should be understood that the one or more relief grooves  107  can be curved or helical, angled or arranged in regular or irregular fashion. 
     The floating piston  120  includes a circumferential groove  122  that receives and retains a circumferential seal  124 . The circumferential seal  124  is located circumferentially on the floating piston  120  and is configured to substantially seal the floating piston  120  to the piston chamber  103 , including during reciprocating motion of the floating piston  120 . The circumferential seal  124  will seal the floating piston  120  with respect to the piston chamber  103  at any point, except for sealing the one or more relief grooves  107 . 
     In some embodiments, circumferential groove  122  is larger than the circumferential seal  124  and the circumferential seal  124  can move in the circumferential groove  122 . Alternatively, the circumferential groove  122  is sized to not let the circumferential seal  124  move with respect to the floating piston  120 . 
     The relief valve  100  includes a biasing device  130  that provides a closing force. The closing force of the biasing device  130  operates to keep the relief valve  100  closed. The biasing device  130  provides a predetermined closing force. The predetermined closing force is equal to the predetermined release pressure of the relief valve  100 . The predetermined closing force allows the floating piston  120  to compress and move past a beginning point of the one or more relief grooves  107  when a predetermined release threshold has been achieved or exceeded. 
     The biasing device  130  is configured to keep the floating piston  120  within a piston float movement range. Fluid is held when the floating piston  120  is within the piston float movement range and the fluid is exhausted when the floating piston  120  exceeds the piston float movement range. 
     In some embodiments, the biasing device  130  may be adjustable. As a consequence, the biasing device  130  may be used to change the predetermined release threshold. 
     The biasing device  130  does not affect a seal contact between the circumferential seal  124  and the piston chamber  103 . The circumferential seal  124  maintains a substantially constant seal contact with the piston chamber  103  at any point in an actuation span of the floating piston  120 . A sealing force between the circumferential seal  124  and the piston chamber  103  is substantially constant even where the fluid pressure varies. 
     The relief valve  100  includes an end portion  105 . The end portion  105  may be assembled to the valve body  101  after the piston  100  and the biasing device  130  have been inserted into the piston chamber  103 . The end portion  105  may be assembled to the valve body  101  in any manner. The end portion  105  may be removably affixed to the valve body  101 . Alternatively, the end portion  105  may be permanently affixed to the valve body  101 . The end portion  105  may include the one or more exhaust ports  114  or may include partial apertures that form the one or more exhaust ports  114  when the end portion  105  is assembled into the valve body  101 . 
     The floating piston  120  further includes a piston shaft  129 . In some embodiments, the piston shaft  129  extends out of the relief valve  100 , such as through a shaft orifice  115  (see  FIG. 3 ). The piston shaft  129  may stabilize the floating piston  120  and prevent the floating piston  120  from moving in any way except in a linear, reciprocating manner in the piston chamber  103 . In addition, the piston shaft  129  may provide a visual indicator of the position of the floating piston  120 , and may include any manner of shape or visual indicia that provides a visual indication when the relief valve  100  is actuated. For example, the piston shaft  129  may include a colored, textured, or other visibly differentiated region that may only be visible when the floating piston  120  is compressed past the predetermined release threshold. In this manner, the differentiated region may only be visible when the relief valve  100  is exhausting fluid and relieving excess fluid pressure. 
       FIG. 3  shows detail of the one or more relief grooves  107  inside the relief valve  100  according to the invention. The one or more relief grooves  107  in this embodiment comprise a lead-in portion  108  and a channel portion  109 . The lead-in portion  108  comprises a varying cross-sectional area that expands from nothing to the cross-sectional area of the channel portion  109 . The channel portion  109  may have a regular cross-sectional area along the length of the groove or may increase or decrease in cross-sectional area (see  FIG. 5  and the accompanying discussion, for example). In some embodiments, the one or more relief grooves  107  may not have a lead-in portion  108 . In some embodiments, the one or more relief grooves  107  may include a lead-out portion  110  (see  FIG. 6 ). 
     As can be seen from the figure, the one or more relief grooves  107  can be substantially regularly spaced around on the sidewall  106 . The one or more relief grooves  107  alternatively can be started in staggered or alternating fashion or in other arrangements (see  FIG. 6 , for example). 
     The one or more relief grooves  107  can extend from a predetermined release threshold (see dashed line) to an end of the piston chamber  103  in some embodiments. In the embodiment shown, the floating piston  120  will always be in fluidic communication with the one or more relief grooves  107  where the floating piston  120  is compressed past the predetermined release threshold. Alternatively, the one or more relief grooves  107  may not extend over a full range of the piston compression span (see grooves  107 A- 107 C of  FIG. 5 ). 
       FIG. 4  shows the relief valve  100  when in a relief state. The fluid pressure, acting against the biasing device  130 , has compressed the floating piston  120  and moved the floating piston  120  to the left in the figure. The floating piston  120  has been at least partially compressed by the fluid pressure provided by the fluid inlet  112  and the floating piston  120  has passed the predetermined release threshold as a result. Consequently, the circumferential seal  124  is positioned over the one or more relief grooves  107 , wherein fluid is allowed to escape through the one or more relief grooves  107  and via the one or more exhaust ports  114 . 
     The floating piston  120  will stay at the compressed, venting position until the fluid pressure drops. As the fluid pressure decreases, the floating piston  120  will move to the right in response. When the fluid release causes the fluid pressure to drop below the predetermined release threshold, the floating piston  120  will move back to a blocking position, wherein fluid cannot reach the one or more relief grooves  107 . No further fluid will be exhausted until fluid pressure again exceeds the predetermined release threshold. 
       FIG. 5  shows the relief valve  100  according to another embodiment of the invention. In this embodiment, a cross-sectional area of a relief groove  107  may increase with increased piston compression travel, allowing a greater rate of fluid venting with greater piston compression. As can be seen from the figure, relief groove  107 A features an increasing depth as it extends from the threshold point. The increasing depth can comprise a linear or non-linear increase in depth. The relief groove  107 A may further include a decreasing depth after a predetermined compression point, wherein the relief groove  107 A does not need to provide a fluid exhaust volume (or an increasing fluid exhaust volume) at an extreme of the compression range. Alternatively, the relief groove  107 A may not decrease and may instead remain substantially constant after the predetermined compression point. 
     In contrast, relief groove  107 B features an increasing width as it extends from the threshold point. The relief groove  107 B may further include a decreasing width after a predetermined compression point, wherein the relief groove  107 B does not need to provide a fluid exhaust volume (or an increasing fluid exhaust volume) at an extreme of the compression range. Alternatively, the relief groove  107 B may not decrease and may instead remain substantially constant after the predetermined compression point. 
     The relief groove  107 C features substantially linear lead-in and lead out portions. The relief groove  107 C may include substantially vertical or angled sidewalls. It should be understood that any of the groove embodiments herein may provide an increasing and/or decreasing cross-sectional area as the floating piston  120  is compressed further by the pressure provided at the fluid inlet  112 . 
       FIG. 6  shows the relief valve  100  according to another embodiment of the invention. In this embodiment, the relief valve  100  includes a first set of relief grooves  107 D that begin at the predetermined release threshold. This embodiment further includes a second set of relief grooves  107 E. The second set of relief grooves  107 E are offset a predetermined distance from the first set of relief grooves  107 D and the predetermined release threshold. As a consequence, the first set of relief grooves  107 D and the second set of relief grooves  107 E may generate a two-stage pressure release, for example, with the second set of relief grooves  107 E only venting when the fluid pressure is excessive (or where the fluid pressure rises abruptly). 
     Like the first set of relief grooves  107 D, the second set of relief grooves  107 E can extend all of the way to the end of the piston chamber  103 , as shown. Alternatively, the second set of relief grooves  107 E can extend only part way to the end. 
     Like the first set of relief grooves  107 D, the second set of relief grooves  107 E can include a lead-in portion  108  and a channel portion  109 . The lead-in portion  108  is optional and may or may not be included. Further, a relief groove  107 E (and any other groove embodiment) can further include an optional lead-out portion  110 . 
       FIG. 7  shows the relief valve  100  according to another embodiment of the invention. In this embodiment, the relief groove or grooves  107  may be formed by boring through the end portion  105 , wherein the boring operation continues partially into the piston chamber  103 , forming the relief grooves  107 . The relief grooves may be of any shape, such as a semi-circular shape as formed by a rotating boring tool. 
     The various embodiments of the invention can be implemented to provide several advantages, if desired. The relief valve according to any of the embodiments features a reduced stiction. The relief valve therefore is much less likely to stick and open erratically and unpredictably. The relief valve is much less likely to have a delayed or erratic opening. The relief valve according to any of the embodiments opens accurately and reliably at a desired pressure. 
     The relief valve according to any of the embodiments does not have the high risk of potential bonding of a face seal to the interior of the piston chamber. 
     The relief valve according to any of the embodiments features a floating piston that does not have a specific closed location. The piston floats with changes in input fluid pressure and seals at various piston locations. 
     The relief valve according to any of the embodiments does not suffer from a reduced sealing contact and/or sealing force with increasing fluid pressure. The piston is not fixed in place. Therefore, the floating piston exhibits less sticking. Movement of the floating piston does not weaken the seal contact or seal face. Therefore, the relief valve will not have regions or instances of premature sealing loss.