Abstract:
Provided is a relief valve with an inlet, and outlet, and a backside of a poppet fluidly connected to an input pressure to increasingly close the poppet as a function of input pressure until a prescribed pressure condition is reached. Upon the prescribed pressure condition being reached, the relief valve decreases pressure on the backside of the poppet to open the poppet and allow fluid flow from the inlet to the outlet. Increasingly closing the poppet allows the relief valve to operate under high pressure conditions and repeatedly open and close to reliable seal without significant leakage after thousands of cycles.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/173,586 filed on Jun. 10, 2015, which is incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates generally to relief valves, and more particularly to relief valves for blow-out preventers. 
       BACKGROUND 
       [0003]    In order to protect hydraulic devices connected at a work port, typically a pressure relief valve is placed in parallel with the workport. The pressure relief valve typically partially or totally exhausts to tank flow going to the workport during pressure limitation. Relief valves are used in some oil and gas applications to prevent leakage of subsurface fluids. 
         [0004]    Leakage of subsurface fluids may pose an environmental threat if released from the wellbore. Equipment, such as blow out preventers, may be positioned about the wellbore to form a seal about a tubular therein to prevent leakage of fluid as it is brought to the surface. Blow out preventers may have selectively actuatable rams or ram bonnets, such as pipe rams or shear rams that may be activated to seal and/or sever a tubular in a wellbore. 
       SUMMARY OF INVENTION 
       [0005]    The present invention provides a relief valve with an inlet, and outlet, and a backside of a poppet fluidly connected to an input pressure to increasingly close the poppet as a function of input pressure until a prescribed pressure condition is reached. Upon the prescribed pressure condition being reached, the relief valve decreases pressure on the backside of the poppet to open the poppet and allow fluid flow from the inlet to the outlet. Increasingly closing the poppet allows the relief valve to operate under high pressure conditions and repeatedly open and close to reliable seal without significant leakage after thousands of cycles. 
         [0006]    According to one aspect of the invention, a relief valve assembly including a valve body having an inlet, an outlet and a valve seat, a poppet having a piston portion and a valve portion for engaging at a front side of the valve portion the valve seat to block flow from the inlet to the outlet, the poppet being movable in the valve body and defining at a backside of the piston portion a biasing chamber, a pressure line configured to provide an input pressure to the biasing chamber to provide the input pressure to the backside of the poppet, whereby in a first state increasing the input pressure increases a force of the poppet against the valve seat to reduce leakage between the valve seat and the poppet, an evacuation line for fluidly connecting the biasing chamber to a drain port, and an unloading valve in the evacuation line for blocking fluid flow from the biasing chamber to the drain port, until pressure in the inlet exceeds a first pressure setting which causes the unloading valve to open to allow fluid flow through the evacuation line from the biasing chamber to the drain port, whereby in a second state pressure of the fluid on the backside of the poppet is reduced below a predetermined proportion of a pressure at the inlet while the front side of the valve portion is exposed to the inlet pressure to allow the poppet to move away from the valve seat thereby allowing fluid to flow between the valve seat and the poppet from the inlet to the outlet. 
         [0007]    The pressure line may be an inlet pressure line that fluidly connects the biasing chamber to the inlet for providing pressure from the inlet to the backside of the poppet, whereby in the first state increasing pressure of fluid at the inlet increases the force of the poppet against the valve seat to reduce leakage between the valve seat and the poppet. 
         [0008]    The relief valve assembly may further include a resilient member biasing the poppet toward a closed position. 
         [0009]    The relief valve assembly may further include a first signal line fluidly connecting the inlet to the unloading valve. 
         [0010]    The first signal line may fluidly connect the inlet pressure line to the unloading valve. 
         [0011]    The pressure line may fluidly connect the biasing chamber to a hydraulic circuit for providing pressure from the hydraulic circuit to the backside of the poppet, whereby in the first state increasing pressure of fluid from the hydraulic circuit increases the force of the poppet against the valve seat to reduce leakage between the valve seat and the poppet. 
         [0012]    The relief valve assembly may further include an adjustable stroke limiter longitudinally spaced from the poppet and operably connected to the piston for adjustably limiting a stroke length of the piston. 
         [0013]    The valve portion may face longitudinally away from the biasing chamber. 
         [0014]    The drain port may be fluidly connected to the outlet downstream of the valve seat. 
         [0015]    In a closed position the backside of the piston portion may have a cross-sectional area greater than a cross-sectional area, of a first portion of the front side of the valve portion exposed to the inlet pressure, by a cross-sectional area of the valve seat isolating a second portion of the front side from the inlet pressure. 
         [0016]    The relief valve assembly may further include an orifice in the inlet pressure line. 
         [0017]    The orifice may be downstream of a first signal line. 
         [0018]    The orifice may be configured to reduce fluid flow from the inlet into the biasing chamber below a maximum flow rate of the unloading valve. 
         [0019]    The unloading valve may include a signal port fluidly connected to a first signal line fluidly connected to the inlet pressure line and configured to open at a predetermined pressure, thereby allowing fluid from the biasing chamber to pass through the relief valve to a drain line. 
         [0020]    The unloading valve may include an inlet port and a tank port fluidly connected to the evacuation line, whereby fluid from the biasing chamber flows into the inlet port and out of the tank port when the unloading valve is open. 
         [0021]    The relief valve assembly may further include an evacuation signal line fluidly connected to an evacuation signal port of the unloading valve for signaling the unloading valve to open above a prescribed pressure. 
         [0022]    The valve body may be remote from an unloading valve body of the unloading valve. 
         [0023]    The unloading valve body may be mounted near a critical component of a hydraulic circuit. 
         [0024]    The unloading valve may be operated by a remote pressure signal from a critical component of a hydraulic circuit. 
         [0025]    According to another aspect of the invention, a method of relieving pressure in a hydraulic circuit providing pressure from an inlet at a backside of a poppet for urging the poppet against a valve seat with a closing force proportionally related to the inlet pressure for urging the poppet closed with increasing force as the inlet pressure increases, providing the inlet pressure at a front side of the poppet for urging the poppet away from the valve seat with an opening force proportionally related to the inlet pressure, and upon the inlet pressure exceeding a prescribed amount, evacuating pressure at the backside of the poppet for allowing the inlet pressure to force the poppet open, thereby allowing fluid flow between the poppet and the valve seat from the inlet to an outlet. 
         [0026]    The method of relieving pressure may further include applying inlet pressure to a surface area of the backside of the poppet that is larger than a surface area of the front side of the poppet receiving the inlet pressure in a first state. 
         [0027]    The method of relieving pressure may further include applying a biasing force from a resilient member urging the poppet closed in combination with the inlet pressure at the backside. 
         [0028]    The method of relieving pressure may further include re-pressurizing the backside of the poppet with inlet pressure. 
         [0029]    The method of relieving pressure may further include closing the poppet using the inlet pressure, thereby preventing fluid flow from the inlet to the outlet. 
         [0030]    The method of relieving pressure may further include providing inlet pressure to an inner portion of the poppet, thereby expanding at least a portion of the valve portion of the poppet to decrease sealing imperfections against the valve seat. 
         [0031]    The hydraulic circuit may include a blow off preventer fluidly connected to the inlet. 
         [0032]    The inlet pressure may be provided remotely from a critical component in the hydraulic circuit. 
         [0033]    The unloading signal may be provided remotely from the inlet pressure. 
         [0034]    According to yet another aspect of the invention, a relief valve including a valve body having an inlet, an outlet, a valve seat, an inlet pressure port, and an evacuation port, a poppet having a piston portion and a valve portion for engaging at a front side of the valve portion the valve seat to block flow from the inlet to the outlet, the poppet being movable in the valve body and defining at a backside of the piston portion a biasing chamber, wherein the inlet pressure port is connectable to an inlet pressure line to fluidly connect the biasing chamber to the inlet for providing pressure from the inlet to the backside of the poppet, whereby in a first state increasing pressure of fluid at the inlet increases a force of the poppet against the valve seat to reduce leakage between the valve seat and the poppet, wherein the evacuation port is connectable to an evacuation line to fluidly connect the biasing chamber to a drain port, whereby when pressure in the inlet exceeds a first pressure setting, fluid flows through the evacuation port from the biasing chamber to the drain port, and whereby in a second state pressure of the fluid on the backside of the poppet is reduced below a predetermined proportion of the inlet pressure while the front side of the valve portion is exposed to the inlet pressure to allow the poppet to move away from the valve seat thereby allowing fluid to flow between the valve seat and the poppet from the inlet to the outlet. 
         [0035]    According to a further aspect of the invention, a relief valve assembly including a valve body having an inlet, an outlet and a valve seat, a poppet having a piston portion and a valve portion for engaging at a front side of the valve portion the valve seat to block flow from the inlet to the outlet, the poppet being movable in the valve body and defining at a backside of the piston portion a biasing chamber, a pressure line fluidly connecting the biasing chamber to a hydraulic circuit for providing pressure from the hydraulic circuit to the backside of the poppet, whereby in a first state increasing pressure of fluid from the hydraulic circuit increases a force of the poppet against the valve seat to reduce leakage between the valve seat and the poppet, an evacuation line for fluidly connecting the biasing chamber to a drain port, and an unloading valve in the evacuation line for blocking fluid flow from the biasing chamber to the drain port, until pressure in the hydraulic circuit exceeds a first pressure setting which causes the unloading valve to open to allow fluid flow through the evacuation line from the biasing chamber to the drain port, whereby in a second state pressure of the fluid on the backside of the poppet is reduced below a predetermined proportion of pressure at the inlet while the front side of the valve portion is exposed to the inlet pressure to allow the poppet to move away from the valve seat thereby allowing fluid to flow between the valve seat and the poppet from the inlet to the outlet. 
         [0036]    The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a schematic view of an exemplary relief valve assembly including a cross-sectional view of a relief valve connected to an unloading valve according to the invention. 
           [0038]      FIG. 2  is a cross-sectional view of the unloading valve. 
           [0039]      FIG. 3  is a schematic view of another exemplary relief valve assembly including a cross-sectional view of a relief valve with a hollow poppet according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    The principles of this present invention have particular application to high pressure hydraulic circuits and relieving pressure from the hydraulic circuits, such as from a blow off preventer connected to a drilling rig, and thus will be described below chiefly in this context. It will of course be appreciated, and also understood, that principles of this invention may be applicable to other hydraulic circuits where it is desirable to relieve excess pressure, such as from a hydraulic circuit in an aircraft. 
         [0041]    Referring to the drawings, and initially to  FIG. 1 , an exemplary relief valve assembly is illustrated generally at reference numeral  10 . The relief valve assembly  10  includes a relief valve  12  and an unloading valve  14  fluidly connected to the relief valve  12  to controllably open and close the relief valve  12  based on pressure provided to the relief valve  12 . The relief valve  12  includes a valve body  20  having an inlet  22 , an outlet  24  and a valve seat  26  between the inlet and outlet, a poppet  28  engageable with the valve seat  26 , a biasing chamber  30  fluidly connected to an inlet pressure line  32  and an evacuation line  34 , and an adjustable stroke limiter  36 . The biasing chamber  30  is formed in the body  20  behind the poppet  28  between the poppet  28  and the stroke limiter  36 . 
         [0042]    The inlet  22  is fluidly connected to the outlet  24  when the poppet  28  is not engaged with the valve seat  26 . Fluid having an inlet pressure enters the valve body  20  through the inlet  22  to pressurize a front side of the poppet exposed the inlet pressure. When the poppet  28  is in a closed position shown in  FIG. 1  against the valve seat  26 , the inlet pressure exerts an opening force that is less than a closing force exerted by the pressure from the inlet pressure line  32  and a biasing force from a spring acting on the backside of the poppet  28 . When the poppet  28  is in an open position, the inlet pressure exerts an opening force that may be equal to or greater than a closing force exerted on the backside of the poppet  28  while the relief valve assembly  10  is in a state with the poppet  28  opening, maintaining an open position, or closing. 
         [0043]    The poppet  28  is movable in the valve body  20  from the closed position to the open position to allow fluid to flow from the inlet  22  to the outlet  24 . The poppet  28  includes a piston portion  40  and a valve portion  42  for engaging the valve seat  26  to block flow from the inlet  22  to the outlet  24  when the poppet  28  is in a closed position. The valve portion  42  extends from the piston portion  40  toward the valve seat  26  longitudinally away from the biasing chamber  30 . For example, the poppet  28  may move in the valve body  20  along a longitudinal axis A of the relief valve  12 . A backside of the piston portion  40  has a surface facing longitudinally in a first direction away from the valve portion  42  with an axially facing surface area greater than an area of a front side surface of the valve portion  42  facing axially in a second direction opposite the first direction when the poppet  28  is in the closed position. 
         [0044]    The biasing chamber  30  is defined by an inner surface  47  of the valve body  20  behind the piston portion  40  within the valve body  20  and fluidly disconnected from the inlet  22  and outlet  24  by the poppet  28 . The biasing chamber  30  is formed behind the backside of the piston portion  40  to allow fluid pressure in the biasing chamber  30  to exert a closing force on the poppet  28 . The piston portion  40  includes a rearwardly extending portion  44  that defines a cavity  46  and allows fluid to flow from the inlet  22  between the rearwardly extending portion  44  and the inner surface  47  of the valve body  20 . Allowing fluid flow allows the relief valve to weigh and/or cost less because neither an extra seal nor a tight machining tolerance between the rearwardly extending portion  44  is necessary to prevent fluid flow. The rearwardly extending portion  44  extends circumferentially near the inner surface  47  to limit fluid flow between the piston portion  40  and the inner surface  47 . Limiting fluid transfer to the unloading valve  14  prevents overloading the unloading valve  14  with fluid from the inlet  22  and allows improved control of the poppet  28  when the poppet  28  is desired to be open. In an alternative embodiment, the poppet, for example the rearwardly extending portion, circumferentially abuts the inner surface of the valve body to prevent fluid from flowing between the piston portion and the inner surface. 
         [0045]    The inner surface  47  includes a ledge  48  for engaging an end face of the rearwardly extending portion  44  to serve as a stop surface for the piston portion  40  and a maximum open position of the poppet  28 . The ledge  48  is longitudinally spaced along the inner surface  47  from a connection between the inlet pressure line  32  and the surface  47  and spaced from a connection between the evacuation line  34  and the surface to allow fluid flow to and from the biasing chamber  30  without interference from the poppet  28  while opening or closing. For example, the ledge  48  allows the poppet to move longitudinally to the maximum open position without any portion of the poppet  28  overlapping any portion of the inlet pressure line  32  or the evacuation line  34 . 
         [0046]    When the poppet  28  is transitioning from the closed position to the open position the pressure at the backside of the piston portion  40  is reduced to allow the fluid from the biasing chamber  30  to drain through the evacuation line  34  fluidly connected the biasing chamber  30  to the outlet  34  through the unloading valve  14 . For example, the signal line  38  may fluidly connect to the inlet pressure line  32  to simplify assembly and manufacturing of the relief valve assembly  10 . The fluid connection between the signal line  38  and the inlet pressure line  32  may fluidly connect the signal line  38  directly to the inlet  22  without a flow or pressure limiter in between. In an embodiment, the evacuation line  34  is fluidly connected through the unloading valve  14  to a remote drain port (not shown) external of the valve body  20 . In another embodiment, an evacuation signal port is not provided and fluid in the biasing chamber  30  is able to evacuate through the evacuation line  34  fluidly connected to the unloading valve  14 . In still another embodiment, the signal line  38  fluidly connects to the inlet  22  remote from the inlet pressure line  32 . 
         [0047]    The inlet pressure line  32  fluidly connects the inlet  22  to the biasing chamber  30  to provide inlet pressure to the backside of the piston portion  40  to maintain the poppet  28  in the closed position. Due to the longitudinally facing area differences between the backside and front side of the valve portion  42  when closed, the closing force acting on the poppet  28  is greater than an opening force. When the poppet  28  is in the open position the inlet pressure may exceed the pressure at the backside of the piston portion  40  allowing the opening force acting on the valve portion  42  to overcome the closing force acting on the piston portion  40 , thereby allowing fluid to flow from the inlet  22  to the outlet  24 . An orifice  50  may be provided in the inlet pressure line  32  to improve stability of the relief valve  12  and to prevent chattering of the valve portion  42  against the valve seat  26 . The orifice  50  reduces fluid flow from the inlet  22  to the biasing chamber  30 , thereby delaying pressure equalization between the inlet  22  and the biasing chamber  30  and preventing rapid opening and closing of the poppet  28  when the unloading valve  14  is open. 
         [0048]    When the relief valve assembly  10  is in a state of the unloading valve  14  being opened by a first pressure value in the signal line  38 , fluid is evacuated from the biasing chamber  30  through the evacuation line  34  and fluid continues to enter through the inlet pressure line  32  to pressurize the backside of the piston portion  40 . As the unloading valve  14  opens, the pressure on the backside of the piston portion  40  drops to below the inlet pressure to allow the poppet  28  to open. If the inlet pressure fluctuates and lowers to a value equal to or below the pressure at the backside of the piston portion  40 , the poppet  28  will close due to less opening force being exerted on the poppet  28  as the inlet pressure drops. Closing the unloading valve  14  allows the pressure on the backside of the piston portion  40  to rise to the level of the inlet pressure and to close the poppet  28  in conjunction with a resilient member  52 . 
         [0049]    When the unloading valve  14  is open, the orifice  50  impedes flow between the inlet  22  and the biasing chamber  30 , which prevents over saturation of the unloading valve  14  and enhancement of stability of the poppet  28 . When the unloading valve  14  is evacuating fluid from the biasing chamber  30 , the rate of evacuation is limited by the maximum flow rate of the unloading valve  14 . Flow above the maximum flow rate over saturates the unloading valve  14  and can cause fluid build up behind the poppet  28  causing the poppet  28  to close or preventing the poppet  28  from closing. The orifice  50  may reduce a fluid flow rate from the inlet  22  through the biasing chamber  30  and to the unloading valve  14  to a rate below the maximum flow rate of the unloading valve  14 . 
         [0050]    When fluid flows between the piston portion  40  and the inner surface  47 , the orifice  50  may reduce the fluid flow rate to the unloading valve  14  to a rate below the maximum flow rate of the unloading valve  14 . The orifice  50  may be an adjustable orifice to allow easy modulation of flow to the unloading valve  14 . Modulating the flow with the orifice  50  allows control of the fluid flow to the unloading valve  14  through the biasing chamber  30  without adjusting the fluid flow between the rearwardly extending portion  44  and the inner surface  47 . In an alternative embodiment, fluid does not flow between the poppet and the inner surface, allowing the orifice to control all fluid flowing to the unloading valve  14 . 
         [0051]    Reducing the flow rate with the orifice  50  below the maximum allows the poppet  28  to remain open while the pressure and flow rate at the inlet  22  rise indefinitely. Keeping the poppet  28  open prevents damage or wear to sensitive components connected to or near the relief valve assembly  10  and/or damage to the relief valve assembly  10  itself that otherwise might occur under high pressure conditions. 
         [0052]    When the unloading valve  14  is open, the orifice  50  allows a pressure differential to form between the inlet  22  and the biasing chamber  30  to increase stability of the poppet  28 . The pressure differential allows a reduction of the pressure within the biasing chamber  30  and fluid flow to the biasing chamber  30 , thus reducing the closing force exerted on the poppet  28  and allowing the poppet  28  to freely open without extra impedance from the fluid behind the poppet  28 . 
         [0053]    While the unloading valve  14  is open and the poppet  28  is open, a pressure differential exists between the biasing chamber  30  and the inlet  22  to increase the opening force compared to the closing force on the poppet  28 , thereby allowing the poppet  28  to more easily remain open. If the inlet pressure drops below the first pressure value, the unloading valve  14  closes and the pressure in the biasing chamber  30  begins to rise to the level of the inlet pressure. As the closing force from the pressure in the biasing chamber  30  approaches the opening force of the pressure in the inlet  22 , the poppet  28  will approach a neutral state where opening force is equal to closing force. The resilient member  52  allows the poppet  28  to close when in or near the neutral state of the inlet pressure being about equal to or slightly greater than the pressure in the biasing chamber  30 . 
         [0054]    The closing force on the poppet  28  is a function of pressure in the biasing chamber  30 , which is equal to or a function of the inlet pressure, and force from the resilient member  52 . Closing the poppet  28  prevents the outlet  24  from receiving excess fluid when the inlet pressure is below the first pressure value of the unloading valve  14 . The resilient member  52  may be a coil spring having one end seated on the piston portion  40  in the cavity  46  and another end seated on the adjustable stroke limiter  36 . The resilient member provides a closing force to a longitudinally facing portion of the piston portion  40  to bias the poppet  28  in the closed position. In an embodiment, the resilient member  52  is configured to provide a closing force only when the poppet  28  is in the open position. In an alternative embodiment the resilient member is not included. 
         [0055]    Referring now to the adjustable stroke limiter  36 , the adjustable stroke limiter  36  adjusts the compression of the resilient member  52  and may adjust the opening position of the poppet  28  allowing flow control of the outlet  24 . The adjustable stroke limiter  36  may be a piston including a radially outward groove  54  that receives a suitable seal  56 , such as an o-ring, against the inner surface  47  to prevent fluid from escaping between the adjustable stroke limiter and the valve body  20 . The piston may include a longitudinally facing surface for abutting the resilient member  52  within the biasing chamber. A nut  58 , such as a jam nut, is threaded for engaging a radially outer surface of the adjustable stroke limiter  36 . The nut  58  includes a longitudinally facing surface to abut the valve body  20  and allows securing the adjustable stroke limiter  36  into a position longitudinally spaced from the inlet pressure line  32  and the evacuation line  36 , opposite the poppet  28 . The adjustable stroke limiter  36  also includes a radially outwardly facing surface  62  abutting the inner surface  47 . The inner surface  47  allows the adjustable stroke limiter  36  to remain aligned with the longitudinal axis A during assembly of the adjustable stroke limiter  36  through the biasing chamber  30  or during adjustment of the nut  58  to longitudinally move the radially outwardly facing surface  62 . 
         [0056]    As the adjustable stroke limiter  36  is adjusted longitudinally toward the poppet  28 , the closing force of the resilient member  52  is increased. The opening stroke of the poppet  28  may be limited by requiring more inlet pressure to open the poppet  28  and/or by creating an interference with the resilient member  52  against itself during compression to stop the poppet  28  from retracting further. Increasing the compression of the resilient member  52  using the adjustable stroke limiter  36  biases the poppet  28  closed and allows inlet pressure to increase relative to the pressure in the biasing chamber  30  before the poppet  28  will open from the closed position or close from the open position. 
         [0057]    Adjusting the stroke length of the poppet  28  using the adjustable stroke limiter  36  allows flow control of the outlet by adjusting a fully-open position of the poppet  28  to reduce or increase a maximum flow rate between the poppet  28  and the valve seat  26 . Modifying the maximum flow rate to a value near or below the flow rate provided to the inlet  22  allows improvement of stability of the relief valve assembly  10  during use. For example, the maximum flow rate produced by a hydraulic circuit and provided to the inlet  22  may be 20 gallons per minute (GPM) and a maximum flow rate through the inlet  22  and between the poppet  28  and the valve seat  26  may be 100 GPM. As inlet pressure increases above the first pressure value to open the unloading valve  14  and the poppet  28 , the inlet pressure quickly drops below the first pressure value causing the unloading valve  14  and the poppet  28  to close. Once the poppet  28  is closed the inlet pressure may build up again above the first pressure value to re-open the unloading valve  14  and poppet  28  again, which may cause chattering of the unloading valve  14  and the relief valve  12 . 
         [0058]    Adjusting the adjustable stroke limiter  36  to limit the fully-open position of the poppet  28  reduces the maximum flow rate between the poppet  28  and the valve seat  26 . For example, adjusting the maximum flow rate to 20 GPM or lower than the 20 GPM hydraulic circuit allows the unloading valve  14  to remain open until pressure in the hydraulic circuit provided to the inlet  22  is below the first pressure value. Adjusting the maximum flow rate for the poppet  28  to remain open until the hydraulic circuit pressure lowers enough to cause the inlet pressure to drop below the first pressure value allows the relief valve  12  to relieve a pressure spike in the hydraulic circuit without the poppet  28  chattering or otherwise repeatedly opening and closing. In an embodiment the maximum flow rate produced by a hydraulic circuit and provided to the inlet  22  may be  50  gallons per minute (GPM) and a maximum flow rate through the inlet  22  and between the poppet  28  and the valve seat  26  may be 10 GPM. 
         [0059]    Raising the inlet pressure above the first pressure value allows the unloading valve  14  to re-open and in turn re-open the poppet  28 . Thus, after the inlet pressure falls below the first pressure value the relief valve assembly  10  enters a closing state with the unloading valve  14  closing and the poppet  28  closing, and after the inlet pressure rises above the first pressure value the relief valve assembly  10  enters an opening state with the unloading valve  14  opening and the poppet  28  opening. For example, the poppet  28  may open or close in response to the unloading valve  14  opening or closing, respectively. 
         [0060]    The unloading valve  14  may be integrated with the relief valve  12 . Integrating the unloading valve  14  and the relief valve  12  allows assembly cost savings by simplifying installation of the relief valve assembly  10  and allows material savings by using lines running shorter distances. Alternatively, the unloading valve  14  may be mounted remote from the relief valve  12 . For example, the unloading valve  14  may be fluidly connected at or near a critical component in the hydraulic circuit to minimize pressure fluctuations over a distance and remotely fluidly connected to the biasing chamber  30  through the evacuation line  34 . Mounting the unloading valve  14  near the critical component allows the unloading valve  14  to be responsive to pressure fluctuations to control the evacuation of the biasing chamber  30 . 
         [0061]    Referring to  FIG. 2 , the unloading valve  14  may be any suitable relief valve. For example, the unloading valve  14  may be a differential area unloading relief valve, such as a series RU101 valve available from Parker-Hannifin Corporation of Cleveland, Ohio, USA, exemplified in  FIG. 2 . The unloading valve  14 , which may be used as a pilot valve in a low flow accumulator unloading circuits, provides a fixed percentage between load and unload pressures. The unloading valve  14  includes an unloading valve body  68 , an evacuation signal port  70 , an inlet port  72 , and a tank port  74 . 
         [0062]    The evacuation signal port  70  is formed in a portion of the valve body  68  and is fluidly connected to the signal line  38  (as shown in  FIG. 1 ). The evacuation signal port  70  allows fluid from the inlet  22  to flow to the unloading valve  14  to indicate whether the unloading valve  14  should be open or closed. For example, the evacuation signal port  70  allows fluid to flow to a piston  76 , which in turn exerts a force on a poppet  80  based on the pressure in the inlet  22  ( FIG. 1 ) communicated through the evacuation signal port  70 . The poppet  80  transfers force against a resilient member  82 , for example a coil spring, that allows the poppet  80  to open by moving away from a valve seat  84  when the pressure communicated through the evacuation signal port  70  reaches a first pressure value. Opening the poppet  80  allows fluid from the inlet port  72  to flow through the unloading valve  14  and out of the tank port  74 , which may be formed in a portion of the valve body  68 . 
         [0063]    The inlet port  72  is formed in a portion of the valve body  68  and is fluidly connected to the evacuation line  34  ( FIG. 1 ). The inlet port  72  allows fluid from the biasing chamber  30  ( FIG. 1 ) to flow through the unloading valve  14  when the valve  14  is open. Fluid entering the inlet port  72  exerts an opening force on the poppet  80  in conjunction with the force from the piston  76 . The fluid from the inlet port  72  exerting an opening force is schematically represented by an evacuation pilot line  86  in  FIG. 1 . The fluid flow from the inlet port  72  through the unloading valve body  68  and out the tank port  74  is schematically represented by an evacuation flow line  88  in  FIG. 1  and illustrated fluidly connected to the tank port  74  through drain line  90  when the unloading valve  14  is open, thereby allowing fluid to flow from the biasing chamber  30  through the evacuation line  34  to a tank, for example through the outlet  24 . 
         [0064]    In another embodiment, the evacuation pilot line is physically connected to the evacuation signal port  70  separate from the evacuation flow line, which is fluidly connected to the inlet port  72 , while the signal line  38  is eliminated. Without the signal line  38  the evacuation line  34  signals the unloading valve  14  to open and evacuates fluid from the biasing chamber  30  when the pressure at the inlet  22  reaches the first pressure value and the unloading valve  14  opens. Using the evacuation line  34  to signal the unloading valve  14  instead of the signal line  38  allows assembly time savings by eliminating the signal line  38  and potential weight savings of the relief valve assembly  10 . In still another embodiment, the evacuation line is connected to inlet port  72 , while the signal line  38  is eliminated. 
         [0065]    Referring again to  FIGS. 1 and 2 , a check line  92  schematically represents a fluid connection between the tank port  74  and the poppet  80  to operate the poppet  80  as a check valve in response to high pressure fluid from the outlet  24 . During operation of the relief valve assembly  10  fluid exits the relief valve  12  through the outlet  24 . At high pressures the fluid may cause fluid to flow in reverse from the outlet  24  to the tank port  74 . The check line  92  allows the poppet  80  to close against the valve seat  84 , thereby preventing fluid from flowing from the outlet  24  through unloading valve  14 to the biasing chamber  30 . 
         [0066]    Turning now to  FIG. 3 , an exemplary embodiment of the relief valve assembly is shown at  110 . The relief valve assembly  110  is substantially the same as the above-referenced relief valve assembly  10 , and consequently the same reference numerals but indexed by  100  are used to denote structures corresponding to similar structures in the relief valve assembly  110 . In addition, the foregoing description of the relief valve assembly  10  is equally applicable to the relief valve assembly  110  except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the relief valve assemblies may be substituted for one another or used in conjunction with one another where applicable. 
         [0067]    The relief valve assembly  110  includes a poppet  128  that is hollow, i.e. defines a cavity  198 . The cavity  198  is fluidly connected to the biasing chamber  30  so that fluid from the biasing chamber  30  flows into the cavity  198  to fill the cavity to force a valve portion  142  of the poppet  128  radially outward and into a valve seat  126 . The force allows the valve portion  142  to expand against the valve seat  126  to decrease sealing imperfections against the valve seat  126 . For example, the valve portion  142  may deform slightly to the shape of a corresponding portion of the valve seat  126 , thereby removing gaps between the valve portion  142  and the valve seat  126 . 
         [0068]    Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.