Abstract:
An apparatus for reducing pressure spikes in a fuel line having a shut-off valve is provided. The apparatus comprises a body housing a biasing member and a moveable separation member. The body has first, second, and third chambers. The first and second chambers are coupled to upstream and downstream sides of the fuel line, respectively. The third chamber is coupled to a return line. When the shut-off valve is open, the separation member is biased toward the first chamber and separates the first and second chambers. When the shut-off valve is closed, the separation member expands the first chamber and places the first chamber and the third chamber in fluid communication once the separation member has gained a significant speed. The expanded first chamber accumulates fuel and the third chamber accumulates and vents the fuel such that transient pressure spikes are reduced and unlikely to damage a turbine system.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to a relief valve and, in more particularly, to a relief valve employable in an industrial turbine system.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the power generation industry, industrial turbine systems are used to generate electricity. The turbine systems include, among other things, an industrial turbine (e.g., a gas turbine), a supply tank, a supply skid, a metering skid, a pump, relief valves, shut-off valves, and connecting piping. The supply skid and metering skid cooperate to supply or feed the industrial turbine with a liquid fuel such as, for example, diesel fuel, jet fuel, kerosene, a gaseous fuel, and the like.  
         [0003]     The characteristics of the fuel are such that a sudden closure of a shut-off valve (i.e., a stop valve) in the turbine system results in a rapid rise in pressure within the system often resulting in a pressure spike. The rise in pressure, or pressure spike, often continues until a pump (e.g., a positive displacement or centrifugal pump) driving the fuel through the system can be effectively shut down or until a relief valve opens. In addition to the continued operation of the pump, the pressure can also rise as a result of the inertia of the pump, control sensing delays, the “water hammer” effect, and the incompressible nature of the fuel being used.  
         [0004]     The rate at which the pressure rises in the turbine system is often compounded when the shut-off valve closes very quickly. For example, in some cases, a shut-off valve used in the turbine system has to be very fast in order to protect the turbine from “overspeed” in certain operational and fault scenarios. The total shut-off time for the shut-off valve can be mere milliseconds. While closing the shut-off valve this quickly meets the requirements for discontinuing fuel flow to the turbine under emergency conditions, a rapid pressure rise of more than one hundred pounds per square inch (psi) per millisecond can be generated just upstream of the shut-off valve. With the pressure rising so quickly, some form of pressure relief must be provided before the pressure limitations of the equipment (e.g., pipes, fittings, etc.) are exceeded.  
         [0005]     In addition to the rapidly rising pressure dilemma, the abrupt closure of the shut-off valve also triggers a large “inertial” pressure oscillation in the piping, which can be seventy feet in length or more, between the supply skid and the metering skid in some installations. The pressure oscillation can potentially damage sensitive equipment used on the skid (e.g., flow and pressure sensors, a filter canister, etc.).  
         [0006]     While some relief valves have been designed to open very quickly to relieve pressure, these valves typically only provide a limited amount of flow. The limited amount of flow make these valves unusable in many turbine applications. As those skilled in the art can appreciate, increasing the flow area of a relief valve and reducing the opening time are conflicting design parameters. For example, attempts were made to design a relief valve that opens very quickly (i.e., in milliseconds or microseconds) to inhibit or prevent pressure spikes and inertial pressure oscillations while maintaining a sufficient effective maximum flow area to accommodate the amount of fuel (e.g., 150 gallons per minute) supplied by the fuel pump. While one embodiment of the relief valve was large enough to provide a full flow capability, the valve was limited to an opening response time of approximately forty milliseconds, which was simply too slow. Further optimization of the relief valve to improve on the forty millisecond response would likely create the potential for undesirable system instability due to relief valve chatter.  
         [0007]     Other possible solutions have been tried by industry. In one instance, to address the transient pressure spike problem, two five gallon gas-charged bladder accumulators were installed upstream of the shut-off valves. These types of accumulators not only provide very fast pressure relief, they also have very large flow absorption rates. However, the pressure in the gas-charged bladder accumulators changes as the temperature varies and this can cause problems. For example, to mitigate the effects of changing gas charge pressure due to temperature, a temperature control system had to be added to regulate the temperature of the accumulators. To ensure that the gas charge remains within allowable limits, periodic monitoring and maintenance of the gas pressure is required. This solution proved costly, complex, potentially unreliable, and resulted in a large, costly peripheral system. As a result, the addition of multiple accumulators to the turbine system to achieve higher reliability would not be fruitful in most applications. In fact, the use of accumulators increases the potential for gas leakage and lowers the overall reliability of the system.  
         [0008]     In another attempt to deal with pressure spikes or transient pressures, three-way shut-off valves have been used in turbine systems. Unfortunately, these devices are generally not very fast (e.g., they need 100 milliseconds to accomplish shut-off) and are not easily scalable to larger sizes while maintaining desired cost and package size. Also, these designs are generally limited to liquid fuel or water applications. Thus, an apparatus that can eliminate or mitigate the effects of pressure spikes and transient pressures in a cost effective, reliable, and efficient manner would be desirable. The invention provides such an apparatus. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     In one aspect, the invention provides an apparatus for reducing transient pressure spikes in a fuel line of a turbine system. The turbine system has a shut-off valve and a relief valve. The relief valve is upstream of the shut-off valve in the fuel line. The apparatus comprises a body, a biasing member, and a moveable separation member. The body forms a first chamber and a second chamber. The first chamber is coupled to the fuel line upstream of the shut-off valve and the second chamber is coupled to the fuel line downstream of the shut-off valve. The biasing member and the moveable separation member are within the body. The moveable separation member is forcibly biased toward the first chamber by the biasing member and separates the first and second chambers when the shut-off valve is open. The moveable separation member is adapted to expand the first chamber and compress the biasing member when the shut-off valve is closed. The expanding first chamber accumulates fuel while the relief valve is opening such that the transient pressure spikes are reduced and unlikely to cause damage to the turbine system.  
         [0010]     In another aspect, the invention provides an apparatus for reducing transient pressure spikes in a fuel line of a turbine system. The turbine system has a shut-off valve. The apparatus comprises a body, a biasing member, and a moveable separation member. The body has first, second, and third chambers. The first chamber is coupled to the fuel line upstream of the shut-off valve and the second chamber is coupled to the fuel line downstream of the shut-off valve. The third chamber is adjacent to and coupleable with the first chamber. The a biasing member and the moveable separation member are within the body. The moveable separation member is biased toward the first chamber by the biasing member and separates the first chamber from the second chamber when the shut-off valve is open. The moveable separation member is adapted to expand the first chamber, compress the biasing member, and place the first chamber and the third chamber in fluid communication when the shut-off valve is closed. At least one of the expanding first chamber and the third chamber accumulate fuel when the shut-off valve is closed. As such, the transient pressure spikes are reduced and unlikely to cause damage to the turbine system.  
         [0011]     In yet another aspect, the invention provides an apparatus for reducing transient pressure spikes in a fuel line of a turbine system. The turbine system has a shut-off valve. The apparatus comprises a body, a biasing member, and a moveable separation member. The body includes first, second, and third chambers. The first chamber is coupled to the fuel line upstream of the shut-off valve and the second chamber is coupled to the fuel line downstream of the shut-off valve. The third chamber is adjacent to and coupleable with the first chamber. The third chamber is coupled to a return line. The biasing member and the moveable separation member are within the body. The moveable separation member is biased toward the first chamber by the biasing member and separates the first chamber from the second chamber. The moveable separation member restricts flow between the first and third chambers when the shut-off valve is open. The moveable separation member is adapted to expand the first chamber, compress the biasing member, and place the first chamber and the third chamber in fluid communication when the shut-off valve is closed. The expanded first chamber accumulates fuel and the third chamber evacuates the fuel through the return line. As such, the transient pressure spikes are reduced and unlikely to cause damage to the turbine system.  
         [0012]     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:  
         [0014]      FIG. 1  is a simplified schematic of a turbine system environment that employs shut-off valves and in which the invention may operate;  
         [0015]      FIG. 2  is a simplified schematic of one exemplary embodiment of an apparatus for elimination of transient pressure spikes in a closed position and constructed in accordance with the teachings of the present invention;  
         [0016]      FIG. 3  is a simplified schematic of another exemplary embodiment of an apparatus for elimination of transient pressure spikes in a closed position and constructed in accordance with the teachings of the present invention;  
         [0017]      FIG. 4  is a simplified schematic of the apparatus of  FIG. 2  in an open position; and  
         [0018]      FIG. 5  is a simplified schematic of the apparatus of  FIG. 3  in an open position. 
     
    
       [0019]     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     The invention performs extremely fast, permits a high fuel flow rate, requires no temperature or pressure control system, alleviates hydraulic and mechanical vibration and/or damage to adjacent upstream and downstream components and sensitive equipment, is suitable for both gas and liquid fuels, is cost effective, and can be integrally constructed with a conventional shut-off valve. Prior to describing the invention in detail, an exemplary environment in which the invention may operate shall be briefly described. Those skilled in the art will recognize that the invention may operate in other environments.  
         [0021]     Referring to  FIG. 1 , a turbine system  10  used to generate electricity is shown. The turbine system  10 , which provides the exemplary environment for the invention, includes, among other things, an industrial turbine  12  (e.g., a gas turbine), a supply tank  14 , a supply skid  16 , and a metering skid  18  linked together by one or more sections of a fuel line  20  or fuel pipe. In some cases, the fuel line  20  between the supply skid  16  and the metering skid  18  can be seventy feet or more in length.  
         [0022]     The industrial turbine can be one of a variety of turbines commercially available in the industry such as, for example, the LMS 100™ High Efficiency Gas Turbine manufactured by GE Power Systems of Houston, Tex. The industrial turbine  12  is supplied or fed with a fuel  22  that is stored in the supply tank  14  and transported through the fuel line  20 . The fuel  22  that powers the industrial turbine  12  is preferably a liquid fuel such as, for example, diesel fuel, jet fuel, kerosene, a gaseous fuel, and the like, as known in the art.  
         [0023]     The supply skid  16  includes, among other things, a pump  24  for pressurizing and pushing the fuel  22  through the fuel line  20 , a filter  26  for removing contaminants from the fuel, and a shut-off valve  28 . The metering skid  18  includes, among other things, metering equipment  30  (e.g., sensors, monitors) and a shut-off valve  32 . One or more relief valves, such as relief valves  34 ,  36 , are adapted to relieve pressure within the fuel line  20  and can be incorporated into the turbine system  10  in a variety of different locations.  
         [0024]     Now that an environment in which the invention may operate has been described, details of the invention shall be articulated. As illustrated in  FIG. 2 , an apparatus  38  for eliminating and/or mitigating transient pressure spikes in a positive fluid system, such as the turbine system  10 , is shown. The apparatus  38  comprises a body  40  forming a first chamber  42 , a second chamber  43 , a third chamber  44 , a biasing member  46 , and a moveable separation member  48 .  
         [0025]     The body  40  can be made of any suitable valve material as known in the art. The body  40  can be integrally formed with the fuel line  20  and the shut-off valve  28  as shown in  FIG. 2  or, alternatively, can be configured such that the apparatus  38  is capable of being retro-fit onto an existing fuel line  20 . As depicted, the body  40  generally houses and incorporates the biasing member  46  and the moveable separation member  48 .  
         [0026]     As shown in  FIG. 2 , the apparatus  38  is coupled to the fuel line  20  and is “straddling” one of the shut-off valves, namely valve  28 . For the purposes of illustration and explanation, the fuel line  20  is referred as having an upstream portion  21  coming from the supply tank  14  and a downstream portion  23  proceeding toward the industrial turbine  12 . The two portions  21 ,  23  are defined and separated by the shut-off valve  28 . The upstream portion  21  is generally at an upstream pressure (P 1 ) while the downstream portion is generally at a downstream pressure (P 2 ) when the shut-off valve  28  is open and permitting full flow as shown in  FIG. 2 .  
         [0027]     The first chamber  42  is defined by portions of the body  40  and portions of the moveable separation member  48 . The first chamber  42  is coupled to the upstream portion  21  of the fuel line  20  by a pressure line  50  (i.e., a relief port). The pressure line  50  permits unrestricted and full fluid communication between the upstream portion  21  of the fuel line  20  and the first chamber  42 . Therefore, the first chamber  42  and the upstream portion  21  generally have an equivalent pressure (P 1 ) when the shut-off valve is open. As illustrated, the first chamber  42  is dimensioned to correspond to the size and shape of the moveable separation member  48 . Preferably, the first chamber  42  is a cylindrical and has smooth inner walls.  
         [0028]     The second chamber  43  is defined by portions of the body  40  and portions of the moveable separation member  48 . Preferably, the second chamber  43  is cylindrical and is larger than the first chamber  42 . Therefore, the intersection of the first and second chambers  42 ,  43  defines an annular opening  49  (i.e., a second relief port) in the body  40  as illustrated in  FIG. 2 . The second chamber  43  is coupled to the downstream portion  23  of the fuel line  20  by a sense line  52 . The sense line  52  preferably includes an orifice  54  that restricts the flow of fuel  22  between the second chamber  43  and the downstream portion  23 . Due to the orifice  54 , the second chamber  43  has a pressure (P 2 ′) that is somewhat lower than the pressure (P 2 ) in the downstream portion  23  of the fuel line  20  when the shut-off valve is open.  
         [0029]     As shown in  FIG. 2 , the third chamber  44  is defined by portions of the body  40 , the moveable separation member  48 , and a plug  45 . The third chamber  44  is generally adjacent to the first chamber  42  and at a third pressure (P 3 ). In a preferred embodiment as shown in  FIG. 3 , where like reference numerals indicate like components, the plug  45  is removed and replaced by a return line  88  that is coupled to the third chamber  44 . The return line  88  is preferably at a low pressure (P 4 ) in the range of zero to about three hundred pounds per square inch gauge. As shown in  FIGS. 2-3 , the third chamber  44  is restricted from fluid communication with the first chamber  42  by the moveable separation member  48  while the shut-off valve  28  is open.  
         [0030]     The biasing member  46  is preferably a resilient component such as, for example, a spring that includes a first end  56  and a second end  58 . The first end  56  is anchored to a back wall  60  of the body  40  in the second chamber  43  while the second end  58  is secured to the moveable separation member  48 . In an alternative embodiment, the biasing member  46  can be disposed in other locations such as, for example, in the first chamber  42  or outside the body  40  altogether. When installed in the apparatus  38 , the biasing member  46  is preferably in at least a partially compressed condition. As such, the biasing member  46  biases the moveable separation member  48  toward the first chamber  42  and into engagement with the body  40 . In other words, the biasing member  46  is provided with a “preload”. The biasing member  46  is indifferent to pressure and temperature changes and, therefore, there is no need for a pressure and/or temperature control system to regulate the environment of the biasing member  46 .  
         [0031]     The moveable separation member  48  separates the first chamber  42  from the second chamber  43 . While the moveable separation member  48  is shown as a plunger in the embodiment depicted in  FIG. 2 , the moveable separation member can be a diaphragm, a piston, a bladder, and the like. The plunger-type moveable separation member  48  includes a cylindrical body  62 , an aperture  63  in the cylindrical body, a circular cross member portion  64  extending transversely between the inner walls of the body, and a flange  66 .  
         [0032]     The aperture  63  in the cylindrical body  62  is offset and misaligned with respect to an opening  47  of the third chamber  44 . In an exemplary embodiment, the aperture  63  and the opening  47  are offset by about one half inch measured from the closest edge of each opening. Also, the generally cylindrical body  62  has a first open end  68  directed toward the first chamber  42  and a second open end  70  directed toward the second chamber  43 . The first open end  68 , the body  62 , and/or the cross member  64  collectively form an accumulation cavity  72  or “cup” adapted to catch and capture the fuel  22 .  
         [0033]     The cylindrical body  62  is dimensioned to allow the moveable separation member  48  to move and translate within the apparatus  38 . Preferably, the moveable separation member  48  is adapted to reciprocate axially back and forth such that portions of the cylindrical body are transitioned from being within the first chamber  42  to the second chamber  43 , and vise versa. As shown in  FIG. 2 , the flange  66  extends radially outwardly from an end of the body  62  disposed in the second chamber  43  and restricts the moveable separation member  48  from progressing entirely into the first chamber  42  by engaging a seating portion  74  of the body  40 . Although not shown, one or more sealing components can be interposed between the cylindrical main body  62  and the body  40  and/or between the flange  66  and the seating portion  74 .  
         [0034]     The moveable separation member  48  is generally positioned across the shut-off valve  28 . In fact, when the shut-off valve is fully opened, the cross member  64  is preferably vertically aligned with the shut-off valve  28  as oriented in  FIG. 2 . When situated in this manner, the moveable separation member  48  is able to automatically sense a pressure differential across the shut-off valve  28 . In other words, the moveable separation member  48  is sensitive to a pressure difference between the first and second chambers  42 ,  44  and between the upstream and downstream portions  21 ,  23  of the fuel line  20 .  
         [0035]     When the turbine  12  is operating at capacity and a maximum amount of fuel  22  is passing through the fuel line  20  and the shut-off valve  28 , there is preferably only a small pressure difference (e.g., about ten pounds per square inch) across the cross member  64  (i.e., between the first and second chambers  42 ,  44  and the upstream and downstream portions  21 ,  23 ). This small pressure differential, which would encourage the moveable separation member  48  to move toward the second chamber  43 , is counteracted by the biasing force provided by the biasing member  46  due to the preload. Therefore, during normal operation with the shut-off valve  28  fully open, the flange  66  from the moveable separation member  48  is biased against a seating portion  68  of the body  40 .  
         [0036]     In an exemplary embodiment, the biasing member  46  has an axial length of about eight inches when in an unbiased, fully-expanded state. Additionally, when interposed in a partially compressed state between the moveable separation member and a back wall  60  of the body  40  in the second chamber  43 , the biasing member  46  exerts approximately one hundred thirty pounds of biasing force on the moveable separation member  48 . Further, the moveable separation member  48  has a diameter of about two inches and six tenths (a radius of one inch and three tenths) in the exemplary embodiment and the biasing member  46  is rated to provide about eighty pounds of force per inch. In such an exemplary embodiment, the moveable separation member  48  has a mass of one and three tenths pounds and the orifice  54  has a diameter of about five hundredths of an inch.  
         [0037]     Continuing with the exemplary embodiment, the static friction between the body  40  and the moveable separation member is about ten pounds per square inch differential while the dynamic friction is about two pounds per square inch. Based on these parameters, the maximum estimated velocity (i.e., speed) of the moveable separation member  48  is about one hundred twenty inches per second.  
         [0038]     In operation, the apparatus  38  is called upon to perform when the shut-off valve  28  is rapidly closed such as, for example, in milli- or microseconds. For example, one of the shut-off valves as known in the art, such as valve  28 , can restrict flow as quickly as sixty-five milliseconds. Since about fifty of those milliseconds are due to cascaded first and second stage delays, the valve  28  actually progresses from permitting maximum flow to permitting no flow in around fifteen milliseconds.  
         [0039]     Referring to  FIG. 2 , when the shut-off valve  28  is quickly closed, the upstream pressure (P 1 ) in the upstream portion  21  of the fuel line  20  rapidly increases. The rate of pressure increase and the pressure increase are greater if the pump  24  ( FIG. 1 ) is still pumping, has not yet been deactivated, and/or deactivates slower than the shut-off valve is able to close. As the pressure (P 1 ) in the upstream portion  21  of the fuel line  20  rises, the pressure (P 1 ) in the first chamber  42  correspondingly rises since fluid communication exists via the pressure line  50 . The rising pressure in the first chamber  42  causes a force to be exerted on the moveable separation member  48 . As the force acting on the moveable separation member  48  increases, the biasing force of the biasing member  46  on the moveable separation member begins to be overcome.  
         [0040]     Additionally, with the shut-off valve  28  closed, the downstream pressure (P 2 ) in the downstream portion  23  of the fuel line begins to rapidly decrease. The rapid decrease in pressure (P 2 ) causes the pressure (P 2 ′) in the second chamber  43  to also decrease since fluid communication exists via sense line  52 . This is much different from a standard accumulator that has an increasing pressure in a second chamber due to an increasing pressure in a first chamber. Since the pressure (P 2 ′) in the second chamber  43  is decreasing simultaneously with an increasing pressure (P 1 ) in the first chamber  42 , the pressure differential across the cross member  64  of the moveable separation member  48  quickly rises. Therefore, the moveable separation member  48  is able to respond and move much quicker than a conventional accumulator. The rate of pressure decrease and pressure decrease in the second chamber  43  might be greater if the turbine  12  ( FIG. 1 ) continues to operate and demand a continuing supply of the fuel  22  in the downstream portion  23  of the fuel line  20 .  
         [0041]     The elevated pressure in the first chamber  42  and the decreased pressure in second chamber  43  collectively begin to rapidly change the pressure differential across the moveable separation member  48 . When the pressure differential across the moveable separation member  48  reaches a particular level, which is determined by the preload and biasing force of the biasing member  46 , the moveable separation member begins to move toward the second chamber  43 . For example, in the exemplary embodiment, the level is about twenty-five to seventy-five pounds per square inch differential. Since the particular amount of pressure differential needed to move the moveable separation member  48  is relatively small, movement of the moveable separation member is almost instantaneous when the shut-off valve  28  is closed.  
         [0042]     The apparatus  38 , and in particular the moveable separation member  48 , is able to move extremely quickly transition from the “closed” position shown in  FIGS. 2-3  to an “open” position as shown in  FIGS. 4-5 . As the moveable separation member  48  translates from the closed position to the open position, the first chamber  42  is expanded such that the apparatus  38 , using the accumulation cavity  72 , functions somewhat like an accumulator. Preferably, the expanding first chamber  42  ( FIGS. 4-5 ) is able to absorb fuel  22  at a rate faster than the pump  24  is able to output the fuel. In the exemplary embodiment, the expanding first chamber  42  can absorb six hundred forty cubic inches of the fuel  22  per second, which is about ten percent more than the pump can output. Since the expanded first chamber  42  can absorb the total pump flow for a brief time, there is more time available to overcome the fluid momentum in return line  88  and the third chamber  44  and the opening  47  can be relatively small.  
         [0043]     After the moveable separation member  48  has moved a sufficient distance toward the second chamber  43 , the aperture  63  is no longer blocked by the body  40  and aligns with the opening  47  of the third chamber  44  as shown in  FIGS. 4-5 . In the open position, the aligned aperture  63  and opening  47  permit additional fuel  22  to be subsequently evacuated from the expanded first chamber  42  and vented into the third chamber  44 . If the third chamber  44  is coupled to a return line  88  as shown in  FIG. 5 , the fuel  22  can also be expelled through the return line. Therefore, not only does the apparatus  38  permit the accumulation of a significant amount of the fuel  22 , the apparatus also permits the fuel to be vented into a third chamber  44  and, in some cases, a return line  88 .  
         [0044]     In the embodiment illustrated in  FIG. 4 , one or more of the accumulation cavity  72 , the expanded first chamber  42 , and the third chamber  44  absorb enough of the fuel  22  to provide one or more of the relief valves  34 ,  36  ( FIG. 1 ) with a sufficient amount of time to open and alleviate the pressure within an upstream portion  21  of the fuel line  20 . In the embodiment illustrated in  FIG. 5 , one or more of the accumulation cavity  72 , the expanded first chamber  42 , the third chamber  44 , and the return line  88  absorb enough of the fuel  22  to dissipate the pressure within the upstream portion  21  of the fuel line  20 . Since the return line  88  is employed, the relief valves  34 ,  36  are generally not needed.  
         [0045]     From the foregoing, it can be seen that the dual functionality (absorb and vent) of the apparatus  38  eliminates pressure spikes and transient pressures that, left uncompensated for, can cause damage throughout the turbine system  10 , both upstream and downstream of the shut-off valve  28 , due to mechanical and/or hydraulic vibrations when one of the shut-off valves  38 ,  32  is rapidly closed. Thus, sensitive components such as, for example, sensors, filter, containers, pipes, and the like are spared from damage.  
         [0046]     Advantageously, the apparatus  38  is self-actuating so that additional control systems are not required, does not require additional pump flow or an actuation source (e.g., an electric, a hydraulic, and a pneumatic source), and operates without an increase in parasitic flow rate. Further, the apparatus  38  does not alter the leakage classification of the shut-off valves  28 ,  32 , eliminates the need to use higher-pressure flanges and piping, and is cost effective, more reliable, and less complex than alternate solutions that attempt to mitigate and/or eliminate transient pressure spikes. Also, flow forces (e.g., Bernoulli forces that tend to resist the motion of the cross member  64 ) cannot cause instability because the cross member is already moving at a maximum speed by the time the aperture  63  is uncovered.  
         [0047]     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.  
         [0048]     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.  
         [0049]     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.