Abstract:
Bypass valve assembly that selectively establishes a bypass path for a fluid delivery system and having a body member with a fluid inlet and a bypass fluid outlet, a slidable piston assembly and a slidable cage assembly. Spring members bias the piston assembly and the cage assembly to a closed position to prevent fluid flow from the fluid inlet to the bypass fluid outlet when the delivery pressure is between an upper first threshold pressure value and a lower second threshold pressure value. When the delivery system pressure exceeds the first threshold pressure value, the piston assembly is moved to a first open position that permits fluid flow to the bypass fluid outlet; and when the delivery system pressure is less than the second threshold pressure value, the piston assembly is moved to a second open position to permit fluid flow to the bypass fluid outlet.

Description:
RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application No. 60/450,999 filed Feb. 28, 2003, entitled Multi-Phase Valve Assembly. 

   FIELD OF THE INVENTION 
   This invention is generally directed to fluid delivery systems and more particularly, but without limitation, to a bypass valve assembly establishing a bypass path when pressure exceeds or falls below set threshold limits. 
   BACKGROUND 
   Pressure relief bypass valves are often used in fluid delivery systems to establish a bypass path in the event of an overpressure condition. A typical bypass valve includes a spring-loaded piston seated on an internal orifice of a pump or other system member. The spring biases the piston into a sealed or closed position, and when the system pressure reaches a level sufficient to overcome the preset bias of the spring—sometimes referred to as the differential pressure set point—the piston is lifted from the orifice to allow fluid flow there through. 
   While effectively compensating for liquid overpressure conditions, bypass valves have not historically aided in the resolution of underpressure conditions, such as when a delivered fluid transitions to a vapor phase and/or entrained air condition. A fluid delivery system of interest is one that is carried out by connecting a hose from a tank of a delivery vehicle to a customer tank. The fluid is typically a liquid/vapor fluid that is pumped and metered from the vehicle to a customer&#39;s tank. 
   In the case of a vaporous fluid, such as hydrocarbon fuels like fuel oil and diesel, government regulations consider the delivery vehicle to constitute the point of sale and prohibit the sale of vapor and/or air, such as can occur should the delivery tank be emptied of liquid and the pump continue operating. Such systems often utilize a positive displacement pump that continues to deliver vapor and/or air after the delivery tank has been emptied of liquid. 
   Meters in the past were often provided with vapor eliminator stages to prevent the metering of vapor, but such meters have not always been effective as they can be overloaded and do nothing to prevent or alleviate the pumping of the fluid when a transition occurs to the vapor state. 
   There is therefore a continuing need for a bypass valve that effectively compensates for both overpressure and underpressure conditions, and which accommodates vapor phase conditions in fluid delivery systems. It is to such an improvement that the present invention is generally directed. 
   SUMMARY OF THE INVENTION 
   The present invention provides a bypass valve assembly which selectively operates to establish a bypass path for a fluid delivery system, the bypass valve assembly having a housing or body member with a fluid inlet that is connectable to the delivery system and is connectable to a bypass fluid outlet conduit. A slidable piston assembly is supported in the body and is moveable to a one of a closed position, a first open position and a second open position. In the closed position the piston assembly is positioned to prevent fluid flow from the inlet to the bypass fluid outlet. 
   Also provided are means that bias the piston assembly to the closed position when the pressure in the delivery system is between an upper first threshold pressure value and a lower second threshold pressure value. When the delivery system pressure exceeds the first threshold pressure value, said means moves the piston assembly to the first open position to permit fluid flow to the bypass fluid outlet; and when the delivery system pressure is less than the second threshold pressure value, said means moves the piston assembly to the second open position so that fluid flow is permitted from the fluid inlet through the bypass fluid outlet. 
   The features, advantages and objects of the present invention will be apparent from reading the following detailed description together with the drawings and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram of a fluid delivery system incorporating the bypass valve assembly of the present invention. 
       FIG. 2  is a semi-detailed, elevational cross-sectional view of the bypass valve assembly of the present invention. 
       FIG. 3  is a perspective view of the slidable cage assembly of the bypass valve assembly of  FIG. 2 . 
       FIG. 4  is a perspective view of the piston assembly of the bypass valve assembly of  FIG. 2 . 
       FIG. 5  is a semi-detailed, elevational cross-sectional view of the bypass valve assembly of  FIG. 2  during an overpressure condition, the system pressure having exceeded a predetermined upper threshold pressure value. 
       FIG. 6  is a semi-detailed, elevational cross-sectional view of the bypass valve assembly of  FIG. 2  during an underpressure condition, the system pressure having dropped to below a predetermined lower threshold pressure value. 
   

   DETAILED DESCRIPTION 
   As embodied herein, the present invention is generally directed to a bypass valve assembly that compensates for both liquid overpressure conditions and underpressure conditions in a fluid delivery system, the underpressure condition occurring when a vapor phase of the delivery fluid and/or air is encountered. Reference is first made to  FIG. 1 , in which is provided a simplified schematic block diagram of a fluid delivery system  100  in which a liquid is delivered from a source vessel to a target vessel. The source vessel typically is a tank on a delivery vehicle, the fluid is a hydrocarbon fuel and the target vessel is a customer tank. 
   A pump  102  (typically a rotary pump) receives fluid from a suction inlet conduit  104 . The pump  102  discharges the fluid to an outlet conduit  106  at a pressure nominally higher than that in the inlet conduit  104 . The particular internal configuration of the pump  102  can take a number of forms, and further details of such are omitted for clarity of discussion. For a description of a rotary pump suitable for use as the pump  102  in the fluid delivery system  100 , see U.S. Pat. No. 5,921,274 issued to Schuller et al., assigned to the assignee of the present application and incorporated herein by reference. Further, numerous valves, piping and control mechanisms commonly incorporated in fluid delivery systems are omitted herein as a description of such, being well known to those skilled in the art, are believed to be unnecessary for an understanding of the present invention. 
   A first bypass conduit  108  is in fluid communication with the fluid outlet conduit  106  and is connected to a bypass valve assembly  110 . A second bypass conduit  111  is connected by its proximal end to the first bypass conduit  108  and is connected to the bypass valve assembly  110  at its distal end. 
   As shown in  FIG. 2 , the bypass valve assembly  110  has a piston assembly  112  and a slidable cage assembly  114 , which are shown individually in  FIGS. 3 and 4 , respectively. With reference to  FIG. 3 , the cage assembly  114  is preferably formed from stainless steel or other suitably rigid, durable material. The cage assembly  114  has a plunger member  116  that has opposing surfaces  118 ,  119 , and a circumferentially extending, recessed O-ring seal  120 . Standoff flange members  122  project upwardly from the plunger  116  to support an annular collar  124  that has a central orifice  126 . 
   The piston assembly  112 , shown more clearly in  FIG. 4 , is also preferably formed of stainless steel or other suitable, rigid and durable material and is configured to be slidingly supported within the central orifice  126  of the cage assembly  114 . The piston assembly  112  includes a disc-shaped base  130  that has opposing seat surfaces  132 ,  134 . A cylindrical spring guide member  136  projects downwardly from the base  124 . A cylindrical flow member  138  extends upwardly from the base  124  and includes an entrance orifice  140  and a number of angularly spaced apart exit orifices  142 . 
   The cage assembly  114  and piston assembly  112  are supported in a housing or body member  144 , as shown in  FIG. 2 . The body  144  has an inlet  146  which is connectable to the first bypass conduit  108  to receive pump discharged fluid from the fluid outlet conduit  106  ( FIG. 1 ). The body  144  further includes a bypass outlet  148  in fluid communication with a bypass discharge conduit  149  ( FIG. 1 ). The body has a bonnet portion  150  that seals the lower end of the body  144 , forming an interior chamber  152  below the cage assembly  114 . The bonnet portion  150  has a pressure inlet orifice  154  communicating with the interior chamber  152  and connectable to the second bypass conduit  111  to assert fluid pressure on the lower surface  119  of the plunger  116 . 
   A coiled first spring  156  has a first end which bears against the top surface  118  of the plunger  116 , and a second end which wraps around the spring guide member  136  and bears against the base  130  of the piston assembly  112 . A coiled second spring  158  is disposed between an insert  160  in the body  144  and the cage assembly  114  to exert a downwardly directed force on the cage assembly  114 . 
   To explain the configuration of the bypass valve assembly  110  under various operational conditions, the following force values will first be defined. As shown in  FIG. 2 , force F 1  denotes the generally downwardly directed force upon the piston assembly  112  by the fluid pressure at the inlet  146 . Force F 2  denotes the generally upwardly directed force by the fluid pressure on the lower surface  119  of the plunger  116  by fluid entering the chamber  152  via the pressure inlet orifice  154  and the second bypass conduit  111 . 
   Because the lower surface  119  of the plunger  116  has a substantially larger surface area than that of an interior surface  162  of the piston assembly  112 , and the respective fluids provided to the inlet  146  and to the pressure inlet orifice  154  are at nominally the same pressure, the force F 2  will generally be substantially greater than the force F 1 . This will hold true regardless of the particular pressures of the respective fluids at the inlet  146  and the inlet orifice  154 . 
   Force F 3  denotes the force exerted by the first spring  156  on the piston assembly  112  with respect to the cage assembly  114 . Force F 4  denotes the force exerted by the second spring  158  on the cage assembly  114  with respect to the body  144  (via insert  160 ). 
     FIG. 2  shows a preferred configuration of the bypass valve assembly  110  during normalized pressure operation of the system  100  as the transported fluid is pumped in a liquid state within a selected operational pressure range. During such operation, the piston assembly  112  remains seated in a closed position (preferably via a metal to metal seal at annular junction  164 ), effectively sealing off the bypass outlet  148  from the inlet  146 . This state is maintained because the following relations are met:
   F 2 &gt;F 1 +F 4; and  (1) F3&gt;F1 
   That is, the force exerted upon the plunger  116  (F 2 ) exceeds the combined force of the inlet fluid against the piston assembly  112  (F 1 ) and the force of the second spring  158  (F 4 ) against the cage assembly  114 . Also, the piston assembly  128  remains biased upwardly against the collar  124  of the plunger  116  of the cage assembly  114  because the force of the first spring  156  (F 3 ) exceeds the inlet fluid force (F 1 ). 
     FIG. 5  shows a preferred configuration of the bypass valve assembly  110  during an overpressure condition of the system during which the transported fluid pumped by the system  100  exceeds a predetermined upper threshold pressure value. During such operation, the piston assembly  112  moves to a first open position, permitting fluid flow through the inlet  146 , through the exit orifices  142  of the piston assembly  112 , through the cage assembly  114  (via the openings between the standoffs  122 ) and out the bypass outlet  148 . It will be noted that the cage assembly  114  remains positioned as shown in  FIG. 2 , but the piston assembly  112  has moved relative thereto. This state can be described as follows:
   F 2 &gt;F 1 +F 4; and  (2) F1&gt;F3 
   In this regard, the bypass valve assembly  110  generally operates in a conventional fashion; that is, the force of the inlet fluid (F 1 ) at inlet conduit  146  is sufficient to compress the first spring  156  (which exerts F 3 ) and move the piston assembly  112  downwardly in the body  144  and away from its normally closed position to the first open position. 
     FIG. 6  shows a preferred configuration of the bypass valve assembly  110  during an underpressure condition of the system during which the transported fluid pumped by the system  100  falls below a predetermined lower threshold pressure value. For example, as discussed above, this can occur during the transition of a transported pressurized fluid from a liquid state to a vapor state, which will tend to result in a significant drop in the fluid pressure. 
   Thus, during operation of the valve assembly  110  as depicted in  FIG. 6  during a low pressure condition, the piston assembly  112  remains fixed relative to the cage assembly  114 , but the piston assembly  112  and the cage assembly  114  advance together downwardly, thereby moving the piston assembly to a second open position in which fluid flow is permitted from the inlet  146  to the bypass outlet  148 . Operation of the system under such condition can be described as follows:
 
 F 4 &gt;F 2 −F 1; and  (3)
 
F3&gt;F1
 
   It will be noted that in this condition, the force (F 4 ) of the second spring  158  is sufficient to overcome the difference between the fluid forces F 2  and F 1 , and the plunger  116  moves down to abut the bonnet  150 .  FIG. 6  also represents the steady state condition of the piston assembly  112  of the bypass valve assembly  110  when no fluid pressure is present (such as during a nonoperational, nonpressurized state of the system  100 ). 
   From the foregoing discussion it will be apparent that the relative surface areas of the interior surface of the piston assembly  112  and the lower surface  119  of the plunger  116 , and the respective spring forces of the first and second springs  156 ,  158 , are preferably selected to meet the above conditions set forth by equations (1) through (3) for a given upper threshold pressure value and a lower threshold pressure value. While coiled springs (such as  156 ,  158 ) have been disclosed as a preferred manner in which to apply biasing forces to the piston assembly  112  and the cage assembly  114 , it will be recognized that any number of other methodologies could readily be employed to supply the respective operational forces. 
   Moreover, while preferred embodiments have contemplated the underpressure condition arising as a result of a transition from a liquid phase to a vapor phase for the transported fluid, such is not limiting to the scope of the invention. Rather, the bypass valve assembly can readily be configured to operate to detect and establish bypass paths for any desired upper and lower pressure thresholds, regardless whether the fluid undergoes a state transition (e.g., from a liquid to a vapor). 
   Based on the foregoing, it will now be understood that the present invention is generally directed to the above described subject matter, without limitation. While the present invention has been described with the reference to a preferred embodiment thereof, those skilled in the art will appreciate various changes in form and detail may be made without departing from the intended scope of the present invention as defined in the appended claims.