Abstract:
A discharge valve including a valve seat and a piston having a head with a bottom surface that is convex across its entirety for engaging the valve seat. The piston has a stem extending upwardly from the head away from the valve seat. A valve guide has a socket for slidably receiving the stem of the piston and a number of apertures intersecting the socket for providing pressure relief thereto. A compressed spring is disposed between the valve guide and the head for normally retaining the piston in engagement with the valve seat.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fluid handling apparatus and, more particularly, to direct response valves of reciprocating type. 
     BACKGROUND OF THE INVENTION 
     It is not uncommon for subterranean reservoir rocks to be fully saturated with oil and gas yet be of such low permeability that they are not feasible to develop in an economic manner. In such cases, production rates are often boosted by resorting to hydraulic fracturing, a technique that increases rock permeability by opening channels through which reservoir fluids can flow to recovery wells. During hydraulic fracturing, a fluid such as water is pumped into the earth under extremely high pressure where it enters a reservoir rock and fractures it. Sand grains, aluminum pellets, glass beads, or other proppants are carried in suspension by the fluid into the fractures. When the pressure is released at the surface, the fractures partially close on the proppants, leaving channels for oil and gas to flow to recovery wells. 
     Specialized pumps are used to develop the pressures necessary to complete a hydraulic fracturing procedure or “frac job.” These pumps are usually provided with so-called fluid ends within which reciprocating plungers place fluids under pressure. Suction and discharge valves control fluid flow to and from the plungers. Improperly locating a valve in the fluid end at the time of manufacture can greatly weaken the fluid end, leading to a catastrophic pump failure. Similarly, a valve that has too many projections can capture or “knock out” enough proppant to block the flow of fluid through a pump requiring, at a minimum, that time and effort be invested to clear the blockage—a costly undertaking in an oilfield environment. 
     Commonly used discharge valves possess a plurality of guides or “wings” that protrude into a valve seat to hold a piston in place. These wings are known to capture proppant from a fracture fluid under certain operating conditions. Such conditions should, however, be virtually nonexistent. 
     SUMMARY OF THE INVENTION 
     In light of the problems associated with fluid ends of pumps used for hydraulic fracturing, it is a principal object of the invention to provide a discharge valve that reduces the likelihood of proppant being knocked out of suspension to create a blockage. The discharge valve of the present invention, thus, offers few impediments (none whatsoever in a pumping chamber of a fluid end) to flow through a fluid end when open so that fracturing fluids can flow smoothly through it. As a result, fracturing fluids with higher than normal concentrations of suspended proppants can be pumped with substantial cost savings to the user. 
     It is an additional object of the invention to provide a discharge valve of the type described that, because of its compact size, can be positioned close to the suction valve that it may be paired with permitting faster transit times for a fluid through a pumping chamber and greater efficiencies in the operation of a pump. 
     It is another object of the invention to provide a discharge valve of the type described that can be seated in a relatively shallow pocket in a fluid end. As is well known, a valve pocket of shallow depth requires that less load-bearing material be removed from the body of a fluid end thereby enhancing the strength and durability of a fluid end. It is less likely, then, that a fluid end configured to receive the discharge valve of the present invention will fail from the development of excessive internal loads and stresses. 
     It is a further object of the invention to provide a discharge valve of the type described that utilizes a valve seat that abuts its supporting surface, i.e., a seat deck, at a shallow incline rather than at right angles as is common. A slope of about 30° has been found to significantly reduce zones of stress transmitted through a fluid end. It is along such stress zones that fluid ends have been known to crack and fail under load. 
     Still another object of the invention is to provide a discharge valve of the type described that includes special porting to reduce the likelihood that the valve will become stuck in either an open position or a closed position during use. Therefore, the valve is virtually failsafe. 
     It is an object of the invention to provide improved elements and arrangements thereof in a discharge valve for the purposes described which is lightweight in construction, inexpensive to manufacture, and dependable in use. 
     Briefly, the discharge valve in accordance with this invention achieves the intended objects by featuring a valve seat and a piston with a bottom surface that is convex across its entirety for engaging the valve seat. The piston has a stem that extends upwardly from the head away from the valve seat and into a socket in a valve guide. The socket is formed in a conical prop projecting downwardly from a disc-like plug. A number of apertures traverse the plug and intersect the socket to providing pressure relief to the socket. A compressed spring is disposed between the valve guide and the head for normally retaining the head in engagement with the valve seat. 
     The foregoing and other objects, features and advantages of the present invention will become readily apparent upon further review of the following detailed description of the preferred embodiment as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be more readily described with reference to the accompanying drawings, in which: 
     FIG. 1 is a side elevational view of a discharge valve in accordance with the present invention with portions broken away to reveal details thereof. 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG.  1 . 
    
    
     Similar reference characters denote corresponding features consistently throughout the accompanying drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the FIGS., a discharge valve in accordance with the present invention is shown at  10 . Valve  10  includes a valve seat  12  for positioning in a discharge passage  14  of a fluid end  16  and a reciprocating piston  18  for controlling the flow of fluid through passage  14 . Piston  18  has a head  20  for engaging the top surface  22  of seat  12  and a stem  24  extending upwardly from head  20 . Stem  24  is slidably positioned in a close-fitting socket  26  in a valve guide  28  positioned above valve seat  12  in passage  14 . A number of apertures  30  connect the inner end of socket  26  with passage  14  to prevent piston  18  from becoming stuck in a raised or open position. A compressed spring  32  is disposed between the valve guide  28  and head  20  to normally retain head  20  in engagement with valve seat  12 . 
     Valve seat  12  is a hollow cylinder or tube with top and bottom surfaces  22  and  34  that are shaped to reduce turbulence. As shown, top surface  22  is beveled such that it slopes downwardly and inwardly toward the center of seat  12  at an angle of about 30°. Bottom surface  34 , however, slopes upwardly and inwardly at an incline that increases evenly from the outer wall  36  of seat  12  to the inner wall  38  thereof. Thus, bottom surface  34  is rounded. 
     Extending outwardly from the top of outer wall  36  of valve seat  12  is a peripheral flange  40 . The bottom of flange  40  slopes downwardly and inwardly toward outer wall  36  at an angle of approximately 30°. This angle corresponds with that of a seat deck  42  in fluid end  16  that surrounds passage  14  thereby ensuring the formation of a strong platform for seat  12  capable of reducing the transmission of stresses to fluid end  16 . To ensure against fluid leaks around seat  12 , outer wall  36  is provided with a pair of peripheral grooves beneath flange  40  within which are positioned O-ring seals  44  and  46  for engaging fluid end  16 . 
     Head  20  of piston  18  has a convex, bottom surface  48  that curves downward like the surface of a sphere, a planar top surface  50  and a circular, peripheral surface  52  that joins bottom and top surfaces  48  and  50  together. Bottom surface  48  is adapted to snugly engage top surface  22  of seat  12 . About the periphery of bottom surface  48  is a band or insert  54  formed of hard plastic that may also engage top surface  50  and serve as seal. Insert  54  has a cross-section resembling an inverted “L” with an upper, horizontal leg  56  from which a vertical leg  58  extends downwardly. A peripheral channel  60  with a corresponding, inverted “L” shape is provided in surface  52  to receive and retain insert  54 . 
     Top surface  50  of head  20  includes a shallow recess  62  about the base of stem  24  Recess  62  is provided to reduce the weight of piston  18  so that it can rapidly respond to fluid pressure changes in passage  14 . Also, recess  62  serves as an abutment for the bottom of spring  32 . A step or shoulder  64  rising from the bottom of recess  62  around step  24  insures that the bottom of spring  32  cannot shift in position and become lodged against the bottom of valve guide  28 . 
     Valve guide  28  includes a disc-shaped plug  66  having a circular, side wall  68  and a circumferential flange  70  projecting outwardly from the top of side wall  68 . Flange  70  engages a seat deck  72  in fluid end  16  surrounding passage  14 . Since guide  28  transmits significantly smaller loads to fluid end  16 , it is not necessary that seat deck  72  be sloped like seat deck  42 . To prevent fluid leaks around plug  66 , side wall  68  is provided with a pair of peripheral grooves beneath flange  70  within which are positioned O-ring seals  74  and  76  for engaging fluid end  16 . 
     A conical prop  78  is integrally formed with plug  66  and has an exterior diameter that decreases gradually from its top, at plug  66 , to its bottom, remote from plug  66 . As shown, prop  78  extends downwardly from the center of plug  66  to provide an abutment for head  20  of piston  18 . Socket  26  extends upwardly through the center of prop  78  and partially through plug  66 . The base of prop  78  is provided with a peripheral ledge or step  80  that provides a surface through which apertures  30  may penetrate to access to the inner end of socket  26  and, in acting as an abutment for spring  32 , keeps the top of spring  32  from blocking apertures  30 . Preferably, guide  28  is provided with six apertures  30  that extend radially outward from socket  26  at even intervals of 60° so that if one aperture  30  happens to become blocked the others can serve as backups. 
     Projecting from the top of plug  66  is a sleeve  82  with interiorly threaded socket  84 . Sleeve  82  is used in a conventional manner to lift guide  28  from passage  14  when it is desired to service valve  10 . 
     From the foregoing, it should be appreciated that use of valve  10  is straightforward. After installation of valve  10  in fluid end  16 , a plunger (not shown) is reciprocated beneath seat  12 . As the plunger moves forward to drive fluid through seat  12 , the compressive force of spring  32  is overcome and piston  18  is elevated to the position shown in FIG.  1 . With head  20  being disengaged from seat  12 , fluid flows smoothly through valve  10  and out port  86  in fluid communication with passage  14 . When the plunger travels back to its starting point, a partial vacuum is created within seat  12  that permits the compressive force of spring  32  to drive concave bottom surface  48  and insert  54  into the top surface  22  of seat  12  thereby preventing fluid in port  86  or passage  14  to travel back through valve  10  toward the plunger. 
     The process of opening and closing valve  10  is entirely automatic and requires mere fractions of a second to accomplish. Since the valve  10  minimizes turbulent flow, there is little likelihood that proppant will be captured by valve  10  to block flow through passage  14  under normal conditions of use. It has been found that the resistance of valve  10  to knocking out proppant is so great that fluids containing greater proppant loads than those normally pumped can be delivered through valve  10  providing great cost savings. 
     While the invention has been described with a high degree of particularity, it will be appreciated by those skilled in the art that modifications may be made thereto. Therefore, it is to be understood that the present invention is not limited to the sole embodiment described above, but encompasses any and all embodiments within the scope of the following claims.