Abstract:
A homogenization valve includes a housing and stacked valve members within the housing. The valve members have central holes therethrough defining a high pressure volume. Each valve member includes a valve seat defining, with a valve surface, gaps through which fluid is expressed radially from an inside high pressure volume to the outer low pressure volume. An actuator closes one end of the central volume and acts on the valve members to control the width of the gaps. A pressure barrier is positioned within the central volume to reduce the force from the central volume acting on the actuator.

Description:
RELATED APPLICATIONS 
     The present application is related to U.S. application Ser. Nos. 09/350,503 entitled “HOMOGENIZATION VALVE WITH OUTSIDE HIGH PRESSURE VOLUME” by Michael Jarchau and Ser. No. 09/350,504 entitled “VALVE MEMBERS FOR A HOMOGENIZATION VALVE” by Michael Jarchau, Harald O. Korstvedt, and Blaine Potter, both applications being filed concurrently with the present application and incorporated herein in their entirety by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Homogenization is the process of breaking down and blending components within a fluid. One familiar example is milk homogenization in which milk fat globules are broken-up and distributed into the bulk of the milk. Homogenization is also used to process other emulsions such as silicone oil and process dispersions such as pigments, antacids, and some paper coatings. 
     The most common device for performing homogenization is a homogenization valve. The emulsion or dispersion is introduced under high pressure into the valve, which functions as a flow restrictor to generate intense turbulence. The high pressure fluid is forced out through a usually narrow valve gap into a lower pressure environment. 
     Homogenization occurs in the region surrounding the valve gap. The fluid undergoes rapid acceleration coupled with extreme drops in pressure. Theories have suggested that both turbulence and cavitation in this region are the mechanisms that facilitate the homogenization. 
     Early homogenization valves had a single valve plate that was thrust against a valve seat by some, typically mechanical or hydraulic, actuating system. Milk, for example, was expressed through an annular aperture or valve slit between the valve and the valve seat. 
     While offering the advantage of a relatively simple construction, the early valves could not efficiently handle high milk flow rates. Homogenization occurs most efficiently with comparatively small valve gaps, which limits the milk flow rate for a given pressure. Thus, higher flow rates could only be achieved by increasing the diameter or size of a single homogenizing valve. 
     Newer homogenization valve designs have been more successful at accommodating high flow rates while maintaining optimal valve gaps. Some of the best examples of these designs are disclosed in U.S. Pat. Nos. 4,352,573 and 4,383,769 to William D. Pandolfe and assigned to the instant assignee, the teachings of these patents being incorporated herein in their entirety by this reference. Multiple annular valve members are stacked one on top of the other. The central holes of the stacked members define a common, high pressure, chamber. Annular grooves are formed on the top and/or bottom surfaces of each valve member, concentric with the central hole. The grooves are in fluid communication with each other via axially directed circular ports that extend through the members, and together the grooves and ports define a second, low pressure, chamber. In each valve member, the wall between the central hole and the grooves is chamfered to provide knife edges. Each knife edge forms a valve seat spaced a small distance from an opposed valve surface on the adjacent valve member. In this design, an optimal valve spacing can be maintained for any flow rate; higher flow rates are accommodated simply by adding more valve members to the stack. Such systems have required high actuator forces and resulting pressures, for example, approximately 500 to 1,000 psi, to maintain the homogenization pressure in the homogenization valve. 
     SUMMARY OF THE INVENTION 
     In accordance with aspects of the present invention, the homogenization valve includes a housing and stacked valve members within the housing. The valve members have central holes therethrough defining a high pressure volume. Each valve member includes a valve seat defining, with a valve surface, gaps through which fluid is expressed radially from an inside high pressure volume to the outer low pressure volume. An actuator closes one end of the central volume and acts on the valve members to control the width of the gaps. A pressure barrier is positioned within the central volume to reduce the force from the central volume acting on the actuator. In particular, the pressure barrier may be a post fixed to the housing and having a fluid seal between the post and actuator. 
     By reducing the amount of actuator force required to maintain a predetermined homogenization pressure, preexisting actuators can be used for applications, such as silicone emulsions in coating fabrics, which require even higher actuator force than presently available. As a consequence of the reduced actuator force that is required, pneumatic actuators that use conventional air supply devices, for example, 85 psi, can be used in accordance with the present invention. Pneumatic actuators eliminate the need for an electric pump, a heat exchanger including cooling coils, and other accessories associated with hydraulic actuators. 
     In accordance with another aspect of the present invention, annular springs that align adjoining pairs of valve members are positioned within spring-grooves in the valve members. Preferably, the springs are positioned in the high pressure volume so that the springs are exposed to less turbulent flow. 
     In accordance with yet other aspects of the present invention, the valve members include integral spacing elements to maintain the gaps at predetermined widths wherein the actuator adjusts the width of substantially all of the gaps by compressing the spacing elements. The spacing elements can be formed from a first material such as stainless steel and the valve seats and valve surfaces can be formed from a second material such as tungsten-carbide. This configuration minimizes wear of the valve seat and surface while allowing compression of the spacing elements to maintain the valve gaps. 
     A flow restrictor may be provided on the outlet of the homogenization valve to create back pressure therein. The valve can further include an axially directed surface exposed to the back pressure to substantially counterbalance forces from the back pressure against the actuator. 
     The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
     FIG. 1 is a cross sectional view of a preferred embodiment of a hydraulically balanced homogenization valve in accordance with the present invention; 
     FIG. 2 is a cross sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 illustrates a plan view of an exemplary valve member with spacer pads in accordance with the present invention; 
     FIG. 4 is a side view of the valve member shown in FIG. 3; 
     FIG. 5 is a cross sectional view taken along line  5 — 5  of FIG. 3; 
     FIG. 6 is an enlarged view of the encircled area referenced as “A” of FIG. 5; 
     FIG. 7 is an enlarged view of the encircled area referenced as “B” of FIG. 5; 
     FIG. 8 is a cross sectional isometric view of an alternative valve member; and 
     FIG. 9 is a cross sectional view of yet another alternative valve member. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a cross sectional view of a hydraulically balanced primary valve assembly  2  for use in a homogenizing system (complete system not shown) that has been constructed according to the principles of the present invention. 
     High pressure fluid driven by a pump (not shown) enters inlet port  4  of inlet flange  6  where it is directed into high pressure central chamber or volume  8 . The high pressure fluid from high pressure chamber  8  is expressed through valve gaps  16  into an outer low pressure chamber or volume  9 . The fluid passing into the low pressure chamber  9  enters outlet port  10  of outlet flange  11 . Inlet flange  6  and outlet flange  11  form part of housing  13  which also surrounds the valve gaps  16  and forms the outer periphery of the low pressure chamber  9 . It is noted that two different embodiments of the invention are shown on either side of longitudinal axis A—A, the one to the left having two valve gaps  16  and the one to the right having four gaps. The number of gaps  16  is controlled by choosing different sets of valve members placed in the assembly  2 . 
     A pneumatic system P delivers high pressure fluid to actuator  12  thereby applying a downward force in the direction of arrows  14 . Thus, the actuator  12  moves the force transfer member  30  downward to compress the valve members  18 . A second actuator  20  may be provided to apply side pressure on member  30  to reduce vibration of the same. 
     As illustrated, gaps  16  and valve springs  22  are provided between each valve member pair. The gaps  16  provided between each valve member pair form a restricted passageway through which the emulsion or dispersion is expressed to the low pressure chamber  9 . The gaps  16  can be constructed according to that illustrated in FIG. 3 of the &#39;769 patent. Preferably, the gaps  16  are constructed according to those disclosed in commonly assigned U.S. Pat. No. 5,749,650, filed Mar. 13, 1997, and U.S. Pat. No. 5,899,564 filed May 11, 1998, the contents of both patents being incorporated herein in their entirety by this reference. 
     More specifically, the height of the gap  16  is preferably between 0.0013 and 0.0018 inches, usually about 0.0015 inches, but in any event less than 0.003 inches. This dimension is defined as the vertical distance between the valve seat or land and the opposed, largely flat, valve surface. Experimentation has shown that the gap should not be simply increased beyond 0.003 inches to obtain higher flow rates since such increases will lead to lower homogenization efficiencies. 
     In the preferred embodiment, the valve seat is a knife-edge configuration. With reference to FIGS. 5-7, on the upstream, high pressure side of the gap, the valve seat or land  24  is chamfered at  60 ° angle sloping toward the valve surface  26 . In the gap, the valve seat  24  is flat across a distance of ideally approximately 0.015 to 0.020 inches, but less than 0.06 inches. On the downstream, low pressure side of the gap  16 , the valve seat  24  slopes away from the valve surface  26  at an angle from 5 to 90° or greater, approximately 45° in the illustrated embodiment. As particularly illustrated in FIG. 7, the valve surface  26  is similarly constructed. The downstream terminations of valve surfaces overlap valve seats or lands by no more than 0.025 inches. Preferably, the downstream terminations of the valve surfaces  26  overlap the valve seats  24  by at least a height of the valve gaps  16 . It has also been found that no overlap between the valve seats  24  and valve surfaces  26  can be effective as well. 
     Returning to FIG. 1, the stack of valve members  18  is sealed against the inlet flange  6  and outlet flange  11  at its lower end by O-rings  28 . The top-most valve member  18  engages force transfer member  30  which is hydraulically or pneumatically urged by actuator  12 . By varying the pressure of a hydraulic fluid or pneumatically in actuator  12 , the pressure applied to member  30  can be dynamically adjusted to control the size of the valve gap  16 . O-rings  32  provide a fluid seal between the top valve member  18  and member  30 . 
     It is known that the valve gaps increase with use of the valve as the fluid wears down the valve seat and valve surfaces. This results in a decreased pressure differential between the inner high pressure chamber  8  and the low pressure chamber  9 . Consequently, the fluid may not be properly homogenized. Prior art systems have employed the actuator to apply an increased downward force to close the desired number of valve gaps (e.g., usually two or three valve gaps to maintain a constant flow area). For example, as disclosed in the &#39;769 patent, the downward force flexes the top valve members to close the desired number of valve gaps to adjust the pressure differential. 
     The inventive valve members  18  include spacing elements or pads which allow the valve members to be compressed by the actuator  12  such that substantially all the valve gaps  16  are adjusted to compensate for wear. This has the advantage of maintaining a predetermined (and often optimized) separational distance between the valve seat and valve surface as wear occurs. 
     FIGS. 3-5 and FIG. 8 illustrate exemplary spacer pads  34  that form part of valve member  18 . Area  36  is machined off leaving the spacer pads  34 . Valve members  18  are stacked on one another with spacer pads  34  of one valve member contacting the underside  38  of a contiguous valve member to form the valve gaps  16  between the valve seat  24  and opposing valve surface  26 . Alternatively, spacers pads  34  can be a separate element coupled to or positioned adjacent the valve members  18 . The spacer pads  34  are small enough such that they can be compressed by the actuator  12 . In a preferred embodiment of the present invention, each spacer pad  34  has a surface area of approximately 11 mm 2  that touches the underside  38  of a contiguous valve member  18  when assembled. This allows each spacer pad  34  to be compressed up to about 0.002 inches (0.0508 mm). 
     The valve members  18  are aligned with respect to each other and maintained in the stack formation by serpentine or wave valve springs  22  that are confined within cooperating spring-grooves  23  formed in each valve member. The valve springs  22  also spread the valve members  18  apart to increase the valve gaps  16  when the actuating pressure is reduced in a valve cleaning operation. Furthermore, the valve spring  22  ends can be bent, for example, 90 degrees, and inserted into machined notches or pockets  60  (see FIGS. 3 and 8) in adjacent valve members such that the stack of valve members maintains preferable angular alignment. Such a configuration prevents rotation of the valve members relative to one another. That is to say, the spacer pads  34  are aligned in vertical rows when preferably aligned. 
     Although the valve gaps  16  of FIG. 1 are shown to be adjacent the high pressure chamber  8 , the valve members  18  can be configured such that the valve gaps are adjacent the low pressure chamber  9 . This configuration is shown by alternative valve member  18 ′ of FIG.  8 . This allows the turbulent expressed fluid into the open chamber  9  and not over the springs, an arrangement which has been found to minimize chattering of the valve members  18 . Chattering of the valve members  18  is undesirable as such can damage the valve members, emit noise, and produce other deleterious effects in the operation of the valve  2 . 
     The high pressure fluid in chamber  8  causes an upward force on member  30  equal to the product of pressure and the area of member  30  exposed to the pressure. In prior systems, that area was the entire area within the circular valve gaps. In accordance with an aspect of the present invention, the area of member  30  which is exposed to the high pressure of chamber  8  is substantially reduced by a pressure barrier or post  40  within the central high pressure chamber which is secured at its lower end to the housing  13  by a nut  42 . 
     At the upper end of pressure barrier  40 , a wider or flared portion  44  provides a surface  46  to absorb the upward force of the high pressure fluid in chamber  8 . The pressure barrier  40  is sealed against the housing  13  at its lower end by O-ring  48 . The pressure barrier is sealed against the top-most valve member  18  at its upper end by O-ring  50 . Essentially, the pressure barrier  40  acts as a plug to absorb the majority of the upward force in chamber  8 , transmitting the force to the housing and thus reducing the net force acting on the actuator. Hence, a valve  2  is provided wherein a lower actuator force is required due to the portion  46  of pressure barrier  40  reducing the net surface area on which the liquid in chamber  8  may push upward against the actuator  12 . Thus, the same actuator can accommodate higher homogenization pressures used in applications such as silicone emulsions in coating fabrics. 
     The valve may further be provided with a single stage valve  52  at the outlet flange that provides back pressure in chamber  9 . Theories suggest that such back pressure suppresses cavitation and increases turbulence in chamber  9 , thereby increasing the efficiency of the valve  2 . The preferred back pressure is between 5% and 20% of the pressure at the inlet port  4 . A back pressure of about 10% has been found particularly suitable. Other suitable flow restrictors can be employed in accordance with the present invention. 
     If valve  52  is employed, significant back pressure may result in chamber  9  which causes an upward force on the actuator  12 . To reduce this upward force, an axially directed surface  54  is provided on member  30  on which the fluid in chamber  9  pushes downward to counteract the upward force. Thus, a counterbalancing mechanism is provided to reduce the force of back pressure on the actuator  12 . The surface  54  extends to an inner radius which approximates or equals the radius of the valve gap. Appropriate counterbalancing is obtained regardless of the level of backpressure without any need for adjusting the actuator force. 
     FIG. 9 illustrates yet another alternative embodiment of the valve member, designated by reference numeral  18 ″. This valve member  18 ″ illustrates the spacer pads  34  adjacent the high pressure volume  8  and the valve seat  24  and valve surface  26  adjacent the low pressure volume  9 . The valve member  18 ″ is formed from at least two materials: a hard, durable material forming the valve seat and valve surface to minimize wear thereof and a relatively soft, compressible material forming the spacer pads to allow compression without cracking thereof. Preferably, an inner ring  56  of a relatively soft material, such as stainless steel, is inserted into an outer ring  58  of a harder, more durable material, such as tungsten-carbide. In a preferred embodiment, the hard material has a Rockwell A-scale hardness number of greater than 90 and the compressible material has a Rockwell A-scale hardness number of not greater than 80. The rings  56 ,  58  are maintained in position by an interference fit or other suitable methods, such as welding. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.