Agitating – Having specified feed means – Pump forces material through restriction
Reexamination Certificate
1999-07-09
2001-10-23
Soohoo, Tony G. (Department: 1723)
Agitating
Having specified feed means
Pump forces material through restriction
C138S043000, C137S625300, C251S063600
Reexamination Certificate
active
06305836
ABSTRACT:
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.
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Leslie W. Phipps; “Effects of main flow reversal in a simple homogenizing valve”; Journal of Dairy Research; pp 525-528; Mar. 1978.
APV North America Inc.
Hamilton Brook Smith & Reynolds P.C.
Soohoo Tony G.
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