Abstract:
A direct steam injector for use in cooking food products by injecting live steam directly into the product to heat the food to cook temperatures. The injector operates under relatively low source steam manifold pressure while urging the valve return spring wide open, thus reducing the pressure of the steam flowing into the product. In addition to reducing the pressure of the steam, the steam injector reduces the velocity of the steam and better distributes it as the steam exits the injector, thereby reducing damage to the food product.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/464,268, filed Mar. 1, 2011 (Mar. 1, 2011). 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       THE NAMES OR PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not applicable. 
       INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    The present invention relates most generally to steam injectors, and more particularly to steam injectors for use in food cooking apparatus, and still more particularly to a low pressure, low velocity steam injector for use in live steam injection food cooking systems. 
         [0007]    2. Background Discussion 
         [0008]    It is commonly known that injecting live steam into food products is a more efficient method of cooking than indirect steam heating. Even so, this method of cooking is not currently used as much as indirect steam heating in a pressurized jacket of the cooking vessel. One reason for this is that direct steam has a tendency to damage food product or cause other problems by cooking the food product too fast. Cooking food products with indirect jacket steam has several disadvantages, most notable among them being the tendency of products to burn onto the heat exchange surfaces. For this reason it is desirable to have a satisfactory direct steam injection food cooking system. 
         [0009]    There are several different kinds of direct steam injectors, ranging from simple holes disposed in the side of the cooking vessel to very sophisticated injector mechanisms that are pneumatically or spring actuated. The most commonly used injectors close automatically in the absence of steam pressure so as to prevent food product from entering the cavity of the injector. The inside of a spring-actuated injector is a complicated mechanism with numerous moving parts, making these injectors very hard to clean, particularly if food product has infiltrated the interior spaces. 
         [0010]    One simple automatically closed injector comprises a round ball of plastic or rubber captured within a housing and disposed over a steam port. As steam is applied to the injector, the ball is urged upward by the steam against a grating or screen at the food product interface. The elevated ball allows steam to escape from the port and functions as a baffle to disperse the steam as it rises into the product. When the steam flow is turned off, the ball will drop by gravity back onto the valve seat, and the weight of the ball will seal the seat preventing product from going into the steam piping. While simple in design, this type of ball valve is vulnerable to food product intrusion into the injector body, because only gravity maintains the ball in place on the valve seat, and this force is quite small. 
         [0011]    Another type of direct steam injector that seals much better than the above-described ball valve is a spring-actuated valve configured much like the poppet (or “mushroom”) valves found in an internal combustion engine. It is urged into its closed position under the force of a helical compression spring.  FIGS. 1A-1D  schematically show an example  10  of such an apparatus. Referring first to  FIG. 1A , this kind of prior art direct steam injector includes a cylindrical housing  12  having an interior void  14  in which a valve seat  16  is disposed. An end cap  18  is placed over a first end  20  of the housing  12  and captures the valve seat between an end cap cup  22  disposed on the interior side  24  of the end cap and upper interior rim  26 . A sanitary gasket  28  is disposed between the end cap and the housing, and an O-ring seal  30  is disposed between the valve seat and the upper interior rim. An annular clamp  32  secures the end cap  18  to the first end  20  of the housing  12 . 
         [0012]    The valve seat  16  includes an internal through bore having a first upper diameter to accommodate a valve stem  34  and a second lower diameter, slightly larger than the first upper diameter, so as to accommodate a spring  35  coaxially disposed around the valve stem. The spring is interposed between a stem seal  36  and the ledge  38  formed at the transition from the first to the second internal bore diameter. The stem seal is disposed around a lower stem extension post  40  terminated by an expanded head  42 . 
         [0013]    The valve head  44  is securely sealed atop an exhaust chamber  46 , around which are disposed a plurality of exhaust ports  48  angled inwardly and upwardly from the housing interior, through the uppermost portion of the valve seat, and into the exhaust chamber. The exhaust ports will direct steam to the underside of the valve head, and when the valve is in the operated position, through the vessel shell  50  and into the cooking chamber  52 . 
         [0014]    The housing  12  includes a steam inlet port  52  coupled to a steam supply from a manifold. These are not shown but are well known and assumed in the views. One or more pressure transfer holes  54  are disposed in the end cap cup to provide a steam flow path for steam into the cup interior  56  and under the stem seal  36 . Steam injection holes  58  are provided in the valve seat so as to provide a steam flow path to and through the exhaust ports  48  to the underside  58  of the valve head  44 . 
         [0015]    Referring now to  FIG. 2B , in operation as steam enters the stem inlet port it is routed along its flow path is pressurized with live steam the valve stem is pushed upward against the spring thereby compressing the spring. The movement of the valve stem moves the valve head off the valve seat and opens the valve. Steam from the steam supply also enters below the valve head and is injected into the product around the valve head through the orifice gap  62 , which is the space between the valve head and the valve seat when the valve is in the open (operated) position. 
         [0016]    This type of injector does distribute the steam in a full 360 degree direction around the valve head. Disadvantageously, however, the velocity of the steam is directly related to the steam pressure and the amount of space or orifice gap between the valve head and the valve seat. Since the spring force urging the valve to close is a function of the spring strength and spring rate of the closure spring, the valve will open to a different spacing depending on the steam supply pressure: the higher the steam supply pressure in relation to the spring force, the more the valve will open and the wider the orifice gap space for steam to escape into the product. 
         [0017]    If the steam supply pressure is reduced, the spring will gradually, partially close, thereby reducing the orifice gap space and causing higher velocity of the steam as it escapes from the injector into the product. 
         [0018]    When food product is damaged due to high steam pressure and steam velocity, the steam supply pressure must be reduced. However, reducing the steam supply pressure does not appreciably reduce the steam velocity, since the spring will tend to close the valve more under a lower steam pressure, thus reducing the orifice gap space where the steam flows into the product. The steam velocity is thus not reduced; only the rate at which steam is injected into the product is reduced. 
         [0019]    Additionally, also disadvantageously, at low pressures, the valve spring in the conventional direct steam injector will begin to flutter and oscillate which results in rapidly changing velocity and considerably reduced spring life. 
         [0020]    Finally, in standard steam injectors the velocity of the steam is very high and unusually variable around the circumference of the valve steam. These high and variable velocities cause a number of problems: First, the high shear can behave as a knife easily cutting most food products such as pasta, meats, vegetables and fruits. Second, the shear effect also decreases the droplet size of fats and water to create an emulsion of oil and water droplets. Separating the cook water from the product is virtually impossible when the fats have emulsified with the water. And third, for viscous and semi-solid food products shear can result in air entrainment and foaming. 
         [0021]    The obvious solution to these problems is to reduce the spring rate minimizing the orifice gap so that a lower steam pressure will open the orifice gap further. It has been found, however, that this solution simply gives rise to other, equally disadvantageous problems. The lower the spring rate, the more erratic the spring becomes. It is necessary to select a spring that will close with enough force to prevent product from infiltrating the injector housing. In addition, if the spring is too soft (low spring rate), it will tend to flutter or vibrate up and down with the variation in the steam flow. If a spring with a stronger spring rate is used in combination with a low steam supply pressure, the valve will again flutter, causing reduced spring life and increased incidents of spring failure. For these reasons a spring must be selected with a high enough spring rate to be stable; yet, the spring with a higher spring rate will operate with a lower orifice gap causing higher velocity of steam being injected into the product. 
         [0022]    Since these variables (high spring rate and low steam velocity) work counter to each other, the end result is that use of this type of direct steam injector for heating many products yields very unsatisfactory results. For example, when cooking ground beef, in order to prevent valve fluttering with enough steam supply pressure to open the valve properly, the flow of steam and steam velocity is so high that it cooks the surface of the meat too quickly, causing the meat to consolidate into large sized meatballs in which the meat in the center of the ball is uncooked. To ensure that all the meat is cooked to a temperature sufficient to kill all pathogens, the meatballs must be cooked for an excessively long time, which results in overcooked portions on the outside of the meat balls. 
         [0023]    Furthermore, the high and variable velocities of steam form an emulsion with the condensate water and the fat as the fat melts. This results in a semi-stable water fat emulsion with entrained air within the emulsion. The emulsion formation makes the separation of water from the oil very difficult. For continuous processes where operation over long periods of time is expected, this emulsion causes concern. Cook yields and product quality decline as the water and product increases in viscosity. 
         [0024]    In cooking another product such as pasta filata cheese (mozzarella), the pressure and temperature of the steam injected into the cheese block is critical. If the milk protein in the cheese is heated too quickly or heated with steam that is too hot, the protein denatures and gets very tough and hard. To avoid such problems, it is necessary to heat the cheese very slowly with the injected steam close to the boiling point (212 degrees F.). This is essentially impossible with a standard direct steam injector because the pressure must be high enough to open the injector and high enough to overcome the back pressure created by stiff cheese being pumped through the continuous cooker. 
         [0025]    It is therefore desirable to have a direct steam injector that: (1) has a sufficiently strong closing spring to firmly seal the valve against the valve seat when there is no steam pressure; (2) while at the same time the steam valve must open fully at low steam pressures so that the steam being injected into sensitive products is at a low temperature and is discharged from the injector at a low velocity so that the steam is diffused evenly all the way around the valve head. 
       BRIEF SUMMARY OF THE INVENTION 
       [0026]    The present invention is an improved low pressure, low velocity direct steam injector for use in commercial and industrial cooking systems that solves the above-described problems. 
         [0027]    It is a principal object and advantage of the present invention to reduce the required pressure of steam entering the injector needed to fully elevate and operate the valve head, while positively seating the valve head on the valve seat using a compression spring when steam pressure is absent. 
         [0028]    To accomplish the forgoing objectives, the direct steam injector of the present invention is designed such that as steam flows into and through the injector, the steam loses pressure as it passes through steam transfer ports into an exhaust chamber under the valve head. This loss in steam pressure as steam flows through the steam transfer ports creates a high pressure area outside of the valve seat relative to the steam pressure in the exhaust chamber. 
         [0029]    These operating advantages are achieved by providing a valve body having a novel pressure piston integral with the valve stem and disposed in an upper portion of the cylinder (or through bore) into which the valve stem is slidably disposed. The pressure piston has close clearances to optimize the driving force provided by the steam allowed to enter the upper portion of the cylinder below the pressure piston. Thus, as steam flows into the injector housing the higher pressure outside the valve seat is transferred to the underside of the pressure piston. Because the pressure under the pressure piston is higher than the pressure above the piston and in the exhaust chamber, the pressure under the piston will act with the pressure under the valve head to raise the valve at a steam pressure in the exhaust chamber lower than would be required in conventional direct steam injectors. 
         [0030]    Further, the steam pressure in the exhaust chamber needed to fully raise the valve (and thus the steam velocity exiting from the injector into the product) can be reduced as much as desired simply by reducing the diameter of the steam transfer holes in the valve seat. 
         [0031]    Other features, objects, and advantages of the invention will be described in the detailed description of the preferred embodiments of the invention which will form the subject matter of the claims appended hereto. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0032]    The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
           [0033]      FIG. 1A  is a cross-sectional side view in elevation of a prior art standard spring actuated injector, showing the valve head in a closed position; 
           [0034]      FIG. 1B  is the same view showing the valve urged into an operated position and the steam flow path through the valve assembly; 
           [0035]      FIG. 1C  is a top plan view thereof of the valve seat, showing steam injection holes, partly in phantom; 
           [0036]      FIG. 1D  is a simplified schematic cross-sectional side view showing the valve seat, valve head and stem (housing and compression spring removed) of a prior art standard spring actuated injector; 
           [0037]      FIG. 2A  is cross-sectional side view in elevation of the improved low pressure, low velocity steam injector of the present invention, this view showing the valve in a closed position; 
           [0038]      FIG. 2B  is the same view showing the valve urged into an operated position and the steam flow path through the valve assembly; 
           [0039]      FIG. 2C  is a top plan view thereof, showing the improved valve seat and steam injection hole configuration; and 
           [0040]      FIG. 2D  is a simplified schematic cross-sectional side view showing the inventive steam injector valve seat, valve head and stem (housing and compression spring removed) with its salient distinctive features shown for a side-by-side comparison with the prior art standard spring actuated injector of  FIGS. 1A-1D . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Referring to  FIGS. 2A through 2D , wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved low pressure, low velocity steam injector, generally denominated  100  herein. The drawings are described using terminology corresponding to the upright orientation of the steam injector, as shown. Accordingly, to the extent that a term such as “above” or “below” is used, it is for purposes of identifying an element or feature under discussion and better appreciating its structural or operational relationship to other features or elements. 
         [0042]    In several respects, the improved direct steam injector of the present invention resembles the prior art injector described in the preceding paragraphs and illustrated in  FIGS. 1A-1D . For instance, the inventive steam injector includes a cylinder housing  102  having an interior void  104  in which a valve seat  106  is disposed. An end cap  108  is placed over a lower open end  110  of the housing  102  and captures the valve seat between an end cap cup  112  disposed on the interior side  114  of the end cap and upper interior rim  116 . A sanitary gasket  118  is disposed between the end cap and the housing, and an O-ring seal  120  is disposed between the valve seat and the upper interior rim. An annular clamp  122  secures the end cap  108  to the first end  110  of the housing  102 . 
         [0043]    It is at this stage of the description that we can appreciate the salient features differentiating the inventive direct steam injector from the standard prior art steam injector. The movable element in the assembly is the valve body, which generally comprises a valve stem  126  and valve head  146 . However, an upper portion of the valve stem of the present invention has been significantly modified to include a coaxially disposed annular pressure piston  128 . The valve seat  106  therefore includes an internal cylindrical through bore (cylinder) having an upper portion  124  with a diameter sufficient to accommodate the pressure piston  128 , which is sized with close tolerances in relation to the cylindrical side of the upper portion  124  of the through bore. The through bore also includes a lower portion  130  with a diameter slightly smaller than the upper portion, yet large enough to accommodate a spring  132  coaxially disposed around the lower stem portion of the valve body. The spring is interposed between a stem seal  134  (or stem lock washer) and a ledge  136  dividing the first portion from the second portion of the through bore. The stem seal is disposed around a lower stem extension post  138 , which is terminated by an expanded head  140 . 
         [0044]    The valve head  142  is securely sealed atop a cylindrical exhaust chamber  144 , around which are disposed a plurality of exhaust ports  146  angling inwardly and upwardly through the uppermost portion  148  of the valve seat to openings in the exhaust chamber. These exhaust ports direct steam to the underside of the valve head, and when the valve is in the operated position, through the vessel shell  148  and into the cooking chamber  150 . 
         [0045]    The housing  102  includes a steam inlet port  152  coupled to a steam supply from a manifold. One or more pressure transfer holes  154  are disposed in both the end cap cup  112  and in the valve seat immediately under the pressure piston to provide a steam flow path for steam into the cup interior  156  under the stem seal  134  and under the pressure piston  128 . Exhaust ports  146  include steam inlet holes  158  disposed in the valve seat so as to provide a steam flow path to and through the exhaust ports  146  to the underside  160  of the valve head  142 . 
         [0046]    In operation, the inventive low pressure steam injector receives steam from the steam supply source and transfers the steam through pressure transfer holes in the end cap cup  112  into the piston chamber below the pressure piston to open the valve. The pressure of the steam in the piston chamber is the same as the steam supply pressure. The surface area of the pressure piston on which the steam pressure is applied is sufficient to compress the closure spring and open the valve at very low static pressures, thus preventing spring flutter and premature spring failure. The steam pressure against the pressure piston is also sufficient to increase the area of the orifice gap  160 . However, the pressure in the exhaust chamber above the pressure piston is reduced, thereby releasing the steam into the product at a lower pressure. Because the pressure piston is forced wide open the orifice gap is large even at low steam pressures, the velocity of the steam released into the product is very low. 
         [0047]    The steam from the steam supply source also passes through a series of exhaust ports  148  into the exhaust chamber  144  above the pressure piston  128  and is then injected into the food product. The exhaust ports are designed to create a pressure drop between the steam supply source and the exhaust chamber since the steam valve is fully open to atmosphere in the product vessel. The flow of steam from steam exhaust ports into the exhaust chamber and thereafter into the product vessel assures that the injection pressure is always lower than the pressure in the piston chamber regardless of the steam supply pressure. Therefore, the steam supply pressure can be adjusted so that the valve is fully open, yet the steam flowing into the product is at a suitably low pressure, temperature, and velocity, thus significantly reducing the damage to fragile products being heated. 
         [0048]    Table 1 shows the benefits of this invention. The Injector Orifice gap is the space (orifice gap  160 ) between the operated valve head and the vale seat. As the supply pressure is increased the orifice gap is increased. However, the orifice gap is approximately 50% larger with the low velocity injector of the present invention compared with the orifice gap of the standard injector. Both injectors have identical springs with exactly the same spring rate, and the valve head and valve seat have identical dimensions and design features. 
         [0049]    In the case of the inventive low velocity, low pressure steam injector, the steam pressure in the piston chamber is essentially the same as the steam pressure in the steam source manifold. However, the steam pressure in the exhaust chamber is substantially less due to the pressure drop in the exhaust chamber caused by the flow of steam into the product through the larger area of the orifice gap. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Injector Orifice Gap 
               
             
          
           
               
                   
                   
                 Low 
               
               
                 Manifold 
                   
                 Velocity 
               
               
                 Pressure 
                 Standard Injector 
                 Injector 
               
               
                   
               
               
                 10 PSI 
                 0.045 inch 
                 0.072 inch 
               
               
                 20 PSI 
                 0.052 inch 
                 0.080 inch 
               
               
                 30 PSI 
                 0.060 inch 
                 0.090 inch 
               
               
                   
               
             
          
         
       
     
         [0050]    The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention, and provides the best mode of practicing the invention presently contemplated by the inventor. While there is provided herein a full and complete disclosure of the preferred embodiments of this invention, it is not desired to limit the invention to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like. 
         [0051]    Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined by the appended claims.