Abstract:
A fluid mixing device, for the continuous mixing of two or more fluids, having a mixing chamber which has fluid contact surfaces defining an internal chamber region, a fluid inlet, for feeding fluid into the chamber region, a fluid outlet, for feeding fluid out of the chamber region, and a fluid mixer within the chamber region which is capable of inducing mixing of two or more fluids within a mixing region. The mixing chamber is configured so that the dead volume within the chamber region is filled in such a way that the mixing region corresponds to the chamber region. A fluid inlet valve for use in the fluid mixing device has entrance and exit aperture sealing means which are adapted to allow passage of fluid respectively into and out of a body portion of the valve, according to a specified pressure differential between the pressure externally of the entrance aperture and the pressure externally of the exit aperture.

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus for rapidly mixing together exactly specified quantities of two or more fluids such as paints, enamels and dyes amongst others to form a homogenised fluid mixture. 
     BACKGROUND ART 
     In general, modem day paint manufacturing processes utilise a set of pigment pastes or concentrates which are mixed together with specified amounts of a white, black or green base paint to produce the desired colour and are diluted by adding specified amounts of solvent or varnish to obtain the required viscosity. In this way, a paint with specified physical properties such as colour, opacity, hue, saturation and viscosity can be obtained. 
     Typically, the time taken to produce a batch of paint is lengthy due to the lack of uniformity between different batches of concentrates and bases, and the subsequent need for an iterative process of testing and adjustment before the desired result is achieved. In most paint manufacturing processes such an iterative process was extremely time consuming, taking of the order of days for the required quantities of concentrates and bases to be determined. However, due to recent advances in paint production techniques, measurement of the physical properties of a paint mixture can be achieved in a matter of seconds, as described in PCT/BR96/00046. This has meant that analysis of the properties of a paint mixture is no longer the most time consuming step in the process of paint manufacture, and, in order to speed up the process still further, attention has needed to be focused on other steps in the process. 
     One of the steps in the paint manufacturing process that is relatively time consuming is the mixing of the various ingredients or components of the desired paint formula to be produced. This must be done so as to achieve a homogenous mixture of exact and repeatable quantities of the various ingredients in as little time as possible. 
     Mixing of the various components of a paint formula usually takes place in a mixing vessel such as a vat or barrel into which each of the components is poured and then mixed. 
     In order to enable mixing of the components, the mixing vessel must have a large enough volume to allow all the components of the formula to be added. 
     Addition of the components can be carried out using any one of three basic dosing systems: 
     (a) Gravimetric Dosing 
     In this system, the vessel is mounted on a weighing structure which is used to weigh the formula to which each component is dosed gravametrically in sequence. 
     (b) Volumetric Dosing 
     In this system, each component to be dosed has an individual dosing system which provides the correct dosage for each of the components to the mixing vessel. Normally, dosing pumps are used for this purpose, these having the inconvenience of requiring periodic calibration. The principal advantage of a volumetric dosing system over a gravimetric dosing system is the speed with which the components can be added to the vessel, since all the components can be added simultaneously. The volumetric dosing system is used to a great extent in commercial dosing machines. 
     (c) Simultaneous Dosing Controlled by Flow Rate Meters 
     This system brings together the individual advantages of each of the systems described above (precision and speed), because the dosing is controlled individually for each component using a mass flow rate meter. Coriolis effect mass flow rate meters provide the best solution for this type of dosing because they directly measure the variable mass and not volume, as do other meters. Measurement and control of the dosing using volumetric flow rate meters is affected by variations in density, temperature, etc. 
     In the dosing systems described in items (b) and (c) above, each of the various components of the paint formula to be dosed typically is injected into the vessel through an injection nozzle. This presents a problem with respect to the reliability of the dosing system, since it is difficult to control exactly the quantities of each of the components entering the mixing vessel, there being the possibility of spitting from the nozzles during injection as well as suck back of partially mixed paint ingredients, immediately after injection, and dripping from the nozzles during mixing. 
     After the components of the paint formula have been added to the mixing vessel, it is necessary to homogenise (mix) the components of the formula, and the time taken to mix the components may take from minutes to hours, depending directly on such factors as the volume of the vessel in which the components are mixed, the pumping capacity of the mixing impeller, as well as the individual differences in viscosity between the components of the formula. It should also be noted that during mixing or homogenisation of the various components of the paint formula the composition of the mixture may alter due to evaporation of the solvents used, since normally the mixing vessels are open. 
     Object of the Invention 
     The object of the present invention is to provide a fluid mixing device, and fluid injection valve for use therewith, for rapidly and continuously mixing together exactly specified quantities of two or more fluids, which overcome the above mentioned problems in the state of the art. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, a fluid mixing device, for the continuous mixing of two or more fluids, comprises: 
     a mixing chamber having fluid contact surface means defining an internal chamber region; 
     at least one fluid inlet means provided in the fluid contact surface means, for feeding at least one fluid into the chamber region; 
     at least one fluid outlet means provided in the fluid contact surface means, for feeding fluid out of the chamber region; 
     fluid mixing means within the chamber region, capable of inducing mixing of two or more fluids within a mixing region; 
     wherein the chamber region has a configuration which substantially corresponds to the configuration of the mixing region. 
     The mixing chamber comprises an outer fluid containment portion and an inner core, a first area of the fluid contact surface means being formed on the fluid containment portion and a second area of the fluid contact surface means being formed on the inner core. 
     For preference, the first area of the fluid contact surface means has a substantially spherical form, and at least one of the fluid inlet means is provided in this area. 
     Preferably, at least one of the fluid outlet means is also provided in the first area of fluid contact surface means, and at least one of the fluid inlet means is located below this outlet means. 
     For further preference, the mixing chamber is further provided with pressure control means, for controlling the pressure within the chamber region in relation to the pressure externally of the chamber. 
     According to a second aspect of the present invention, a valve means for use in the fluid mixing device according to the first aspect of the present invention, comprises: 
     a body portion having at least one fluid entrance aperture, for allowing fluid to flow into the body portion; 
     a fluid exit aperture, for allowing fluid to flow from the body portion; 
     entrance aperture sealing means having biasing means for biasing the entrance aperture sealing means into a sealing position in which the fluid entrance aperture is sealed; and 
     exit aperture sealing means having biasing means for biasing the exit aperture sealing means into a sealing position in which the fluid exit aperture is sealed; 
     wherein the entrance and exit aperture sealing means are adapted to allow passage of fluid respectively into and out of the body portion, according to a specified pressure differential between the pressure externally of the entrance aperture and the pressure externally of the exit aperture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 shows a partial sectional diagram of a fluid mixing device according to the present invention, including a mixing unit, motor unit, damper unit, thermo-siphon unit and support unit; 
     FIG. 2 shows a sectional diagram of the fluid mixing device according to the present invention, including details of the mixing and motor units; 
     FIG. 3 shows a sectional diagram of the fluid mixing device, including details of the mixing unit; 
     FIG. 4 shows a sectional diagram of an upper portion of the mixing unit of the device according to the present invention; 
     FIG.  5 ( a ). shows one configuration of an impeller for use in the mixing unit of the mixing device according to the present invention; 
     FIG.  5 ( b ) shows another configuration of an impeller for use in the mixing unit of the mixing device according to the present invention; 
     FIG.  5 ( c ) shows a further configuration of an impeller for use in the mixing unit of the mixing device according to the present invention; 
     FIG.  5 ( d ) shows yet another configuration of an impeller for use in the mixing unit of the mixing device according to the present invention; 
     FIG.  5 ( e ) shows the preferred configuration of an impeller for use in the mixing unit of the mixing device according to the present invention; 
     FIG.  5 ( f ) shows another configuration of an impeller for use in the mixing unit of the mixing device according to the present invention; 
     FIG. 6 shows a sectional diagram of a fluid injection valve according to the present invention; and 
     FIG. 7 shows a sectional diagram of a fluid injection valve having two fluid inlets. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1 of the drawings, a fluid mixing device, according to the presently preferred embodiment of this invention, comprises a fluid mixing unit  1  connected to a motor unit  2 , to a hydraulic damper unit  3  and to a thermo-siphon unit  4 . Each of units  1  to  4  is supported on a support unit  5  which comprises a base-plate  501 , to which a vertical stand  502  is attached. A support  503  extends horizontally from stand  502  and is attached to mixing unit  1 . Thermo-siphon unit  4  is connected to the upper end of stand  502 , and a motor support  504  also extends therefrom. Hydraulic damper unit  3  is attached to motor support  504  which is connected to motor unit  2  by a vertically slidable motor carriage  201 . 
     Motor unit  2 , which is shown in greater detail in FIGS. 2 and 3, comprises a three phase electric motor, not shown, which is contained within a motor housing  202 , supported on one side by motor carriage  201  and motor support  504  (both shown in FIG.  1 ), and which is attached at a lower end to a castle  203 . The motor has a drive shaft  204  extending downwardly from motor housing  202  into castle  203 . The lower end of drive shaft  204  is coupled via an elastic coupling  205  to an impeller drive shaft  101  which, as shown in FIGS. 2 to  4 , is coupled at its lower end to an impeller  118 . 
     With reference to FIGS. 2 and 3, a lower end of castle  203  is connected to an upper end of a bearing unit  206 . Bearing unit  206  comprises an upper bearing race  207 , having combined angular contact bearings  208 , and a lower bearing race  209 , having combined angular contact bearings  210 . Referring to FIG. 2, lower and upper bearing races  207 ,  209  are held in place by bearing race retainers  211  above and below each of bearing races  207 ,  209 . There is a lubricating oil reservoir  212  extending between the upper end of upper bearing race  207  and below lower bearing race  209 . The upper and lower ends of oil reservoir  212  are connected to each other by an oil circulation tube  213 . In the lower end of oil reservoir  212  there is a rotor  214  which is attached to impeller drive shaft  101 , and which circulates the oil in reservoir  212  via tube  213  when it rotates. 
     The lower end of bearing unit  206  is attached to a fluid sealing unit  102  of mixing unit  1 , for preventing fluid from mixing unit  1  leaking into bearing unit  206 , and for preventing lubricating oil from bearing unit  206  from leaking into mixing unit  1 . Referring to FIGS. 2 and 3, fluid sealing unit  102  comprises a mechanical seal  103  which consists of a sleeve  104 , surrounding impeller drive shaft  101 , shaft  101  being rotatable within sleeve  104 . In operation, shaft  101  rotates at high velocity causing heating of sleeve  104  which leads to breakdown of the material of the seal. For this reason, sleeve  104  is lubricated and cooled by a suitable fluid, such as monoethileneglicol. Control of the cooling and lubrification of sleeve  104  is achieved using thermo-siphon unit  4 , shown in FIG.  1 . Thermo-siphon unit  4  is connected to seal unit  102  by tubes  401  and  402 . Tube  401  is connected between a cooling fluid outlet  403  in the lower end of thermo-siphon unit  4 , and a cooling fluid inlet  105  (shown in FIG. 4) in the lower part of fluid sealing unit  102 . Tube  402  is connected between a cooling fluid inlet  404  in the side of thermo-siphon unit  4 , and a cooling fluid outlet  106  in the upper part of fluid sealing unit  102 . The level of fluid used in lubricating and cooling of mechanical seal  103  is controlled by a capacitative level switch  405  above thermo-siphon unit  4 . Circulation of the cooling and lubricating fluid within mechanical seal  103  is controlled by a small centrifugal pump  406 . Referring again to FIG. 2, an inspection window  107  provided in the wall of fluid sealing unit  102 , at its upper end, is used for checking whether there is any leakage of fluid from sealing unit  102  or bearing unit  206 . 
     Referring to FIGS. 2 and 3, the lower end of sealing unit  102  is connected to an upper portion  108  of a mixing chamber  109 . Upper portion  108  of mixing chamber  109  has a conical internal fluid contact surface  110  and has a lower flange wall  111  which, in a closed configuration, is connected, via a sealing gasket  112 , to an upper end wall  113  of a lower portion  114  of mixing chamber  109 . Lower portion  114  has a hemispherical internal fluid contact surface  115  and has a cylindrical drain  116  at its apex extending vertically downwards therefrom. Drain  116  is connected to a drain tube  116   a , shown in FIG. 2, which allows fluid to be drained out of mixing chamber  109 . 
     Impeller drive shaft  101  extends through sealing unit  102  and through an opening  117  in upper portion  108  of mixing chamber  109 . In a preferred embodiment of the present invention, drive shaft  101  extends approximately two-thirds of the way into lower portion  114  and has an impeller  118  connected approximately half-way along the length of shaft  101  protruding into mixing chamber  109  through opening  117 . 
     Impeller  118  can have a number of different configurations, some of which are shown in FIGS.  5 ( a ) to  5 ( f ). In the presently preferred embodiment of the present invention the impeller shown in FIG.  5 ( e ) is used. Impeller  118  comprises a circular disc  119  having an upper surface  120  and a lower surface  121 , and is attached at its radial center to impeller shaft  101  which extends perpendicularly therethrough. Impeller blades  122  extend from the outer edge of disc  119  alternately from upper and lower surfaces  120  and  121  perpendicuarly to the plane thereof. 
     When in operation, motor unit  2  rotates impeller shaft  101 , and consequently impeller  118 , at velocities between 500 and 8000 rpm, depending on the viscosity of the fluids to be mixed in mixing chamber  109 . Rotation of impeller  118  creates a turbulent flow of the fluid within mixing chamber  109  in a mixing region, while in a region of mixing chamber  109  above and below impeller  118  there is little or no turbulent mixing. This region is referred to here as the dead volume, and in the device according to the present invention is occupied by a dead volume filler or inner core  123  having a fluid contact surface  123   a.    
     Referring to FIGS. 2 to  4 , inner core  123  comprises an upper portion  124 , attached to upper surface  120  of impeller disc  119  and configured to fill the dead volume above impeller  118 , and a lower portion  125 , attached to lower surface  121  of impeller disc  119 , configured to fill the dead volume below impeller  118 . It should be observed that inner core  123  may also be attached to impeller drive shaft  101 , as well as, or instead of, to upper and lower surfaces  120 ,  121  of impeller disc  119 , or as a further alternative may be connected to upper and/or lower portions  108 ,  114  of mixing chamber  109 , so that they do not rotate with impeller  118 . 
     The efficiency of mixer unit  1  is related directly to the mixing capacity of a determined volume of fluid in a certain time, that is the speed with which a particular volume of fluid can be mixed. In the device according to the present invention, due to filling of the dead volume within mixing chamber  109 , homogenisation of a mixture of both high and low viscosity fluids (e.g. 2000 cp) can be achieved with efficiency, having a residence time within mixing chamber  109  of only a few seconds. 
     Upper portion  108  of mixing chamber  109  is provided with a number of through openings  126  perforating and extending perpendicularly outward from internal conical fluid contact surface  110  at spaced intervals therearound. FIG. 2 shows a PT100 temperature sensor  127  fixed in one of through openings  126 , and a damper inlet  128  fixed in another of through openings  126 . Temperature sensor  127  is used to monitor the temperature of a fluid within mixing chamber  109 . Referring to FIG. 1, damper inlet  128  is connected by flexible tubing  301  to hydraulic damper unit  3  which comprises a compressed air reservoir  302 . When fluid is being mixed in mixing chamber  109 , rotation of impeller  118  produces highly turbulent fluid flow with consequent fluctuations in pressure within chamber  109 . In order to damp out such pressure fluctuations, which have an adverse effect on the mixing process, mixing chamber  109  is in direct communication with air reservoir  302  via damper inlet  128  and flexible tubing  301 . In this way, fluctuations in pressure within mixing chamber  109  are damped by compression of the air within reservoir  302 . 
     FIG. 3 shows a cleaning fluid injection valve  129  fixed in one of through openings  126 , and a principal fluid exit tube  130  fixed in another of through openings  126 . Cleaning fluid injection valve  129  is used for cleaning mixing chamber  109  by injecting a mixture of solvent and compressed nitrogen gas therein in order to remove fluid residues from fluid contact surfaces  110  and  115 . Cleaning fluid injection valve  129  will be described in greater detail later in this description. Fluid exit tube  130  allows fluid to be fed out of mixing chamber  109 . 
     Referring now to FIG. 4, a fluid sample exit valve  131  is fixed in one of through openings  126 , and may be used continuously to collect a sample of the fluid mixed in mixing chamber  109  which can then be fed to a fluid analysis system such as that described in PCT/BR96/00046. In a preferred embodiment of the present invention, when analysis of the fluid exiting from mixing chamber  109  is required, approximately 95% of the total volume of fluid mixed in mixing chamber  109  exits through principal fluid exit tube  130 , and the remaining 5% exits through sample exit valve  131 . 
     Again referring to FIGS. 1 and 2, lower portion  114  of mixing chamber  109  is connected via support  503  of support unit  5  so that upper portion  108  of mixing chamber  109  can be moved away from lower portion  114 , using motor carriage  201 . This allows access to the interior of mixing chamber  109  for maintenance and adjustment purposes. 
     With reference to FIGS. 2 and 3, lower portion  114  of mixing chamber  109  is provided with a series of through openings  132  which give access to the interior of chamber  109 . Fluid injection valves  133  are fixed in through openings  132  and are used to inject the fluids to be mixed, into mixing chamber  109 . A further cleaning fluid injection valve  129  is provided in lower portion  114 , as shown in FIG. 2, so that thorough cleaning of fluid contact surfaces  110  and  115  of upper and lower portions  108 ,  114  of chamber  109 , and the surfaces  123   a  of volume filler  123  can be achieved. Referring to FIGS. 2 and 3, a pressure sensor  134  is fixed in one of through openings  132 , and is used to measure the pressure within mixing chamber  109 . The signal from pressure sensor  134  is analysed by a pressure control means (not shown), which operates an automatic high speed pressure control valve (not shown), to open or close fluid exit tube  130  depending on the pressure in chamber  109 . 
     The approximately hemispherical form of inner surface  115  of lower portion  114  of mixing chamber  109  permits a maximum number of fluid injection valves  129 ,  133  to have access thereto, and therefore enables a maximum number of fluid ingredients to be injected into mixing chamber  109 . 
     Fluid injection valves  129  and  133  will now be described in detail with reference to FIGS. 6 and 7. Fluid injection valve  133  is shown in FIG. 6, and comprises a cylindrical body portion  135 , which is circularly symmetric about a central axis, and has a fluid exit aperture  136  at one end, for allowing fluid to exit from body portion  135 , and an access aperture  137  at the opposite end, for allowing access to the internal workings of the valve. The end face  138   a  of body portion  135  which defines exit aperture  136  is chamfered inwards towards the central axis, and three internal shoulders  139 ,  140  and  141  are spaced at intervals therefrom along the length of body portion  135 , shoulder  139  being the closest to exit aperture  136 , and shoulder  141  being furthest therefrom. Internal cylinder walls  142 ,  143 ,  144  and  145  extend between end face  138   a  and shoulder  139 , shoulder  139  and shoulder  140 , shoulder  140  and shoulder  141 , and between shoulder  141  and an end face  138   b  of body portion  135  respectively. The cylinder formed by cylinder wall  142  has a smaller radius than that formed by cylinder wall  143 , which is smaller than that formed by cylinder wall  144 , which in turn is smaller than that formed by cylinder wall  145 . It should be noted that cylinder walls  143 ,  144  and  145  are parallel, but that cylinder wall  142  is angled slightly towards exit aperture  136 . 
     Exit aperture  136  of body portion  135  is sealable with an exit aperture seal  146  comprising a seal guide  147 , an exit aperture seal shaft  148  and an exit aperture seal head  149 . Seal guide  147  comprises a hollow cylindrical body  150  and guide arms  151 . When in position within body portion  135  of fluid injection valve  133 , the axis of seal guide body  150  corresponds to the central axis of body portion  135 . Seal guide body  150  has a closed end  152  facing access aperture  137  and an open end  153  facing exit aperture  136 . Guide arms  151  extend radially outwards from the cylindrical wall of guide body  150  and are bent perpendicularly towards access aperture  137  when they reach internal cylinder wall  144  so that guide body  150  is slidable in the cylinder formed between shoulders  140  and  141 . 
     One end of exit aperture seal shaft  148  enters open end  153  of seal guide body  150  and is held therein. The other end of shaft  148  extends towards exit aperture  136  and is fixed to seal head  149  which comprises a frusto-conical shaped stopper  154  having a groove  155  containing an o-ring  156 . A conical spring  157  has one end wound around seal guide body  150  between guide arms  151  and open end  153 , and the other end butting against shoulder  139 . When valve  133  is in its sealed position, spring  157  is compressed slightly so that o-ring  156  butts against end face  138   a , part of which comprises a seat for the o-ring, to seal exit aperture  136 . 
     A valve cap  158  is fixed to body portion  135  to partially close access aperture  137 . Valve cap  158  is formed with a fluid entrance aperture  159  which, when valve cap  158  is fixed to body portion  135 , has its axis along that of the central axis of body portion  135 . End face  138   b  of body portion  135  is sealed against an internal shoulder  160  of valve cap  158  by a gasket  161 . 
     Entrance aperture  159  is sealable by an entrance aperture seal  162  which comprises a guide portion  163  and a seal portion  164 . Guide portion  163  comprises a small cylindrical tube  165  which is provided with guide arms  166  at its extremity furthest from access aperture  137 . Cylindrical tube  165  has its longitudinal axis corresponding with the central axis of body portion  135  and is held in place by guide arms  166  which extend radially outwards from tube  165  and are bent perpendicularly towards access aperture  137  when they reach cylinder walls  145 . Guide arms  166  butt against shoulder  141  to hold guide portion  163  in place within body portion  135 . 
     Seal portion  164  of entrance aperture seal  162  comprises a hollow cylindrical tube  167  and a head  168 . Hollow cylindrical tube  167  fits over cylindrical tube  165  of guide portion  163  and is free to move towards and away from entrance aperture  159 . Head  168  has a conical end surface  169  which fits inside entrance aperture  159 , and has a groove  170  containing an o-ring  171 . A shoulder  172  is formed at the junction of cylindrical tube  167  with head  168  and one end of a spring  173  is attached buttingly thereagainst. The other end of spring  173  is wound around cylindrical tube  165  and butts against guide arms  166 . When valve cap  158  is attached to body portion  135  of valve  133 , spring  173  is compressed sufficiently so that o-ring  171  is pushed against an inner angled surface  174  of valve cap  158 , to seal entrance aperture  159 . 
     Valve cap  158  is supplied with a connection nut  175  which is used to connect fluid entrance aperture  159  to either a rigid or flexible tube (not shown) for supplying the fluid to be injected into mixing chamber  109  from a fluid reservoir (not shown). 
     Referring to FIGS. 2 and 6, in operation with mixer unit  1 , valves  133  are fixed in respective through openings  132  in lower portion  114  of mixing chamber  109  so that the exit aperture  136  of each valve  133  lies flush with fluid contact surface  115  thereof. 
     Normally, the pressure within mixing chamber  109  is maintained at a pressure of 1 Kg cm −2  below the pressure in the tubes connected to entrance apertures  159  of valves  133 , due to the loss of pressure caused by the action of springs  157  and  173  to hold o-rings  156  and  171  against their respective seats. In order for fluid to be injected into mixing chamber  109 , the pressure externally to the entrance apertures  159  of valves  133  is raised so that entrance aperture seal head  168  is pushed into body  135  of valve  133  against the action of spring  173 , to break the seal formed between o-ring  171  and surface  174  of valve cap  158 , allowing fluid to flow into body portion  135  of valve  133 . The resulting rise in pressure of the fluid within valve  133  pushes exit aperture seal head  149  into mixing chamber  109 , breaking the seal formed between oaring  156  and end face  138   a  of body portion  135  of valve  133 , allowing fluid to flow into mixing chamber  109 . As soon as the pressure externally to entrance aperture  159  is reduced in relation to the pressure exerted by springs  157  and  173 , fluid exit aperture seal  146  and fluid entrance aperture seal  162  close to seal respective exit and entrance apertures  136  and  159 . 
     The lower pressure within mixing chamber  109  in relation to that externally thereof ensures that the fluid is injected into mixing chamber  109  smoothly, without spitting, and that fluid does not leak or drip from valves  133  into chamber  109 , and the double seal formed by exit and entrance aperture seals  146  and  162  of valves  133  ensures that fluid does not return from mixing chamber  109  into the fluid supply tubes. 
     Fluid injection valve  129 , which may be used for injecting cleaning fluid into mixing chamber  109 , is shown in FIG.  7 . Valve  129  comprises the same body portion  135  as fluid injection valve  133 , having the same fluid exit aperture seal  146  but, does not have a fluid entrance aperture seal held therein. Instead, a valve cap  176  is provided which seals against body portion  135  in the same manner as for valve  133 , but instead of forming a single fluid entrance aperture is provided with two entrance apertures  177  and  178 . Entrance aperture  177  is formed by a neck portion  179  in valve cap  176  and has its axis corresponding to the central axis of body portion  135 . Entrance aperture  178  is formed in an internal frusto-conical shaped wall  180  of valve cap  176  and has a feed tube  181  extending outwardly therefrom at an angle to the central axis of body portion  135 , the external end of feed tube  181  being formed with a seal receptacle portion  181   a . A feed funnel  182 , comprising a conical entrance aperture  183  and a feed tube  184 , is held within valve cap  176 , with feed tube  184  extending through neck portion  179  into body portion  135 . Two entrance aperture seals  185  and  186  are held within seal holders  187  and  188 , which are fixed within valve cap  176  abutting feed funnel  182  and the external opening of feed tube  181  respectively. Entrance seals  185  and  186  are similar to entrance seal  162  of valve  133 . 
     When used for cleaning mixing chamber  109 , compressed nitrogen gas is forced under pressure through feed funnel  182  into valve  129  while at the same time solvent is forced under pressure through entrance aperture  178  of valve  129  and thence through exit aperture  136  into mixing chamber  109 . Rotation of impeller  118  in combination with high pressure injection of nitrogen gas and solvent ensures extremely rapid cleaning of the internal surfaces  110  and  115  of mixing chamber  109 . 
     It should be appreciated that the above described invention can be carried out in a variety of different embodiments. For example, mixing of fluid within mixing chamber  109  may be achieved by swirling the fluids to be mixed at high pressure as they enter the mixing chamber. In this case there may be a number of dead volumes within mixing chamber  109 , and a series of inner cores  123  may be provided to fill these dead volumes. Also, inner core  123  may be inflatable and deflatable to vary the volume of mixing chamber  109  according to different fluid mixtures having different viscosities and therefore different dead volumes around impeller  118 . 
     Other modifications may be made to fluid injection valves  129  and  133  without going beyond the scope of the present invention. For example, fluid injection valve  129  may be provided with more than two entrance apertures so that more fluids may be injected into mixing chamber  109  through the same injection valve. 
     Apart from the above mentioned modifications, other changes may be obvious to those skilled in the art and, as such, the scope of the present invention should be limited only by the terms and interpretation of the following claims.