Abstract:
A metering valve for delivering liquids from a reservoir includes a rotatable valve plug having at least one well in the valve plug. The valve plug prevents direct communication across the valve. Rotating the valve plug transfers the liquid from the reservoir into the well on the valve plug. Rotating the valve plug further transfers the liquid in the well from the valve plug to the point of delivery. The rotation of the valve plug can be repeated to transfer more liquid. The metering valve can be used to deliver vaporizable germicides to a sterilization chamber. A single metering valve can be used to deliver varying amounts of vaporizable germicide to different sizes of sterilization chamber by rotating the valve plug an appropriate number of times. The valve plug can contain multiple wells to deliver large volumes of liquid quickly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a metering valve for delivering liquid vaporizable germicide to a sterilizer. 
     2. Description of the Related Art 
     Sterilization is used in a broad range of industrial and medical applications. Sterilization is the complete destruction or the irreversible inactivation of all the microorganisms in the system. Sterilization can be performed, for example, with heat or chemical treatment. Heat sterilization is normally done using steam. Some equipment cannot withstand the heat or the moisture of stem treatment. As a result, chemical sterilization is now commonly used. 
     Chemical sterilization can be done using alcohols, aldehydes such as formaldehyde, phenols, ozone, ethylene oxide, chlorine dioxide, or hydrogen peroxide. Hydrogen peroxide is commonly used for chemical sterilization. 
     U.S. Pat. No. 4,653,876, incorporated herein by reference, discloses an exemplary sterilization process in which a vaporizable germicide such as hydrogen peroxide is introduced into an evacuated sterilization chamber. The vaporizable germicide vaporizes and is allowed to disperse throughout the chamber and onto the items to be sterilized. After a period of time, electrical energy is applied to an electrode to form a plasma to complete the sterilization cycle. 
     The STERRAD® Sterilization System is an exemplary hydrogen peroxide sterilization system, commercially available from Advanced Sterilization Products, Irvine, Calif. Advanced Sterilization Products is a Division of Ethicon Endo-Surgery, Inc. The system employs an automated delivery system in which a measured amount of the liquid germicide, typically aqueous hydrogen peroxide, is delivered to the sterilization chamber. Measured portions of the liquid germicide are provided in rupturable cells within a liquid cassette housing. The cassette and the delivery system are fully described in the Williams et al. patents, U.S. Pat. No. 4,817,800, issued Apr. 4, 1989; U.S. Pat. No. 4,913,196, issued Apr. 3, 1990; U.S. Pat. No. 4,938,262, issued Jul. 3, 1990; and U.S. Pat. No. 4,941,518, issued Jul. 17, 1990, all of which are incorporated herein by reference. 
     Although the cassette and the delivery system work well, the delivery system is complex and expensive. There is a need for a delivery system which is simpler and less expensive than the cassette delivery system. Further, the volumes of vaporizable germicide which can be delivered to the sterilization chamber with the cassette delivery system are limited to incremental volumes of single cells on the cassette. For example, 1½ cells of hydrogen peroxide cannot easily be delivered with the cassette delivery system. Because the amount of hydrogen peroxide required for sterilization depends on the size of the sterilization chamber, the quantity of equipment in the chamber to be sterilized, the materials from which the equipment to be sterilized is made, and many other factors, there are times when it would be useful to be able to add small additional increments of hydrogen peroxide into the sterilization chamber rather than being limited to adding an entire cell of vaporizable germicide from a cassette. 
     There is a need for a simple, inexpensive system for metering vaporizable germicide into a sterilization chamber in which the amount of vaporizable germicide can be varied in small incremental increments. There is a need for a simple vaporizable germicide delivery system which can deliver a wide range of volumes of vaporizable germicide to match the needs of various sizes of sterilization chambers. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention involves a metering valve for delivering liquid to system. The metering valve includes a body having at least a first and a second orifice; and a rotatable valve plug located in the body, where the rotatable valve plug prevents direct fluid communication between the first orifice and the second orifice. The valve plug includes at least one well, where the well comes into fluid communication separately with the first orifice and the second orifice as the valve plug is rotated. 
     Advantageously, the orifices are located approximately 180 degrees apart in the valve body. The valve plug can be rotated manually or with a motor. In an embodiment, the valve plug includes at least two wells. The two wells may have different sizes or shapes. Preferably, the first orifice is never brought into direct fluid communication with the second orifice as said rotatable valve plug is rotated. 
     Another aspect of the invention involves a system for sterilizing equipment, where the system includes a metering valve. The metering valve includes a body with at least two orifices and a rotatable valve plug located in the body. The valve plug prevents direct fluid communication between the two orifices. The valve plug includes at least one well. The well comes into fluid communication separately with the two or more orifices as the valve plug is rotated. The system also includes a reservoir connected to a first orifice on the metering valve. The reservoir contains vaporizable germicide. The system also includes a sterilization chamber, where the sterilization chamber receives vaporizable germicide from a second orifice on the metering valve. 
     Preferably, the system also includes a vaporizer connected to the second orifice on the metering valve. The vaporizer is in fluid communication with the sterilization chamber. Advantageously, the system also includes a vacuum pump connected to the sterilization chamber. The system may include a source of plasma. An accumulator may be located between the second orifice on the metering valve and the sterilization chamber. An on/off valve may optionally be located between the metering valve and the sterilization chamber and/or between the metering valve and the reservoir. Advantageously, the vaporizable germicide is hydrogen peroxide. 
     Another aspect of the invention involves a method for sterilizing an article in a chamber. The method includes providing a source of vaporizable germicide, a chamber, and a metering valve for delivering germicide to the chamber. The metering valve includes a body having at least two orifices and a rotatable valve plug located in the body. The valve plug prevents direct fluid communication between the two orifices. There is at least one well in the valve plug. The well comes into fluid communication separately with the orifices as the valve plug is rotated. The metering valve is in fluid communication with the chamber and the source of vaporizable germicide. Rotating the valve plug transfers vaporizable germicide from the source of germicide into the well and from the well into the chamber. 
     Advantageously, the method also includes reducing the pressure in the chamber. Preferably, reducing the pressure vaporizes the vaporizable germicide, sterilizing the article in the chamber. In a preferred embodiment, the vaporizable germicide is accumulated in an accumulator located between the metering valve and the chamber. The article may be contacted with plasma. Preferably, the vaporizable germicide is hydrogen peroxide. The method may also include opening or closing a valve between the metering valve and the source of vaporizable germicide or between the metering valve and the chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing showing a sterilization system and a cross section of a metering valve according to an embodiment of the invention; 
     FIG. 2 is a schematic drawing of the sterilization system and metering valve of FIG. 1, where there are no optional on/off valves between the metering valve and the reservoir or the vaporizer; 
     FIG. 3A shows a schematic cross sectional side view of a metering valve according to an embodiment of the invention, where there is one well in the valve plug; 
     FIG. 3B shows a schematic cross sectional view of the metering valve of FIG. 3A along the  3 B— 3 B axis of FIG. 3A; 
     FIG. 4A shows a schematic cross sectional side view of a metering valve according to an embodiment of the invention, where there are two wells in the valve plug; 
     FIG. 4B shows a schematic cross section of the metering valve of FIG. 4A along the  4 B— 4 B axis of FIG. 4A; 
     FIG. 5 shows a schematic drawing of the sterilization system and metering valve of FIG. 1 after vaporizable germicide has been admitted into the orifice on the top of the metering valve of FIG. 1; 
     FIG. 6 shows a schematic drawing of the sterilization system and metering valve of FIG. 5 after the handle of the metering valve has been turned, transferring the vaporizable germicide in the well of the metering valve to the top of the on/off valve above the vaporizer; 
     FIG. 7 shows a schematic drawing of the sterilization system and metering valve of FIG. 6 after the on/off valve above the vaporizer has been opened, allowing liquid vaporizable germicide to be transferred from the top of the on/off valve into the vaporizer; and 
     FIG. 8 is a schematic drawing showing a sterilization system, a cross section of the metering valve of FIG. 3A, and an accumulator above the vaporizer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a schematic diagram of a sterilization chamber  10  with a metering valve  20  according to an embodiment of the invention. The sterilization chamber  10  and its components and methods of use are described in detail in U.S. Pat. No. 4,756,882, issued Jul. 12, 1988; U.S. Pat. No. 5,656,238, issued Aug. 12, 1997; and U.S. Pat. No. 6,060,019, issued May 9, 2000, all of which are incorporated herein by reference. The metering valve  20  is mounted below a reservoir  24  which contains vaporizable germicide  26  and above a vaporizer  28  which is located above and which is fluidly attached to the sterilization chamber  10 . Optional on/off valves  30  and  32  are located between the reservoir  24  and the metering valve  20  and/or between the metering valve  20  and the vaporizer  28 . A vacuum pump  36  and a shutoff valve  40  are fluidly connected with the sterilization chamber  10 . 
     Although the metering valve  20  is described in the context of a metering valve for delivering vaporizable germicide to a sterilization chamber  10 , it is to be understood that the application of the metering valve  20  to sterilization is illustrative only. The metering valve  20  of the present invention has many uses, and the example of delivering vaporizable germicide to a sterilization chamber  10  with the metering valve  20  is not meant to be limiting. The term germicide is meant to include either germicide or disinfectant. Further, the metering valve  20  can be used to deliver liquids, solids, and slurries of solids in one or more liquids. 
     FIG. 2 shows a schematic diagram of a sterilization chamber  10  and metering valve  20  in which there are no optional on/off valves  30  and  32  located between the reservoir  24  and the metering valve  20  and between the metering valve  20  and the vaporizer  28 . 
     FIGS. 3A and 3B show two views of a metering valve  20  according to an embodiment of the invention. The metering valve  20  has a generally rectangular shaped body  44  with open orifices  48  at a top and a bottom of the body  44 . As seen in cross-sectional side view FIG.  3 A and cross sectional end view FIG. 3B, the two orifices  48  form an open tube extending through the body  44  of the metering valve  20 . An roughly cylindrical valve plug channel  50  extends through the body  44  perpendicular to the first open tube formed by the two orifices  48 . The valve plug channel  50  forms a second tube in the body  44  perpendicular to the first open tube formed by the two orifices  48 . The valve plug channel  50  in FIGS. 3A and 3B contains a valve plug  52 . 
     Although the body  44  shown in FIGS. 3A and 3B has a roughly rectangular shape, the body  44  may have other shapes such as a cylindrical shape or other appropriate shapes. 
     The valve plug  52  has a generally cylindrical center section, the barrel  56 , with a rod-like valve stem  60  extending from an end of the barrel  56 . A handle  64  is connected to the valve stem  60 . Alternatively, a motor (not shown) can be connected to the valve stem  60  in place of, or in addition to, the handle  64 . 
     The tube formed by the two orifices  48  is plugged by the barrel  56  of the valve plug  52 . The barrel  56  of the valve plug  52  prevents fluid communication between the two orifices  48  on the body  44  of the metering valve  20 . The ends of the barrel  56  and the valve stems  60  form a seal with the body  44  of the metering valve  20 . The valve plug  52  may be rotated in the body  44  of the metering valve  20  by turning the handle  60  or motor (not shown). The valve plug  52  is held in place in the body  44  of the metering valve  20 . 
     In other embodiments, the valve plug  52  can have other shapes. For example, in an embodiment, the valve plug  52  has the shape of a tapered cylinder rather than a simple cylinder, as in the embodiment shown in FIGS. 3A and 3B. What is important that the valve plug  52  block the fluid communication between the two orifices  48  and that the valve plug  52  provide a seal with the body  44  of the metering valve  20 . 
     There is a well  68  having a roughly semicircular shaped cross section in the barrel  56  of the valve plug  52  in the embodiment of the metering valve  20  shown in FIGS. 3A and 3B. The well  68  extends through only part of the barrel  56 . In other embodiments, the well  64  can have other cross-sectional shapes such as a rectangular shape, a V-shape, or a trapezoid shape. As seen in FIG. 3B, the well  68  is located under one of the orifices  48  when the valve plug  52  is placed in the body  44  of the metering valve  20  and when the well  68  is oriented so that the well  68  is oriented with an open side of the well  68  directed upward. In other embodiments, the well  68  is not centered under the orifice  48  but is located asymmetrically below the orifice  48 . At least a portion of the well  68  is in fluid communication with the orifice  48  when the open side of the well  68  is directed toward the orifice  48 . Unlike a conventional valve, the orifices  48  of the metering valve  20  of FIGS. 3A and 3B are never in fluid communication with each other, no matter how the valve plug  52  is rotated. 
     The size of the well  68  may depend on the size of the sterilization chamber  10 . In an exemplary embodiment, the well  68  has a size which is appropriate for holding an amount of vaporizable germicide  26  which is appropriate for the smallest sterilization chamber  10  to which the metering valve  10  is to be applied. In an embodiment appropriate for the STERRAD® sterilizer, the well  68  has a volume of approximately 1 milliliter. In embodiments appropriate for other sterilization chambers  10 , the well  68  has a volume larger or smaller than 1 milliliter. 
     FIGS. 4A and 4B show an alternative embodiment of the metering valve  20  in which there are two wells  68  in the barrel  56  of the valve plug  52 . The wells  68  are positioned on the valve plug  52  so that at least a portion of each of the wells  68  is in fluid communication with an orifice  48  when the orifice  48  is aligned with the well  68 . In the embodiment of the metering valve  20  shown in FIGS. 4A and 4B, the two wells  68  are located on opposite sides of the valve plug  52 . In the embodiment of FIGS. 4A and 4B, when the well  68  at the top of the valve plug  52  is in fluid communication with the orifice  48  at the top of the metering valve  20 , the well  68  at the bottom of the valve plug  52  is in fluid communication with the orifice  48  at the bottom of the metering valve  20 . The two wells  68  are never in fluid communication with each other, no matter how the valve plug  52  is rotated. 
     The two wells  68  of the metering valve  20  of FIGS. 4A and 4B are approximately 180° apart from each another. In other embodiments of the metering valve  20  with two wells  68 , the wells  68  are at not 180° apart from each other, and only one of the wells  68  may be in fluid communication with an orifice  48  at any one time. In this embodiment, rotating the valve plug  52  causes the other well  68  to be in fluid communication with the orifice  48 . In other embodiments, there may be three or more wells  68  in the valve plug  52 . In all of the embodiments of the valve plug  20 , the wells  68  are not in direct fluid communication with each other, and the orifices  48  are not in direct fluid communication with each other. In the embodiments of the metering valve  20  with at least two wells  68 , the wells  68  can have different sizes or shapes. 
     The metering valve  20  can be made from a wide range of materials, including metal, glass, or plastic. Suitable metals include steel or aluminum. Stainless steel is an exemplary metal for forming the metering valve  20 . TEFLON™ is an exemplary material for forming the metering valve  20 . TEFLON™ is the tradename for polytetrafluoroethylene. 
     The seal between the valve plug  52  and the body  44  of the metering valve  20  can be achieved in several ways, depending on the material from which the metering valve is fabricated. If the valve plug  52  and the body  44  of the metering valve are both made of TEFLON™, the valve plug  52  and the body  44  can be fabricated so that the contact between the TEFLON™ valve plug  52  and the TEFLON™ body  44  forms a seal. 
     In another embodiment, the valve plug  52  is made of TEFLON™, and the body  44  is made of metal. If the valve plug  52  and the body  44  are properly fabricated, the contact between the TEFLON™ valve plug  52  and the metal body  44  forms a seal. In another embodiment, the valve plug  52  is made of TEFLON™, and the body  44  is made of glass. In another embodiment, both the valve plug  52  and the body  44  are made of metal. O-rings or packing can be placed on the valve plug  52  to form a seal between the valve plug  52  and the body  44 . 
     If O-rings or packing are used in the metering valve  20 , the O-rings or packing are preferably formed of a material which is resistant to the vaporizable germicide  26  which is used. VITON™ is an exemplary material for forming the O-rings or packing. TEFLON™ or silicone may also be used to form the O-rings or packing. 
     Returning to FIG. 1, vaporizable germicide  26  is placed in the reservoir  24  above the optional on/off valve  30 . The vaporizable germicide  26  can be any liquid vaporizable germicide including hydrogen peroxide, peracetic acid, chlorine dioxide, ozone, or formaldehyde. In an exemplary embodiment, the vaporizable germicide  26  comprises aqueous hydrogen peroxide. In a preferred embodiment, the vaporizable germicide  26  is approximately 59 wt % aqueous hydrogen peroxide. The shutoff valve  40  between the vacuum pump  36  and the sterilization chamber  10  is opened, and the sterilization chamber  10  is evacuated to a pressure of less than 50 torr, more preferably less than 10 torr, and most preferably less than 1 torr with the vacuum pump  36 . After the sterilization chamber  10  is evacuated, shutoff valve  40  between the vacuum pump  36  and the sterilization chamber  10  may be closed to isolate the sterilization chamber  10  from the vacuum pump  36 . In an alternative embodiment which will be described in more detail later, the shutoff valve  40  between the vacuum pump  36  and the sterilization chamber  10  is left open. 
     In FIG. 5, the on/off valve  30  between the reservoir  24  and the metering valve  20  has been opened, allowing vaporizable germicide  26  to enter the orifice  48  and the well  68  on the metering valve  20 . 
     In FIG. 6, the handle  64  or motor on the metering valve  20  has been rotated, rotating the valve plug  52 . As the valve plug  52  rotates, the vaporizable germicide  26  in the well  68  in the valve plug  52  of the metering valve  20  falls out of the well  68  onto the top of on/off valve  32 . 
     In FIG. 7, on/off valve  32  has been opened, allowing the vaporizable germicide  26  which was on top of the on/off valve  32  in FIG. 6 to enter the vaporizer  28 . The vaporizer  28  is fluidly connected to the interior of the sterilization chamber  10 . The vaporizer is maintained at a temperature of 60 to 70° C. As the vaporizable germicide  26  enters the hot vaporizer  28 , the vaporizable germicide  26  vaporizes, and the germicide vapor enters the sterilization chamber  10 . The germicide vapor contacts the equipment to be sterilized (not shown) in the sterilization chamber  10 , sterilizing the equipment. Optionally, plasma is introduced into or is generated in the sterilization chamber  10  to enhance the sterilization by the germicide vapor or to remove the germicide residual. 
     Returning to FIG. 6, the handle  64  or the motor on the metering valve  20  can optionally be rotated more than one time. Each time the handle  64  is rotated, a volume of vaporizable germicide  26  equal to the volume of the well  68  is delivered to the top of the on/off valve  32 . When the desired amount of vaporizable germicide  26  has been delivered to the top of the on/off valve  32 , the on/off valve  32  is opened, allowing the vaporizable germicide  26  to enter the vaporizer  28 . By knowing the volume of the well  68  and the number of times the handle  64  or motor has been rotated, the amount of vaporizable germicide  26  which has been delivered to the vaporizer  28  can be determined. 
     In the embodiment of the metering valve  20  shown in FIGS. 4A and 4B, there are two wells  68  on the valve plug  52 . Each rotation of the handle  64  on the metering valve  20  delivers a volume of vaporizable germicide  26  equal to the volume of the two wells  68 , rather than the volume of a single well  68 . The embodiment of the metering valve  20  shown in FIGS. 3A and 3B thus delivers twice as much vaporizable germicide  26  for each rotation of the valve plug  52  as the embodiment of the metering valve  20  shown in FIGS. 3A and 3B. Vaporizable germicide  26  can enter the well  68  at the top of the metering valve  20  from the orifice  48  at the top of the metering valve  20  at the same time that vaporizable germicide  26  exits the well  68  at the bottom of the metering valve  20 . 
     In an alternative embodiment of the apparatus such as shown in FIG. 2, there is no on/off valve  32  below the metering valve. In the alternative embodiment, the vaporizable germicide  26  enters the vaporizer  28  directly after leaving the well  68 . The handle  64  on the metering valve  20  can be rotated multiple times to add more vaporizable germicide  26 . In the alternative embodiment, the vaporizable germicide  26  enters the vaporizer.  28  incrementally each time the handle  64  is rotated rather than at one time when the on/off valve  32  is opened. 
     FIG. 8 shows another embodiment of the apparatus suitable for delivering larger volumes of vaporizable germicide  26  than the embodiment of the apparatus shown in FIG.  1 . In the embodiment of the apparatus shown in FIG. 8, there is no on/off valve  30  between the reservoir  24  and the metering valve  20 . In another embodiment, there is an on/off valve  30  between the reservoir  24  and the metering valve  20 . An accumulator  76  is located between the metering valve  20  and the on/off valve  32  located above the vaporizer  28 . The volume of the accumulator  76  is larger than the volume of the orifice  48  at the bottom of the metering valve  20 . By including the accumulator  76  in the apparatus, a larger volume of vaporizable germicide  26  can be placed on top of the on/off valve  32  above the vaporizer  28  than in the embodiment of the apparatus shown in FIG. 1, where the volume of vaporizable germicide  26  on top of the on/off valve  32  is limited to the volume of the orifice  48  at the bottom of the metering valve  20 . After the desired volume of vaporizable germicide  26  has been delivered to the accumulator  76 , the on/off valve  32  is opened, delivering the vaporizable germicide  26  to the vaporizer  28 . 
     Accumulating larger volumes of vaporizable germicide  26  in the accumulator  76  of FIG. 8 has advantages over simply allowing the vaporizable germicide  26  to enter the vaporizer  28  directly, when the vaporizable germicide  26  comprises hydrogen peroxide and water. Water has a higher vapor pressure than hydrogen peroxide. If the valve  40  between the sterilization chamber  10  and the vacuum pump  36  is left open when the on/off valve  32  is opened, allowing the vaporizable germicide  26  to enter the vaporizer  28 , water is preferentially removed from the sterilization chamber  10  into the vacuum pump  36 , because the water has a higher vapor pressure than hydrogen peroxide, and the vapor in the sterilization chamber  10  is enriched in water vapor compared to the vaporizable germicide  26  in the accumulator  76 . Removing water from the aqueous hydrogen peroxide in the accumulator  76  by removing the water vapor in the sterilization chamber  10  concentrates the hydrogen peroxide. 
     After a certain period of time apparent to one of ordinary skill in the art, the valve  40  leading to the vacuum pump  36  is closed, and the concentrated hydrogen peroxide is allowed to vaporize from the vaporizer  28  into the sterilization chamber  10 . The concentrated hydrogen peroxide in the vaporizer  28  vaporizes to produce a vapor which has a higher concentration of hydrogen peroxide than if water had not been removed from the aqueous hydrogen peroxide in the accumulator  76  by preferential vaporization. The concentrated hydrogen peroxide vapor is more effective at sterilization than hydrogen peroxide vapor produced from a less concentrated solution of aqueous hydrogen peroxide. 
     Allowing the aqueous hydrogen peroxide vaporizable germicide to accumulate in the accumulator  76  is therefore a preferred embodiment. The aqueous hydrogen peroxide in the accumulator  76  can be concentrated by removing water vapor from the sterilization chamber  10  through the valve  40  and the vacuum pump  36 , improving the effectiveness of the sterilization. 
     The metering valve  20  of the present invention is an apparatus which provides a way to readily deliver a wide range of volumes of vaporizable germicide  26  to the sterilization chamber  10  without having to change the size of the delivery system, depending on the size of the sterilization chamber  10 . The metering valve  20  of the present invention is a simple device which is inexpensive to manufacture and easy to use. The volume of vaporizable germicide  26  which is delivered to the vaporizer  28  can be controlled by rotating the handle  64  or motor (not shown) on the metering valve  20 . Each rotation of the handle  64  delivers a volume of vaporizable germicide  26  equal to the volume of the well  68  on the valve plug  52 . The incremental volumes of vaporizable germicide  26  to be delivered to the sterilization chamber  10  are not limited to the volume of a cell on a sterilization cassette. If multiple wells  68  are present on the valve plug  52 , each rotation of the handle  64  delivers a volume of vaporizable germicide  26  equal to the volume of each well  68  times the number of wells  68  on the valve plug  52 . 
     In some embodiments, more than one metering valve  20  may be located in parallel between the reservoir  24  and the vaporizer  28 . The metering valves  20  can have wells  68  of differing sizes or shapes. In this embodiment, the metering valve  20  can be selected for use which has a well  68  with a size which is optimal for the size of the sterilization chamber  10 . 
     Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that the invention is not limited to the embodiments disclosed therein, and that the claims should be interpreted as broadly as the prior art allows.