Patent Publication Number: US-2022218531-A1

Title: Negative pressure treatment including mechanical and chemical pump

Description:
BACKGROUND 
     Negative pressure therapy is a therapeutic treatment that utilizes negative pressure for skin treatments and restorative purposes. Negative pressure is a term used to describe a pressure that is below normal atmospheric pressure. Negative pressure therapy is utilized for several sites on the skin, such as a wound or an incision. Furthermore, negative pressure therapy is useful to manage wounds with complex healing concerns. Additionally, negative pressure therapy could also be used for cosmetic purposes like removing wrinkles. 
     Generally, negative pressure therapy is achieved by maintaining a reduced pressure beneath a dressing on a dressing site. A vacuum generation source, such as a pump, applies reduced pressure to the inside of the dressing on the dressing site. However, when a vacuum source that operates using a chemical reaction is first activated, a desirable negative pressure may not be obtained for the first few minutes of the operation of the vacuum source. As a result, if the dressing is not properly sealed at the beginning of the negative pressure therapy, an indication that the dressing is not sealed may not be noticeable for a few minutes. Furthermore, when a reduced pressure is finally obtained, the negative pressure may be susceptible to decreasing below a target pressure range for the negative pressure therapy (e.g., too much vacuum is applied on the skin). When the negative pressure decreases below the target pressure range, the dressing may be uncomfortable for the patient. 
     SUMMARY 
     In view of the foregoing, a negative pressure assembly includes a drape, a sealing element, a reactor, and a mechanical pump assembly. The drape covers a dressing site on a patient and when sealed against the skin upon application of a vacuum is capable of maintaining a negative pressure underneath the drape. When applied to the skin, the sealing element cooperates with the drape to define an enclosed volume covered by the drape and surrounded by the sealing element. The reactor is configured to react with and consume a selected gas found in air, and is located with respect to the drape and the sealing element to be in fluid communication with the enclosed volume when the drape is covering the dressing site. The mechanical pump assembly is fluidly connectable to the enclosed volume and has a pump chamber in fluid communication with the enclosed volume to draw air from the enclosed volume into the pump chamber. 
     The negative pressure assembly described above may further include a dressing including the drape and an absorbent material. Additionally, the reactor may be disposed in the dressing. Furthermore, a relief valve may be disposed on the dressing. The relief valve is in fluid communication with the enclosed volume and ambient. When a pressure differential between ambient and the enclosed volume is outside a predetermined pressure range, the relief valve allows gas from ambient to enter the enclosed volume. 
     The mechanical pump assembly can be connected to the dressing, and the pump chamber of the mechanical pump assembly is in fluid communication with the enclosed volume. The mechanical pump assembly can be connected to the dressing via a valve, a fitting, or a hose. The valve may be configured to allow gas to exit through the valve and into the pump chamber of the mechanical pump assembly while also preventing ambient air from entering into the enclosed volume through the valve. Alternatively, the valve may be a bidirectional valve configured to allow gas to exit through the valve when ambient pressure is below that of the enclosed volume and to allow gas from ambient to enter the enclosed volume through the valve when the pressure differential between ambient and the enclosed volume is outside a predetermined pressure range. Furthermore, the mechanical pump assembly may include a manually-actuated actuator and a biasing mechanism operatively connected with a movable pump element. When the manually-actuated actuator is actuated, the biasing mechanism moves the movable pump element. In result, air is drawn into the mechanical pump assembly. The biasing mechanism can be a spring, and the movable pump element can be a piston. 
     The negative pressure assembly described above may further include a chemical pump assembly including a chemical pump housing having a chamber. In this embodiment, the reactor is positioned in the chamber of the chemical pump housing instead of the dressing. Furthermore, the chemical pump assembly may include a diaphragm which moves toward the chamber to indicate when the chamber is under negative pressure. Additionally, the relief valve may alternatively be disposed on the chemical pump assembly instead of the dressing or may remain on the dressing. 
     The chemical pump housing may be connected to the dressing via a valve, a fitting, or a hose. Furthermore, the chemical pump assembly may be connected to a second dressing covering a second dressing site via a second valve, a second fitting, or the hose. The hose may be Y-shaped to connect the chemical pump assembly to the dressing and the second dressing at the same time. When the chemical pump housing is connected to the dressing, the chamber of the chemical pump assembly is in fluid communication with the enclosed volume. The hose may be retractable into the chemical pump assembly. Alternatively, the hose can be wound around a wrap element disposed on the chemical pump assembly. Also, when the chemical pump assembly is connected with the dressing via a fitting, the mechanical pump assembly may also be connected with the dressing via the fitting when the chemical pump assembly is not connected to the dressing via the fitting. Alternatively, the chemical pump assembly and the mechanical pump assembly may be connected to the dressing via separate valves, fittings, and/or hoses. 
     In still another embodiment, the mechanical pump assembly can be connected to the chemical pump assembly. In result, the pump chamber of the mechanical pump assembly is in fluid communication with the enclosed volume via the chemical pump assembly. The mechanical pump assembly can be connectable with the chemical pump housing via a valve, a fitting, or a hose. In the embodiment with the valve, gas can exit through the valve and into the pump chamber while also preventing ambient air from entering the chamber through the valve. 
     A negative pressure assembly according to another embodiment includes a drape, a sealing element, a valve, and a mechanical pump assembly. The drape covers a dressing site on a patient and is capable of maintaining a negative pressure underneath the drape when sealed against the patient&#39;s skin upon application of a vacuum. The sealing element cooperates with the drape when applied to the skin to define an enclosed volume covered by the drape and surrounded by the sealing element. The valve is disposed on the drape and has a first operating state in which gas exits the enclosed volume through the valve and a second operating state in which gas is precluded from exiting the enclosed volume through the valve. The mechanical pump assembly includes a pump chamber fluidly connectable to the enclosed volume through the valve when the valve is in the first operating state. The mechanical pump assembly is also configured to draw air from the enclosed volume into the pump chamber when fluidly connected with the enclosed volume. 
     The negative pressure assembly may further include a dressing including the drape, the sealing element, and an absorbent material. The mechanical pump assembly is connectable to the dressing through the valve so that the pump chamber is in fluid communication with the enclosed volume. The negative pressure assembly may also include a reactor located with respect to the drape and the sealing element so that the reactor is in fluid communication with the enclosed volume when the drape is covering the dressing site. The reactor reacts with a selected gas found in air and consumes the selected gas. In one embodiment, the reactor is disposed in the dressing. In another embodiment, the negative pressure assembly further includes a chemical pump assembly having a chemical pump. housing in which the reactor is disposed in the chemical pump housing. 
     Furthermore, a relief valve may be disposed on the dressing. The relief valve is in fluid communication with the enclosed volume and ambient. The relief valve allows gas from ambient to enter the enclosed volume through the relief valve when a pressure differential between ambient and the enclosed volume is outside a predetermined pressure range. Alternatively, the valve may be a bidirectional valve that allows gas to exit through the valve when ambient pressure is below that of the enclosed volume and allows gas from ambient to enter the enclosed volume through the valve when the pressure differential between ambient and the enclosed volume is outside a predetermined pressure range. The predetermined pressure range may be between 50 and 200 mmHg below atmospheric pressure. 
     Additionally, the mechanical pump assembly may include a manually-actuated actuator and a biasing mechanism operatively connected with a movable pump element. The actuation of the manually-actuated actuator results in the biasing mechanism moving the movable pump element. In result, air is drawn into the mechanical pump assembly. The biasing mechanism may be a spring, and the movable pump element may be a piston. A hose may also be retractable into the mechanical pump assembly. Alternatively, the hose may be wound around a wrap element on the mechanical pump assembly. The mechanical pump assembly may further be connected to a second dressing covering a second dressing site via a valve, a fitting, or a hose. 
     A negative pressure assembly according to another embodiment includes a drape for covering a dressing site on a patient and capable of maintaining a negative pressure underneath the drape when sealed against skin upon application of a vacuum and a sealing element that when applied to the skin cooperates with the drape to define an enclosed volume covered by the drape and surrounded by the sealing element. The negative pressure assembly also includes a reactor located with respect to the drape and the sealing element so as to be in fluid communication with the enclosed volume when the drape is covering the dressing site. The reactor is configured to react with a selected gas found in air so as to consume the selected gas. The negative pressure assembly also includes a valve including at least one movable element. The valve has a first operating state in which gas is drawn from the enclosed volume through the valve. The negative pressure assembly also includes a mechanical pump assembly including a pump chamber fluidly connectable to the enclosed volume through the valve when the valve is in the first operating state. The mechanical pump is configured to fluidly connect with the enclosed volume and draw air from the enclosed volume into the pump chamber of the mechanical pump assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a negative pressure kit. 
         FIG. 2  is a schematic cross-sectional view of a dressing and a mechanical pump assembly of the negative pressure kit according to one embodiment. 
         FIG. 3  is a perspective view of a dressing and a mechanical pump assembly. 
         FIG. 4  is a perspective view of the dressing in  FIG. 3  and a chemical pump assembly prior to connection of the chemical pump assembly to the dressing. 
         FIG. 5  is a schematic cross-sectional view of the chemical pump assembly according to one embodiment. 
         FIG. 5A  is a schematic cross-sectional view of the chemical pump assembly according to yet another embodiment. 
         FIG. 6  is a schematic cross-sectional view of the mechanical pump assembly before actuation. 
         FIG. 7  is a schematic cross-sectional view of the mechanical pump assembly after actuation. 
         FIG. 8  is a perspective view of the dressing and the chemical pump assembly after connection of the chemical pump assembly to the dressing, but prior to negative pressure in a therapeutic range underneath the dressing. 
         FIG. 9  is a perspective view of the dressing, the chemical pump assembly and the mechanical pump assembly (in schematic cross-section) after connection of the chemical pump assembly to the dressing and connection of the mechanical pump assembly to the chemical pump assembly, but prior to actuation of the mechanical pump assembly. 
         FIG. 10  is a perspective view of the dressing, the chemical pump assembly and the mechanical pump assembly after connection of the chemical pump assembly to the dressing and connection of the mechanical pump assembly to the chemical pump assembly, and after actuation of the mechanical pump assembly after actuation. 
         FIG. 11  is a perspective view of the dressing and the chemical pump assembly after connection of the chemical pump assembly to the dressing, and after negative pressure in a therapeutic range has been achieved underneath the dressing and a diaphragm inverts toward a chamber in the chemical pump assembly. 
         FIG. 12  is a perspective view of the dressing, the chemical pump assembly and the mechanical pump assembly before connection of the chemical pump assembly to the dressing and after connection of the mechanical pump assembly to the dressing, but prior to actuation of the mechanical pump assembly. 
         FIG. 13  is schematic cross-sectional view of a portion of a chemical pump housing including a wrap element. 
         FIG. 14  is a perspective view of the chemical pump assembly and the dressing and a second dressing after negative pressure in a therapeutic range underneath the dressing according to another embodiment. 
         FIG. 15  is a perspective view of the mechanical pump assembly (in schematic cross-section) and the dressing after connection of the mechanical pump assembly to dressing, but before the actuation of the mechanical pump assembly according to still another embodiment. 
         FIG. 16  is a perspective view of a mechanical pump assembly. 
         FIG. 17  an exploded perspective view of the mechanical pump assembly of  FIG. 16 . 
         FIG. 18  is a perspective view of a chemical pump assembly. 
         FIG. 19  is a sectional elevation view of the chemical pump assembly of  FIG. 18 . 
         FIG. 20  is a perspective view of the chemical pump assembly of  FIG. 18  and two dressings. 
         FIG. 21  is a schematic sectional view of a mechanical pump assembly and a chemical pump assembly according to an embodiment prior to activation of the mechanical pump assembly. 
         FIG. 22  is a schematic sectional view of a mechanical pump assembly and a chemical pump assembly according to an embodiment prior to activation of the mechanical pump assembly. 
         FIG. 23  is a sectional view of a dressing. 
         FIG. 24  is a sectional view of a dressing after connection with and activation of the mechanical pump assembly. 
         FIG. 25  is a sectional elevation view of a chemical pump assembly having a mechanical pump located in an internal chamber of a chemical pump housing. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a negative pressure kit  10  useful for negative pressure therapy. Negative pressure described herein is pressure below atmospheric pressure. The negative pressure kit  10  includes a tray kit  12  and a negative pressure assembly. In the embodiment depicted in  FIG. 1 , the negative pressure assembly includes at least one dressing  14 , a chemical pump assembly  16 , and a mechanical pump assembly  18 . 
     The tray kit  12  comprises a top cover  20  and a bottom cover  22 . At least one recess  24  may be provided on the bottom cover  22  for storing the at least one dressing  14 , the chemical pump assembly  16 , and the mechanical pump assembly  18 . Spacer walls  26  can be added to maintain space between the top cover  20  and bottom cover  22  when the tray kit  12  is closed. The spacer walls  26  can at least partially surround the perimeter of the at least one recess  24 . The bottom cover  22  may further include securing elements for securing the components in the at least one recess  24 . Also, the tray kit  12  may comprise a closing element for keeping the top cover  20  and bottom cover  22  closed, and may further include locking attachments for locking the tray kit  12  when the tray kit  12  is closed. 
     With reference to  FIG. 2 , the dressing  14  is placed over a dressing site  28  on a patient&#39;s skins. The dressing site  28  can be, but is not limited to, a wound, an incision, or skin where there is no wound or incision. In the illustrated embodiment, the dressing  14  includes a drape  40 , a wicking or absorbent element  42  and a fitting  44 . The dressing  14  can include further components, such as a sealing element  46 , and can be similar construction to the dressings described in U.S. application Ser. No. 16/114,813 and/or PCT/US2016/059364. The drape  40  can be made from a flexible material and can be made from a thin, flexible elastomeric film. Examples of such materials include polyurethane or polyethylene films. The drape  40  can include at least one opening  48  (see  FIG. 1 ), which can cooperate with the fitting  44 . The drape  40  in the illustrated embodiment is a thin film capable of maintaining a negative pressure underneath the drape  40  when sealed against the skin upon application of a vacuum when the opening  48  is not in communication with ambient. 
     The drape  40  further comprises a drape top  52  and a drape edge  54 . The drape top  52  and the drape edge  54  can be made from one continuous piece or multiple pieces fused together. The drape edge  54  is placed around the dressing site  28 , and the drape top  52  covers the dressing site  28 . The drape  40  can be made in a variety of shapes and sizes to cover a variety of dressing sites  28 . The opening  48  extends through the drape top  52 . 
     With continued reference to  FIG. 2 , the sealing element  46  cooperates with the drape  40  and the skin S to create an enclosed volume  60  defined between the drape  40  and the dressing site  28  and surrounded by the sealing element  46 . The sealing element  46  can be separate from the dressing  14  or a component of the dressing  14 . The sealing element  46  functions like a gasket, as the sealing element  46  prevents fluid (including air) from escaping between the drape  40  and the skin S. When properly sealed, air or select gases found in air can selectively exit the dressing  14  through the at least one opening  48  and fitting  44 . Thus, the sealing element  46  helps maintain negative pressure within the dressing  14 . The sealing element  46  can be made from a material such as silicone or a hydrogel material. 
     The dressing  14  may further include a wound contact layer  68 . The drape top  52  covers the wound contact layer  68  and/or the wicking or absorbent element  42 . The wound contact layer  68  can be made of an elastomeric material, such as a polymeric material that has rubber-like properties. Furthermore, the wound contact layer  68  can be an elastomeric material that is a thin, flexible elastomeric film. Some examples of such materials include a silver coated nylon, a perforated silicone mesh, or other materials that will not stick to the patient&#39;s tissue. The wound contact layer  68  contacts the dressing site  28 . The wound contact layer  68  can include at least one opening to cooperate with the absorbent element  42  to retain exudate traveling from the dressing site  28  into the enclosed volume  60 . The sealing element  46  can also be disposed on the side of the wound contact layer  68  that contacts the dressing site  28  (or the absorbent element  42  if the wound contact layer  68  is not included). 
     A drape release liner (not shown) is disposed on the bottom surface of the drape edge  54 . The drape release liner is removed before the dressing  14  is applied to the dressing site  28 . When the drape release liner is removed, an adhesive  66  on the bottom surface of the drape edge  54  is exposed. As the dressing  14  is placed on the patient, the adhesive  66 , which can be an acrylic-based adhesive that is distinct from the sealing element  46 , secures the drape edge  54  to the patient&#39;s skin S around the dressing site  28 . Thus, contact is maintained between the drape edge  54  and the skin S. 
     The wicking or absorbent element  42  is made from an absorbent material that is capable of absorbing exudate from the dressing site  28 . The absorbent element  42  can be made from super absorbent polymers, absorbent beads, foams, or natural absorbents. Also, the absorbent element  42  can provide appropriate voids for gases found in air so that reduced pressure can be maintained. For example, the absorbent element  42  can be made from a relatively more rigid foam as compared to the drape  40  so that gas voids are maintained while absorbing exudate from the wound. The absorbent element  42  could also be made from the superabsorbent polymers described above that expand and form gas voids, for example between adjacent beads, to provide aforementioned volume control. The absorbent element  42  can also be a hydroactive wound pad available under the trademark Vilmed®, which chemically absorbs exudate and precludes the exudate from passing through the wicking element toward the vacuum source unlike a sponge. 
     The dressing  14  can also include an air permeable liquid impervious membrane  70  covering the opening  48  in the drape top  52 . In an embodiment, the air permeable liquid impervious membrane  70  is disposed on the bottom surface of the drape top  52 . Air is allowed to travel through the air permeable liquid impervious membrane  70 , whereas liquid is prevented from traveling through the air permeable liquid impervious membrane  70 . Therefore, exudate is not able to flow through the air permeable liquid impervious membrane  70 . In another embodiment, the air permeable liquid impervious membrane  70  is disposed on the top surface of the drape top  52 . Furthermore,  FIG. 2  depicts a chemical pump  82  in the form of a reactor disposed in the dressing  14  beneath the drape  40 . The chemical pump  82  can be located elsewhere, which will be described in more detail below. 
       FIG. 3  depicts the dressing  14  connected with the mechanical pump assembly  18  via a hose  62  (schematically depicted). When the mechanical pump assembly  18  is connected to the dressing  14 , the mechanical pump assembly  18  is in fluid communication with the enclosed volume  60  via the fitting  44  in a manner described in more detail below. Actuation of the mechanical pump assembly  18  draws air from the enclosed volume  60  through the opening  48 , fitting  44 , and hose  62  into the mechanical pump assembly  18 . As such, the sealing of the dressing  14  against the skin S can be checked in that the drape  40  would be drawn toward the skin S. The hose  62  can then be removed from the fitting  44 , which would allow air into the enclosed volume  60  resulting in the enclosed volume  60  returning towards atmospheric pressure. 
       FIG. 4  depicts the dressing  14  and the chemical pump assembly  16 . The chemical pump assembly  16  includes a chemical pump housing  80 , a chemical pump  82  (shown in phantom in  FIG. 4 ) positioned in a chamber  84  (see  FIG. 5 ), and a lower opening  86  disposed on the bottom of the chemical pump housing  80  and in fluid communication with the chamber  84 . When connected with the fitting  44 , the chamber  84  in the chemical pump housing  80  is in fluid communication with the enclosed volume  60  via the lower opening  86 , the at least one opening  48 , and the fitting  44  on the drape  40 . The chemical pump assembly  16  applies reduced pressure on the inside of the dressing  14  in a manner that will be described in more detail below. 
     The chemical pump  82  in the chemical pump assembly  16  is a reactor configured to react with a selected gas found in air. The chemical pump  82  is located with respect to the drape  40  and sealing element  46  so that the chemical pump  82  can be in fluid communication with the enclosed volume  60 . The chemical pump  82  consumes the selected gas from the enclosed volume  60 , thereby removing the gas and reducing the gas pressure. As such, even though the chemical pump  82  does not include an inlet and an exhaust that moves a fluid from one location to another like that of a conventional pump, it does remove a gas from air thus lowering the gas pressure within the enclosed volume  60 . Examples of reactors that can be used in the chemical pump assembly  16  are described in US 2014/0109890A1 and PCT/US2016/059364. The chemical pump  82  can be actuated by exposing the chemical pump  82  to ambient by providing a hermetic seal around the chemical pump until it is ready to be activated. Alternatively, an electrolyte solution, such as the one found in the impregnated pad in US 2014/0109890A1, could be provided in a rupturable package and later ruptured so as to react with a reducing agent found on a substrate. In the case of a therapeutic negative pressure system, utilized for wound care, the range of reported operating pressures, relative to standard atmospheric pressure of 760 mmHg, are −50 mmHg to −200 mmHg (absolute pressure of 560 to 710 mmHg). When the pressure is less than 560 mmHg, the at least one dressing  14  can become uncomfortable for the patient. When the pressure is above 710 mmHg, the negative pressure therapy may not be as effective compared to pressures below 710 mmHg. However, smaller target pressure ranges within the 560 to 710 mmHg may be desired. Thus, the reactor  82  can be configured to maintain a reduced pressure range within a predetermined target pressure range. 
     The chemical pump assembly  16  is configured to maintain a predefined chamber volume, as the chemical pump  82  consumes the selected gas from the enclosed volume  60 . The size of the reactor  82  is dependent on the volume of the chamber  84 , the hose  62  and the enclosed volume  60 , among other factors. In another embodiment, the reactor  82  can be disposed in the dressing  14  instead of the chemical pump assembly  16 , as depicted in  FIG. 2 . As a result, the chemical pump assembly  16  may be eliminated in the method of applying negative pressure within the dressing  14 . 
     In the illustrated embodiment of  FIG. 5 , an upper opening  90 , in which a first valve  92  is disposed, is provided on the top of the chemical pump housing  80 . Additionally, the upper opening  90  and first valve  92  can be disposed on a side of the chemical pump housing  80  and elsewhere on the chemical pump housing  80 . In another embodiment, a valve that operates similarly to the first valve  92  can be disposed on the dressing  14 . The first valve  92  is configured to work with the mechanical pump assembly  18 . In the first operating state, the first valve  92  allows air to exit the chamber  84  through the first valve  92  when the mechanical pump assembly  18  is inserted into the first valve  92 . In the second operating state, the first valve  92  precludes ambient air from entering the chamber  84  through the upper opening  90  and first valve  92  when the mechanical pump assembly  18  is not inserted into the first valve  92 . Examples of such valves include, but are not limited to, a spring-biased check valve and a valve comprising flaps.  FIG. 5  depicts the first valve  92  having flaps  94 . The flaps  94  on the first valve  92  are closed before the mechanical pump assembly  18  is introduced into the upper opening  90 . No gas is allowed to escape through the upper opening  90  and the first valve  92  unless the mechanical pump assembly  18  is introduced. The flaps  94  on the first valve  92  return to the closed position by their resilient forces, as the mechanical pump assembly  18  is removed. 
     In the illustrated embodiment, a sealing member  96  is disposed on the bottom of the chemical pump housing  80 . Also, the sealing member  96  can be disposed on a side of the chemical pump housing  80  and elsewhere on the chemical pump housing  80 . In the illustrated embodiment, the sealing member  96  is positioned in the lower opening  86  and configured to work with the fitting  44 . The sealing member  96  allows air to enter the chamber  84  through the lower opening  86  when the chemical pump assembly  16  is pressed onto and fitted with the fitting  44 . The sealing member  96  prevents ambient air from entering the chamber  84  when the chemical pump assembly  16  is not fitted onto the fitting  44 .  FIG. 5  depicts the sealing member  96  having flaps  98 . The flaps  98  on the sealing member  96  are closed before the chemical pump assembly  16  is fit onto the fitting  44 . No gas is allowed to enter through the sealing member  96  unless the flaps  98  are moved from their initial closed position. Alternatively, the sealing member  96  can be foil or another member capable of being punctured when pressed against the fitting  44 . 
     With reference to  FIG. 4 , a negative pressure indicator, which in the illustrated embodiment is a diaphragm  100 , may be disposed on the chemical pump housing  80  to provide an indication to the user that the system is under negative pressure. Referring to  FIG. 4 , the diaphragm  100  can be dome shaped protruding out of the chemical pump housing  80  when the pressure in the chamber  84  is at or above a predetermined pressure, which can be atmospheric pressure. The diaphragm  100  can be made from an elastic material. As the pressure in the chemical pump assembly  16  or dressing  14  decreases below the target pressure range, the diaphragm  100  is drawn into the chemical pump housing  80 . As the diaphragm  100  is drawn towards the inside of the chemical pump housing  80 , the diaphragm  100  is inverted. When the diaphragm  100  is inverted, this provides an indication to the user that the system is under negative pressure. Alternatively, the indicator can be disposed on the dressing  14 . 
       FIGS. 6 and 7  schematically depict the mechanical pump assembly  18 . In the illustrated embodiment, the mechanical pump assembly  18  is a single action vacuum source used to create negative pressure in the enclosed volume  60  of the dressing  14 . When the chemical pump assembly  16  is initially installed on the dressing  14  (see  FIG. 8 ), negative pressure in the enclosed volume  60  of the dressing  14  is not created until the chemical pump assembly  16  is in full operation, i.e., until the reactor  82  scavenges the selected gas found in air from the chamber  84  and the enclosed volume  60 . Therefore, the mechanical pump assembly  18  can also assist in the negative pressure maintenance of the dressing  14 . Furthermore, the mechanical pump assembly  18  can assist in drawing the dressing  14  towards the dressing site  28 . 
     In one embodiment, the mechanical pump assembly  18  may include a manually-actuated actuator and a biasing mechanism operatively connected with a movable pump element. The actuation of the manually-actuated actuator results in the biasing mechanism moving the movable pump element so as to draw air into the mechanical pump assembly. In result, negative pressure is created in the enclosed volume  60 . Thus, the mechanical pump assembly  18  can be a pneumatic piston cylinder. With reference to  FIG. 6 , the mechanical pump assembly  18  comprises a mechanical pump housing  120 , and a pump chamber having a first chamber  138  and a second chamber  140 . An actuator  144  may be disposed on the side of the mechanical pump housing  120 . The actuator  144  can be manually operated and used to activate the operation of the mechanical pump assembly  18 . Examples of such actuators include, but are not limited to, a button, a switch, or a trigger. 
     An internal wall  122  may be used to separate the first chamber  138  from the second chamber  140 . The internal wall  122  includes a rod opening  142  for accepting a piston rod  130 . A seal  124  encircles the internal wall  122  to prevent any gas from passing between the first chamber  138  and the second chamber  140  around the internal wall  122 . Alternatively, the internal wall  122  can be integrally formed with the mechanical pump housing  120 . Furthermore, a second seal  146  in the rod opening  142  can enclose the piston rod  130  so that gas is prevented from passing between the first chamber  138  and the second chamber  140  through the rod opening  142  without restricting the movement of the piston rod  130 . 
     The mechanical pump housing  120  includes a tip  134  disposed at the bottom. The tip  134  includes a tip opening  136  in fluid communication with the first chamber  138 . Furthermore, the mechanical pump assembly  18  can also be in fluid communication with the opening  48  on the drape  40  via the hose  62  that can connect with the tip  134  or via the tip connecting directly with the fitting  44 . The hose  62  can be any length, thus a long hose  62  can be utilized. Therefore, the mechanical pump assembly  18  can be operated on the dressing  14  before the chemical pump assembly  16  is installed on the dressing  14 . This can help seal the dressing  14  at the dressing site  28 . In result, the mechanical pump assembly  18  can directly apply reduced pressure to the dressing  14 . 
     In the illustrated embodiment, the biasing mechanism is a spring  126 , and the movable element is a piston  128 . The spring  126  and the piston  128  are disposed in the first chamber  138 . Before the mechanical pump assembly  18  is activated, a majority of the piston rod  130  is also located in the first chamber  138 . Also, a head  132  disposed on the top of the piston rod  130  is disposed in the second chamber  140 . When the mechanical pump assembly  18  is introduced to the first valve  92  ( FIG. 9 ) of the chemical pump assembly  16  or connected with the fitting  44  by the hose  62  ( FIG. 3 ), the actuator  144  is used to activate the operation of the mechanical pump assembly  18 . As the mechanical pump assembly  18  is activated, a connector  170  (see  FIG. 6 ) between the actuator  144  and the piston rod  130  releases the piston rod  130 , and air enters first chamber  138  of the mechanical pump housing  120  through the tip opening  136 . The connector  170  can reengage the piston rod  130 . Thus, the mechanical pump assembly  18  may be reusable. As depicted in  FIG. 7 , the spring  126  biases the piston  128  toward the internal wall  122 , which draws air into the first chamber  138 . The piston rod  130  moves into the second chamber  140 , and the head  132  moves towards the top surface of the mechanical pump housing  120 . As a result, the negative pressure of the dressing  14  is created. 
     The negative pressure assembly can be susceptible to reaching a negative pressure below the target pressure range, e.g. too much vacuum or negative pressure may be achieved in the enclosed volume  60 . In order to maintain the target pressure range, as shown in  FIG. 5 , a relief valve  148  may be disposed on the chemical pump housing  80  to release pressure as needed. Alternatively, a relief valve similar in operation to the relief valve  148  can be disposed on the drape  40  of the dressing  14 . The relief valve  148  can be any valve that can manually or automatically release pressure as needed.  FIG. 5  depicts one embodiment in which the relief valve  148  is disposed on the chemical pump assembly  16 . It is to be understood that the relief valve  148  functions similarly in an embodiment in which the relief valve  148  is disposed on the dressing  14 . Referring to  FIG. 5 , the relief valve  148  comprises a flexible cap  160  protruding into the chemical pump housing  80  connected with a post  162 . The flexible cap  160  normally covers an opening  164 . The flexible cap  160  can be made from an elastic material. As a pressure differential between ambient and the dressing  14  or ambient and the chamber  84  in the chemical pump assembly  16  moves outside of a predetermined pressure range, which can be set for example between 50 mmHg and 200 mmHg, the flexible perimeter  190  of the flexible cap  160  is drawn into the chemical pump housing  80  or the drape  40 . As the flexible perimeter  190  of the flexible cap  160  is drawn toward the inside of the chemical pump housing  80  or the dressing  14 , a space is created around the perimeter of the flexible cap  160  so that air can pass through the opening  164 . When the opening  164  is not covered by the flexible cap  160 , air from the ambient enters the chemical pump assembly  16  or the dressing  14  until the internal pressure reaches the pressure at which the perimeter  190  of the flexible cap  160  relaxes onto the inner surface of the chemical pump housing  80  to reseal and close the opening  164 . The chemical pump assembly  16  and/or the dressing  14  are then subject to the amount of negative pressure at which the relief valve  148  reseals, which can be different than the pressure differential at which the opening  164  is opened while still being within the therapeutic range, e.g., between 50 mmHg and 200 mmHg. 
     In another embodiment, a bidirectional valve  184  is disposed on the chemical pump housing  80  instead of the first valve  192  and the relief valve  148 , as depicted in  FIG. 5A . Alternatively, the bidirectional valve  184  can be disposed on the at least one dressing  14 . In yet another embodiment, the bidirectional valve  184  may be similar construction to the valve described in U.S. Pat. No. 5,439,143. The chemical pump assembly  16  may be in fluid communication with the enclosed volume  60  through the bidirectional valve  184 . Additionally, the mechanical pump assembly  18  may also be in fluid communication with the enclosed volume  60  through the bidirectional valve  184 . As depicted in  FIG. 15 , the hose  62  can be attached to the mechanical pump assembly  18  and inserted into the bidirectional valve  184 . In result, the mechanical pump assembly  18  is in fluid communication with the enclosed volume  60 . 
     The bidirectional valve  184  may include three operating states. In the first operating state, gas is allowed to exit the chamber  84  and/or the enclosed volume  60  through the bidirectional valve  184  when the external pressure is below that of the enclosed volume  60  and/or the chamber  84 . In the second operating state, the bidirectional valve  184  precludes gas from entering or exiting the enclosed volume  60  and/or the chamber  84  through the bidirectional valve  184  when the pressure of the chamber  84  and/or the enclosed volume  60  is between the first predetermined threshold and a second predetermined threshold. In the third operating state, the bidirectional valve  184  allows gas from ambient to enter the enclosed volume  60  and/or the chamber  84  through the bidirectional valve  184  when the pressure in the enclosed volume  60  and/or the chamber  84  is below the predetermined threshold. In one embodiment, the predetermined threshold is 560 mmHg or 200 mmHg below atmospheric. In yet another embodiment, the bidirectional valve  184  may include springs that automatically actuate the bidirectional valve  184  when a pressure differential is at the first or second predetermined threshold. 
     In still another embodiment, the mechanical pump assembly  18  is connected to multiple dressings. Furthermore, the mechanical pump assembly  18  can be connected to the multiple dressings at the same time. For example, the mechanical pump assembly  18  can be connected to a second dressing  188 . The hose  62  can include a Y-shaped fitting  186  to connect the mechanical pump assembly  18  to the dressing  14  and the second dressing  188  at the same time. Furthermore, the chemical pump assembly  16  can also be connected to multiple dressings and can be connected to the multiple dressings at the same time. As depicted in  FIG. 14 , the hose  62  can include the Y-shaped fitting  186  to simultaneously connect the chemical pump assembly  16  to the dressing  14  and the second dressing  188 . 
     A method for achieving negative pressure therapy with the negative pressure kit  10  will be described hereinafter. First, at least one dressing  14  is removed from the tray kit  12 , and the drape release liner is removed to expose the adhesive  66  on the bottom surface of the drape edge  54 . The drape edge  54  is placed on skin S around at least one dressing site  28  and is secured to the skin S by the adhesive  66 . 
     With reference to  FIG. 8 , the drape  40  is secured over the dressing site  28 , and the sealing member  96  on the chemical pump assembly  16  is introduced to the fitting  44  on the drape  40 . The sealing member  96  is placed over the fitting  44 , and the flaps  98  are opened. When the flaps  98  are open, the chemical pump assembly  16  is in fluid communication with the dressing  14 . The reactor  82  begins to consume the selected gas from the enclosed volume  60  but is not complete at this time. 
     Afterwards, the mechanical pump assembly  18  is inserted into the first valve  92  disposed on the chemical pump assembly  16  to open the flaps  94 , as depicted in  FIG. 9 . As the flaps  94  are opened, the mechanical pump assembly  18  is in fluid communication with the chamber  84  in the chemical pump assembly  16 . Alternatively, the mechanical pump assembly  18  is inserted into the bidirectional valve  184 . Also, the mechanical pump assembly  18  is in fluid communication with the enclosed volume  60  via the chemical pump assembly  16 . When the mechanical pump assembly  18  is in fluid communication with the chemical pump assembly  16 , the actuator  144  is used to activate the operation of the mechanical pump assembly  18 , as depicted in  FIG. 10 . Then, the spring  126  pushes the piston  128  towards the internal wall  122 . As the piston  128  moves, air enters the first chamber  138  of the mechanical pump assembly  18 , and the dressing  14  is drawn toward the skin S. The mechanical pump assembly  18  is then removed, and the flaps  94  of the first valve  92  are closed by their resilient forces, as depicted in  FIG. 11 . In the embodiment with the bidirectional valve  184 , the bidirectional valve  184  moves to the second operating state, as the mechanical pump assembly  18  is removed from the bidirectional valve  184 . The reactor  82  in the chemical pump assembly  16  can continue to apply or maintain reduced pressure to the dressing  14 . In result, the pressure in the dressing  14  is reduced to a negative pressure, and the negative pressure indicator  100  signals when the negative pressure has been achieved. At any time the reduced pressure decreases below a target pressure range, the relief valve  148  or the bidirectional valve  184  releases pressure as needed to restore the reduced pressure to a predetermined pressure differential. 
     In another embodiment, the mechanical pump assembly  18  can be inserted prior to the chemical pump assembly  16 . First, the at least one dressing  14  is placed and secured over the at least one dressing site  28 . Then, the mechanical pump assembly  18  is connected to the fitting  44  on the dressing  14  by the hose  62 . Alternatively, the first valve  92  or bidirectional valve  184  is disposed on the dressing  14  instead of the chemical pump assembly  16  to provide direct fluid communication between the dressing  14  and the mechanical pump assembly  18 . As a result, the mechanical pump assembly  18  is in fluid communication with the enclosed volume  60 . The first valve  92  or bidirectional valve  184  may further replace the fitting  44 . In these alternate embodiments, the mechanical pump assembly  18  is inserted into the first valve  92  or the bidirectional valve  184  on the dressing  14 . 
     After the mechanical pump assembly  18  is connected to the dressing  14 , the mechanical pump assembly  18  is activated with the actuator. In result, the piston  128  moves toward the internal wall  122 , and air enters the first chamber  138  of the mechanical pump assembly  18 . The mechanical pump assembly  18  is removed and replaced by the chemical pump assembly  16 . The reactor  82  in the chemical pump assembly  16  begins reacting with a selected gas found in air to maintain the negative pressure of the dressing. When the negative pressure in the enclosed volume  60  is achieved, the indicator on the dressing  14  and/or the chemical pump assembly  16  signals when the dressing  14  reaches a negative pressure. As needed, the relief valve  148  or the bidirectional valve  184  releases pressure when the reduced pressure decreases below a target pressure range. 
     In still another embodiment, the chemical pump assembly  16  and the mechanical pump assembly  18  are both connected to the at least one dressing  14 . In this embodiment, a first valve, fitting, or hose and a second valve, fitting or hose are disposed on the dressing  14 . The chemical pump assembly  16  is connected to the dressing via the first valve, fitting, or hose. The mechanical pump assembly  18  is connected for the second valve, fitting, or hose. For example, the chemical pump assembly  16  is connected to the dressing  14  via the fitting  44  disposed on the dressing  14 , while the mechanical pump assembly  18  is connected to the dressing  14  via the hose  62  and a second fitting  166  disposed on the dressing  14 , as depicted in  FIG. 12 . Also, in particular when the dressing  14  that includes at least one relief valve similar to the relief valve  148  described above, the chemical pump assembly  16  could be replaced with an electro-mechanical pump similar to those now used with known negative pressure wound therapy devices. Different than known negative pressure wound therapy devices, however, the relief valve(s) on the dressing  14  can open and close (as described above) to maintain the enclosed volume underneath the dressing within the therapeutic range. Also, in lieu of the relief valves, the dressing  14  could include a bidirectional valve similar to the bidirectional valve  184  that could cooperate with the mechanical pump assembly  18  while an electro-mechanical pump similar to those now used with known negative pressure wound therapy devices could connect with the fitting  44  shown in  FIG. 12 . 
     Furthermore, at least one attachment can be disposed on the mechanical pump assembly  18  or the chemical pump assembly  16  for storing the hose  62 . An example of such an attachment is, but is not limited to, a wrap element. With reference to  FIG. 13 , the chemical pump assembly  16  may include a wrap element  176  disposed on the chemical pump housing  80  around which the hose  62  can be wound. Alternatively, the wrap element  176  can be disposed on the mechanical pump housing  120 . The hose  62  can be coiled around the at least one attachment so that the hose  62  is secured during storage and transportation. In another embodiment, the hose  62  can retract into the chemical pump assembly  16 . In yet another embodiment, the hose  62  can retract into the mechanical pump assembly  18 . Alternatively, the tray kit  12  can include an additional recess for storing the hose  62 . 
     With attention to  FIGS. 16-17 , an alternative mechanical pump assembly  200  is shown. The mechanical pump assembly  200  includes a proximal end  202  and a distal end  204  that are disposed at opposite ends. The mechanical pump assembly  200  includes a mechanical pump  206  and a pump chamber  208  fluidly connectable to an inner chamber  212  of a chemical pump housing  214  of a chemical pump assembly  216  ( FIGS. 18-22 ) and/or an enclosed volume  60 ′ of a negative pressure assembly  218  ( FIGS. 23-24 ), as will be discussed in more detail hereinafter. 
     With reference once again to  FIGS. 16-17 , the mechanical pump assembly  200  may include a charging button  220 , an actuator  222 , and a biasing mechanism (not shown, but similar to the spring  126  in  FIG. 7 ) operatively connected with a movable pump element (not shown, but similar to the piston  128  in  FIG. 7 ). In practice, the charging button  220  can be actuated (e.g., depressed —moved from the distal end  204  toward the proximal end  202 ) to expel air from the pump chamber  208  so as to define a charged position as shown in  FIG. 17 . 
     Due to an internal assembly within the mechanical pump assembly  200 , the charging button  220  remains in the charged position until the actuator  222  is actuated. Actuation of the actuator  222  results in the biasing mechanism moving the movable pump element so as to draw air into the pump chamber  208 . As a result, negative pressure is created in the pump chamber  208 . For reference,  FIG. 16  illustrates the mechanical pump assembly  200  after the actuator  222  has been actuated. 
     The mechanical pump assembly  200  also includes a nozzle  224  disposed at the proximal end  202 . With continued attention to  FIGS. 16-17 , the nozzle  224  can be received by a shroud  226  that at least partially surrounds the nozzle  224 . The shroud  226  in the illustrated embodiment is in the shape of a plunger. 
     The shroud  226  can be disposed at the proximal end  202  of the mechanical pump assembly  200 . The shroud  226  can be made of any number of materials that provide sufficient pliability and rigidity to allow for fluidic sealing between the mechanical pump  206  and the object to which the mechanical pump assembly  200  is to be connected. 
     It is noted that the mechanical pump assembly  200  can be used without the shroud  226  or the shroud  226  may not be provided in certain circumstances, as shown by  FIG. 22 . When the shroud  226  is utilized, the shroud  226  can contact a drape  40 ′ of the negative pressure assembly  218  as is shown in  FIG. 24  and will be described in more detail hereinafter. Further, the shroud  226  defines an interior volume  228  that may be fluidicly disposed between the enclosed volume  60 ′ and the pump chamber  208 . 
     As shown in  FIGS. 16-17 , the shroud  226  includes a sealing lip  232 , a barrel portion  234 , a cup portion  236 , and a joining region  238 . The sealing lip  232 , the barrel portion  234 , the cup portion  236 , and the joining region  238  can all be made of the same material(s). Alternatively, the sealing lip  232 , the barrel portion  234 , the cup portion  236  and the joining region  238  can be made of different materials from one another. 
     The sealing lip  232  contacts the drape  40 ′ and defines a sealing lip inner diameter  232   a  and a sealing lip outer diameter  232   b . The sealing lip inner diameter  232   a  and the sealing lip outer diameter  232   b  can be of uniform diameters when extending in the proximal-distal axis. The sealing lip  232  can include an engagement face  232   c  that directly contacts the drape  40 ′ and/or the chemical pump housing  214  to ensure good fluid communication between the mechanical pump assembly  200  and the inner chamber  212  of the chemical pump housing  214  of the chemical pump assembly  216  or the enclosed volume  60 ′ of the negative pressure assembly  218 . 
     The barrel portion  234  defines a barrel portion inner diameter and a barrel portion outer diameter. The barrel portion inner diameter and the barrel portion outer diameter can maintain uniform respective diameters when extending in the proximal-distal axis. The barrel portion  234  is disposed at an opposite side of the shroud  226  as the sealing lip  232  and can include a mounting face  234   a  that faces in an opposite direction as the engagement face  232   c  of the sealing lip  232 . The mounting face  234   a  can directly contact the mechanical pump  206 . The mounting face  234   a  can also be offset slightly from the mechanical pump  206 . The nozzle  224  is received in the shroud  226  so as to directly contact the inner diameter of the barrel portion  234  of the shroud  226 . 
     The cup portion  236  is disposed between the sealing lip  232  and the barrel portion  234 . The cup portion  236  defines a cup portion outer diameter that decreases in size when extending from the sealing lip  232  toward the barrel portion  234 . Further, the cup portion  236  defines a cup portion maximum outer diameter at a junction with the sealing lip  232 . Further still, the cup portion  236  defines a cup portion minimum outer diameter at a junction with the joining region  238 . Additionally, the cup portion minimum outer diameter is greater than or equal to at the junction with the barrel portion outer diameter. 
     Finally, the joining region  238  is disposed between the barrel portion  234  and the cup portion  236 . Further, the joining region  238  defines a joining region outer diameter  238   a  that increases in size when extending from the barrel portion  234  to the cup portion  236 . However, the sealing lip outer diameter  232   b  is greater than the joining region outer diameter  238   a.    
     The aforementioned layout of the shroud  226 , and more particularly, the components that make up the shroud  226 , provide numerous advantages. For example, the shroud  226  does not penetrate a valve  244  ( FIGS. 21, 24 ), as will be described in more detail hereinafter, thereby minimizing the risk of introducing undesirable material into the inner chamber  212  or the enclosed volume  60 ′. Further, as will also be detailed hereinafter, the compact size ensures easy and good fluid engagement with the valve  244 , so that air can be easy and quickly removed from the inner chamber  212  and the enclosed volume  60 ′. 
     The mechanical pump assembly  200  can be utilized with a variety of components. For example, as shown in the  FIGS. 21-22 , the mechanical pump assembly  200  can be used with the chemical pump housing  214  of the chemical pump assembly  216  that includes a reactor  242 . The reactor  242  can be similar to the chemical pump  82  described above. As shown in  FIG. 22 , the mechanical pump assembly  200  can cooperate the valve  244  on the chemical pump housing  214  to produce the desired negative pressure in the inner chamber  212  and beneath a dressing in fluid communication with the inner chamber  212 . 
     With reference to  FIGS. 18-22 , the chemical pump housing  214  of the chemical pump assembly  216  includes at least one wall  256  that defines the inner chamber  212 . The at least one wall  256  can include a top wall  258 , a bottom wall  262 , and at least one side wall  264 . The top wall  258  is spaced from the bottom wall  262  by the inner chamber  212 . As shown in  FIG. 19 , the bottom wall  262  can define an opening  266  for receipt of the valve  244 ; however the opening  266  and the valve  244  can be located elsewhere and on other walls of the chemical pump housing  214 . 
     The top wall  258  can include a top wall exterior surface  258   a  and a top wall interior surface  258   b . Further, the bottom wall  262  can include a bottom wall exterior surface  262   a  and a bottom wall interior surface  262   b . As illustrated, the bottom wall interior surface  262   b  faces in a direction opposite the bottom wall exterior surface  262   a  and in a same direction as the top wall exterior surface  258   a . A slit  248  can be disposed on the top wall  258  for receipt of the pull tab  252 . 
     As shown in  FIG. 18 , the pull tab  252  could include a first pull tab  252   a  and a second pull tab  252   b . In one embodiment, the first pull tab  252   a  and the second pull tab  252   b  are separate elements, whereas, in another embodiment, the first pull tab  252   a  and the second pull tab  252   b  could be connected or integral. 
     The reactor  242  is disposed in the inner chamber  212 . Further, the first pull tab  252   a  extends from the inner chamber  212  to the air through the slit  248  and a removable layer  254  is connected to the pull tab  252  to shield the reactor removable layer  254  is removed. The reactor  242  is configured to react with a selected gas found in air so as to consume the selected gas when the reactor  242  is exposed to air. In the illustrated embodiment, the reactor  242  is configured to react with a selected gas, e.g., oxygen, found in air. 
     The elongate slit  248  in the illustrated embodiment is disposed on the chemical pump housing  214  of the chemical pump assembly  216 . When not covered, the slit  248  exposes the inner chamber  212  to ambient. The pull tab  252  extends from the inner chamber  212  to ambient through the slit  248 . 
     A packet  268  including the removable layer  254  covers the reactor  242  so as to prevent the reactor  242  from being exposed to ambient until after removal of the removable layer  254  from the packet  268 . The packet  268  can be a foil packet  268  that is hermetically sealed around the reactor  242 . The first pull tab  252   a  extends through the slit  248  and is connected to removable layer  254 . The first pull tab  252   a  can be pulled to remove the first pull tab  252   a  from the slit  248 . 
     When the first pull tab  252   a  is pulled through the slit  248 , the removable layer  254  is removed from the packet  268  and, if desired, from the inner chamber  212  through the slit  248 , exposing the reactor  242  to ambient. After the removal of the removable layer  254 , the reactor  242  begins to react with a selected gas, e.g., oxygen, in the inner chamber  212 . The first pull tab  252   a  is preferably removed after connection to a dressing  14 ′ as will be described in more detail hereinafter. However, the first pull tab  252   a  can be removed prior to affixing the pump assembly to the dressing  14 ′. 
     The second pull tab  252   b  is connected to a thin film  282 , which is placed over and adhered to a portion of the top wall exterior surface  258   a . The thin film  282  includes a flap  284  and, as depicted in  FIG. 22 , the slit  248  is disposed underneath the flap  284 . The second pull tab  252   b  is connected to a release layer  286  (shown in phantom in  FIG. 18 ) provided on a bottom surface of the flap  284 . The release layer  286  covers an adhesive on the bottom surface of the thin film  282 . When the second pull tab  252   b  is pulled, the second pull tab  252   b  disconnects the release layer  286  from the flap  284  and the adhesive disposed on the bottom surface of the flap  284  is exposed. The flap  284  is then moved towards the top wall exterior surface  258   a  to cover the remainder of the top wall exterior surface  258   a  and thus also covers the slit  248 . In result, the inner chamber  212  is no longer exposed to ambient via the slit  248 . When the thin film  282  covers the slit  248 , the reactor  242  reacts with the selected gas found in the enclosed volume  60 ,  60 ′ under the dressing, and if already connected to the dressing via the hose  62 ′ creates a closed system. Reduced pressure is therefore developed the enclosed volume. When the inner chamber  212  is under negative pressure, the thin film  282  is drawn in through the slit  248  toward the inner chamber  212 . As such, the thin film  282  cooperating with the slit  248  can provide an indication to the user that the inner chamber  212  is under negative pressure. Indicia  290 , e.g. lines, a cross or the like, can also be provided on the thin film  282  in the vicinity of the slit  248  to provide further indication of negative pressure. 
     As shown in  FIG. 18-22 , the chemical pump housing  214  of the chemical pump assembly  216  can further includes a hose fitting  274 . The hose fitting  274  can be tubular and includes a passage in communication with the inner chamber  212 . In one embodiment, the hose fitting  274  is disposed on the opposite side of the chemical pump housing  214  as the slit  248 . The hose fitting  274  may be disposed on a concave section of the chemical pump housing  214 ; however, the hose fitting  274  may be disposed on any surface of the chemical pump housing  214 . 
     A hose  62 ′ attaches to the hose fitting  274  to connect the pump assembly to the dressing  14 ′. As illustrated in  FIG. 20 , the chemical pump housing  214  of the chemical pump assembly  216  may be simultaneously connected to multiple dressings. In particular, the hose  62 ′ can include the Y-shaped fitting  186  to simultaneously connect the chemical pump housing  214  to the dressing  14 ′ and the second dressing  188 . It is noted that  FIG. 20  merely shows the connection in schematic form and is in no way limiting. For example, the chemical pump housing  214  could be connected to a dressing as shown in  FIGS. 23-24 . 
     With reference to  FIGS. 19 and 21-22 , the valve  244  is disposed on the chemical pump housing  214  so as to be in fluid communication with the inner chamber  212 . Alternatively, the valve  244  can be disposed on the drape  40 ′ as shown in  FIGS. 23-24 . For reference, the valve  244  disposed on the chemical pump housing  214  and the valve  244  disposed on the drape  40 ′ are identical in construction. For clarity, the valve  244  disposed on the chemical pump housing  214  will firstly be discussed. 
     The valve  244  includes at least one movable element  244   a  to obstruct the opening  266  and a mounting portion  244   b  that is flush with the at least one wall  256 . The mounting portion  244   b  of the valve  244  can directly contact the bottom wall  262  to attach the valve  244  to the bottom wall  262  of the chemical pump housing  214 . The mounting portion  244   b  may also be recessed or received further into the inner chamber  212  than that shown in  FIGS. 19, 21 and 22 , or a boss can extend from the bottom wall exterior surface  262   a  around the opening  266 . By recessing the valve  244  into the inner chamber  212  or surrounding the opening  266  with a boss, the movable element  244   a  is protected from contact as it moves toward a dome shape, similar to that shown in  FIG. 24 , upon activation of the mechanical pump assembly  200 . As noted hereinbefore, the opening  266  can be disposed on the bottom wall  262  of the chemical pump housing  214 . However, it will be appreciated that the opening  266 , and hence the valve  244 , could be located on other walls (e.g., the top wall  258 , the at least one side wall  264 ) of the chemical pump housing  214  without departing from the scope of the disclosure. 
     The valve  244  can be received by the bottom wall  262  such that a distance between the top wall interior surface  258   b  and the bottom wall exterior surface  262   a  is greater than a distance between the top wall interior surface  258   b  and the valve  244 . Further, a distance between the movable element  244   a  of the valve  244  and the top wall  258  is less than a distance between the mounting portion  244   b  and the top wall  258 . 
     The movable element  244   a  is disposed so as to not outwardly protrude past an exterior surface of the at least one wall  256 . For example, the at least one wall  256  could be the bottom wall  262 . This orientation of the valve  244  can provide numerous advantages. For example, this orientation ensures that the valve  244  is not accidently actuated. Further, a risk of the valve  244  making inadvertent contact with an object exterior to the chemical pump housing  214  is reduced. 
     With attention to  FIGS. 23-24 , the dressing  14 ′ is shown. For reference, the dressing  14 ′ of  FIGS. 23-24  is similar to the dressing  14  illustrated in  FIG. 2 , except as otherwise noted. Notably, an opening  48  of the dressing  14 ′ of  FIGS. 23-24  includes the valve  244  previously described with reference to  FIGS. 18-22 , as compared to the fitting  44  of  FIG. 2 . Further, the dressing  14 ′ of  FIGS. 23-24  can include a boss  278  that surrounds the valve  244  so as to attach the valve  244  to the drape  40 ′. The boss  278  can provide additional structural stability to the arrangement and sufficient recess of the valve  244  to protect the movable element  244   a  and interference from outside contacts. Thus, the boss  278  can contact a drape top  52 ′ of the drape  40 ′. As these are the primary differences, only an abbreviated description of  FIGS. 23-24  will be provided. It should be apparent that  FIGS. 23 and 24  are schematic and not drawn to scale, especially considering that the drape  40 ′ can be made from a thin film. 
     The negative pressure assembly  218  includes the drape  40 ′ for covering a dressing site on a patient. The negative pressure assembly  218  is capable of maintaining a negative pressure underneath the drape  40 ′ when sealed against skin S upon application of a vacuum. This vacuum can be provided by the chemical pump housing  214  and/or the mechanical pump  206 . The negative pressure assembly  218  also includes a sealing element  46  that when applied to the skin S, cooperates with the drape  40 ′, to define the enclosed volume  60 ′. The enclosed volume  60 ′ is covered by the drape  40 ′ and surrounded by the sealing element  46 . 
     Like the valve  244  shown in  FIGS. 19 and 21-22 , the valve  244  shown in  FIGS. 23-24  has a first operating state in which gas exits the enclosed volume  60 ′ through the valve  244  and a second operating state in which gas is precluded from entering or exiting the enclosed volume  60 ′ through the valve  244 . The valve  244  opens (i.e., unseals or first operating state) at a pre-determined pressure and closes (i.e., seals or second operating state) thereafter in order to allow gas to be removed from the inner chamber  212 /enclosed volume  60 ′ while simultaneously preventing gas from entering into the inner chamber  212 /enclosed volume  60 ′. Notably, once an activation pressure occurs, the valve  244  will open, allowing the gas to flow. Then again, when the activation pressure is no longer present, the valve  244  will close automatically, stopping the movement of gas into or out of the inner chamber  212 /enclosed volume  60 ′. 
     The valve  244  can have a non-tortuous flow path and allow bi-directional flow. Further, the valve  244  can be made of a variety of elastomeric materials including, for example, silicone, hydrocarbon resistant fluorosilicone rubber, fluoroelastomers, and perfluorelastomers. Further still, the valve  244  can include a variety of cuts  246  in the movable element  244   a  to allow the passage of gas there through (i.e., communication between ambient and the inner chamber  212 /enclosed volume  60 ′). For example, it is envisioned that the valve  244  could have a single cut or multiple cuts. Further, the cut  246  could define a straight line, a curved line, a shape, or a combination thereof. For example, the cut could be shaped in the form of an X or a cross. 
     By way of example only, the valve  244  can include an X-cut and be made with 50 durometer silicone material, thereby causing the valve  244  to open (i.e., unseal) at about 60 mmHg and close (i.e., reseal) at about 55 mmHg. Alternatively, the valve  244  could be made with 60 durometer silicone material with an X-cut and open at about 120 mmHg and close at about 85 mmHg. With the X-cut, the valve  244  may have very slow pressure deterioration and the X may not perfectly realign after actuation. 
     By way of another example, which is in no way limiting, the valve  244  could have a single 3.85 mm long cut and be made with 60 durometer silicone material. This could result in the valve  244  opening at 180 mmHg and provide excellent resealability of the valve  244 . Another non-limiting example could be a valve  244  with a single 2.55 mm slit with 60 durometer silicon material. This could result in the valve  244  opening at 220 mmHg. 
     As shown in  FIGS. 21-22 , the pump chamber  208  of the mechanical pump  206  is fluidly connectable to the inner chamber  212  through the valve  244  to draw air from the inner chamber  212  into the pump chamber  208 . Further, the mechanical pump  206  is configured to draw air from the inner chamber  212  into the pump chamber  208  when fluidly connected with the inner chamber  212  such that the valve  244  does not penetrate the mechanical pump  206 . As shown in  FIG. 21 , the mechanical pump  206  is configured to draw air from the inner chamber  212  into the pump chamber  208  when fluidly connected with the inner chamber  212  such that the mechanical pump  206  does not penetrate the valve  244 . 
     With reference to  FIG. 24 , the mechanical pump  206  and the pump chamber  208  of the mechanical pump assembly  200  are fluidly connectable to the enclosed volume  60 ′ through the valve  244  when the valve  244  is in the first operating state. The mechanical pump  206  is configured to fluidly connect with the enclosed volume  60 ′ and draw air from the enclosed volume  60 ′ into the pump chamber  208  of the mechanical pump assembly  200  while being offset from the at least one movable element  244   a . Further, the mechanical pump  206  is configured to draw air from the enclosed volume  60 ′ into the pump chamber  208  when fluidly connected with the enclosed volume  60 ′ such that the mechanical pump assembly  200  does not penetrate the valve  244 . 
     A method for achieving negative pressure therapy will be described hereinafter. The drape  40 ′ can be applied to cover the dressing  14 ′ site on a patient, the drape  40 ′ can be sealed against skin S of the patient to define the enclosed volume  60 ′ covered by the drape  40 ′, and a chemical pump can be activated so as to consume a selected gas in the enclosed volume  60 ′. 
     The method can also include positioning a mechanical pump assembly  200  to fluidly connect the mechanical pump assembly  200  to the enclosed volume  60 ′ through the bidirectional valve  244 , and reducing air from the enclosed volume  60 ′ with the mechanical pump  206  such that all portions of the mechanical pump  206  are spaced from the bidirectional valve  244 . Further, the bidirectional valve  244  does not penetrate the mechanical pump  206  when the air is reduced from the enclosed volume  60 ′ and the mechanical pump  206  does not penetrate the bidirectional valve  244  when the air is reduced from the enclosed volume  60 ′. 
       FIG. 25  depicts an embodiment in which a mechanical pump assembly  300  and a chemical pump assembly  302  are provided together. The chemical pump assembly  302  is similar in very many aspects to the chemical pump assembly  216  described above, as such only an abbreviated description of the chemical pump assembly  302  will be provided. The chemical pump assembly  302  includes a chemical pump housing  304 . A slit  306 , which is similar to the slit  248  described above, is provided in the chemical pump housing  304 . A hose fitting  308  is also provided on the chemical pump housing  304  and is in fluid communication with an inner chamber of  312  of the chemical pump housing  304 . 
     A reactor  320 , similar to the reactor  242  described above, is provided in the inner chamber  312 . The reactor  320  is configured to react with the gas found in air so as to consume the gas. In the illustrated embodiment, the reactor  320  is hermetically sealed within a packet  322  including a removable layer  324 . A first pull tab  330  extends from ambient through the slit  306  and connects with the removable layer  324 . The first pull tab  330  can be pulled through the slit  306  so as to remove the removable layer  324  from the packet  322  thus exposing the reactor  320  to the air found in the inner chamber  312 . 
     A thin film  332  is provided on an exterior of the chemical pump housing  304 . The thin film  332  includes a flap  334 , and a release layer (not visible in  FIG. 25 ) is provided on an underside of the flap to cover adhesive of the underside of the flap. A second pull tab  336  connects with the release layer on the flap  334 . Pulling the second pull tab  336  results in removal of the release layer thus exposing the adhesive on the flap  334 . With the adhesive exposed, the flap  334  can be brought over the slit  306  in a similar manner to the chemical pump assembly  216  described above. 
     The embodiment shown in  FIG. 25  combines the chemical pump assembly and the mechanical pump assembly into a single unit. The embodiment depicted in  FIG. 25  also includes a valve  350  including at least one movable element  352 . The valve  350 , however, is provided within the inner chamber  312  as opposed to being exposed to the exterior of the housing such as the valve  242  shown in  FIG. 19 . The mechanical pump assembly  300  includes a pump chamber  360  that is fluidly connectable to an enclosed volume (see for example enclosed volume  60  shown in  FIG. 3 ) beneath a dressing (similar to the dressing  14  shown in  FIG. 3 ) when a hose (similar to the hose  62 ′ in  FIG. 20 ) is provided on the fitting  308  connecting the dressing to the assembly shown in  FIG. 25 . 
     The mechanical pump assembly  300  includes a mechanical pump housing  362  that defines the pump chamber  360 . A piston  364  is provided in the mechanical pump housing  362  to define the pump chamber  360 . The piston  364  can be connected with a rod  366  in a conventional manner. A biasing mechanism, which in the illustrated embodiment is a spring  368 , operates to bias the piston  364  in a manner so as to expand the pump chamber  360  (to the left as depicted in  FIG. 25 ). 
     An actuator  380 , which can be a button covered by a resilient cover  382  connected to the chemical pump housing  304  in an air-tight manner, is provided to actuate the mechanical pump assembly  300 . As illustrated in  FIG. 25 , the mechanical pump assembly  300  is depicted prior to actuation and thus prior to drawing air from the enclosed volume (for example the enclosed volume  60  in  FIG. 3 ). The actuator  380  is operatively connected with the rod  366 . Actuation of the actuator  380 , e.g., pressing the actuator  380  to the right (per the orientation shown in  FIG. 25 ) against the biasing force of the spring  368  results in an outlet valve  386 , which is connected with ambient via an outlet air line  388 , expelling air from the pump chamber  360 . When the force is removed from the actuator  380 , the spring  368  biases the piston to the left (per the orientation shown in  FIG. 25 ). Accordingly, air within the inner chamber  312  and the enclosed volume (for example see the enclosed volume  60  in  FIG. 3 ) is drawn into the pump chamber  360 , thus drawing a vacuum beneath the dressing. The actuator  380  can then be actuated again until the desired pressure beneath the dressing is achieved. The reactor  320 , can then further remove selected gas, e.g., oxygen, from the inner chamber  312  and the enclosed volume beneath the dressing. 
     The mechanical pump assembly  300  is depicted inside the chemical pump housing  304  in  FIG. 25 . Alternatively, the mechanical pump assembly  300  could be provided external to, although connected with, the chemical pump housing  304 . Also, a relief valve (similar to the relief valve  148  on the chemical pump housing  80  described above) may be provided on the chemical pump housing  304  to release pressure as needed to avoid too low of pressure beneath the dressing. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives or varieties thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.