Abstract:
A modulating check valve and method of operating the modulating check valve adapted for mounting to an inlet of a compressor. The modulating check valve includes a flow section through which fluid flow. The flow section has an intake portal and an outlet portal connected to the inlet of the compressor. A flapper valve is disposed in the flow section to prevent backflow from the outlet portal to the intake portal. An actuator controls the flapper valve allowing the flapper valve to open, close and modulate the fluid flow from the intake portal to the outlet portal of the flow section in response to fluid pressure at an outlet of the compressor.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to rotary screw type compressor systems and to check valves, and, more specifically, the present invention relates to a disk- or flapper-type check valve that can be mechanically modulated to a fully open, fully closed or a partially closed position during fluid flow. 
       BACKGROUND OF THE INVENTION 
       [0002]    Compressors are used in a wide variety of industrial and residential applications. Compressors are also used to inflate or otherwise impart a fluid force on an external object such as tires or pneumatic tools. It is always desirable that a compressor provide consistent and efficient operation to ensure that the particular application (e.g., pneumatic tools) functions properly. To that end, modulation of compressor inlet conditions, e.g., of flow rate and pressure, and to prevent back flow, can provide reliable and efficient compressor and system operation. Intake modulation is also desired at start-up of the compressor to reduce the usual start-up strain and power requirement on the compressor motor. 
         [0003]    Rotary-screw air compressors are equipped with the usual oil feed system which responds to pressure developing in the air receiver after start-up to feed lubricating cooling oil to the moving components of the compressor so a check valve to prevent back flow is required. 
       SUMMARY OF THE INVENTION 
       [0004]    According to the present invention, a modulating check valve adapted for mounting to an inlet of a compressor including a flow section through which fluid flow. The flow section has an intake portal and an outlet portal connected to the inlet of the compressor. A flapper valve is disposed in the flow section to prevent backflow from the outlet portal to the intake portal. An actuator controls the flapper valve allowing the flapper valve to open, close and modulate the fluid flow from the intake portal to the outlet portal of the flow section in response to fluid pressure at an outlet of the compressor. 
         [0005]    Further according to the present invention, a method for modulating the fluid flow to a compressor includes directing fluid flow through a flow section of a modulating check valve having an intake portal and an outlet portal connected to the inlet of the compressor. The method includes preventing backflow from the outlet portal to the intake portal and in response to fluid pressure at an outlet of the compressor, the fluid flow is modulated from the intake portal to the outlet portal of the flow section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying figures (Figures). The figures are intended to be illustrative, not limiting. 
           [0007]    Certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. The cross-sectional views may be in the form of slices, or near-sighted cross-sectional views, omitting certain background lines which would otherwise be visible in a true cross-sectional view, for illustrative clarity. 
           [0008]    Often, similar elements may be referred to by similar numbers in various figures (Figures) of the drawing, in which case typically the last two significant digits may be the same, the most significant digit being the number of the drawing figure (Figure). 
           [0009]      FIG. 1  is an orthogonal top view of a modulating check valve, according to the present invention. 
           [0010]      FIG. 2  is an orthogonal cross sectional side view of the modulating check valve, according to the present invention. 
           [0011]      FIG. 3  is schematic line diagram of the location of the modulating check valve in relation to other systems it is intended for use in conjunction with. 
           [0012]      FIG. 4  is an orthogonal cross sectional side view of the flapper valve of the modulating flapper valve in an open position, according to the present invention. 
           [0013]      FIG. 5A  is an orthogonal hinge axis view of the closure device (flapper) of the modulating check valve, according to the present invention. 
           [0014]      FIG. 5B  is an orthogonal exhaust view of the flapper valve of the modulating check valve, according to the present invention. 
           [0015]      FIG. 5C  is an orthogonal hinge end-on view of the flapper valve of the modulating check valve, according to the present invention. 
           [0016]      FIG. 5D  is an orthogonal inlet view of the flapper valve of the modulating check valve, according to the present invention. 
           [0017]      FIG. 5E  is a sectioned detail view of the O-ring seal in the flapper valve of the modulating check valve, according to the present invention. 
           [0018]      FIG. 5F  is a perspective exhaust view of the flapper valve of the modulating check valve, according to the present invention. 
           [0019]      FIG. 5G  is a perspective inlet view of the flapper valve of the modulating check valve according to the present invention. 
           [0020]      FIG. 6A  is an orthogonal cross sectional view of the piston portion of the modulating check valve, according to the present invention. 
           [0021]      FIG. 6B  is a perspective view of the piston portion of the modulating check valve, according to the present invention. 
           [0022]      FIG. 6C  is an orthogonal, cross-sectional view of the piston and stem portions of the modulating check valve, according to the present invention. 
           [0023]      FIG. 6D  is a perspective view of the piston and stem portions of the modulating check valve, according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]    The present embodiment relates to a modulating check valve  10  designed for use with a rotary-screw type gas compressor  30 , as shown in  FIG. 3 . The modulating check valve  10  is shown in top view in  FIG. 1 . The modulating check valve  10  consists of a flow section  12 , through which a fluid, such as gas, flows into a rotary-screw type gas compressor  30 , and an actuator section  14 , which contains a pneumatic cylinder and piston, as shown in  FIGS. 2 and 4 , that modulates the gas flow through the flow section  12 , in ways described below. While rotary-screw type gas compressor  30  can compress many types of fluids including gasses, it is typically used to compress air, and called an air compressor herein. 
         [0025]    As shown in  FIG. 2 , the flow section  12  of the modulating check valve  10  incorporates a conduit  16  through the flow section  12 . The conduit  16  has an intake portal  18  having a first diameter d1 at one end and a valve seat section  20  downstream and adjacent to intake portal  18  having a second diameter d2. The conduit  16  further includes an intermediate section  22  disposed downstream and adjacent the valve seat section  20  and having a third diameter d3 being greater than the second diameter d2. Continuing, the conduit  16  further includes an outflow portal  24  downstream and adjacent the intermediate section  22  and having a fourth diameter d4 being less than the third diameter d3. Further, as shown in  FIG. 2 , the flow section  12  of the modulating check valve  10  has a side opening  26  communicating with the intermediate section  22  and adapted to receive actuator section  14 . 
         [0026]    The modulating check valve  10 , according to the present invention, is self-modulating in a way that becomes evident upon contemplation of the orthogonal, cross-sectional, side view of the modulating check valve  10  in  FIGS. 2 and 4 , through the section A-A indicated in  FIG. 1 . In  FIG. 2 , a valve closure device, typically a disk-type flapper valve  28  is shown in a closed position against the valve seat  20   a  on the downstream side of valve seat section  20 . In this condition, no air would flow though the conduit  16 . Alternatively, if the flapper valve  28  were open as shown in  FIG. 4 , the air, see arrows, would flow through the intake portal  18  of conduit  16 , across the valve seat section  20 , through intermediate section  22 , out of outflow portal  24  and to a rotary-screw compressor  30 . 
         [0027]    Referring again to  FIGS. 2 and 4 , there is illustrated a cross sectional view of the actuator section  14  of the modulating check valve  10 . As shown in  FIG. 1 , the actuator section  14  consists of a cylinder  26  having an end plate  26   a  secured thereto and to a flange  32  that is mounted to the side opening  26  of the flow section  12  by threaded rods  29  and nuts  31 . 
         [0028]    Returning now to the orthogonal cross sectional view of  FIG. 2 , the cylinder  26  of the actuator section  14  houses a piston  34  that is slidably received within the cylinder. The piston  34 , as shown in detail in  FIGS. 6A-6D , is biased towards flange  32  by a compression spring  36  that engages the interior surface  26   b  of the end plate  26   a.    
         [0029]    A stem  38  is slidably mounted (as indicated by the two-headed arrow) within bushing  40  which is fixed within the flange  32 . One end of the stem  38  has a reduced diameter portion  38   a  that is secured within a receptacle  42  of piston  34 . The opposite end of stem  38  has a spherical end knob  44 . While a spherical end knob  44  is illustrated, it is within the terms of the preferred embodiment to employ another end, such as a roller ball. The spherical end knob  44  engages the disk-type flapper valve  28 . As discussed in more detail below, high air pressure in variable cylinder volume  46  at one end of cylinder  26  acts against piston  34  so as to push it to the right against the bias of compression spring  36  and thereby force the spherical end knob  44  of stem  38  to the right so that the flapper valve  28  will open by air flow through conduit  16 . The high-pressure air is provided by a control valve  45  in line  60  when the pressure from the output side of the compressor  30  is below a certain predetermined value. The high-pressure air from control valve  45  enters the cylinder volume  46  within cylinder  26  and acts against surface  48  of the piston  34 , so as to push the piston and stem  38  to the right. Compression spring  36  acts against piston  34  so as to push it to the left against the action of high-pressure air in cylinder volume  46  opposing the motion of the piston to the right. As should be evident to those skilled in the art, when air pressure within the cylinder volume  46  is sufficiently high to overcome the force of compression spring  36 , the piston  34 , along with stem  38 , moves to the right as shown in  FIG. 4  such that the spherical end knob  44  of stem  38  will move away from ramp portion  28   b  of the flapper valve  28 , thereby allowing the flapper valve to open. 
         [0030]    Before continuing the discussion of the components and the operation of the modulating check valve  10 , it would be useful to understand how the check valve is disposed in relation to a rotary screw compressor  30 , as shown in  FIG. 3 . The modulating check valve  10  is disposed within the air induction or intake side  50  of the compressor  30 . More specifically the modulating check valve  10 , shown within flow section  12 , is disposed between an air filter  52  and the rotary screw compressor  30 . A conduit  54  communicates air from the air filter  52  to the modulating check valve  10 , and another conduit  56  communicates air from the modulating check valve to the compressor  30 . Compressed air, indicated by black arrow CA, exits the compressor  30  by way of conduit  58  which communicates with machinery or storage tanks (not shown) which receive compressed air from the compressor. A tube or conduit  60  conveys a pressure signal from conduit  58 , or, more generally, from the output side of the compressor  30 , to the control valve  45  which directs pressurized air to the cylinder volume  46  in actuator section  14  of the modulating check valve  10 . 
         [0031]    The detailed operation of the modulating check valve invention  10  can now be described with reference to the cross-sectional view of the modulating check valve  10  as illustrated in  FIGS. 2 and 4 . The disk-type flapper valve  28  is hinged about a hinge pin  62 . A closing device, such as a torsional spring  64 , using the hinge pin  62  as a fulcrum, is anchored at one end  64   a  in a recess  23  in the flange  32 , with its other end  64   b  exerting a closing force against the flapper valve  28 . The torsional spring  64  provides a weak closing force against a ramp portion  28   b  of the disk-type flapper valve  28  such that the flapper valve tends toward a closed position when the air flow rate through the flow section  12  is minimal, regardless of the orientation of the modulating check valve  10 . 
         [0032]    Referring to  FIG. 4 , the flapper valve  28  illustrated in an open position, shows an angle w that defines the degree of openness. When the flapper valve  28  is closed, as shown in  FIG. 2 , the flapper valve angle w is 0 degrees. At maximum opening, the flapper valve angle w is about 85 degrees. Under that condition, air pressure in the cylinder volume  46  is sufficient that the assembly of the piston  34  and stem  38  are pushed to the extreme of their rightward motion within the cylinder  26 , and the spring  36  is at its most compressed condition. Under conditions of normal operation for the compressor  30 , the flapper valve  28  opens according to the pressure at the outlet side of the compressor, between a minimum of about 0 degrees and the maximum of about 85 degrees. 
         [0033]    Referring to  FIGS. 5A-5G , the flapper type, check valve  28  is shown in detail.  FIG. 5A  shows the pivot pin view of the flapper valve  28 . The flapper valve  28  consists of a disk portion  28   a , a ramp portion  28   b , the inlet portal valve seating surface  28   c  of the disk (flapper) portion  28   a , the ramp surface  28   d  and two hinge pin bosses  68   a ,  68   b .  FIG. 5B  shows the flapper type check valve  28  in the view from the outlet portal  24 ;  FIG. 5C  shows the flapper type check valve in view from actuator  14 ; and  FIG. 5D  shows the flapper type check valve in the view from the intake portal  18 , wherein the valve seating surface  28   c  of the flapper valve disk which seats against valve seat  20   a  has an O-ring  70  held within a circumferential groove  72 . The disposition of the O-ring  70  within the circumferential groove  72  is revealed more specifically in  FIG. 5E , which is section view B-B indicated in  FIG. 5D .  FIG. 5F  and  FIG. 5G  are, respectively, perspective views of flapper valve  28  from the outlet portal  24  and intake portal  18 , respectively. 
         [0034]    Returning now to the orthogonal cross sectional view of  FIG. 2 , note that the ramp portion  28   b  of the flapper valve  28  is in contact with spherical end knob  44  of stem  38  which is slidably mounted (as indicated by the two-headed arrow) within bushing  40  which is fixed within the flange  32 . Stem  38 , at the end opposite the spherical end knob  44 , has a reduced diameter portion  38   a  which engages with a receptacle  42  of piston  34 . While a spherical end knob  44  is illustrated, it is within the terms of the preferred embodiment to employ another end, such as a roller ball. Piston  34  slides within the cylinder  26 . The piston  34  is actuated by, and forced to the right by (as shown in  FIG. 4 ), a low-pressure air signal from the output side  41  ( FIG. 3 ) of the compressor  30  causing the control  45  to direct high-pressure air into the cylinder volume  46  within cylinder  26 . The high-pressure air in the cylinder volume  46  acts against piston surface  48  of the piston  34 , so as to push the piston and stem  38  to the right. Compression spring  36  acts against piston  34  so as to push it to the left against the action of high-pressure air in cylinder volume  46  opposing the motion of the piston to the right. As should be evident to those skilled in the art, when air pressure within the cylinder volume  46  is sufficiently high to overcome the force of compression spring  36 , the piston  34 , along with stem  38 , moves to the right in  FIG. 2  such that the spherical end knob  44  of stem  38  will move away from ramp portion  28   b  of the flapper valve  28 , thereby allowing the flapper valve to open up, as shown in  FIG. 4 .  FIG. 6A  through  FIG. 6D  shows detailed views of the piston  34  individually and the piston and stem  38  assembled together.  FIG. 6A  shows the piston  34  in orthogonal cross sectional view including the piston surface  48  against which compressed air acts to make the piston move, and the receptacle  42  which receives the opposite end  38   a  of the stem  38 . Around the larger circumference  72  of the piston  34  there is a groove  74  within which is held an O-ring seal  76 .  FIG. 6B  is a perspective view of piston  34  showing the piston surface  48 , larger circumference  72 , and O-ring  76 .  FIG. 6C  is an orthogonal side of the piston  34  with the stem  38  inserted in place within receptacle  42  as indicated in  FIGS. 2 and 4 . 
       Operation of the Modulating Check Valve 
       [0035]      FIG. 2  shows the modulating check valve  10  with the flapper valve  28  in a closed position, blocking the flow of air through the conduit  16  of the modulating check valve  10 . 
         [0036]      FIG. 4  shows the modulating check valve  10  with the flapper valve  28  in an open position having an angle w that defines the degree of openness. When the flapper valve  28  is closed, of course, the angle w is 0. At maximum opening, the angle w is about 85 degrees. Under the latter condition, air pressure in the cylinder volume  46  is sufficient that the assembly of the piston  34  and stem  38  are pushed to the extreme of their rightward motion within the cylinder  26 , and the spring  36  is at its most compressed condition. 
         [0037]    Under conditions of normal operation, when the airflow rate into the compressor  30  is high, the flapper valve  28  opens a maximum of about 85 degrees, according to pressure at the outlet of the compressor. 
         [0038]    When the compressor  30  is not operating, the flapper valve  28  is in a fully closed position, as shown in  FIG. 2 , because of the low pressure in volume  46  allows spring  36  to move the piston  34  to the right. When the compressor  30  is started, the flapper valve  28  remains essentially closed and only a small amount of leakage air flows into the compressor. When the pressure in the conduit  58  on the output side of the compressor  30  rises to a predetermined level, a pressure signal is delivered to the control  45  by way of conduit  60 , as seen in  FIG. 3 , which in turn directs high pressure air to the cylinder volume  46  of the actuator section  46  of the modulating check valve  10 . The increased air pressure within the cylinder volume  46  forces piston  34  and stem  38  to the right, thereby allowing the flapper valve  28  to open up in response to the air being drawn through intake side  50  of the compressor  30  so that air freely flows to the inlet of compressor  30 . The idea here is to allow a small amount of air into the compressor through a bleed valve or small hole (not shown), through compressor  30  until it has got up to speed, thereby reducing the startup load on the compressor motor that drives the compressor and allowing time for the compressor and its motor to get up to operating speed. Once the pressure on the output side of the compressor has reached a predetermined level, a pressure signal is sent to the controller  45  to allow the flapper valve  28  to fully open as discussed hereinbefore. During the normal operation of the compressor  30 , the pressure in the conduit  58  on the output side of the compressor  30  varies depending on the requirements of compressed air usage by machinery or storage tanks (not shown) which receive compressed air from the compressor. As the flow rate requirement for the air decreases, as the demand for compressed air compressed goes down, the pressure in the conduit  58  on the output side of the compressor  30  rises so that an increasing high pressure signal delivered by way of conduit  60  to the controller  45 , which in turn directs a decreasing low air pressure to the cylinder volume  46  of the modulating check valve  10 . As the pressure in the cylinder volume  46  decreases, the piston  34  and stem  38  move to the left causing the flapper valve  28  to close as the need for air decreased. 
         [0039]    Alternatively, as the demand for compressed air compressed goes back up because of the increased demand for compressed air by the machinery or storage tanks, the pressure in the conduit  58  on the output side of the compressor  30  drops so that a lower pressure signal is delivered by way of conduit  60  to the controller  45 . The controller  45  in turn directs a higher air pressure to the cylinder volume  46  of the modulating check valve  10 . The higher pressure in the cylinder volume  46  causes the piston  34  and stem  38  to move to the right allowing the flapper valve  28  to open more and more as the need for air increases. 
         [0040]    As described above, the flapper valve  28  moves from an initially closed position when the compressor is off or idling, to a fully open position when the pressure at the outlet of the compressor reaches a predetermined minimum and then the valve begins to be closed by the stem  38  as the pressure at the outlet of the compressor increases. The effect is that the flapper valve  28  modulates the amount of air being delivered to the input of the compressor depending on the requirements of compressed air usage by machinery or storage tanks which receive compressed air from the compressor. 
         [0041]    In the event that there is an emergency shutoff of the compressor  30 , air flow from the air filter  52  and through the flow section  12  to the inlet of compressor  30  is minimal. In that case, the torsion spring  64 , which provides a weak closing force against a ramp portion  28   b  of the disk-type flapper valve  28 , biases the flapper valve toward a closed position, regardless of the orientation of the modulating check valve  10 . Being that when the rotary-screw compressor suddenly closes down, compressed air and lubricant in the compressor will flow momentarily backwards into the modulating check valve  10 . Since the flapper valve is closed or already nearly closed against the valve seat  20   a , the back flow of the compressed air and lubricant from the compressor will cause the flapper valve  28  to slam shut and thereby block the back flow of compressed air as well as the lubricant through the modulating check valve device  10  and into the air cleaner  52 . 
         [0042]    Although the modulating check valve  10  is described with an actuator section  14  which contains a pneumatic cylinder and piston that moves a stem  38  to close the flapper valve  28  when the compressor has shut down, allowing the flapper valve  28  to be fully open once outlet pressure of the compressor reaches a predetermined minimum or the modulates the flapper valve as the outlet pressure of the compressor increases and decreases, it is within the terms of another embodiment to move the stem with an electric motor such as a stepper motor. 
         [0043]    Also, while a single flapper valve is illustrated, it is within the terms of the preferred embodiment to provide two or more flapper valves that close against valve seats on the downstream side of valve seat section  20 . Each of the two or more flapper valves include an actuator section to individually control their respective valve. The effect of a plurality of flapper valves is to more finely control the air flow through the modulating check valve to the compressor. 
         [0044]    Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, certain equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, etc.) the terms (including a reference to a means) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more features of the other embodiments as may be desired and advantageous for any given or particular application.