MODULATING CHECK VALVE

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.

FIELD OF THE INVENTION

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

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.

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

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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present embodiment relates to a modulating check valve10designed for use with a rotary-screw type gas compressor30, as shown inFIG. 3. The modulating check valve10is shown in top view inFIG. 1. The modulating check valve10consists of a flow section12, through which a fluid, such as gas, flows into a rotary-screw type gas compressor30, and an actuator section14, which contains a pneumatic cylinder and piston, as shown inFIGS. 2 and 4, that modulates the gas flow through the flow section12, in ways described below. While rotary-screw type gas compressor30can compress many types of fluids including gasses, it is typically used to compress air, and called an air compressor herein.

As shown inFIG. 2, the flow section12of the modulating check valve10incorporates a conduit16through the flow section12. The conduit16has an intake portal18having a first diameter d1 at one end and a valve seat section20downstream and adjacent to intake portal18having a second diameter d2. The conduit16further includes an intermediate section22disposed downstream and adjacent the valve seat section20and having a third diameter d3 being greater than the second diameter d2. Continuing, the conduit16further includes an outflow portal24downstream and adjacent the intermediate section22and having a fourth diameter d4 being less than the third diameter d3. Further, as shown inFIG. 2, the flow section12of the modulating check valve10has a side opening26communicating with the intermediate section22and adapted to receive actuator section14.

The modulating check valve10, 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 valve10inFIGS. 2 and 4, through the section A-A indicated inFIG. 1. InFIG. 2, a valve closure device, typically a disk-type flapper valve28is shown in a closed position against the valve seat20aon the downstream side of valve seat section20. In this condition, no air would flow though the conduit16. Alternatively, if the flapper valve28were open as shown inFIG. 4, the air, see arrows, would flow through the intake portal18of conduit16, across the valve seat section20, through intermediate section22, out of outflow portal24and to a rotary-screw compressor30.

Referring again toFIGS. 2 and 4, there is illustrated a cross sectional view of the actuator section14of the modulating check valve10. As shown inFIG. 1, the actuator section14consists of a cylinder26having an end plate26asecured thereto and to a flange32that is mounted to the side opening26of the flow section12by threaded rods29and nuts31.

Returning now to the orthogonal cross sectional view ofFIG. 2, the cylinder26of the actuator section14houses a piston34that is slidably received within the cylinder. The piston34, as shown in detail inFIGS. 6A-6D, is biased towards flange32by a compression spring36that engages the interior surface26bof the end plate26a.

A stem38is slidably mounted (as indicated by the two-headed arrow) within bushing40which is fixed within the flange32. One end of the stem38has a reduced diameter portion38athat is secured within a receptacle42of piston34. The opposite end of stem38has a spherical end knob44. While a spherical end knob44is illustrated, it is within the terms of the preferred embodiment to employ another end, such as a roller ball. The spherical end knob44engages the disk-type flapper valve28. As discussed in more detail below, high air pressure in variable cylinder volume46at one end of cylinder26acts against piston34so as to push it to the right against the bias of compression spring36and thereby force the spherical end knob44of stem38to the right so that the flapper valve28will open by air flow through conduit16. The high-pressure air is provided by a control valve45in line60when the pressure from the output side of the compressor30is below a certain predetermined value. The high-pressure air from control valve45enters the cylinder volume46within cylinder26and acts against surface48of the piston34, so as to push the piston and stem38to the right. Compression spring36acts against piston34so as to push it to the left against the action of high-pressure air in cylinder volume46opposing the motion of the piston to the right. As should be evident to those skilled in the art, when air pressure within the cylinder volume46is sufficiently high to overcome the force of compression spring36, the piston34, along with stem38, moves to the right as shown inFIG. 4such that the spherical end knob44of stem38will move away from ramp portion28bof the flapper valve28, thereby allowing the flapper valve to open.

Before continuing the discussion of the components and the operation of the modulating check valve10, it would be useful to understand how the check valve is disposed in relation to a rotary screw compressor30, as shown inFIG. 3. The modulating check valve10is disposed within the air induction or intake side50of the compressor30. More specifically the modulating check valve10, shown within flow section12, is disposed between an air filter52and the rotary screw compressor30. A conduit54communicates air from the air filter52to the modulating check valve10, and another conduit56communicates air from the modulating check valve to the compressor30. Compressed air, indicated by black arrow CA, exits the compressor30by way of conduit58which communicates with machinery or storage tanks (not shown) which receive compressed air from the compressor. A tube or conduit60conveys a pressure signal from conduit58, or, more generally, from the output side of the compressor30, to the control valve45which directs pressurized air to the cylinder volume46in actuator section14of the modulating check valve10.

The detailed operation of the modulating check valve invention10can now be described with reference to the cross-sectional view of the modulating check valve10as illustrated inFIGS. 2 and 4. The disk-type flapper valve28is hinged about a hinge pin62. A closing device, such as a torsional spring64, using the hinge pin62as a fulcrum, is anchored at one end64ain a recess23in the flange32, with its other end64bexerting a closing force against the flapper valve28. The torsional spring64provides a weak closing force against a ramp portion28bof the disk-type flapper valve28such that the flapper valve tends toward a closed position when the air flow rate through the flow section12is minimal, regardless of the orientation of the modulating check valve10.

Referring toFIG. 4, the flapper valve28illustrated in an open position, shows an angle w that defines the degree of openness. When the flapper valve28is closed, as shown inFIG. 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 volume46is sufficient that the assembly of the piston34and stem38are pushed to the extreme of their rightward motion within the cylinder26, and the spring36is at its most compressed condition. Under conditions of normal operation for the compressor30, the flapper valve28opens 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.

Referring toFIGS. 5A-5G, the flapper type, check valve28is shown in detail.FIG. 5Ashows the pivot pin view of the flapper valve28. The flapper valve28consists of a disk portion28a, a ramp portion28b, the inlet portal valve seating surface28cof the disk (flapper) portion28a, the ramp surface28dand two hinge pin bosses68a,68b.FIG. 5Bshows the flapper type check valve28in the view from the outlet portal24;FIG. 5Cshows the flapper type check valve in view from actuator14; andFIG. 5Dshows the flapper type check valve in the view from the intake portal18, wherein the valve seating surface28cof the flapper valve disk which seats against valve seat20ahas an O-ring70held within a circumferential groove72. The disposition of the O-ring70within the circumferential groove72is revealed more specifically inFIG. 5E, which is section view B-B indicated inFIG. 5D.FIG. 5FandFIG. 5Gare, respectively, perspective views of flapper valve28from the outlet portal24and intake portal18, respectively.

Returning now to the orthogonal cross sectional view ofFIG. 2, note that the ramp portion28bof the flapper valve28is in contact with spherical end knob44of stem38which is slidably mounted (as indicated by the two-headed arrow) within bushing40which is fixed within the flange32. Stem38, at the end opposite the spherical end knob44, has a reduced diameter portion38awhich engages with a receptacle42of piston34. While a spherical end knob44is illustrated, it is within the terms of the preferred embodiment to employ another end, such as a roller ball. Piston34slides within the cylinder26. The piston34is actuated by, and forced to the right by (as shown inFIG. 4), a low-pressure air signal from the output side41(FIG. 3) of the compressor30causing the control45to direct high-pressure air into the cylinder volume46within cylinder26. The high-pressure air in the cylinder volume46acts against piston surface48of the piston34, so as to push the piston and stem38to the right. Compression spring36acts against piston34so as to push it to the left against the action of high-pressure air in cylinder volume46opposing the motion of the piston to the right. As should be evident to those skilled in the art, when air pressure within the cylinder volume46is sufficiently high to overcome the force of compression spring36, the piston34, along with stem38, moves to the right inFIG. 2such that the spherical end knob44of stem38will move away from ramp portion28bof the flapper valve28, thereby allowing the flapper valve to open up, as shown inFIG. 4.FIG. 6AthroughFIG. 6Dshows detailed views of the piston34individually and the piston and stem38assembled together.FIG. 6Ashows the piston34in orthogonal cross sectional view including the piston surface48against which compressed air acts to make the piston move, and the receptacle42which receives the opposite end38aof the stem38. Around the larger circumference72of the piston34there is a groove74within which is held an O-ring seal76.FIG. 6Bis a perspective view of piston34showing the piston surface48, larger circumference72, and O-ring76.FIG. 6Cis an orthogonal side of the piston34with the stem38inserted in place within receptacle42as indicated inFIGS. 2 and 4.

Operation of the Modulating Check Valve

FIG. 2shows the modulating check valve10with the flapper valve28in a closed position, blocking the flow of air through the conduit16of the modulating check valve10.

FIG. 4shows the modulating check valve10with the flapper valve28in an open position having an angle w that defines the degree of openness. When the flapper valve28is 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 volume46is sufficient that the assembly of the piston34and stem38are pushed to the extreme of their rightward motion within the cylinder26, and the spring36is at its most compressed condition.

Under conditions of normal operation, when the airflow rate into the compressor30is high, the flapper valve28opens a maximum of about 85 degrees, according to pressure at the outlet of the compressor.

When the compressor30is not operating, the flapper valve28is in a fully closed position, as shown inFIG. 2, because of the low pressure in volume46allows spring36to move the piston34to the right. When the compressor30is started, the flapper valve28remains essentially closed and only a small amount of leakage air flows into the compressor. When the pressure in the conduit58on the output side of the compressor30rises to a predetermined level, a pressure signal is delivered to the control45by way of conduit60, as seen inFIG. 3, which in turn directs high pressure air to the cylinder volume46of the actuator section46of the modulating check valve10. The increased air pressure within the cylinder volume46forces piston34and stem38to the right, thereby allowing the flapper valve28to open up in response to the air being drawn through intake side50of the compressor30so that air freely flows to the inlet of compressor30. The idea here is to allow a small amount of air into the compressor through a bleed valve or small hole (not shown), through compressor30until 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 controller45to allow the flapper valve28to fully open as discussed hereinbefore. During the normal operation of the compressor30, the pressure in the conduit58on the output side of the compressor30varies 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 conduit58on the output side of the compressor30rises so that an increasing high pressure signal delivered by way of conduit60to the controller45, which in turn directs a decreasing low air pressure to the cylinder volume46of the modulating check valve10. As the pressure in the cylinder volume46decreases, the piston34and stem38move to the left causing the flapper valve28to close as the need for air decreased.

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 conduit58on the output side of the compressor30drops so that a lower pressure signal is delivered by way of conduit60to the controller45. The controller45in turn directs a higher air pressure to the cylinder volume46of the modulating check valve10. The higher pressure in the cylinder volume46causes the piston34and stem38to move to the right allowing the flapper valve28to open more and more as the need for air increases.

As described above, the flapper valve28moves 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 stem38as the pressure at the outlet of the compressor increases. The effect is that the flapper valve28modulates 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.

In the event that there is an emergency shutoff of the compressor30, air flow from the air filter52and through the flow section12to the inlet of compressor30is minimal. In that case, the torsion spring64, which provides a weak closing force against a ramp portion28bof the disk-type flapper valve28, biases the flapper valve toward a closed position, regardless of the orientation of the modulating check valve10. 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 valve10. Since the flapper valve is closed or already nearly closed against the valve seat20a, the back flow of the compressed air and lubricant from the compressor will cause the flapper valve28to slam shut and thereby block the back flow of compressed air as well as the lubricant through the modulating check valve device10and into the air cleaner52.

Although the modulating check valve10is described with an actuator section14which contains a pneumatic cylinder and piston that moves a stem38to close the flapper valve28when the compressor has shut down, allowing the flapper valve28to 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.

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 section20. 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.