Patent Description:
In one aspect, an unloader valve includes a seat including a plurality of inlet apertures, each inlet aperture spaced apart from the other inlet apertures and extending through the seat along one of a plurality of parallel inlet axes. A manifold plate is fixedly connected to the seat and includes a plurality of outlet apertures, each spaced apart from the other outlet apertures and extending through the manifold plate along one of a plurality of parallel outlet axes. The unloader valve also includes a plurality of blind plug holes, each centrally aligned along one of the plurality of parallel inlet axes, a control chamber formed in the manifold plate, and a control space fully defined by the manifold plate and arranged to fluidly connect the control chamber and each of the blind plug holes to one another. The unloader valve also includes a control member disposed within the control chamber and movable between a first position in which the control space is exposed to a pressure source, and a second position in which the control space is isolated and a plurality of plugs, each plug positioned within one of the blind plug holes and movable between a closed position in which each plug closes one of the inlet apertures and an open position in which the plurality of inlet apertures are in fluid communication with the plurality of outlet apertures.

In another aspect, an unloader valve for use with a reciprocating gas compressor having a compression space defined by a piston and a cylinder includes a seat including a plurality of inlet apertures, and a manifold plate fixedly connected to the seat. The manifold plate includes a plurality of outlet apertures, a plurality of plug holes, a control chamber formed in the manifold plate, and a control space fully defined by the manifold plate and arranged to fluidly connect the control chamber and each of the plug holes to one another. The unloader valve also includes a control member disposed within the control chamber and movable between a first position in which the control space is exposed to the compression space, and a second position in which the control space is isolated from the compression space. The unloader valve for use also includes a plurality of plugs, each plug positioned within one of the plug holes, each plug movable from a closed position in which each plug closes one of the inlet apertures to an open position in response to the control member being disposed in the first position and a pressure within the control space being below a predetermined pressure, and where each plug is maintained in the open position in response to the control member being in the second position.

In another aspect, an unloader valve for use with a reciprocating gas compressor having a compression space defined by a piston and a cylinder includes a seat including a plurality of inlet apertures, a manifold plate including a plurality of outlet apertures and a plurality of attachment apertures, a control seat threadably coupled to the manifold plate to fixedly attach the seat and the manifold plate, and an interface plate positioned between the seat and the manifold plate and cooperating with the manifold plate to define a control space. A plurality of valve cups are arranged with each valve cup threadably connected to the manifold plate and operable to sandwich the interface plate between the valve cups and the manifold plate. A control member is disposed within the control seat and is movable between a first position in which the control space is exposed to the compression space, and a second position in which the control space is isolated from the compression space. A plurality of plugs is arranged with each plug positioned within one of the valve cups and movable from a closed position in which each plug closes one of the inlet apertures to an open position in response to the control member being disposed in the first position and a pressure within the control space being below a predetermined pressure, and where each plug is maintained in the open position in response to the control member being in the second position.

As used herein, the terms "component" and "system" are intended to encompass hardware, software, or a combination of hardware and software. Thus, for example, a system or component may be a process, a process executing on a processor, or a processor. Additionally, a component or system may be localized on a single device or distributed across several devices.

Further the phrase "at least one" before an element (e.g., a processor) that is configured to carry out more than one function/process may correspond to one or more elements (e.g., processors) that each carry out the functions/processes and may also correspond to two or more of the elements (e.g., processors) that respectively carry out different ones of the one or more different functions/processes.

Also, it should be understood that the words or phrases used herein should be construed broadly, unless expressly limited in some examples. For example, the terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation. The singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The term "or" is inclusive, meaning and/or, unless the context clearly indicates otherwise. The phrases "associated with" and "associated therewith," as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.

Also, although the terms "first", "second", "third" and so forth may be used herein to refer to various elements, information, functions, or acts, these elements, information, functions, or acts should not be limited by these terms. Rather these numeral adjectives are used to distinguish different elements, information, functions or acts from each other. For example, a first element, information, function, or act could be termed a second element, information, function, or act, and, similarly, a second element, information, function, or act could be termed a first element, information, function, or act, without departing from the scope of the present disclosure.

In addition, the term "adjacent to" may mean that an element is relatively near to but not in contact with a further element or that the element is in contact with the further portion, unless the context clearly indicates otherwise. Further, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise.

<FIG> illustrates a portion of a reciprocating gas compressor <NUM> that is driven by a prime mover, such as an electric motor or other engine to produce a compressed gas. The reciprocating gas compressor <NUM> includes one or more casings <NUM> that each define a cylinder <NUM> that supports a piston <NUM> for reciprocating movement. The piston <NUM> and the casing <NUM> cooperate to define a compression space <NUM> that has a volume that various with the reciprocating motion of the piston <NUM> to draw in gas to be compressed and to compress the gas as is well known.

A gas inlet <NUM> is provided in the casing <NUM> to receive a supply of gas to be compressed and a gas outlet <NUM> is formed in the casing to collect the compressed gas produced by the reciprocating gas compressor <NUM>. As will be discussed in greater detail, a number of unloader valves <NUM> are coupled to the casing <NUM> and are positioned between the gas inlet <NUM> and the compression space <NUM> to control the admission of uncompressed gas into the compression space <NUM>. Similarly, a number of discharge valves <NUM> are provided between the compression space <NUM> and the gas outlet <NUM> to control the outflow of compressed gas.

<FIG> illustrates a portion of the reciprocating gas compressor <NUM> that includes the casing <NUM> and defines a number of inlet/outlet bores <NUM>. One unloader valve <NUM> is attached to each of four of the inlet/outlet bores <NUM> with four discharge valves <NUM> (not shown) attached to the remaining four inlet/outlet bores <NUM>. Of course, other arrangements could have more or fewer unloader valves <NUM> and discharge valves <NUM> as may be required for the particular design.

<FIG> illustrates one of the unloader valves <NUM> of <FIG> with all the unloader valves <NUM> being substantially the same. The unloader valve <NUM> includes a valve housing <NUM> that supports the remaining components in their desired operating positions and a flange <NUM> that is arranged to facilitate the attachment of the unloader valve <NUM> to the casing <NUM>. In the illustrated construction, the flange <NUM> includes a plurality of apertures arranged to receive fasteners that attach the unloader valve <NUM> to the casing <NUM>.

An actuator <NUM> is positioned adjacent the flange in a position that ultimately is outside of the casing <NUM> during operation. As will be discussed in greater detail, the actuator <NUM> can be an electrical, hydraulic, pneumatic or any other type of actuator desired. A control member <NUM> (better illustrated in <FIG>) is coupled to the actuator <NUM> for movement as will be discussed in greater detail.

The unloader valve <NUM> also includes a seat <NUM> and a manifold plate <NUM> positioned at one end of the valve housing <NUM> such that when the unloader valve <NUM> is attached to the casing <NUM> in its operating position, the manifold plate <NUM> is positioned nearest to the piston <NUM>.

<FIG> illustrates the manifold plate <NUM>, the seat <NUM>, and the control member <NUM> with the remainder of the unloader valve <NUM> omitted. The control member <NUM> includes an elongated shaft that extends from the seat <NUM> to a position within the actuator <NUM> to allow the actuator <NUM> to move the control member <NUM> between a first position and a second position. A control seat <NUM> is coupled to one of the seat <NUM> and the manifold plate <NUM> and cooperates with the control member <NUM> during operation of the control member <NUM>.

The seat <NUM> includes a plurality of inlet apertures <NUM> with each inlet aperture <NUM> passing through the seat <NUM>. The inlet apertures <NUM> are arranged in a series of rows and columns with other arrangements being possible. In the illustrated construction, forty-eight inlet apertures <NUM> are employed with typical applications including twenty or more. Of course, any suitable number of inlet apertures <NUM> could be employed as required.

<FIG> illustrates one possible embodiment of a manifold plate <NUM>. In the illustrated construction, the manifold plate <NUM> includes a central bore <NUM>, a series of outlet apertures <NUM>, and a series of plug bores <NUM>. The central bore <NUM> is sized to receive the control seat <NUM> which, as illustrated in <FIG> also serves to attach the seat <NUM> to the manifold plate <NUM>. Specifically, the control seat <NUM> threadably engages the manifold plate <NUM> and includes a collar <NUM> that retains the seat <NUM> in the desired position.

The outlet apertures <NUM> and the plug bores <NUM> are arranged adjacent one another in a series of rows and columns. With this arrangement, each outlet aperture <NUM> is most closely surrounded by four plug bores <NUM>. Similarly, each plug bore <NUM> is most closely surrounded by four outlet apertures <NUM>. Each of the plug bores <NUM> is aligned with and coaxial with an inlet aperture <NUM> of the seat <NUM> while the outlet apertures <NUM> are arranged parallel to the inlet apertures <NUM> but are offset or misaligned.

<FIG> is a section view taken through the rows or columns described with regard to <FIG>. Each of the plug bores <NUM> is a blind plug bore <NUM> (closed at one end) and receives a biasing member <NUM> and a plug <NUM>. Each plug bore <NUM> is aligned coaxially with one of the inlet apertures <NUM> such that the biasing member <NUM> operates to bias the plug <NUM> toward a closed position in which the plug <NUM> contacts a plug seat <NUM> formed as part of the seat <NUM>. In the closed position, each plug <NUM> closes the inlet aperture <NUM> with which it is aligned, thereby inhibiting flow through the seat <NUM>. Each plug <NUM> is further movable from the closed position to an open position in which the plug <NUM> is retracted from the plug seat <NUM> and flow can pass through the inlet apertures <NUM> and through the outlet apertures <NUM> to enter the compression space <NUM>.

The manifold plate <NUM> includes a control space <NUM>, a control seat <NUM>, and a control opening <NUM> formed as part of the manifold plate <NUM>. In preferred constructions, these features are formed as part of a one-piece or unitary manifold plate <NUM> and cannot be separated without destroying the manifold plate <NUM>. Due to the preferred shape of these features, the most viable method of forming the manifold plate <NUM> is an additive manufacturing process. Conventional manufacturing processes are generally not capable of forming the desired shapes of these features, with the desired surface finishes, and in particular are not capable of forming the control space <NUM>.

The control opening <NUM> provides for fluid communication between the compression space <NUM> and the control space <NUM>. The control seat <NUM> is positioned such that the control member <NUM> is movable into a position that blocks fluid communication between the compression space <NUM> and the control space <NUM> such that the control space <NUM> is effectively sealed and isolated. Thus, when the control member <NUM> moves to the second position and isolates the control space <NUM>, the pressure within the control space <NUM> becomes fixed at whatever point it was at just prior to the movement of the control member <NUM> into the second position.

<FIG> is a reverse image of a portion of the manifold plate <NUM> such that the spaces that define the control space <NUM> are shown as solid and the solid areas are removed. As can be seen, the control seat <NUM> and the control opening <NUM> define a large control chamber <NUM> that is capable of receiving fluid. Four distribution channels <NUM> connect the control chamber <NUM> to a series of runners <NUM> that interconnect each of the plug bores <NUM> to the control space <NUM> such that a plug space <NUM> is in fluid communication with the control space <NUM>.

To operate the construction of <FIG> and <FIG>, the unloader valve <NUM> is first assembled into a reciprocating gas compressor <NUM> as is schematically illustrated in <FIG>. Specifically, the manifold plate <NUM> is in fluid communication with the compression space <NUM> and the seat <NUM> is positioned in fluid communication with a source of gas to be compressed. The actuator <NUM> is coupled to a controller <NUM> that operates to move the control member <NUM> between the first position and the second position. In some constructions a digital control such as a programmable logic controller (PLC) is employed to drive an electronic actuator <NUM> that ultimately moves the control member <NUM>.

With the control member <NUM> in the first position (shown in <FIG>), the control space <NUM> is exposed to the compression space <NUM> which acts as a pressure source. As the piston <NUM> retracts (note that the piston <NUM> is shown rotated <NUM> degrees as compared to the piston of <FIG>), the compression space <NUM> becomes larger and the pressure drops. When the pressure within the control space <NUM> reaches a predetermined point, the biasing force of the biasing members <NUM> is overcome and the plugs <NUM> are pulled into an open position. As gas to be compressed flows into the compression space <NUM>, the pressure could increase which would allow the biasing members <NUM> to return the plugs <NUM> to a closed position. To stop this, once the plugs <NUM> move to the open position, the control member <NUM> is moved via the controller <NUM> and the actuator <NUM> to the second position to seal and isolate the control space <NUM>. This effectively holds the plugs <NUM> in the open position regardless of the pressure within the compression space <NUM>. At some point just before, as, or just after the piston <NUM> begins its compression stroke, the controller <NUM> moves the control member <NUM> back to the first position and the control space <NUM> fills with higher pressure gas which allows the plugs <NUM> to return to the closed position during the compression stroke. This process is repeated with each rotational cycle and for each individual inlet/outlet bore <NUM> and unloader valve <NUM> to compress the gas as desired.

<FIG> illustrate an alternative construction of an unloader valve <NUM>. The unloader valve <NUM> includes a manifold plate <NUM>, an interface plate <NUM>, a control seat <NUM>, and a seat <NUM> that is very similar to the prior described seat <NUM>. The manifold plate <NUM> includes a plurality of outlet apertures <NUM> similar to those described earlier. In addition, the manifold plate <NUM> includes a series of attachment apertures <NUM> (best illustrated in <FIG>) that are threaded to receive one of a plurality of valve cups <NUM>.

The control seat <NUM> is similar to the control seat <NUM> and attaches to and retains the seat <NUM> and the manifold plate <NUM> as previously described. The control seat <NUM> includes one or more control passages <NUM> that are arranged to selectively provide fluid communication between the control opening <NUM> and a control space <NUM>.

The control space <NUM> is formed between the manifold plate <NUM> and the interface plate <NUM>. The interface plate <NUM>, better illustrated in <FIG> engages the manifold plate <NUM> and is held in place by the plurality of valve cups <NUM> that are threaded into the manifold plate <NUM> with the interface plate <NUM> sandwiched therebetween. The manifold plate <NUM> and the interface plate <NUM> define spaces that correspond with the valve cups <NUM> such that fluid can enter the valve cups <NUM> via cup holes <NUM> formed therein and positioned in the control space <NUM> between the manifold plate <NUM> and the interface plate <NUM>.

As illustrated in <FIG>, the interface plate <NUM> includes a plate portion <NUM>, a central bore <NUM>, a series of cup openings <NUM>, and a series of outlet bores <NUM>. The plate portion <NUM> is substantially planar and is shaped to fit within the manifold plate <NUM>. The central bore <NUM> is formed at or near the center of the plate portion <NUM> and is sized to allow for the passage of the control seat <NUM> therethrough.

The outlet bores <NUM> are bores that pass through the plate portion <NUM>. The outlet bores <NUM> could include threads that are sized and arranged to threadably receive the valve cups <NUM>. Alternatively, the outlet bores <NUM> are through bores and the attachment apertures <NUM> in the manifold plate <NUM> are threaded. The outlet bores <NUM> are arranged in a series of rows and columns that extend around the central bore <NUM>.

The cup openings <NUM> are through bores that extend through the plate portion <NUM> and that each include a wall portion <NUM> that surrounds the cup opening <NUM> and extends away from the plate portion <NUM> in a direction away from the manifold plate <NUM>. The cup openings <NUM> are arranged in a series of rows and columns that extend around the central bore <NUM>.

While <FIG> illustrates the rows of cup openings <NUM> and the rows of outlet bores <NUM> arranged in an alternating fashion, other arrangements such as rows and columns that include both cup openings <NUM> and outlet bores <NUM> could be employed. The arrangement of the cup openings <NUM> and the outlet bores <NUM> should not limit the invention in any way.

<FIG> is an enlarged section view of a portion of the unloader valve <NUM> of <FIG>. The interface plate <NUM> is positioned on the inner surface of the manifold plate <NUM> to define the control space <NUM> that includes the spaces between the wall portions <NUM> and the manifold plate <NUM>. Each of the valve cups <NUM> includes a threaded cup stem <NUM> that threadably engages one of the cup openings <NUM>. As the valve cup <NUM> is installed, it eventually contacts the wall portion <NUM> surrounding its respective cup opening <NUM> to form a seal between the valve cup <NUM> and the wall portion <NUM>. Each cup stem <NUM> includes one or more cup holes <NUM> that provide fluid communication between the control space <NUM> and the interior of the valve cup <NUM>. Each valve cup <NUM> contains a plug <NUM> that seals the control space <NUM> behind the plug <NUM>. Thus, the valve cups <NUM>, the interface plate <NUM>, and the manifold plate <NUM> cooperate to fully enclose the control space <NUM> with the only opening, the control opening <NUM> being selectively opened or closed by the control member <NUM>.

The unloader valve <NUM> operates in much the same way as the unloader valve <NUM> with the main difference being in how the control space <NUM> is formed and shaped.

As illustrated in <FIG>, a seal can be formed between a mushroom plug <NUM> or a cylindrical plug <NUM> and the valve cups <NUM> to reduce the likelihood of unwanted leakage. <FIG> illustrates alternatives for forming this seal with the two different shaped plugs. The first two images include a mushroom plug <NUM> that includes a cylindrical body that moves within the valve cup <NUM> and an enlarged cylindrical head. This arrangement allows for the use of a smaller diameter valve cup <NUM> with a larger head. The next two images include a uniform cylindrical plug <NUM> that moves within the valve cup <NUM>.

A first seal member 1202a is positioned within a seal groove formed in the mushroom plug <NUM>. The first seal member 1202a is relatively short when compared to the length of the plug <NUM> within the valve cup <NUM>. The first seal member 1202a could be formed from a resilient material such as rubber, or a more rigid material such as TEFLON, brass, or bronze with these more rigid materials also enhancing the ability of the plug <NUM> to slide within the valve cup <NUM>. A fourth seal member 1202d is similar to the first seal member 1202a but is applied to the cylindrical plug <NUM> rather than the mushroom plug <NUM>.

A second seal member 1202b is positioned within a seal groove formed in the valve cup <NUM> rather than in the mushroom plug <NUM> or the cylindrical plug <NUM>. The second seal member 1202b is much longer than the first seal member 1202a but can be made using the same materials as the first seal member 1202a if desired. A third seal member 1202c is similar to the second seal member 1202b but is applied to the valve cup <NUM> for use with a cylindrical plug <NUM> rather than the mushroom plug <NUM>.

<FIG> illustrates an alternative arrangement of a manifold plate <NUM> and interface plate <NUM> suitable for use with any of the prior embodiments described that employ an interface plate. The manifold plate <NUM> includes a manifold base <NUM> that is surrounded by a manifold wall <NUM> to define a manifold interior <NUM>. The interface plate <NUM> is positioned on top of and in direct contact with the manifold base <NUM>. A valve cylinder <NUM> is positioned on top of the interface plate <NUM> such that it too is disposed within the manifold interior <NUM> and so that a portion of the interface plate <NUM> is sandwiched between the manifold plate <NUM> and the valve cylinder <NUM>.

Each of the manifold plate <NUM> and the interface plate <NUM> includes a number of plug bores <NUM> and a number of outlet apertures <NUM> that are aligned with one another when the interface plate <NUM> is positioned within the manifold interior <NUM>. The plug bores <NUM> and the outlet apertures <NUM> can be arranged in any pattern desired, including those arrangements already described.

The valve cylinder <NUM>, illustrated in <FIG> is a cylindrical component having an annular cross-section that defines a central bore <NUM>. A first end of the valve cylinder <NUM> includes a shoulder <NUM> and an extension <NUM> that are arranged to sandwich the interface plate <NUM> between the manifold plate <NUM> and the valve cylinder <NUM> as will be described in greater detail with regard to <FIG>.

Turning to <FIG>, the manifold interior <NUM> is illustrated with the valve cylinder <NUM> and the interface plate <NUM> removed. As illustrated, the manifold base <NUM> includes a number of plug bores <NUM> and a number of outlet apertures <NUM> arranged in a pattern that matches the pattern of the interface plate <NUM> to assure the desired level of alignment. The number of plug bores <NUM> and the number of outlet apertures <NUM> need not exactly match the quantity in the interface plate <NUM>. However, in preferred embodiments, the number of plug bores <NUM> in the manifold base <NUM> matches the number of plug bores <NUM> in the interface plate <NUM>.

A castellated spacer <NUM> is positioned at the center of the manifold plate <NUM> within the manifold interior <NUM>. In the illustrated construction, the castellated spacer <NUM> is formed as a single component with the manifold plate <NUM> and includes a number of wedge bosses <NUM> that extend from the manifold base <NUM>. The wedge bosses <NUM> are wedge-shaped bosses that are positioned in a circular pattern in a manner that defines gaps between the individual wedge bosses <NUM>. The wedge bosses <NUM> are arranged to define an inner diameter that is sized to receive the extension <NUM> of the valve cylinder <NUM> adjacent the shoulder <NUM> as will be described with regard to <FIG>. The term "castellated" refers to the appearance of the castellated spacer <NUM> which includes alternating high features (wedge bosses <NUM>) with alternating low spaces (the gaps) therebetween.

<FIG> illustrates the contact side of the interface plate <NUM> in greater detail. Each of the plug bores <NUM> is defined by a wall that contacts the manifold base <NUM>. The walls also cooperate to form a control space between the manifold base <NUM> and the interface plate <NUM> to allow for a flow of fluid. A plate bore <NUM> is formed in the interface plate <NUM> and is sized to receive the extension <NUM> of the valve cylinder <NUM> as will be described with reference to <FIG>.

<FIG> is a cross-section of the valve cylinder <NUM>, manifold plate <NUM>, and the interface plate <NUM> in the assembled or operating position. As illustrated, the interface plate <NUM> is positioned on the manifold base <NUM> with each of the plug bores <NUM> of the manifold plate <NUM> aligned with a corresponding plug bore <NUM> of the interface plate <NUM>.

The plate bore <NUM> is sized such that a portion of the interface plate <NUM> rests on the castellated spacer <NUM> and specifically contacts each of the wedge bosses <NUM>. However, the plate bore <NUM> has a larger diameter then the inner diameter of the castellated spacer <NUM> such that a portion of each of the wedge bosses <NUM> remains uncovered when the interface plate <NUM> is in place.

The valve cylinder <NUM> is positioned on top of the interface plate <NUM> such that the shoulder <NUM> contacts the interface plate <NUM> and the extension <NUM> defined by the shoulder <NUM> contacts the exposed portions of the wedge bosses <NUM>. The valve cylinder <NUM> can be biased or pushed toward the manifold base <NUM> to sandwich the interface plate <NUM> between the shoulder <NUM> and the wedge bosses <NUM>. With this arrangement, the shoulder <NUM> and the interface plate <NUM> cooperate to define a seal therebetween. In addition, the interface plate <NUM> is held in place due to its contact with the shoulder <NUM> and the wedge bosses <NUM>. However, there is no seal formed between the castellated spacer <NUM> and the interface plate <NUM> due to the gaps between the wedge bosses <NUM>. This arrangement provides a flow path into the control space formed between the interface plate <NUM> and the manifold plate <NUM>. The control space functions much like the control spaces <NUM>, <NUM> previously described.

Although an exemplary embodiment of the present disclosure has been described in detail, those skilled in the art will understand that various changes, substitutions, variations, and improvements disclosed herein may be made without departing from the scope of the disclosure in its broadest form.

Claim 1:
An unloader valve (<NUM>) comprising:
a seat (<NUM>) including a plurality of inlet apertures (<NUM>), each inlet aperture (<NUM>) spaced apart from the other inlet apertures (<NUM>) and extending through the seat (<NUM>) along one of a plurality of parallel inlet axes;
a manifold plate (<NUM>) fixedly connected to the seat (<NUM>), the manifold plate (<NUM>) including
a plurality of outlet apertures (<NUM>), each outlet aperture (<NUM>) spaced apart from the other outlet apertures (<NUM>) and extending through the manifold plate (<NUM>) along one of a plurality of parallel outlet axes;
a plurality of blind plug holes (<NUM>), each blind plug hole (<NUM>) centrally aligned along one of the inlet axis of the plurality of parallel inlet axes;
a control chamber (<NUM>) formed in the manifold plate (<NUM>); and
a control space (<NUM>) defined by the manifold plate (<NUM>) and arranged to fluidly connect the control chamber (<NUM>) and each of the blind plug holes (<NUM>) to one another;
a control member (<NUM>) disposed within the control chamber (<NUM>) and movable between a first position in which the control space (<NUM>) is exposed to a pressure source, and a second position in which the control space (<NUM>) is isolated; and
a plurality of plugs (<NUM>), each plug positioned within one of the blind plug holes (<NUM>) and movable between a closed position in which each plug (<NUM>) closes one of the inlet apertures (<NUM>) and an open position in which the plurality of inlet apertures (<NUM>) are in fluid communication with the plurality of outlet apertures (<NUM>) .