Patent Description:
Hydraulic actuators are commonly used in applications that require high levels of force, rapid movement, or both. Typical hydraulic actuators require a supply of high-pressure fluid that is provided by a remote, centralized source that provides high-pressure fluid to multiple actuators. Piping between the supply and the actuators can be expensive and can be a source for undesirable leakage. <CIT> discloses a hydraulic system including at least one hydraulic actuator, a distribution means in fluid communication with the at least one hydraulic actuator, at least one source of hydraulic fluid in fluid communication with the distribution means and a control means communicating with the at least one source. <CIT> discloses an hydraulic power system for controlling a double-acting hydraulic power cylinder.

The present invention provides an actuator operable to move a valve stem between an opened position and a closed position according to claim <NUM>.

The present invention further provides a method of operating an actuator according to claim <NUM>.

The foregoing has outlined rather broadly the technical features of the present invention so that those skilled in the art may better understand the detailed description that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiments disclosed as a basis for modifying or designing other structures, within the scope of the claims, for carrying out the same purposes of the present invention.

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings, but is only limited by the claims.

Various technologies that pertain to systems and methods will now be described with reference to the drawings, where like reference numerals represent like elements throughout. The drawings discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention as defined by the claims. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged apparatus. It is to be understood that functionality that is described as being carried out by certain system elements may be performed by multiple elements. Similarly, for instance, an element may be configured to perform functionality that is described as being carried out by multiple elements. The numerous innovative teachings of the present application will be described with reference to exemplary non-limiting embodiments.

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 "including," "having," and "comprising," 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.

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. Terms "about" or "substantially" or like terms are intended to cover variations in a value that are within normal industry manufacturing tolerances for that dimension. If no industry standard as available a variation of <NUM> percent would fall within the meaning of these terms unless otherwise stated.

<FIG> schematically illustrates a self-contained hydraulic actuator <NUM> that can be used to control movement of any number of devices including control valve stems <NUM>, stop valves, vane positioners, etc. The actuator <NUM> includes a cylinder <NUM>, a first pair of pumps <NUM> for moving the actuator <NUM> in a first direction <NUM>, and a second pair of pumps <NUM> for moving the actuator <NUM> in a second direction <NUM> opposite the first direction <NUM>.

The cylinder <NUM> in the illustrated construction is a double acting cylinder with a biasing member in the form of a spring return <NUM> and a cushion on the closing side of the cylinder <NUM>. The cylinder <NUM> includes a movable piston <NUM> that divides the cylinder <NUM> into an open side <NUM> and a close side <NUM>. A shaft <NUM> extends out of the cylinder <NUM> and connects to an object to be moved such as the control valve stem <NUM>. The spring return <NUM> biases the piston <NUM> to one side of the cylinder <NUM>. In constructions in which a valve is operated, the bias is typically toward a closed position. However, different applications may bias the device or valve toward an open position. The cushion is provided to allow fast movement in one direction without causing damage to the cylinder <NUM>. While the illustrated cylinder <NUM> is a double acting cylinder with a biasing member and a cushion, other suitable cylinders could be single acting, and could omit or include any of the features discussed with regard to the cylinder <NUM>. In addition, the cushion or biasing member could be positioned on the opposite ends of the cylinder or omitted if desired.

The first pair of pumps <NUM> includes two substantially identical micro-piston pumps <NUM> as illustrated in <FIG>. Each pump <NUM> is connected to a motor <NUM>, and preferably a DC motor that is operated at a desired speed to provide the desired quantity of fluid. The illustrated pumps <NUM> are fixed displacement pumps <NUM> which are preferable as the volume of fluid delivered can be easily controlled by varying the speed of the motors <NUM>. However, variable displacement pumps could also be employed if desired. The first pair of pumps <NUM> include an output <NUM> arranged to deliver a high-pressure fluid to the open side <NUM> of the cylinder <NUM> and an inlet <NUM> arranged to draw low-pressure fluid into the first pair of pumps <NUM>.

The second pair of pumps <NUM> is substantially the same as the first pair of pumps <NUM> and includes two pumps <NUM> each connected to and driven by its own motor <NUM>. The second pair of pumps <NUM> include an output <NUM> arranged to deliver a high-pressure fluid to the close side <NUM> of the cylinder <NUM> and an inlet <NUM> arranged to draw low-pressure fluid into the second pair of pumps <NUM>. While the illustrated construction illustrates two pairs of pumps <NUM>, <NUM>, a single pump <NUM> for opening and a second single pump <NUM> for closing could be employed if desired. In addition, three or more pumps <NUM> could be employed in place of each pair of pumps <NUM>, <NUM>. Two or more pumps <NUM> for each of the open side <NUM> and close side <NUM> are preferred as it provides some redundancy in case one of the pumps <NUM> fails or does not operate properly.

In some constructions, each of the pumps <NUM> includes a check valve that inhibits reverse flow through the pump <NUM> when the pump is idle. Some pumps <NUM> may omit this check valve as their design itself inhibits such flow.

A first accumulator <NUM> is provided to collect or hold excess fluid and to deliver low pressure fluid to the first pair of pumps <NUM> as will be described. A second accumulator <NUM>, similar to the first accumulator <NUM> is provided to collect or hold excess fluid and to deliver low pressure fluid to the second pair of pumps <NUM> as will be described. In some constructions, a single accumulator functions as the first accumulator <NUM> and the second accumulator <NUM>.

A controller <NUM> (e.g., a PLC) communicates with each of the motors <NUM> to control their operation and speed. External controllers such as a turbine control or other control device can be used as the controller. Each pump <NUM> of the pairs of pumps <NUM>, <NUM> are operated together and in one of three modes including a first or open mode <NUM> in which the first pair of pumps <NUM> operate while the second pair of pumps <NUM> are idle, a second or close mode <NUM> in which the second pair of pumps <NUM> operate while the first pair of pumps <NUM> are idle, and a third or maintain mode in which both the first pair of pumps <NUM> and the second pair of pumps <NUM> are idle. In the third mode of operation, the flow paths into or out of the cylinder <NUM> are blocked such that the cylinder <NUM>, and the control valve stem <NUM> to which the cylinder <NUM> is attached remain fixed in their current position. Thus, the actuator <NUM> is able to selectively move the cylinder <NUM>, and the control valve stem <NUM> or other component connected thereto to any point between an open position and a closed position.

Four pilot-operated check valves <NUM>, <NUM>, <NUM>, <NUM> and two check valves <NUM>, <NUM> are provided to control the flow of fluid within the self-contained actuator <NUM>. The first check valve <NUM> is positioned in a first high-pressure line <NUM> between the output <NUM> of the first pair of pumps <NUM> and the open side <NUM> of the cylinder <NUM>. The first check valve <NUM> is arranged to open in response to pressure being produced by the first pair of pumps <NUM> during operation to allow for the delivery of high-pressure fluid to the open side <NUM> of the cylinder <NUM>. When the first pair of pumps <NUM> are not operating, the first check valve <NUM> moves to a closed position. The second check valve <NUM> is positioned in a second high-pressure line <NUM> between the output <NUM> of the second pair of pumps <NUM> and the close side <NUM> of the cylinder <NUM>. The second check valve <NUM> is arranged to open in response to pressure being produced by the second pair of pumps <NUM> during operation to allow for the delivery of high pressure fluid to the close side <NUM> of the cylinder <NUM>. When the second pair of pumps <NUM> are not operating, the second check valve <NUM> moves to a closed position. In some constructions, the pumps <NUM> each include a check valve that performs this function such that the check valve <NUM> is not needed.

The first pilot-operated check valve <NUM> is positioned between the first accumulator <NUM> and the inlet <NUM> of the first pair of pumps <NUM> to control access to the fluid within the first accumulator <NUM>. A first pilot line <NUM> extends from the second high-pressure line <NUM> to the first pilot-operated check valve <NUM> to open the first pilot-operated check valve <NUM> in response to operation of the second pair of pumps <NUM>. When the first pilot-operated check valve <NUM> opens, low-pressure fluid can fill a first suction line <NUM> that feeds fluid to the first pair of pumps <NUM>. The second pilot-operated check valve <NUM> is positioned between the second accumulator <NUM> and the inlet <NUM> of the second pair of pumps <NUM> to control access to the fluid within the second accumulator <NUM>. A second pilot line <NUM> extends from the first high-pressure line <NUM> to the second pilot-operated check valve <NUM> to open the second pilot-operated check valve <NUM> in response to operation of the first pair of pumps <NUM>. When the second pilot-operated check valve <NUM> opens, low-pressure fluid can fill a second suction line <NUM> that feeds fluid to the second pair of pumps <NUM>.

The third pilot-operated check valve <NUM> is positioned in a first connector line <NUM> that connects the second high-pressure line <NUM> to the first suction line <NUM>. A third pilot line <NUM> extends from the first high-pressure line <NUM> to the third pilot-operated check valve <NUM> to open the third pilot-operated check valve <NUM> in response to high-pressure fluid flowing from the first pair of pumps <NUM>. When the third pilot-operated check valve <NUM> opens, high-pressure is released from the first pilot line <NUM> which closes the first pilot-operated check valve <NUM> and cuts off any flow from the first accumulator <NUM> to the first pair of pumps <NUM>. The close side <NUM> of the cylinder <NUM> is then connected through the third pilot-operated check valve <NUM> to the first suction line <NUM> such that fluid for the first pair of pumps <NUM> is drawn from the close side <NUM> of the cylinder <NUM> and delivered to the open side <NUM> of the cylinder <NUM> at high pressure.

The fourth pilot-operated check valve <NUM> is positioned in a second connector line <NUM> that connects the first high-pressure line <NUM> to the second suction line <NUM>. A fourth pilot line <NUM> extends from the second high-pressure line <NUM> to the fourth pilot-operated check valve <NUM> to open the fourth pilot-operated check valve <NUM> in response to high-pressure fluid flowing from the second pair of pumps <NUM>. When the fourth pilot-operated check valve <NUM> opens, high-pressure fluid is released from the second pilot line <NUM> which closes the second pilot-operated check valve <NUM> and cuts off any flow form the second accumulator <NUM> to the second pair of pumps <NUM>. The open side <NUM> of the cylinder <NUM> is then connected through the fourth pilot-operated check valve <NUM> to the second suction line <NUM> such that fluid for the second pair of pumps <NUM> is drawn from the open side <NUM> of the cylinder <NUM> and delivered to the close side <NUM> of the cylinder <NUM> at high pressure.

<FIG> illustrates the first or open mode <NUM> of operation when the first pair of pumps <NUM> are operating to direct fluid to the open side <NUM> of the cylinder <NUM> and to move the control valve stem <NUM> toward the open position. High-pressure fluid flows from the output <NUM> of the first pair of pumps <NUM>, fills the first high-pressure line <NUM> and flows into the open side <NUM> of the cylinder <NUM>, in turn forcing the piston <NUM> to move toward the close side <NUM>. High-pressure fluid also flows along the second pilot line <NUM> to the second pilot-operated check valve <NUM>. The high-pressure fluid causes the second pilot-operated check valve <NUM> to open, thereby opening the second accumulator <NUM> to the second suction line <NUM> to allow the second pair of pumps <NUM> to draw fluid from the second accumulator <NUM> upon their start-up.

The first high-pressure line <NUM> is also connected to the third pilot-operated check valve <NUM> such that the high-pressure fluid within the first high-pressure line <NUM> opens the third pilot-operated check valve <NUM>. With the third pilot-operated check valve <NUM> opened, the first suction line <NUM> is directly connected to the close side <NUM> of the cylinder <NUM> such that fluid is drawn from the close side <NUM> by the first pair of pumps <NUM>, pressurized, and delivered to the open side <NUM> of the cylinder <NUM>. When the third pilot-operated check valve <NUM> is opened, pressure in the first pilot line <NUM> is reduced and the first pilot-operated check valve <NUM> closes to inhibit fluid from flowing from the first accumulator <NUM> to the first pair of pumps <NUM>. In preferred constructions, the third pilot-operated check valve <NUM> opens before the first check valve <NUM> opens to assure a supply of fluid is available to the first pair of pumps <NUM> during operation.

With continued reference to <FIG>, the second pair of pumps <NUM> are in an idle state assuring that the second high-pressure line <NUM> is at a neutral or low pressure and the second check valve <NUM> is biased in its closed position. A small orifice <NUM> (<NUM> GPM) or other passage may be provided between the third pilot line <NUM> and the first suction line <NUM>. When the first pair of pumps <NUM> are in an idle position, the orifice <NUM> relieves pressure in the third pilot line <NUM> by directing high pressure fluid to the first suction line <NUM> and to the first accumulator <NUM> via the first pilot operated check valve <NUM> to assure that the third pilot operated check valve <NUM> closes. The fourth pilot-operated check valve <NUM> is also closed to assure that high-pressure fluid from the first pair of pumps <NUM> is not fed to the second suction line <NUM>. The second pilot-operated check valve <NUM> is in the open position as noted such that the second accumulator <NUM> is in fluid communication with the second suction line <NUM>.

Immediately upon starting the first pair of pumps <NUM>, there is no pressure in the first high-pressure line <NUM>. Without high-pressure from the first pair of pumps <NUM>, the third pilot-operated check valve <NUM> is closed and the first pilot-operated check valve <NUM> is closed with an initial supply of fluid for the first pair of pumps <NUM> being disposed in the first suction line <NUM> after being supplied by the first accumulator <NUM>. Once pressure is established in the first high-pressure line <NUM>, the state of the third pilot-operated check valve <NUM> switches and fluid is drawn from the close side <NUM> of the cylinder <NUM> rather than the first accumulator <NUM>.

For clarity, the following table illustrates the state of the various valves <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> during operation in the first, or open mode <NUM> in which the first pair of pumps <NUM> are active.

Turning now to <FIG>, the actuator <NUM> is illustrated during operation in the second mode in which the second plurality of pumps <NUM> are active to direct high-pressure fluid to the close side <NUM> of the cylinder <NUM> to move the control valve stem <NUM> toward a closed position.

With the second pair of pumps <NUM> in operation, the second high-pressure line <NUM> fills with high-pressure fluid, the second check valve <NUM> opens, and high-pressure fluid is directed along the first pilot line <NUM> and the fourth pilot line <NUM> to open the first pilot-operated check valve <NUM> and the fourth pilot-operated check valve <NUM> respectively. With the first pilot-operated check valve <NUM> open, the first suction line <NUM> is open to the first accumulator <NUM> to allow starting of the first pair of pumps <NUM>.

The opening of the fourth pilot-operated check valve <NUM> exposes the second suction line <NUM> to the open side <NUM> of the cylinder <NUM>, thereby allowing the second pair of pumps <NUM> to draw fluid from the open side <NUM> of the cylinder <NUM>. Opening the fourth pilot-operated check valve <NUM> also removes pressure from the second pilot line <NUM> which allows the second pilot-operated check valve <NUM> to close to inhibit fluid flow from the second accumulator <NUM> to the second suction line <NUM>. In preferred constructions, the fourth pilot-operated check valve <NUM> opens before the second check valve <NUM> opens to assure a supply of fluid is available to the second pair of pumps <NUM> during operation.

When the second pair of pumps <NUM> operate, the first pair of pumps <NUM> remain idle, thereby reducing the pressure in the first high-pressure line <NUM> such that the third pilot-operated check valve <NUM> closes. A small orifice <NUM> (<NUM> GPM) or other passage may be provided between the fourth pilot line <NUM> and the second suction line <NUM>. When the second pair of pumps <NUM> are in an idle position, the orifice <NUM> relieves pressure in the fourth pilot line <NUM> by directing high pressure fluid to the second suction line <NUM> and to the second accumulator <NUM> via the second pilot operated check valve <NUM> to assure that the fourth pilot operated check valve <NUM> closes.

Immediately upon starting the second pair of pumps <NUM>, there is no pressure in the second high-pressure line <NUM>. Without high-pressure from the second pair of pumps <NUM>, the fourth pilot-operated check valve <NUM> is closed and the second pilot-operated check valve <NUM> is closed such that the initial supply of fluid to the second pair of pumps <NUM> comes from fluid disposed in the second suction line <NUM> that was added to the second suction line <NUM> by the second accumulator <NUM> prior to the closure of the second pilot-operated check valve <NUM>. Once pressure is established in the second high-pressure line <NUM>, the state of the fourth pilot-operated check valve <NUM> switches and fluid is drawn from the open side <NUM> of the cylinder <NUM> rather than the second accumulator <NUM>.

For clarity, the following table illustrates the state of the various valves <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> during operation in the second, or close mode <NUM> in which the second pair of pumps <NUM> are active.

In operation, the controller <NUM> or control system operates to control the control valve stem <NUM> or other device being controlled by the actuator <NUM>. In one example, the control valve stem <NUM> is a control valve stem <NUM> for a control valve in a steam turbine. The control system monitors speed or load and adjusts the position of the control valve stem <NUM> to achieve a desired speed or load. If the control system determines that the position of the control valve stem <NUM> needs to change, a signal is sent to the appropriate pair of pumps <NUM>, <NUM> to activate the pair of pumps and to set a desired speed of operation. The speed of operation of the pair of pumps <NUM>, <NUM> controls the rate of flow of fluid to the cylinder <NUM> and therefore controls the speed at which the control valve stem <NUM> moves. If the control valve is being opened, the first pair of pumps <NUM> operate and the valves <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are configured as illustrated and described with regard to <FIG>. If the control valve is being closed, the second pair of pumps <NUM> operate and the valves <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are configured as illustrated and described with regard to <FIG>.

In one construction, a programable logic controller (PLC) is used to drive the motors <NUM> at the desired speed. In preferred constructions, pulse width modulation (PWM) is used to vary the speed of the motors <NUM>.

During operation, some fluid inevitably leaks from the actuator <NUM> or is otherwise lost. As illustrated in <FIG>, each of the first accumulator <NUM> and the second accumulator <NUM> includes a reservoir <NUM> and a level switch <NUM> that allows for the addition of fluid to the actuator <NUM> should such additions be necessary. In some actuators, a single reservoir <NUM> feeds both the first accumulator <NUM> and the second accumulator <NUM>.

<FIG> also illustrate a relief valve <NUM> that is coupled to both the open side <NUM> and the close side <NUM> of the cylinder <NUM>. The relief valve <NUM> operates to drain high-pressure fluid should a predetermined pressure be reached or exceeded within the cylinder <NUM>.

While the actuator <NUM> is described as using DC motors <NUM>, other motors such as AC, brushless DC, or switched reluctance motors could also be employed if desired.

While the constructions described with regard to <FIG> include check valves and pilot operated check valves, other types of valves could be used in place of the check valves and the pilot operated check valves. As such, the invention should not be limited to constructions that include only check valves and the pilot operated check valves. For example, solenoid-operated valves could be employed in place of or in conjunction with the check valves and the pilot operated check valves.

Claim 1:
An actuator (<NUM>) operable to move a valve stem (<NUM>) between an opened position and a closed position, the actuator (<NUM>) comprising:
a cylinder (<NUM>) including an open side (<NUM>) and a close side (<NUM>), wherein the cylinder (<NUM>) is intended to be coupled to the valve stem (<NUM>);
a first pump (<NUM>) connected to the cylinder (<NUM>) and operable to deliver a first high-pressure fluid to the open side (<NUM>) of the cylinder (<NUM>) to move the valve stem (<NUM>) toward the opened position; and
a second pump (<NUM>) separate from the first pump (<NUM>), the second pump (<NUM>) connected to the cylinder (<NUM>) and operable to deliver a second high-pressure fluid to the close side (<NUM>) of the cylinder (<NUM>) to move the valve stem (<NUM>) toward the closed position,
characterized in that the first pump (<NUM>) draws a first supply of fluid from the close side (<NUM>) of the cylinder (<NUM>) to deliver the first high-pressure fluid to the open side (<NUM>), and the second pump (<NUM>) draws a second supply of fluid from the open side (<NUM>) of the cylinder (<NUM>) to deliver the second high-pressure fluid to the close side (<NUM>).