Patent Description:
Fluid power equipment, such as, steam turbines employed in power plants, for example, thermoelectric power plants, nuclear power plants, or the like, typically employ valve arrangements, in order to regulate flow of steam according to load changes or to stop the flow of steam altogether. Such valve arrangements typically constitute single seated valve arrangements and double seated valve arrangements. A single seated valve arrangement, typically, employs one or more actuators and these are required to be operated at high pressures for circulating pressurized fluid such as oil through the actuators. However, the single seated valve arrangement involves complex piping design and high oil pressure hydraulic operation, and is therefore, not only cumbersome in construction but also a costly arrangement.

A double seated valve arrangement typically supports regulation of large volumes of fluid at a comparatively lower actuating force than the single seated valve arrangement thereby, enabling hydraulic actuation at low oil pressures. The double seated valve arrangement conventionally involves a pair of valve discs mutually separated from one another by a predefined distance, and designed to rest against a pair of valve seats during shutoff operation. However, in practicality, manufacturing of a valve arrangement typically involves faults that result in failure to achieve the desired precision, due to which positioning of valve seats within a valve arrangement is such that the valve discs fail to simultaneously rest on both the valve seats. Moreover, the valve discs fail to completely rest against the valve seats, thereby failing to provide a secure sealing at, at least one of the valve seats, which further results in an unwanted leakage of the steam leading to an uncontrolled steam turbine operation. However, leakage of the steam may also occur due to some other constructional features of a double seated valve arrangement.

<FIG> illustrates a sectional perspective view of a double seated valve arrangement <NUM> for a steam turbine (not shown), according to state of the art. Typically, such arrangement has a housing <NUM> having therein two or three control valves 102A, 102B and 102C, all of which have a combined actuation mechanism including a spindle <NUM> and control valve springs <NUM>, allowing the steam to flow out from the outlets 104A, 104B, and 104C when the control valves 102A, 102B, and 102C are in an open position and stop the outflow of steam through the outlets 104A-104C when the valves 102A-102C are in a closed position. The control valve springs <NUM> of the combined actuation mechanism are in direct contact with steam flowing, thereby affecting stiffness of the spring <NUM> which in turn leads to an incomplete closure of the control valves 102B and 102C when in closed position. This results in steam leakage which makes the steam turbine to run-up to certain speed levels which may not be acceptable by end customers.

In addition to the fluid leakage problem, double seated valve actuation arrangement requires higher machining and assembly time due to common actuation provided across valves. Furthermore, accessibility to the valves during servicing and maintenance becomes largely inconvenient. Furthermore, due to combined actuations, the valves must be operated, that is opened, in a sequential manner only resulting in a restricted operability, for example, being usable for inlet steam temperatures in the range of <NUM>-<NUM>. For higher inlet steam temperatures, a single seated valve arrangement must be used which results in higher costs.

Document <CIT> (describing a double seated valve arrangement according to the preamble of claim <NUM>) discloses a valve arrangement, comprising a housing and three control valves <NUM>, <NUM>, <NUM>, at least partially accommodated within the housing and displaceable between a closed position and an open position for controlling flow of a fluid in the fluid power equipment. Furthermore, D1 discloses two or more actuating mechanisms <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>, actuating the valves <NUM>, <NUM>, <NUM> and being in an operable connection with the two or more control valves <NUM>, <NUM>, <NUM>, respectively. Each of the actuating mechanisms <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM> is positioned axially perpendicular to a direction of fluid flowing through the housing.

Document <CIT> informs about a mixing valve arrangement <NUM>, comprising a housing <NUM>, and two valves <NUM>, <NUM>, located within a mixing chamber <NUM>, wherein the mixing chamber <NUM> is located within the housing. <FIG> shows the first valve <NUM> in an open position, whereas <FIG> shows said valve in a closed position. The arrangement <NUM> furthermore comprises two actuating mechanisms (valve member assembly <NUM>, <NUM>') for actuating the valves <NUM>, <NUM> and for being in an operable connection with the valves <NUM>, <NUM>, respectively.

Document <CIT> discloses a double seated valve arrangement <NUM>, comprising two valves <NUM>, <NUM>; <NUM>, <NUM>, accommodated in a housing <NUM>. The valves <NUM>, <NUM>; <NUM>, <NUM> are arranged in series in direction of flow <NUM>, <NUM>, <NUM>, <NUM>. There are control mechanisms <NUM>, <NUM> for actuating the valves <NUM>, <NUM>; <NUM>, <NUM> and by a valve spindle <NUM> they are in an operable connection with the valves <NUM>, <NUM>; <NUM>, <NUM>, respectively.

Therefore, it is an object of the present invention to provide a double seated valve arrangement to be employed, for example, in a fluid power equipment of the aforementioned kind, wherein the double seated valve arrangement has a housing at least partially accommodating there-within two or more control valves displaceable between a closed position and an open position for controlling flow of a fluid in the fluid power equipment, which is simple to design, is cost effective, and ensures leak-free operation within the fluid power equipment offering a higher degree of freedom while operating the fluid power equipment.

The double seated valve arrangement disclosed herein achieves the aforementioned object, by two or more actuating mechanisms that are in an operable connection with the two or more control valves respectively.

According to a first aspect of the present invention, a double seated valve arrangement as defined in claim <NUM> is provided. Advantageously, the double seated valve arrangement is provided for a fluid power equipment to control flow of fluid into the fluid power equipment. As used herein, "fluid power equipment" refers to turbomachinery, for example, a steam turbine.

The double seated valve arrangement disclosed herein, includes a housing. As used herein, the term "housing" refers to a valve chest unit of the fluid power equipment. The double seated valve arrangement includes two or more control valves at least partially accommodated within the housing. Advantageously, the double seated valve arrangement has three control valves. According to an embodiment, each of the control valves has a moveable member such as a valve stem which is displaceable between a closed position and an open position for controlling flow of a fluid in the fluid power equipment. The valve stem is displaceable, for example, slidable in a valve cage so as to assume either an open position or a closed position.

The double seated valve arrangement includes two or more actuating mechanisms actuating the two or more control valves. Advantageously, the double seated valve arrangement has three actuating mechanisms. The two or more actuating mechanisms are in an operable connection with the two or more control valves, respectively. As used herein, "actuating mechanism" refers to control mechanism, such as actuators controlling opening and closing of the control valves. The number of actuating mechanisms employed equals the number of control valves present in the double seated valve arrangement. The actuating mechanism includes a spindle coupled via a coupling element to the valve stem of the control valve so as to generate an axial reciprocating movement of the valve stem over the valve cages to open and close the control valve.

According to an embodiment of the present disclosure, the actuating mechanism is a linear actuator, for example, a linear servo motor. According to another embodiment of the present disclosure, the actuating mechanism is a rotary actuator, for example, a rotary servo motor. Advantageously, the actuating mechanism is a pull-type servo motor. A pull-type servo motor allows for insertion of the spindle from same side as the servo motor which results in a lower assembly time, ease of access for repair and maintenance, as well as lower machining requirements.

According to the present invention, the actuating mechanisms are configured to be operable independent of one another. The mutual exclusivity of control operation is achieved by having one actuating mechanism per control vale thereby, allowing independence of actuation. Further according to the present invention, the actuating mechanism is positioned to be generally axially perpendicular to a direction in which the fluid flows in and out of the housing, that is, the valve chest. This allows for minimal contact between the actuating mechanism, that is, the spring in the actuating mechanism and the fluid which allows the springs to retain their stiffness, which in turn improves the overall reliability of the design.

Also disclosed herein is a fluid power equipment, for example, a steam turbine comprising the aforementioned double seated valve arrangement for controlling flow of a fluid flowing therein, having one actuating mechanism per control valve employed. The double seated valve arrangement of the fluid power equipment is configured such that there is minimal contact established between each of the actuating mechanisms and the fluid flowing there-within.

The above-mentioned and other features of the invention will nc be addressed with reference to the accompanying drawings of the present invention. The illustrated embodiments are intended to illustrate, but not limit the invention.

Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide thorough understanding of one or more embodiments.

<FIG> illustrates a perspective view of a double seated valve arrangement <NUM> for a steam turbine (not shown), according to the present invention, having steam flowing therein in a direction shown by the flow arrows <NUM>. As illustrated in <FIG>, the double seated valve arrangement <NUM> comprises a housing <NUM>, that is, a valve body including there-within three valves (not shown) each of which have valve covers <NUM>, <NUM>, and <NUM>. The steam flows out through the outlets <NUM>, <NUM>, and <NUM> upon operation of respective valves. The valves are in connection with and are operable via actuating mechanisms <NUM>, <NUM>, and <NUM> respectively. The actuating mechanism <NUM>, <NUM>, and/or <NUM> includes a servomotor, for example, a pull type servomotor. Each actuating mechanisms <NUM> is positioned such that an axis A-A' passing axially there-through intersects nearly orthogonally with an axis C-C' passing axially through the housing <NUM> representing direction of fluid inflow and with an axis B-B' passing through the corresponding control valve and its outlet <NUM> representing direction of fluid outflow. This arrangement of the actuating mechanisms helps establish near zero contact of the control springs therein with the fluid flowing.

<FIG> illustrate sectional elevation views of actuation mechanism <NUM> employed for one of the control valves <NUM> of the double seated valve arrangement <NUM> shown in <FIG>, during an open position of the control valve <NUM> and a closed position of the control valve <NUM> respectively in <FIG> and <FIG>, according to the present disclosure. The servomotor <NUM> upon receiving a control pulse actuates a spindle 209A which in turn is connected to a valve stem 301B of the control valve <NUM>, via a coupling 301C. The movement is thus transferred from the spindle 209A to the valve stem 301B thereby, aligning or misaligning itself with valve cage 301A. As shown in <FIG>, the valve stem 301B is in alignment with the valve cage 301A thereby, putting the control valve <NUM> in an open position. As shown in <FIG>, the valve stem 301B is not in alignment with the valve cage 301A thereby, putting the control valve <NUM> in a closed position.

Claim 1:
A double seated valve arrangement (<NUM>) for a fluid power equipment, having:
- a housing (<NUM>);
- two or more control valves (<NUM>) at least partially accommodated within the housing (<NUM>) and displaceable between a closed position and an open position for controlling flow of a fluid in the fluid power equipment;
- two or more actuating mechanisms (<NUM>, <NUM>, or <NUM>) actuating the two or more control valves (<NUM>), wherein the two or more actuating mechanisms (<NUM>, <NUM>, <NUM>) are in an operable connection with the two or more control valves (<NUM>), respectively,
the double seated valve arrangement being characterised in that:
each of the two or more actuating mechanisms (<NUM>, <NUM>, <NUM>) are configured to be operable independent of one another,
and in that
each of the actuating mechanisms (<NUM>, <NUM>, <NUM>) is positioned generally axially perpendicular to a direction in which the fluid flows in (<NUM>) the housing (<NUM>) and a direction in which the fluid flows out (<NUM>) of the housing (<NUM>), and wherein the direction of fluid flowing in (<NUM>) the housing (<NUM>) is positioned generally axially perpendicular to the direction of fluid flowing out (<NUM>) of the housing (<NUM>).