Patent Publication Number: US-9903221-B2

Title: Electronically controllable and testable turbine trip system and method with redundant bleed manifolds

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 61/657,366, filed on Jun. 8, 2012, which is hereby incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     This patent relates generally to a redundant electronically controllable and testable trip system for use with, for example, a turbine and, more particularly, to an apparatus and method for controlling and testing turbine trip components while a turbine is operating in a manner that does not prevent the turbine from being tripped during the test and in a manner that enables disconnection and removal of bleed components of the trip system while the turbine trip system is operating on-line. 
     BACKGROUND 
     Hydraulic control systems are commonly used to control power generation machines, such as turbines. Known hydraulic control systems may include a trip control system or other protection system configured to stop the turbine (i.e., trip the turbine) upon the detection of an abnormal operating condition or other system malfunction. Unfortunately, the failure of one or more components associated with the trip control system to operate properly can prevent a turbine trip operation from occurring during emergency situations, which can lead to extensive damage to the turbine as well as other catastrophes, such as harm or injury to plant personnel. 
     Existing emergency trip systems such as, for example, the mechanical emergency trip system manufactured by General Electric Company (GE), include several components (e.g., valves, governors, blocks, ports, etc.) piped together to form a mechanically operated trip system. In a purely mechanical version, block and bleed functions are performed using non-redundant hydraulically actuated valves. However, in some cases, this system has been retrofit to include electronically controlled redundant bleed valves that perform a bleed operation to dump or remove pressure from a steam valve trip circuit that operates the turbine based on a two-out-of-three voting scheme. Once a bleed operation is performed, however, the GE mechanical trip system requires that the delivery of hydraulic fluid to the control port of the steam valve be blocked. Such a mechanical system results in a large, complex design having separate parts that may be expensive to manufacture. Additionally, the GE mechanical trip system requires an operator to manually perform tests of the blocking components. Still further, the mechanical nature of the blocking system of the GE mechanical trip system requires that an operator travel to the site of the turbine, which is undesirable. 
     While automatic trip systems have been developed in which the mechanical governor and associated linkages are replaced with a controller that automatically performs a trip operation, such automatic tripping systems typically include single, isolated valves or are limited to the bleed functionality of the tripping system. In particular, as described above with respect to the retrofit GE turbine system, it is known to use a set of three control valves connected to a controller to perform a two out of three voting scheme for performing a bleed function within a turbine trip control system. In this configuration, each of the control valves operates two DIN valves which are connected to one another in a manner that assures that, if two out of the three control valves are open, a hydraulic path is created through a set of two of the DIN valves to cause pressure to be bled from the trip port of the steam valve that provides steam to the turbine. The loss of pressure at the trip port of the steam valve closes the steam valve and trips or halts the operation of the turbine. With this configuration, the failure of any one of the control valves will not prevent a trip operation from being performed when desired or required and likewise, will not cause a trip to occur when such a trip is not desired. Additionally, because of the two out of three voting scheme, the individual components of this bleed circuit can be tested while the turbine is in operation without causing a trip to occur. 
     Unfortunately, the block circuit or block portion of a trip control system is an important part of the control circuit and, in many systems, there is no manner of being able to provide redundancy in the block circuit to assure proper operation of the block circuit if one of the components thereof fails, and no manner of electronically testing or operating the block circuit. In fact, the block circuit of many known turbine trip control systems must be operated manually, which is difficult to do as it requires an operator to go to and actually manually operate components of the block circuit (generally located near the turbine) after the bleed portion of the trip operation has occurred. Likewise, in systems that use manually operated components, there is no simple remote manner of testing the operation of the block portion of the trip control system. 
     In an attempt to address many of the shortcomings of these systems, U.S. Pat. No. 7,874,241 discloses a trip control system for use with, for example, turbines, that includes a block circuit having two or more redundant blocking valves connected in series within a pressure supply line to block the supply of hydraulic fluid within the pressure supply line and a bleed circuit having two or more bleed valves connected in parallel between the trip line and a return or dump line to bleed to the hydraulic fluid from the trip. The blocking valves and the bleed valves are actuated by one or more control valves under control of a process or safety controller which operates to cause a trip by first performing a bleed function using at least one of the bleed valves and then a block function using at least one of the blocking valves. Additionally, pressure sensors are disposed at various locations within the tripping control system and provide feedback to the controller to enable the controller to test each of the blocking and bleed valves individually, during operation of the turbine, without causing an actual trip of the turbine. In this manner, the trip control system of U.S. Pat. No. 7,874,241 provides reliable trip operation by providing redundant block and bleed functionality in combination with enabling the individual components of the block and bleed circuits to be tested while the turbine is online and operating but without preventing the turbine from being tripped, if necessary, during the test. 
     While the trip control system disclosed in U.S. Pat. No. 7,874,241 overcomes some of the problems with known trip control systems, it still has some shortcomings. In particular, while the trip control system described in U.S. Pat. No. 7,874,241 can be used to detect faulty solenoids or valves within the bleed circuit while operating on-line, the faulty components of the bleed circuit cannot be repaired or replaced until the turbine system is shut down or otherwise put out of service, making repair of the faulty components harder to implement. Additionally, the trip control system of U.S. Pat. No. 7,874,241 provides pressure from a pressure line to the trip valves and to trip header lines via orifices which must be sized to provide sufficient pressure at the trip header line during normal operation of the turbine to prevent a trip, while being small enough not to bleed a lot of oil (or other hydraulic fluid) from the pressure line to the trip header line and then to the drain or tank when a trip has been engaged. The use and sizing of these orifices, and therefore the operation of these orifices, always involves a trade-off of performance when in the normal operating state versus the tripped state. Moreover, the trip control system described in U.S. Pat. No. 7,874,241 includes manifolds that require various oil lines to be coupled thereto with tubes and fittings, leading to a system that is harder to install and configure, as well as one that has a lot of failure points with respect to the oil supply. 
     SUMMARY 
     A trip control system for use with, for example, turbines, includes a porting manifold that supports and provides fluid to two or more trip manifolds, wherein each of the trip manifolds includes a bleed circuit having two or more bleed valves connected in parallel between a trip header line and a return or dump line to bleed the hydraulic fluid pressure from the trip header line to thereby cause a trip. The bleed valves of each of the tripping manifolds are actuated by one or more control valves under control of a process or safety controller which operates to cause a trip by first performing a bleed function using at least one of the bleed valves and then a block function using blocking valves mounted in a block circuit. Additionally, pressure sensors are disposed at various locations within each of the trip manifolds and these sensors provide feedback to the controller to enable the controller to test each of the bleed valves individually, during operation of the turbine, without causing an actual trip of the turbine. In this manner, the trip control system provides reliable trip operation by providing redundant bleed functionality in combination with enabling the individual components of the bleed circuits to be tested while the turbine is online and operating but without preventing the turbine from being tripped, if necessary, during the test. Moreover, because of the use of the porting manifold and multiple trip manifolds to implement the bleed circuit, one of the trip manifolds can be removed from or isolated from the trip control system using various valves during on-line operation of the turbine to enable replacement of the one of the trip manifolds and/or of any of the various components installed thereon while the other trip manifold continues to operate to control a trip, if needed. In this manner, the trip control system is doubly redundant in that the trip control system includes (1) redundant trip manifolds operating in parallel so that each of the trip manifolds is able to be used to independently engage a trip of the turbine, meaning that one of the trip manifolds can be isolated and removed or repaired while the other trip manifold continues to operate to force a trip of the turbine, if necessary and (2) each of the trip manifolds includes redundant sets of valves and other trip components that enable the trip manifold to operate to engage a trip of the turbine in the presence of a failure of one of the sets of components on a trip manifold, or while various components of the trip manifold are being tested. 
     Still further, a porting manifold for use in a trip control system for controlling the operation of a controlled device using system pressure delivered from a fluid pressure source to an input of the controlled device includes a first trip manifold having a first bleed trip circuit and a second trip manifold having a second bleed trip circuit. The porting manifold includes a first fluid channel for coupling to a system pressure line. The first fluid channel is disposed within the porting manifold and extends between a system pressure inlet port, a first system pressure outlet port, and a second system pressure outlet port, wherein the first system pressure outlet port facilitates hydraulic coupling of the first fluid channel to the first trip manifold and the second system pressure outlet port facilitates hydraulic coupling of the first fluid channel to the second trip manifold. Additionally, the porting manifold includes a second fluid channel for coupling to a system drain line. The second fluid channel is disposed within the porting manifold and extends between a system drain outlet port, a first system drain inlet port, and a second system drain inlet port, wherein the first system drain line inlet port facilitates hydraulic coupling of the second fluid channel to the first trip manifold and the second system drain line inlet port facilitates hydraulic coupling of the second fluid channel to the second trip manifold. 
     Still further, a redundant trip manifold system for use in a trip control system for controlling the operation of a controlled device using system pressure delivered from a fluid pressure source to an input of the controlled device includes a bleed circuit hydraulically coupled between a trip header line and a return line, wherein the bleed circuit hydraulically and controllably connects the trip header line to the return line to reduce the fluid pressure within the trip header line at the controlled device. The bleed circuit includes a porting manifold having a plurality of fluid channels disposed within the porting manifold. Each fluid channel includes an inlet port at a surface of the porting manifold and an outlet port at the surface of the porting manifold. Additionally, the bleed circuit includes a first and second trip manifold removably coupled to the porting manifold. The first trip manifold includes a first bleed system having a plurality of redundant valve systems creating redundant bleed fluid paths connected in parallel between the trip header line and the return line, and the second trip manifold includes a second bleed system having a plurality of redundant valve systems creating redundant bleed fluid paths connected in parallel between the trip header line and the return line, wherein the first and second bleed systems are hydraulically coupled to operate simultaneously and independently of one another to remove system pressure from one or both of the trip header lines. 
     Still further, a trip control system for controlling the operation of a controlled device using fluid pressure delivered from a fluid pressure source to an input of the controlled device includes a controller, a fluid pressure line adapted to be connected between the fluid pressure source and the controlled device, a low pressure fluid return line, a block circuit disposed at least partially in the fluid pressure line and coupled to the low pressure fluid return line, and a bleed circuit hydraulically coupled between a fluid pressure line and a low pressure fluid return line, wherein the bleed circuit hydraulically and controllably connects the fluid pressure line to the low pressure fluid return line to reduce the fluid pressure within the fluid pressure line at the controlled device. The bleed circuit includes a porting manifold having a plurality of fluid channels. Each fluid channel of the plurality of fluid channels extends through the porting manifold from a first port at a surface of the porting manifold to a second port at the surface of the porting manifold. A first trip manifold is removably coupled to the porting manifold and includes a first bleed system, and a second trip manifold is removably coupled to the porting manifold and includes a second bleed system, wherein the first and second bleed systems are hydraulically coupled to operate simultaneously and independently of one another to remove system pressure from one or both of the trip header lines. 
     Still further, a trip manifold system for use in a trip control system for controlling the operation of a controlled device using system pressure delivered from a fluid pressure source to an input of the controlled device includes a bleed circuit hydraulically coupled between a trip header line and a return line, wherein the bleed circuit hydraulically and controllably connects the trip header line to the return line through a plurality of trip branches to reduce the fluid pressure within the trip header line at the controlled device. The bleed circuit includes a plurality of control valve systems, wherein each control valve system include an actuator valve hydraulically and controllably coupled to the control input of a supply pressure cutoff valve and the control inputs of a pair of trip valves, wherein operation of two or more of the control valve systems causes at least one bleed path to be created between the trip header line and the return line, while operation of only one of the control valve systems does not create a bleed path between the trip header line and the return line. 
     Still further, the trip control system includes a separate valve located within each of the redundant paths of each of the trip manifolds that operates to fully connect the system pressure line to the trip header line when the system is in a non-tripped state and to fully disconnect the system pressure line from the trip header line when the system is in a tripped state. This configuration enables a full pressure connection between the pressure line and a trip header line during a non-tripped condition to minimize false or inadvertent trips due to an under pressure condition at the trip header line, while preventing excessive bleeding from the pressure line to the tank or bleed circuit via the trip header line during a tripped condition. 
     Still further, the bleed portion of the redundant trip control circuit can be integrated into a small, single package that can be easily fit onto existing turbine systems, and uses o-ring fittings at the port connecting various fluid lines in the manifolds to one another to minimize the need to install tubing between various ones of the trip system components. These features enable an existing turbine trip control system to be retrofit or upgraded relatively inexpensively. 
     Still further, a method for operating a controlled device using a redundant trip manifold system providing control pressure delivered from a system pressure source to an input of the controlled device in a manner that enables one of a pair of redundant trip manifolds to be removed from a porting manifold while the controlled device is operating without preventing a tripping action includes disconnecting a first redundant trip manifold from the system pressure source, disconnecting the first redundant trip manifold from the control pressure, disconnecting the first redundant trip manifold from a drain line, removing the first redundant trip manifold from the porting manifold, and continuing to operate the controlled device in a manner that does not prevent a tripping action on a second redundant trip manifold while the first redundant trip manifold is removed. 
     Still further, a method of operating a controlled device using a trip manifold to deliver control pressure from a system pressure source to an input of a controlled device includes receiving a trip signal from a controller and executing a tripping action of the trip manifold in response to receiving the trip signal from the controller. The tripping action includes de-energizing an actuator valve of a first control valve system to couple a control input of a control valve of the first control valve system to a drain line, wherein the control valve closes a first fluid path between the system pressure line and a control pressure line, de-energizing an actuator valve of a second control valve system to couple a control input of a control valve of the second control valve system to the drain line, wherein the control valve closes a second fluid path between the system pressure line and the control pressure line, and de-energizing an actuator valve of a third control valve system to couple a control input of a control valve of the third control valve system to the drain line, wherein the control valve closes a third fluid path between the system pressure line and the control pressure line, and wherein the control pressure line is sealed from the system pressure line by the control valves of the first, second and third control valve systems. 
     Still further, a method of testing the operation of a redundant trip manifold system delivering control pressure to an input of a controlled device from a system pressure source in a manner that enables one of a plurality of control valve systems to be tested without preventing a tripping action includes de-energizing an actuator valve of a first control valve system to couple a control input of a control valve of the first control valve system to a drain line, wherein the control valve closes a fluid path between the system pressure line and a control pressure line. The de-energized actuator valve of the first control valve system further causing a first trip valve of the first control valve system to be coupled to the drain line and a control input of a second trip valve of the first control valve system to be coupled to the drain line. The method includes monitoring pressure at an output of the first trip valve of the first control valve system and monitoring pressure at an input of the second trip valve of the first control valve system. The method further includes comparing the monitored pressure at the output of the first trip valve of the first control valve system to a first redundant trip valve outlet pressure level, comparing the monitored pressure at the input of the second trip valve of the first control valve system to a second redundant trip valve inlet pressure level, executing a first command indicating an operating condition of the first trip valve of the first control valve system based on the comparison of the monitored pressure at the output of the first trip valve of the first control valve system to the first redundant trip valve outlet pressure level; and executing a second command indicating an operating condition of the second trip valve of the first control valve system based on the comparison of the monitored pressure at the inlet of the second trip valve of the first control valve system to the first redundant trip valve inlet pressure level. 
     In further accordance with the inventive aspects described herein, any one or more of the foregoing embodiments may further include any one or more of the following forms. 
     In one form, an attachment mechanism attaches the first and/or second trip manifolds to the porting manifold. The attachment mechanism may include a bore for receiving a bolt to removably attach the first trip manifold or the second trip manifold to the porting manifold. The bore may further include a threaded portion. 
     In another form, a first valve may be mounted to the porting manifold and coupled to the first system pressure outlet port to open the first system pressure outlet port and hydraulically couple the first trip manifold to the first fluid channel or close the first system pressure outlet port and hydraulically isolate the trip manifold from the first fluid channel. The first valve may be a pin valve that is electronically or manually controllable. 
     In another form, a second valve may be mounted to the porting manifold and coupled to the second system pressure outlet port to open the second system pressure outlet port and hydraulically couple the second trip manifold to the first fluid channel or close the second system pressure outlet port to hydraulically isolate the second trip manifold from the second fluid channel. The second valve may be a pin valve that is electronically or manually controllable. 
     In another form, a first surface and/or side of the porting manifold includes the system pressure outlet port, the second system pressure outlet port, the first system drain inlet port, and the second system drain inlet port; a second surface and/or side of the porting manifold includes the system pressure inlet port and the system drain outlet port; and a third surface and/or side includes the first valve of the first and/or second set of valves. 
     In another form, a third valve may be mounted to the porting manifold and coupled to the first drain inlet port to open the first drain inlet port and hydraulically couple the first trip manifold to the second fluid channel or close the first drain inlet port to hydraulically isolate the first trip manifold from the second fluid channel. The third valve may be a pin valve that is electronically or manually controllable. 
     In another form, a fourth valve may be mounted to the porting manifold and coupled to the second drain inlet port to open the second drain inlet port and hydraulically couple the second trip manifold to the second fluid channel or close the second drain inlet port to hydraulically isolate the second trip manifold from the second fluid channel. The fourth valve may be a pin valve that is electronically or manually controllable. 
     In another form, the porting manifold includes a third fluid channel for coupling to a first trip header line. The third fluid channel is disposed within the porting manifold and extends between a first trip header inlet port and a first trip header outlet port, wherein the first trip header inlet port facilitates hydraulic coupling of the third fluid channel to the first trip manifold. 
     In another form, the porting manifold includes a fifth valve coupled to the first trip header inlet port that opens the first trip header inlet port to hydraulically couple the first trip manifold to the third fluid channel or closes the first trip header inlet port to hydraulically isolate the first trip manifold from the third fluid channel. 
     In another form, the porting manifold includes a fourth fluid channel for coupling to a second trip header line. The fourth fluid channel is disposed within the porting manifold and extends between a second trip header inlet port and a second trip header outlet port, wherein the second trip header inlet port facilitates hydraulic coupling of the fourth fluid channel to the second trip manifold. 
     In another form, the porting manifold includes a sixth valve coupled to the second trip header inlet port that opens the second trip header inlet port to hydraulically couple the second trip manifold to the fourth fluid channel or closes the second trip header inlet port to hydraulically isolate the second trip manifold from the fourth fluid channel. 
     In another form, the porting manifold includes a fifth fluid channel for coupling to a tank. The fifth fluid channel is disposed within the porting manifold and extends between a first tank inlet port and a first tank outlet port, wherein the first tank inlet port facilitates hydraulic coupling of the first trip manifold to the tank. 
     In another form, the porting manifold includes a seventh valve coupled to the first tank inlet port that opens the first tank inlet port to hydraulically couple the first trip manifold to the fifth fluid channel or closes the first tank inlet port to hydraulically isolate the first trip manifold from the fifth fluid channel. 
     In another form, the porting manifold includes a sixth fluid channel for coupling to the tank. The sixth fluid channel is disposed within the porting manifold and extends between a second tank inlet port and a second tank outlet port, wherein the second tank inlet port facilitates hydraulic coupling of the second trip manifold to the tank. 
     In another form, the porting manifold includes an eighth valve coupled to the second tank inlet port that opens the second tank inlet port to hydraulically couple the second trip manifold to the sixth fluid channel or closes the second tank inlet port to hydraulically isolate the second trip manifold from the sixth fluid channel. 
     In another form, the first and/or second bleed system of the trip manifold system, or a redundant trip manifold system, includes a first, second, and third valve system. Each of the first, second, and third valve systems of the bleed system includes an actuator valve to operate two trip valves and a supply pressure cutoff valve, wherein operation of two or more of the first, second, and third valve systems of the bleed system causes at least one bleed fluid path to be created between the fluid pressure line and the low pressure fluid return line, while operation of only one of the valve systems of the first bleed system does not create a bleed fluid path between the fluid pressure line and the low pressure fluid return line. 
     In another form, a bleed path includes an open pair of trip valves within a trip branch. 
     In another form, a pressure transmitter is operatively coupled between a pair of trip valves within a trip branch, in particular, between the outlet port of the first trip valve and the inlet port of the second trip valve. 
     In another form, a pressure reduction orifice is operatively coupled between an outlet port of the first trip valve of a trip branch, an inlet port of the second trip valve of the trip branch, and the trip header line. 
     In another form, a first pressure reduction orifice is operatively coupled between an outlet port of the first trip valve of a trip branch, an inlet port of the second trip valve of the trip branch, and the drain line. 
     In another form, a take-off port is operatively coupled to the control input of the trip valve to facilitate connection with a controlling and/or monitoring device. 
     In another form, the flow path through the trip valve is larger than a flow path through the supply pressure cutoff valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of an embodiment of a hydraulic control system for a turbine including a bleed circuit and a block circuit; 
         FIG. 2  is a perspective view of one embodiment of a bleed circuit of a hydraulic trip control system having redundant electronically testable trip circuits on multiple trip manifolds; 
         FIG. 3  is a perspective view of a porting manifold illustrated in  FIG. 2 ; 
         FIG. 4  is a flow circuit diagram of the bleed circuit for the bleed circuit of the hydraulic trip control system of  FIGS. 1 and 2  including the porting manifold of  FIGS. 2 and 3  and the electronically testable trip manifolds of  FIG. 2 ; 
         FIG. 5  is a functional block diagram of an embodiment of a bleed circuit disposed on one of the trip manifolds of  FIGS. 2 and 4 ; 
         FIG. 6  is a more detailed schematic diagram of the bleed circuit components on one of the trip manifolds of  FIGS. 2 and 4 ; and 
         FIG. 7  is a three-dimensional perspective view of the bleed circuit having multiple trip manifolds a porting manifold and a tank as well as various valve and sensor components removably mounted thereto to form an integrated trip bleed circuit. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a trip control system  10  for use with a turbine  11  includes a block circuit  20  that provides internally (automatically) actuated and testable block functionality in combination with a bleed circuit  30  that provides redundant electronically actuated and testable bleed functionality and which, together, control the operation of a steam valve  40  to provide reliable trip operation for the turbine  11  during a safety trip and in a manner that enables components of the system to be repaired or replaced while the trip control system  10  and/or the turbine  11  are operating. 
     Generally speaking, the block circuit  20  and the bleed circuit  30  include redundant blocking and redundant bleed functionality that enables the components of the block circuit  20  and the bleed circuit  30  to be tested and replaced while the turbine  11  is online and operating and in a manner that does not prevent a tripping action during the testing or replacement of any of the components of the block circuit  20  or the bleed circuit  30 . Furthermore, the block circuit  20  and/or the bleed circuit  30  can be integrated into a small, single package that can be easily fit onto existing turbine trip control systems to enable such existing systems to be retrofit with the enhanced redundant, testable and replaceable bleed functionality described herein. 
     As will be understood from  FIG. 1 , a line  50  supplies hydraulic fluid at system pressure from a fluid or pressure source (not shown) through the block circuit  20  and then to the bleed circuit  30  to generally provide control pressure to individual valves within these circuits as well as to charge a trip header line. More particularly, the line  50  is connected to the hydraulic fluid source upstream of the block circuit  20 , and the fluid source supplies hydraulic fluid at system pressure to the line  50  both upstream and downstream of the block circuit  20 . Hydraulic fluid is also provided at or slightly below system pressure in one or more lines  52  (referred to herein as trip headers or trip header lines) downstream of the block circuit  20  depending on the operation of the block circuit  20 . The line or lines  52  are used in the bleed circuit  30  and are connected to a control input (also referred to herein as a trip input) of the steam valve  40  to control the operation of the steam valve  40 . Generally speaking, pressure over a certain amount within the trip header line  52  at the input of the steam valve  40  causes the steam valve  40  to remain open, which allows steam to enter the turbine  11  via the line  55  thereby allowing or causing operation of the turbine  11 . Additionally, a return hydraulic or pressure line  60 , which is a low pressure fluid line, is coupled from the steam valve  40  through the bleed circuit  30  to a return reservoir  62  (also called a tank) while a drain line  70 , which is also a low pressure fluid line, connects the bleed circuit  30  and the block circuit  20  to a hydraulic fluid drain  72 . If desired, the fluid drain  72  and the return reservoir or tank  62  may be the same reservoir, and thus the low pressure fluid lines  60  and  70  may be hydraulically coupled together via the tank  62  or otherwise. 
     As illustrated in  FIG. 1 , a controller  75 , which may be a safety controller, a process controller or any other desired type of controller and which may be implemented using distributed control system DSC technology, PLC technology, or any other type of control technology, is operatively coupled to each of the block circuit  20  and the bleed circuit  30 . During operation, the controller  75  is configured to automatically operate the bleed circuit  30  which removes pressure from the trip header line(s)  52  causing a trip of the turbine  11  and causing the block circuit  20  to close automatically due to the loss of pressure in the passage from the trip pressure line  52 . Additionally, the controller  75  is configured to receive pressure measurements from the block circuit  20  and the bleed circuit  30 , which enables the controller  75  to perform tests of the individual components of the block circuit  20  and the bleed circuit  30  to thereby test the operation of the components of these circuits. However, as will be understood from the discussion below, the block circuit  20  and the bleed circuit  30  are configured to operate to be able to perform a trip both while these circuits are being tested as well as while individual components of at least the bleed circuit  30  are being repaired or replaced. This functionality enables repair and replacement of components during operation of the turbine  11 , while in the past repair (at least of the bleed circuit  30 ) could only be performed when the turbine  11  was shut down. 
     It should be understood that the controller  75  may be remote from or local to the block circuit  20  and the bleed circuit  30 . Furthermore, the controller  75  may include a single control unit that operates and tests the block circuit  20  and the bleed circuit  30  or multiple control units, such as distributed control units, which are each configured to operate different ones of the block circuit  20  and the bleed circuit  30 . Generally speaking, the structure and configuration of the controller  75  are conventional and, therefore, are not discussed further herein. 
     During normal operation of the turbine  11 , which may be configured to drive a generator, for example, hydraulic fluid under pressure (e.g., operating oil) is supplied from a hydraulic fluid source (e.g., a pump) to the block circuit  20  and the bleed circuit  30  via the line  50 , and to the steam valve  40  via the hydraulic fluid path made up of the trip header line or lines  52  which are coupled to the line  50  as described in more detail herein. The hydraulic fluid may include any suitable type of hydraulic material that is capable of flowing along the hydraulic fluid paths  50  and  52  as well as the return path  60  and drain line  70 . As noted above, when the pressure in the fluid line(s)  52  at the trip input to the steam valve  40  is at a predetermined system pressure, the steam valve  40  allows or enables the flow of steam to the turbine  11 . However, when the pressure in the fluid line(s)  52  at the trip input of the steam valve  40  drops to a predetermined amount or a significant amount below system pressure or trip header pressure (which is typically slightly less than system pressure), the steam valve  40  closes or trips, which causes a shutdown of the turbine  11 . 
     Generally speaking, to cause a trip of the turbine  11 , the controller  75  first operates the bleed circuit  30  to bleed fluid from one or more of the trip header line(s)  52  at the trip input of the steam valve  40  to the return line  60  and then to the tank  62  to thereby remove the system pressure from the trip input of the steam valve  40  and cause a trip of the turbine  11 . Once a trip of the turbine  11  has occurred, the block circuit  20  automatically operates due to the loss of trip pressure in the line  52  to block the flow of hydraulic fluid within the line(s)  52  to prevent continuous supply of hydraulic fluid from the supply line  50  to the line(s)  52  while the turbine  11  is in a trip state. Additionally, as will be discussed in more detail, the controller  75  may control various components of the bleed circuit  30  and the block circuit  20  during normal operation of the turbine  11  to test those components without causing a trip of the turbine  11 . This testing functionality enables the components of the trip system  10  to be periodically tested, and replaced if necessary, during operation of the turbine  11  without requiring the turbine  11  to be shut down or taken off line either during the testing activities or the repair and replacement activities. This testing functionality also enables failed components of the block and bleed circuits  20  and  30  to be detected and replaced or repaired prior to the actual operation of a trip, thereby helping to assure reliable trip operation when needed. As will also be described in more detail, the bleed circuit  30  is configured to enable components of this circuit to be repaired or replaced during operation of the turbine without affecting the ability of the controller  75  to cause a trip of the turbine  11  via the steam valve  40 . 
     In one embodiment, the controller  75  operates the bleed circuit  30  to perform a trip of the turbine  11  in response to the detection of one or more abnormal conditions or malfunctions within the plant in which the turbine  11  is located. To help ensure that a trip operation is performed even if one or more components associated with the bleed circuit  30  fails to operate properly or while components of the bleed circuit  30  are being repaired or replaced, the bleed circuit  30  preferably includes a plurality, e.g., two, bleed systems that operate simultaneously and in parallel to one another. 
     Moreover, each of the bleed systems within the bleed circuit  30  preferably includes a plurality of redundant valve systems that create redundant bleed fluid paths connected in parallel between the trip header line(s)  52  and the return line  60 , wherein operation of any one of the parallel bleed fluid paths is sufficient to remove trip header pressure from the trip input of the steam valve  40  and thereby cause a trip of the turbine  11 . In one embodiment, each bleed system of the bleed circuit  30  may include three such valve systems, and each of the valve systems may include an actuator valve that controls two trip valves and a supply pressure cutoff valve. In this case, as will be described in more detail, operation of two or more of the valve systems of either of the bleed systems causes at least one bleed fluid path to be created between one of the lines  52  and the return line  60 , while operation of only one of the valve systems of either of the bleed systems does not create a bleed path between the lines  52  and the return path  60 . This configuration is known as a two out of three voting system, and assures that a malfunction of a single one of the valve systems of either of the bleed systems cannot cause a trip when the controller  75  is not trying to initiate a trip, while also assuring that a malfunction of a single one of the valve systems in each of the bleed systems will not prevent a trip from occurring when the controller  75  is trying to initiate a trip. 
       FIG. 2  illustrates a perspective view of an embodiment of a hydraulic bleed circuit  80  that may be used as the bleed circuit  30  of  FIG. 1 . The hydraulic bleed circuit  80  of  FIG. 2  includes a tank  82  (which may be the tank  62  of  FIG. 1 ), a porting manifold  84  and two trip manifolds  86   a  and  86   b  (also referred to as bleed trip manifolds) having various components mounted thereon. As will be understood, each of the bleed trip manifolds  86   a  and  86   b  includes valves, transmitters (or sensors), fluid paths and control lines needed to implement the bleeding operations described below with respect to a bleed system, and the bleed trip circuits implemented by the trip manifolds  86  and  86   b  operate independently and simultaneously to perform bleeding functions that initiate or prevent a trip of the steam valve  40  of  FIG. 1 . As illustrated in  FIG. 2 , the trip manifolds  86   a  and  86   b  are mounted onto and mate with the porting manifold  84  to establish various fluid paths between the trip manifolds  86   a  and  86   b , the porting manifold  84  and the tank  82  (which is mounted on the opposite side of the porting manifold  84  than the trip manifolds  86   a  and  86   b ). In particular, a pressurized fluid line, one or more trip header lines, a return or tank line and a drain line are disposed within the porting manifold  84  and are coupled to the bleed trip manifolds  86   a  and  86   b  and in some cases to the tank  82 . The bleed circuit implemented by each of the bleed trip manifolds  86   a  and  86   b  operates independently, but at the same time, to remove system pressure (or near system pressure) from one or both of the trip header lines  52  in response to the controller  75  (not shown in  FIG. 2 ) to thereby cause a trip of the turbine  11  of  FIG. 1 . However, as will be described in more detail below, one of the trip manifolds  86   a  or  86   b  may be removed from the porting manifold  84  while the other trip manifold  86   a  or  86   b  continues to operate so as to allow parts of the trip circuits implemented on the trip manifolds  86   a ,  86   b  to be repaired or replaced while the turbine  11  is on-line and without negating the ability of the controller  75  to initiate a trip during this repair or replacement activity. 
     As illustrated in  FIG. 2 , the porting manifold  84  includes fluid input and output ports  90 ,  91   a ,  91   b  and  92  in the form of a system pressure input port  90 , two trip header output ports  91   a ,  91   b  and a drain line output port  92 . The porting manifold  84  also includes tank ports on the top and bottom thereof (not shown in  FIG. 2 ). Additionally, in the embodiment of  FIG. 2 , eight mechanically or manually actuated valves  95 , for example, pin valves, are disposed on one side of the porting manifold  84  and various ones of the valves  95  are fluidly connected to and operable to close off one of a set of fluid lines within the porting manifold  84  connected between the ports  90 - 92 , the various ports of one of the trip manifolds  86   a  and  86   b  or fluid lines connected between the trip manifolds  86   a  and  86   b  and the tank  82 . Likewise, as can be seen in  FIG. 2 , bolts  97  extend through the trip manifolds  86   a  and  86   b  and operate to secure the trip manifolds  86   a  and  86   b  to the porting manifold  84  via threaded engagement with the porting manifold  84 . 
       FIG. 3  illustrates an expanded view of the porting manifold  84  of  FIG. 2  with the trip manifolds  86   a  and  86   b  and the tank  82  removed. As illustrated in dotted relief in  FIG. 3 , the porting manifold  84  includes a set of fluid channels or lines (i.e., fluid paths) disposed therein generally connecting the ports  90 - 92  and various other ports disposed in the top and the bottom of the porting manifold  84  as illustrated in  FIG. 3  with one another. In particular, a fluid channel  100  is disposed between the system pressure inlet port  90  and two system pressure outlet ports  110   a  and  110   b  and this fluid channel  100  may be the system pressure fluid line  50  of  FIG. 1 . Likewise, a fluid channel  101   a  is disposed between the trip header outlet port  91   a  and a trip header inlet port  111   a  while a fluid channel  101   b  is disposed between the trip header outlet port  91   b  and a trip header inlet port  111   b . The channels  101   a  and  101   b  may implement the trip header fluid lines  52  (also referred to herein as lines  52   a  and  52   b ) of  FIG. 1 . A fluid channel  102  is disposed between the drain line output port  92  and drain line inlet ports  112   a  and  112   b  and may used to implement the drain line  70  of  FIG. 1 . Still further, tank fluid lines  116   a  and  116   b  are connected between tank inlet ports  117   a  and  117   b  disposed in the top of the porting manifold  84 , and tank outlet ports  118   a  and  118   b  disposed in the bottom of the porting manifold  84 , respectively. Moreover, as illustrated schematically in  FIG. 3 , various different ones of the pin valves  95  are mounted on the side of the porting manifold  84  and operate to connect or isolate various different ones of the ports  110 ,  111 ,  112 , and  117  from the fluid channels  100 ,  101 ,  102  and  116 . As will be understood, a first set of four pin valves  95  labeled as A in  FIG. 3  are associated with the ports  110   a ,  111   a ,  112   a , and  117   a  which mate with ports on the first trip manifold  86   a  (not shown in  FIG. 3 ) while a second set of four pin valves  95  labeled as B in  FIG. 3  are associated with the ports  110   b ,  111   b ,  112   b , and  117   b  which mate with ports on the second trip manifold  86   b  (not shown in  FIG. 3 ). While the pin valves  95  are described herein as being manually actuated valves, these valves could be other types of valves or fluid switches that are manually or electronically controlled in any desired manner and that operate to close or isolate the ports on the porting manifold that connect the trip manifolds  86   a  and  86   b  to the rest of the trip circuit. 
       FIG. 4  illustrates a functional schematic diagram of the tank  82 , and the control elements disposed on the porting manifold  84  and on the trip manifolds  86   a  and  86   b  when the trip manifolds  86   a  and  86   b  on the one hand and the tank  82  on the other hand are mounted onto the opposite sides the porting manifold  84  (illustrated in  FIG. 3 ). As will be seen, when mounted together in this manner, the fluid lines  100 ,  101   a ,  101   b ,  102 ,  116   a  and  116   b  extend through the porting manifold  84  as described with respect to  FIG. 3  and are connected to various fluid lines in the trip manifolds  86   a  and  86   b . As illustrated in  FIG. 4 , the tank  82  includes a tank outlet port  119  that may be fluidly connected to a return or low pressure oil sump or reservoir via, for example a hose connection. As also illustrated in  FIG. 4 , a separate one of the pin valves  95  is connected in each of the fluid lines  100 ,  101   a ,  101   b ,  102 ,  116   a  and  116   b  and is operable to cut off or allow flow in the respective fluid line  100 ,  101   a ,  101   b ,  102 ,  116   a  and  116   b  from one port to another to thereby either isolate or connect the ports  90 ,  91   a ,  91   b ,  92 ,  118   a  and  118   b  from the various ports on the trip manifolds  86   a  and  86   b . As will be understood, the pin valves  95  may generally be two position (open or close) type valves that allow full flow through a fluid channel or that seal the channel in which the pin valve is installed. However, other types of valves may be used instead, including valves that are controllable to be disposed over a range of positions between a fully open position and a fully closed position. 
       FIG. 5  illustrates a general operational diagram of one of the bleed systems disposed on one of the trip manifolds  86   a  or  86   b  of  FIG. 4  disposed within and on one of the trip manifolds  86   a  or  86   b  in more detail, it being understood that the other bleed system disposed on the other trip manifold  86   a  or  86   b  is similar in construction and operation. In particular, the portion of the bleed circuit  30  disposed on the trip manifold  86   a  or  86   b  includes a plurality of redundant trip branches  200 ,  210  and  220  through which hydraulic fluid may flow from the system pressure line  50  to the pressure trip header line  52  and from the trip header line  52  to the return path  60  during a trip operation, thereby removing or bleeding pressure from the line  52  at the trip input of the steam valve  40  to stop operation of the turbine  11 . As indicated in  FIG. 5 , each of the trip branches  200 - 220  includes a control valve system (e.g., one of valve systems  232 ,  234 , or  236 ) and two trip valves (e.g., trip valves  230  and  280 ,  240  and  260 , or  250  and  270 ). When two or more of the control valve systems  232 ,  234  and  236  are operating, and both trip valves of a single trip branch are open, a bleed path is created between trip header line  52  and the return path  60 , and hydraulic fluid is thereby permitted to flow from the trip header  52  to the return path  60 , which reduces the pressure in the trip header line  52 . However, when either of the two valves of a single branch  200 - 220  is closed, hydraulic fluid is blocked or prevented from flowing from the trip header line  52  to the return line  60  through that branch. If all branches are blocked, then the pressure in the trip header line  52  remains at or near system pressure which keeps the steam valve  40  ( FIG. 1 ) open and allows the turbine  11  to continue to run. 
     As can be seen from  FIG. 5 , the plurality of trip valves  230 - 280  includes a first trip valve (A1)  230 , a second trip valve (B1)  240 , a third trip valve (C1)  250 , a fourth trip valve (C2)  260 , a fifth trip valve (A2)  270 , and a sixth trip valve (B2)  280 . In one embodiment, each of the first through sixth trip valves  230 - 280  may be a two-way DIN cartridge valve having a pair of operational ports (A, B) and a control port (X) in which the operational ports (A, B) may be normally biased in an open position (i.e., in which fluid flow between the two ports is allowed) by a spring or other mechanical device (not shown). In the biased position, hydraulic fluid may pass through or between the operational ports (A, B) of the trip valves  230 - 280  and thus the valves  230 - 280  will open in response to the loss of control pressure at the control port (X). DIN cartridge valves are well known in the art and are, therefore, not described in further detail herein. As will be understood, when any of the trip valves  230 - 280  is in the open position, hydraulic fluid may flow from port A to port B of that valve. To the contrary, when control pressure is applied at the control port (X) of any of the trip valves  230 - 280 , the trip valves  230 - 280  to which control pressure is provided locks the valve in a closed position to thereby block or prevent the flow of hydraulic fluid between the operational ports (A, B) of that valve. As will be described in more detail below, the control valve systems  232 ,  234 , or  236  operate to control the flow of fluid from the system pressure line  50  to the trip header line  52  in each of the branches  200 - 220  as well as to control the flow of fluid from the system pressure line  50  to the control inputs (X) of the valves  230 - 280  to thereby control operation of the a trip valves  230 - 280 . 
     As illustrated in  FIG. 5 , the first trip branch  200  includes the first trip valve (A1)  230  and the sixth trip valve (B2)  280  coupled between the hydraulic fluid path  52  (i.e., the trip header line) and the return path  60 . Specifically, port A of the first trip valve (A1)  230  is hydraulically coupled to the hydraulic fluid path  52  via a hydraulic conduit  282 , port B of the first trip valve (A1)  230  is hydraulically coupled to port A of the sixth trip valve (B2)  280  via hydraulic conduit  283 , and port B of the sixth trip valve (B2)  280  is hydraulically coupled to the return path  60  via a hydraulic conduit  284 . 
     As is evident in  FIG. 5 , the second trip branch  210  includes the second trip valve (B1)  240  and the fourth trip valve (C2)  260  coupled between the hydraulic fluid path  52  (i.e., the trip header line) and the return path  60 . Specifically, port A of the second trip valve (B1)  240  is hydraulically coupled to the hydraulic fluid path  52  via a hydraulic conduit  285 , port B of the second trip valve (B1)  240  is hydraulically coupled to port A of the fourth trip valve (C2)  260  via a hydraulic conduit  286 , and port B of the fourth trip valve (C2)  260  is hydraulically coupled to the return path  60  via a hydraulic conduit  287 . 
     Still further, the third trip branch  220  includes the third trip valve (C1)  250  and the fifth trip valve (A2)  270  coupled between the hydraulic fluid path  52  and the return path  60 . Specifically, port A of the third trip valve (C1)  250  is hydraulically coupled to the hydraulic fluid path  52  via a hydraulic conduit  288 , port B of the third trip valve (C1)  250  is hydraulically coupled to port A of the fifth trip valve (A2)  270  via a hydraulic conduit  289 , and port B of the fifth trip valve (A2)  270  is hydraulically coupled to the return path  60  via a hydraulic conduit  290 . 
     For the sake of illustration, the control valves that make up the control valve systems  232 ,  234  and  236  which operate to control the operation of the trip valves  230 - 280  are not depicted in  FIG. 5 . However, as illustrated in  FIG. 5 , each control valve system  232 ,  234 ,  236  is coupled between the system pressure line  50  and the trip header line  52  and each control valve system  232 ,  234 ,  236  is connected to control the operation of two different trip valves in different ones of the trip branches  200 - 220 . Thus, as illustrated in  FIG. 5 , the first control valve system  232  is connected to the control input (X) of the trip valve  230  (in the first trip branch  200 ) and to the control input (X) of the fifth trip valve  270  (in the third trip branch  220 ). Likewise, the second control valve system  234  is connected to the control input (X) of the trip valve  240  (in the second trip branch  210 ) and to the control input (X) of the sixth trip valve  280  (in the first trip branch  200 ) while the third control valve system  236  is connected to the control input (X) of the third trip valve  250  (in the third trip branch  220 ) and to the control input (X) of the fourth trip valve  260  (in the second trip branch  210 ). 
     As will be described in more detail with respect to  FIG. 6 , one or more control valves or actuators within the control valve systems  232 ,  234 ,  236  control the operation of each of a pair of the trip valves  230 - 280 . More particularly, a first actuator in the valve system  232  simultaneously controls the operation of the valves A1 and A2 ( 230 ,  270 ), a second actuator in the valve system  234  simultaneously controls the operation of the trip valves B1 and B2 ( 240 ,  280 ), and a third actuator in the valve system  236  simultaneously controls the operation of the trip valves C1 and C2 ( 250 ,  260 ). 
       FIG. 6  illustrates an example schematic diagram depicting one manner of implementing the bleed circuit depicted in  FIG. 5  in which the first through sixth trip valves (A1, A2, B1, B2, C1, C2)  230 - 280  are connected between the hydraulic fluid line  52  and the return line  60 . In addition, each of the valve systems  232 ,  234 ,  236  is illustrated as including two control valves  232   a ,  232   b , or  234   a ,  234   b , or  236   a ,  236   b  with the control valves  232   a ,  234   a ,  236   a  being labeled as A3, B3 and C3, respectively. In addition, each of the valves  232   b ,  234   b ,  236   b  is an electronically controlled solenoid valve that is coupled to and controlled by the controller  75  of  FIG. 1 . These solenoid valves are also labeled as SOL-A, SOL-B, SOL-C in  FIG. 6 . During operation, when a solenoid valve  232   b ,  234   b  or  236   b  is energized, the solenoid valve  232   b ,  234   b ,  236   b  opens to connect the system pressure line  50  to the control inputs of two of the trip valves, as described with respect to  FIG. 5  and to provide system pressure to the control input (3) of the other control valve  232   a ,  234   a  or  236   a . When energized (i.e., when system pressure is applied to the control input 3), the control valve  232   a ,  234   a  or  236   a  opens to provide a connection between the system pressure line  50  and the trip header line  52  to thereby establish trip header pressure at the trip header line  52 . Generally speaking, the valve systems  232 ,  234 ,  236  are configured to be fail safe, so that the controller  75  must energize the solenoid valves  232   b ,  234   b ,  236   b , to cause the system pressure line  50  to be fluidly connected to the trip header line  52  and to cause the pairs of trip valves A1, A2 or B1, B2, or C1, C2 (controlled by the solenoid valves  232   b ,  234   b ,  236   b ) to be closed to block the bleed paths between the trip header line  52  and the return line  60 . In this case, loss of electronic control of a solenoid valve  232   b ,  234   b , or  236   b  will result in the closure of the associated control valve  232   a ,  234   a  or  236   a  (and thus the disconnection of one of the paths from the system pressure line  50  to the trip header line  52 ) as well as opening of the trip valves having control inputs connected to the solenoid valve (which may open a bleed path from the trip header line  52  to the return line  60 ). 
     Again, as illustrated in  FIG. 6 , the first solenoid actuator  232   b  within the valve system  232  is operatively coupled to a control port (3) of both the first trip valve (A1)  230  and the fifth trip valve (A2)  270  via hydraulic conduit  295  and simultaneously controls the application of control pressure at the control port (3) of both the first trip valve (A1)  230  and the fifth trip valve (A2)  270 . When energized, the first actuator  232   b  is configured to activate both the first trip valve (A1)  230  and the fifth trip valve (A2)  270  to lock the first and fifth trip valves  230 ,  240  in their closed position. Simultaneously, the actuator  232   b  provides control pressure to control valve  232   a  (A3) to open the control valve  232   a  and provide a first fluid connection between the system pressure line  50  and the trip header line  52 . Similarly, the second actuator  234   b  is operatively coupled to a control port (3) of both the second trip valve (B1)  240  and the sixth trip valve (B2)  280  via hydraulic conduit  296  and controls the application of control pressure at the control port (3) of both the second trip valve (B1)  250  and the sixth trip valve (B2)  280 . Thus, when energized, the second actuator  232   b  is configured to activate both the second trip valve (B1)  240  and the sixth trip valve (B2)  280  to lock the second and third trip valves  240 ,  280  in their closed position. Simultaneously, the actuator  234   b  provides control pressure to control valve  234   a  (B3) to open the control valve  234   a  and provide second a fluid connection between the system pressure line  50  and the trip header line  52 . Still further, the third actuator  236   b  is operatively coupled to a control port (3) of both the third trip valve (C1)  250  and the fourth trip valve (C2)  260  via hydraulic conduit  297  and controls the application of control pressure at the control port (3) of both the third trip valve (C1)  250  and the fourth trip valve (C2)  260 . When energized, the third actuator  236   b  is thus configured to activate both the third trip valve (C1)  250  and the fourth trip valve (C2)  260  to lock the third and the fourth trip valves  250 ,  260  in their closed position. Simultaneously, the actuator  236   b  provides control pressure to control valve  236   a  (C3) to open the control valve  236   a  and provide a third fluid connection between the system pressure line  50  and the trip header line  52 . The flow paths through the trip valves  230  to  280  may be sized to be larger than the flow paths through or between the inputs (1) and (2) of the control valves  232   a ,  234   a  and  236   a  to assure that any one bleed path can bleed trip header pressure from the line  52  even if two or more of the control valves  232   a ,  234   a  and  236   a  is open. 
     As will be understood, each of the first, second, and third actuators  232   b ,  234   b ,  236   b  is operatively coupled to the controller  75 , which is configured to energize and de-energize each of the first, second, and third actuators  232 , b ,  234   b ,  236   b  either separately or simultaneously. In one embodiment, each of the first, second, and third actuators  232   b ,  234   b ,  236   b , when energized by the controller  75 , supplies control pressure from the system pressure line  50  to the control port of the associated trip valves  230 - 280  to lock the associated trip valves  230 - 280  in their closed position. Likewise, when de-energized by the controller  75 , the first, second and third actuators  232   b ,  234   b ,  236   b  connect the control port of the associated trip valves  230 - 280  to the drain line  70 . 
     As depicted in  FIGS. 5 and 6 , the bleed circuit  30  disposed on each trip manifold  86   a  and  86   b  further includes a pressure reduction orifice  299   a  located between the hydraulic conduit  283  and the hydraulic fluid path  52 , a pressure reduction orifice  299   b  located between the hydraulic conduit  286  and the hydraulic fluid path  52 , and a pressure reduction orifice  299   c  located between the hydraulic conduit  289  and the hydraulic fluid path  52 . Additionally, the bleed circuit  30  includes a pressure reduction orifice  301   a  located between the hydraulic conduit  283  and the drain line  70 , a pressure reduction orifice  301   b  located between the hydraulic conduit  286  and the drain line  70 , and a pressure reduction orifice  301   c  located between the hydraulic conduit  289  and the drain line  70 . During normal operating conditions when all of the first-sixth trip valves  230 - 280  are in the closed position, the pressure in the hydraulic conduit  283 , the pressure in the hydraulic conduit  286 , and the pressure in the hydraulic conduit  289  are all maintained at a reduced pressure that is less than trip pressure (i.e., the pressure within the line  52 ) but at a pressure above zero, with the amount or value of the fluid pressure being based on the size and configuration of the orifices  299   a - 299   c  and  301   a - 301   c . Generally speaking, the orifices  299   a - 299   c  are sized to permit a gradual flow of fluid from the line  52  into the conduits  283 ,  286  and  289  while the orifices  301   a - 301   c  are sized to permit a gradual flow of fluid out of the conduits  283 ,  286  and  289  when the pressure in the conduits  283 ,  286  and  289  reaches a predetermined amount (which will be a pressure less than the pressure in the line  50 , such as at about half of the system pressure in the line  50 ). In one embodiment, the orifices  299   a - 299   c  and  301   a - 301   c  may be approximately 0.031 inches in diameter, although other sizes may be used if desired. The purpose of providing the reduced fluid pressure in the conduits  283 ,  286  and  289  will be described in more detail in the following discussion. 
     To ensure that all of the components work properly to perform a trip operation when required or desired, the components associated with the bleed circuit  30  may be tested while the turbine  11  is operating online without interrupting operation of the turbine  11 . For testing purposes, the bleed circuit  30  includes first, second, and third pressure transmitters (PT1-PT3)  300 - 320  configured to sense the pressure between the trip valves in the first, second, and third trip branches  200 - 220 , respectively, and, in particular, to sense the fluid pressure in the conduits  283 ,  286  and  289 , respectively. Additionally, as illustrated best in  FIG. 6 , the bleed circuit  30  may include first, second, and third take offs for externally connected pressure sensors labeled as TP-A, TP-B and TP-C in  FIG. 6 , which are configured to enable the sensing of the fluid pressure in hydraulic conduits  295 - 297 , respectively. Likewise, as illustrated in  FIG. 6 , pressure sensor connection may be established at other points in the circuit, so as to measure pressure in the drain line  70  (at TP-DR), pressure in the system pressure line  50  (at TP-P), pressure in the trip header line  52  (at TP-TH) and pressure in the return line  60  (at TP-R). While Schrader valves are used in the embodiment of  FIG. 6 , other types of valve may be used to enable externally pressure sensors to be mounted or connected to the trip circuit of  FIG. 6 . Alternatively, pressure sensors or pressure transmitters may be mounted on or in the trip manifolds to measure these or other pressures within the trip circuit. 
     In any event, as illustrated in  FIG. 6 , a pressure sensor could be connected at TP-A to sense the fluid pressure in the hydraulic conduit  295  which couples the first actuator  232   b  to the control port of both the first trip valve (A1)  230  and the fifth trip valve (A2)  270 , a pressure sensor could be connected at TP-B to sense the fluid pressure in the hydraulic conduit  296  that couples the second actuator  234   b  to the control port of both the second trip valve (B1)  240  and the sixth trip valve (B2)  280 , and a pressure sensor could be connected at TP-C to sense the fluid pressure in a hydraulic conduit  297  that couples the third actuator  236   b  to the control port of both the third trip valve (C1)  250  and the fourth trip valve (C2)  260 . If desired, these pressure sensors could also be connected the controller  75  although they need not be. As will be described in greater detail below, the operation of the components associated with each of the plurality of redundant valve systems or branches  200 - 220  may be tested by monitoring the fluid pressure in each of the hydraulic conduits  283 ,  286 ,  289  and, if desired,  295 ,  296 ,  297 . 
     During normal operating conditions (i.e., when the turbine  11  is not tripped), the controller  75  is configured to simultaneously energize each of the first, second, and third solenoid actuators  232   b ,  234   b ,  236   b  to activate the first-sixth trip valves  230 - 280 . When the first, second, and third solenoid actuators  232   b ,  234   b ,  236   b  are energized, control pressure is supplied at the control port of each of the first-sixth trip valves  230 - 280 , thereby causing the first-sixth trip valves  230 - 280  to be locked in the closed position. At this time, hydraulic fluid is blocked or prevented from flowing between the operational ports of those valves and, as a result, no direct path exists between the hydraulic fluid path  52  and the return path  60 . This configuration maintains sufficient hydraulic pressure within the hydraulic fluid path  52  at the trip input of the steam valve  40  to hold the steam valve  40  in the open position. When the steam valve  40  is held in the open position, steam is delivered to the turbine  11  and the turbine  11  operates normally. 
     During abnormal conditions or malfunctions, it may be desirable to stop operation of the turbine  11  to prevent damage to the turbine  11  and/or to prevent other catastrophes. To do so, the controller  75  creates a bleed fluid path between the hydraulic fluid path  52  and the return path  60  to thereby remove hydraulic pressure from the hydraulic fluid path  52 . The bleeding of pressure from the fluid path  52  causes the trip input of the steam valve  40  to become depressurized, thereby moving the steam valve  40  to the closed position and preventing the delivery of steam to the turbine  11 . This action causes and is referred to as a tripping or halting of the turbine  11 . 
     To determine if a trip is needed, the controller  75  may monitor turbine parameters such as, for example, turbine speed, turbine load, vacuum pressure, bearing oil pressure, thrust oil pressure, and the like using various sensors (not shown). As will be understood, the controller  75  may be configured to receive information from these sensors during operation of the turbine  11  to monitor operating conditions of the turbine  11 , to thereby detect abnormal operating conditions and problems associated with the turbine  11  that may require that the turbine  11  be shut down. In response to information received from the operational sensors such as, for example, the detection of an overspeed condition, the controller  75  may cause a trip operation to be performed. To actually effectuate such a trip, the components associated with only two of the redundant valve systems or branches  200 - 220  of the bleed circuit  30  need to operate properly. However, to cause a trip, the controller  75  will generally operate (actually deactivate) each of the actuators  232   b ,  234   b ,  236   b  to thereby attempt to open each of the trip valves  230 - 280  and create three parallel bleed fluid paths between the hydraulic fluid line  52  and the return path  60 . In this manner, the trip control system helps to assure that a trip will be performed even if one of the components of the bleed circuit  30  fails to operate properly because, in that case, at least one bleed fluid path will still be created or opened between the hydraulic fluid path  52  and the return path  60 , thus causing a trip. 
     More particularly, during a trip operation, the controller  75  may be configured to simultaneously de-energize each of the first, second, and third actuators  232   b ,  234   b ,  236   b , so that hydraulic fluid is permitted to flow through each of the first trip branch  200 , the second trip branch  210 , and the third trip branch  220 , thereby dumping pressure off the trip input of the steam valve  40  to stop operation of the turbine  11 . Additionally, the control valves  232   a ,  234   a ,  236   a  will close due to loss of pressure at their control inputs and disconnect the system pressure line  50  from the trip header line  52 . As will be understood from  FIG. 3 , when the controller  75  de-energizes the first actuator  232   b , the control ports of both the first trip valve (A1)  230  and the fifth trip valve (A2)  270  are coupled through the actuator  232   b  to the drain  70 . As a result, control or system pressure from the system pressure line  50  is released or removed from each of the control ports of the first trip valve (A1)  230  and the fifth trip valve (A2)  270 , and the pressure within the control line for these valves is diverted or bled to the drain or tank  70 . At this time, both of the first trip valve (A1)  230  and the fifth trip valve (A2)  270  move from the closed position to the open position and hydraulic fluid is permitted to flow through the operational ports (A, B in  FIG. 5  or 1, 2 in  FIG. 6 ) of the first trip valve (A1)  230  and the fifth trip valve (A2)  270 . 
     Similarly, when the controller  75  de-energizes the second actuator  234   b , the control ports of both the second trip valve (B1)  240  and the sixth trip valve (B2)  280  are coupled through the actuator  234   b  to the drain  70 . As a result, control or system pressure from the line  50  is released or removed at each of the control ports of the second trip valve (B1)  240  and the sixth trip valve (B2)  280 , and the pressure within the control line for these valves is immediately diverted or bled to the drain  70 . At this time, both of the second trip valve (B1)  240  and the sixth trip valve (B2)  280  move from the closed position to the open position which enables hydraulic fluid to flow through the operational ports of the second trip valve (B1)  240  and the sixth trip valve (B2)  280 . 
     Likewise, when the controller  75  de-energizes the third actuator  236   b , the control ports of both the third trip valve (C1)  250  and the fourth trip valve (C2)  260  are coupled through the actuator  236   b  to the drain  70 . As a result, control or system pressure is released or removed from each of the control ports of the third trip valve (C1)  250  and the fourth trip valve (C2)  260 , and the pressure within the control line for these valves is immediately diverted or bled to the drain  70 . At this time, both of the third trip valve (C1)  250  and the fourth trip valve (C2)  260  move from the closed position to the open position which permits hydraulic fluid to flow through the operational ports of the third trip valve (C1)  250  and the fourth trip valve (C2)  260 . 
     As will be understood, to effectuate a trip operation, hydraulic fluid in the fluid path  52  need only flow to the return path  60  via one of the first, second, or third trip branches  200 - 220  to, thereby depressurize the trip input of the steam valve  40  and stop operation of the turbine  11 . As a result, the components associated with only two of the redundant valve systems A1, A2, A3, B1, B2, B3 or C1, C2, C3 need to operate properly to perform a trip operation. In other words, if all of the components associated with the first valve system (e.g., the first actuator  232   b , the first trip valve (A1)  230 , the fifth trip valve (A2)  270  and the control valve (A3)  232   a ) operate properly, and if all of the components associated with the second valve system (e.g., the second actuator  234   b , the second trip valve (B1)  240 , and the sixth trip valve (B2)  280  and the control valve (B3)  234   a ) operate properly, then hydraulic fluid may flow from the hydraulic fluid path  52  to the return path  60  via the first trip branch  200 , thereby dumping trip pressure off the steam valve  40  and stopping operation of the turbine  11 . Similarly, if all of the components associated with the second valve system operate properly, and if all of the components associated with the third valve system (e.g., the third actuator  236   b , the third trip valve (C1)  250 , and the fourth trip valve (C2)  260  and the control valve (C3)  236   a ) operate properly, then hydraulic fluid may flow from the hydraulic fluid path  52  to the return path  60  via the second trip branch  210 , thereby dumping trip pressure off the steam valve  40  and stopping operation of the turbine  11 . Still further, if all of the components associated with the third and first valve systems operate properly, then hydraulic fluid may flow from the hydraulic fluid path  52  to the return path  60  via the third trip branch  220 , thereby dumping trip pressure off the steam valve  40  and stopping operation of the turbine  11 . In this manner, redundancy is achieved by requiring that the components associated with only two of the three valve systems operate properly to perform a trip operation. In other words, the failure of one or more components associated with one of the branches  200 - 220  will not prevent the controller  75  from performing a trip operation to stop the turbine  11 . 
     Still further, it is desirable, from time to time, to test the components associated with the bleed circuit  30  while the turbine  11  is online and operating to ensure that all of these components work properly. However, it is desirable to test these components without interrupting the operation of the turbine  11 , as stopping the turbine  11  for testing or maintenance is costly and undesirable. In the system illustrated in  FIGS. 5 and 6 , the controller  75  may remotely test the operation of each of the redundant valve branches  200 - 220  individually while the turbine  11  is online and operating. In particular, to perform a test, the controller  75  may actuate (or de-actuate) the actuators  232   b ,  234   b ,  236   b  individually and monitor the pressure in one or more of the hydraulic conduits  283 ,  286 ,  289  and, if desired the conduits  295 ,  296 , and  297 , using the pressure transmitters (PT1-PT3)  300 ,  310 ,  320 , and those connected at, for example, TP-A, TP-B and TP-C to determine if the components associated with the bleed circuit  30  are operating properly. In this manner, a human operator is not required to perform manual tests on the various valves (A1, A2, B1, B2, C1, C2)  230 - 280  and actuators  232   b ,  234   b ,  236   b , which requires that the turbine  11  be shut down. Moreover, when the controller  75  is testing the components associated with the bleed circuit  30 , the controller  75  maintains the ability to stop operation of the turbine  11  (i.e., trip the turbine  11 ) upon the occurrence of an abnormal condition or malfunction to prevent damage to the turbine  11  and/or to prevent other catastrophes. 
     More specifically, to test the operation of the first actuator system  232  (including the control valve  232   a  and the solenoid valve  232   b ), the first trip valve (A1)  230 , and the fifth trip valve (A2)  270  associated with the first valve system  232 , the controller  75  de-energizes the solenoid valve  232   b  while keeping the solenoid valves  234   b  and  236   b  energized. When the controller  75  de-energizes the first solenoid valve  232   b , the control ports of both the first trip valve (A1)  230  and the fifth trip valve (A2)  270  should be coupled to the drain  70  and thus control pressure should be released or removed from each of the control ports of the first trip valve (A1)  230  and the fifth trip valve (A2)  270 . Additionally, the control valve  232   a  (which loses fluid pressure at the control port thereof), should close, thereby disconnecting the path from the system pressure line  50  to the trip header line  52 . If all of these components are operating properly, when the first actuator  232   b  is de-energized, both of the first trip valve (A1)  230  and the fifth trip valve (A2)  270  should thus move from the closed position to the open position. By monitoring the pressure sensed by the first pressure transmitter (PT1)  300  at the hydraulic conduit  283 , the pressure sensed by the second pressure transmitter (PT2)  310  at the hydraulic conduit  286 , and/or the pressure sensed by the third pressure transmitter (PT3)  320  at the hydraulic conduit  289 , the controller  75  can determine whether one or more of the first actuator  232   b , the first trip valve (A1)  230 , and the fifth trip valve (A2)  270  are operating properly. 
     In particular, if each of the first solenoid actuator  232   b , the first trip valve (A1)  230 , and the fifth trip valve (A2)  270  is operating properly when the controller  75  de-energizes the first solenoid actuator  232   b , the first pressure transmitter (PT1)  300  should sense system or trip header pressure at the hydraulic conduit  283  (due to the opening of the first trip valve (A1)  230 , the second pressure transmitter (PT2)  310  should sense a small or negligible pressure change at the hydraulic conduit  286  and the third pressure transmitter (PT3)  320  should sense drain pressure at the hydraulic conduit  289  due to the fifth trip valve (A2)  270  opening to connect the conduit  289  to the return line  60 . 
     However, if the first pressure transmitter (PT1)  300  senses no or only a small pressure change at the hydraulic conduit  283  after the controller  75  de-energizes the first actuator  232   b  while sensing drain pressure at the transmitter (PT3)  320 , the controller  75 , to the extent it receives a measurement from the pressure transmitter  300 , may determine that the first trip valve (A1)  230  is not working properly. On the other hand, if the first pressure transmitter (PT1)  300  senses trip header pressure at the hydraulic conduit  283  after the controller  75  de-energizes the first actuator  232   b  while sensing no or little pressure change at the transmitter (PT3)  320 , the controller  75  may determine that the fifth trip valve (A2)  270  is not working properly. In the case in which both the first pressure transmitter (PT1)  300  and the third pressure transmitter (PT3)  320  senses no or only a small pressure change at the hydraulic conduits  283  and  289  after the controller  75  de-energizes the first actuator  232   b , the controller  75  may determine that the solenoid valve  232   b  is not working properly. In any of these cases, the controller  75  may generate a fault or alarm signal or take any other desired action to notify a user of the specific problem. Of course, the controller  75  may also sense a problem with the solenoid valve  232   b  if the controller senses changes to the pressures measured by the pressure transmitters PT1 and PT3 when the controller  75  is energizing the solenoid valve  232   b , as this means that the solenoid valve  232   b  may have stopped functioning and closed in response to the bias on that valve. 
     The second valve system  234 , the second trip valve (B1)  250 , and the sixth trip valve (B2)  280  associated with the second valve system  234  may be tested in a manner similar to the manner described above with respect to the first valve system  232 . Specifically, when the controller  75  de-energizes the second actuator  234   b , while keeping the first solenoid actuator  223   b  and the third solenoid actuator  236   b  energized, the control ports of both the second trip valve (B1)  250  and the sixth trip valve (B2)  280  should be coupled through the actuator  234   b  to the drain  70  and thus control or system pressure should be released or removed from each of the control ports of the third trip valve (B1)  250  and the sixth trip valve (B2)  280 . Thus, if the second valve system  234  is operating properly when the actuator  234   b  is de-energized, both of the third trip valve (B1)  250  and the sixth trip valve (B2)  280  should move from the closed position to the open position. By monitoring the pressure sensed by the first pressure transmitter (PT1)  300  at the hydraulic conduit  283 , the pressure sensed by the second pressure transmitter (PT2)  310  at the hydraulic conduit  286 , and/or the pressure sensed by the third pressure transmitter (PT3)  320  at the hydraulic conduit  289 , the controller  75  may determine whether one or more of the second actuator  234   b , the third trip valve (B1)  250 , and the sixth trip valve (B2)  280  are operating properly. 
     In particular, if the second actuator  234   b , the third trip valve (B1)  250 , and the sixth trip valve (B2)  280  are operating properly when the controller  75  de-energizes the second actuator  234   b , the first pressure transmitter (PT1)  300  should detect drain pressure at the hydraulic conduit  283  due to the opening of the trip valve  280  that couples the outlet of the first trip valve (A1)  230  to return line  60 . Additionally, the second pressure transmitter (PT2)  310  should sense trip header pressure at the conduit  286  due to the opening of the valve  240  (B1) while the trip valve (C2)  260  remains closed. Moreover, the third pressure transmitter (PT3)  320  should sense only a small or negligible pressure change in the hydraulic conduit  289  as operation of the trip valves  250  and  270  remain unaffected. 
     However, if the second pressure transmitter (PT2)  310  senses no or only a small pressure change at the hydraulic conduit  286  after the controller  75  de-energizes the second actuator  234   b  while sensing drain pressure at the transmitter (PT1)  300 , the controller  75  may determine that the second trip valve (B1)  240  is not working properly. On the other hand, if the first pressure transmitter (PT2)  310  senses trip header pressure at the hydraulic conduit  286  after the controller  75  de-energizes the first actuator  234   b  while sensing no or little pressure change at the pressure transmitter (PT1)  300 , the controller  75  may determine that the sixth trip valve (B2)  280  is not working properly. In the case in which both the first pressure transmitter (PT1)  300  and the second pressure transmitter (PT3)  310  senses no or only a small pressure change at the hydraulic conduits  283  and  286  after the controller  75  de-energizes the second solenoid actuator  234   b , the controller  75  may determine that the solenoid valve  234   b  is not working properly. In any of these cases, the controller  75  may generate a fault or alarm signal or take any other desired action to notify a user of the specific problem and the detected source or cause of the problem. Of course, the controller  75  may also sense a problem with the solenoid valve  234   b  if the controller  75  senses changes to the pressures measured by the pressure transmitter PT1 and PT2 when the controller  75  is energizing the solenoid valve  234   b , as this situation means that the solenoid valve  234   b  may have stop functioning and closed in response to the bias on that valve without being instructed by the controller  75  to do so. 
     The third actuator or valve system  236 , the third trip valve (C1)  250 , and the fourth trip valve (C2)  260  associated with the third valve system  236  may be tested in a similar manner as the first valve system and the second valve system. Specifically, when the controller  75  de-energizes the third solenoid actuator  236   b , while keeping the first solenoid actuator  232   b  and the second solenoid actuator  234   b  energized, the control ports of both the third trip valve (C1)  250  and the fourth trip valve (C2)  260  should be coupled to the drain  70  and control pressure should be released or removed from each of the control ports of the third trip valve (C1)  250  and the fourth trip valve (C2)  260 . Moreover, if the third solenoid actuator  236   b  is operating properly when de-energized by the controller  75 , both of the third trip valve (C1)  250  and the fourth trip valve (C2)  260  should move from the closed position to the open position. By monitoring one or more of the pressures sensed by the second pressure transmitter (PT2)  310  at the hydraulic conduit  286 , the pressure sensed by the third pressure transmitter (PT3)  330  at the hydraulic conduit  289 , the controller  75  may determine whether one or more of the third actuator system  236 , the third trip valve (C1)  250 , and the fourth trip valve (C2)  260  are operating properly. 
     In particular, if each of the third actuator  236   b , the fourth trip valve (C1)  250 , and the fifth trip valve (C2)  260  is operating properly when the controller  75  de-energizes the third actuator  236   b  while keeping the first actuator  232   b  and the second actuator  234   b  energized, the second pressure transmitter (PT2)  310  should drain pressure at the hydraulic conduit  286  that couples the second trip valve (B1)  240  to the fourth trip valve (C2)  260  due to the opening of the fourth trip valve (C2)  260 . Additionally, the third pressure transmitter (PT3)  320  should sense trip header pressure at the hydraulic conduit  289  due to the third trip valve (C1)  250  being in the open position and the fifth trip valve (A2)  270  being in the closed position. The controller  75  may determine which components are faulty by monitoring the pressures at the pressure transmitters PT2 and PT3 in a manner similar to that described above with respect to the testing of the other fluid paths. 
     Of course, if desired, the controller  75  may receive signals from other pressure sensors mounted at locations illustrated in  FIG. 6  if so desired, and may also or instead use these signals to diagnose one or more faults within or associated with the trip valves in addition to or instead of using the signals from the pressure transmitters PT1, PT2 and PT3 in the manner discussed above. 
     As can be seen, the operation of a trip of the turbine  11  is not prevented during the testing of any one of the valve systems  232 ,  234 ,  236  associated with the trip valves  230 - 280  because, during a test, the controller  75  is essentially controlling one of the three valve systems to simulate a trip for that valve system. Thus, to actuate an actual trip during a test, the controller  75  need only send a trip signal to one or both of the other valve systems (not undergoing the test) by de-energizing one or both of the actuators  232   b ,  234   b ,  236   b  associated with the other valve systems. 
     Moreover, as illustrated in  FIG. 6 , manually operated valves, such as needle valves  350 , may be disposed between the pressure transmitters  300 ,  310  and  320  and the lines to which these transmitters attach to, for example, to enable these transmitters to be isolated from the fluid lines to allow these transmitters to be repaired or replaced. Still further, if desired, another valve, such as a manually operated needle valve may be disposed between the line  50  which supplies system pressure to the bleed circuit  30  and the line  52  to enable a user to manually pressurize the line  52  at any desired time or to compensate for leakage in the line  52 . 
     As will be understood, the bleed circuit  30  described above is configured to electronically perform a trip operation from a remote location in response to abnormal conditions or malfunctions by bleeding the hydraulic fluid in the hydraulic fluid path  52  to the return path  60  using a two out of three voting scheme, thereby removing pressure from the trip input of the steam valve  40 . In addition, because of the two out of three redundancy, the components of this bleed circuit  30  can be tested individually during operation of the turbine  11 , but without preventing the controller  75  from effectuating an actual trip during the test. As a result, a human operator is not required to manually operate or test the components associated with the bleed circuit  30 . Furthermore, the plurality of redundant valve systems associated with the bleed circuit  30  described above helps to ensure that a trip operation can be performed even if one of the components associated with the bleed circuit fails to operate. As a result, the bleed circuit  30  described herein provides greater reliability that a trip operation will be performed when desired or required. 
     However, due to the operation of the porting manifold  84  and the needle valves  95  disposed thereon, and due to the inclusion of two trip manifolds  86   a  and  86   b , each having an independent bleed circuit disposed thereon, components on one of the trip manifolds  86   a  or  86   b  can be repaired or replaced while the other trip manifold  86   a  or  86   b  continues to operate so as to enable tripping of turbine  11  if needed. In fact, one of the trip manifolds  86   a  or  86   b  can be isolated from and physically removed from the porting manifold  84  while the turbine  11  is on-line and running without affecting the ability of the other trip manifold to operate to cause a trip of the turbine  11  if needed. After being removed, the various components thereon can be repaired or replaced and the trip manifold can then be reconnected to the system while the turbine  11  is running. This bleed circuit configuration thus provides for the use of redundant trip manifolds in conjunction with the needle valves  95  (which are used to isolate one of the trip manifolds from the bleed circuit while the other trip manifold continues to operate) to enable components of the bleed circuit to be removed and repaired or replaced while the turbine and the trip system is operating on-line. This configuration thus provides a system that does not require an operator or other user to shut down the turbine  11  in order to fix problems or faulty components detected during the testing operations described above. 
     More particularly, to isolate one of the trip manifolds during on-line operation of the turbine, an operator, maintenance person or other person may actuate the needle valves  95  associated with the trip manifold being removed (either of set A or B as illustrated in  FIG. 3 ) so as to isolate the ports of the trip manifold being removed from the fluid lines within the porting manifold  84 . Then, the bolts  97  ( FIG. 2 ) for of the associated trip manifold may be loosened and removed to enable the trip manifold to be removed from the porting manifold. However, because the bleed circuit on the other trip manifold operates independently and in parallel to the bleed circuit on the trip manifold being removed, no trip of the turbine is caused by this action, thereby enabling one of the trip manifolds to be removed while the turbine and trip control system continue to operate on-line. Generally, it is desirable to close the needle or pin valve  95  in a particular order to assure that removal of the trip manifold does not cause a reduction of pressure in the trip header line  52 . In particular, it is desirable to close the pin or needle valve  95  that isolates the trip header line ( 52   a  or  52   b ) connected to the trip manifold being removed first, and to then close the pin or needle valve  95  that isolates the system pressure line  50  from the trip manifold being removed. Thereafter, the drain and tank lines may be isolated in either order by actuating the appropriate pin or needle valve  95 . Of course, the opposite order may be used to connect a trip manifold and associated components to the porting manifold  84  when the turbine  11  is operating on-line to assure proper continued operation without a trip. While not illustrated as such in  FIGS. 2-3 , the pin or needle valves  95  may be disposed in line along the side of the porting manifold  84  in the order (e.g., right to left or left to right) in which these valves should be actuated to remove or connect the trip manifold  86  to the porting manifold  84  while the turbine  11  is operating on-line without causing a trip. 
     Still further, to make mounting of the trip manifolds  86   a  and  86   b  onto the porting manifold  84  easier, O-ring connections  360  are used at each of the ports between these two manifolds. Such O-ring connections  360  are illustrated in  FIG. 6  at each of the connections of the drain line  70 , the system pressure line  50 , the trip header  52  and the return line  60 . These O-ring connectors  360  provide a sealed connection between the porting manifold  86  and the trip manifold  86  when the bolts  97  ( FIG. 2 ) are tightened without the need of tubing or external fluid conduits. Such O-ring connections may be used at the ports  90 ,  91   a ,  91   b  and  92  of the porting manifold  84  as well to enable the porting manifold  84  to be mounted directly to manifolds holding other circuits, such as a block circuit. 
     Moreover, because each of the bleed paths of the bleed circuits on the trip manifolds  86   a ,  86   b  has a control valve (i.e., one of the valves  232   a ,  234   a ,  236   a ) that opens in response to the operation or actuation of the associated solenoid valve  232   b ,  234   b ,  236   b ) to connect the system pressure line  50  to the trip header line  52 , there is always, when a trip state is not initiated, one or more fully open fluid paths between the system pressure line  50  and the trip header line  52  so that full pressure can be supplied to the trip header line  52  during this time. Moreover, when the solenoid valves  232   b ,  234   b ,  236   b  are closed or are de-energized, e.g., during a trip state, the control valves  232   a ,  234   a ,  236   a  fully close to seal all of the connection between the system pressure line  50  and the trip header line  52 . This operation eliminates the need for disposing small fluid ports between these lines, as has been done in the past, which ports needed to be sized in a manner that was a trade-off between best operation during a non-tripped state and best operation during a tripped state. The control valve systems described herein in the bleed circuit overcome this problem and operate automatically in conjunction with the control system. 
     By way of example,  FIG. 7  depicts one configuration of a bleed trip circuit illustrating the manner in which various of the components described with respect to  FIGS. 5 and 6  may be mounted on the trip manifolds  86   a  and  86   b  and the porting manifold  84 . Of course, other manners of implementing the described bleed circuit described herein could be used instead. 
     Referring back to  FIG. 1 , when the bleed circuit  30  of  FIGS. 1-6  performs a bleed function to thereby initiate a trip of the turbine  11 , the block circuit  20  operates to prevent or block the flow of hydraulic fluid from the hydraulic fluid source to the turbine trip header while the turbine  11  is in the trip state. As illustrated in  FIG. 1 , the block circuit  20  is hydraulically located upstream from and is coupled to the bleed circuit  30  to perform the block function. In particular, the block circuit  20  may operate to block the pressure line  52  from the hydraulic pressure source (not shown in the figures but located upstream of the block circuit  20 ) or to block the system pressure line  50 , to prevent unnecessary cycling of hydraulic fluid through the pressure lines  50  and  52  and the return path  60  during a trip state of the turbine  11 . The block circuit  20  may operate automatically by sensing the loss of turbine trip header pressure  52 . If the block circuit  20  fails to adequately block system pressure to the turbine trip header after the bleed circuit  30  removes the pressure in the line  52 , the hydraulic pressure pump or source unnecessarily operates in an attempt to increase the pressure in the line  50  which, of course, cannot happen due to the operation of the bleed circuit  30  during the trip. 
     Preferably, the block circuit  20  includes redundancy to enable the block circuit  20  to work correctly in the presence of a failed component within the block circuit  20 . Furthermore, the block circuit  20  is preferably remotely testable during operation of the turbine  11  in a manner that does not trip the turbine  11  but that enables the turbine  11  to be tripped, if necessary, during the testing of the block circuit  20 . In one embodiment, the block circuit  20  may include a plurality of redundant blocking components connected in series within the hydraulic fluid line  50  and configured to block system pressure to the turbine trip header in a redundant manner after a trip has occurred. However, many different block circuits are known and can be used with the bleed circuit described herein. As a result, the specifics of the block circuit will not be described in detail herein. However, one such block circuit is described in U.S. Pat. No. 7,874,241, and the disclosure of this circuit is hereby expressly incorporated by reference herein. 
     It should be understood that the trip control system  10 , as described above, may be retrofitted with existing mechanical hydraulic control (MHC) turbines by, for example, removing the emergency trip valve, associated linkages and other components, and inserting the tripping control system  10  in the hydraulic fluid path  50 . Still further, it will be understood that, while the valves, actuators and other components have been variously described as being electronically or hydraulically controlled components biased to particular normally open or closed positions, individual ones of these actuators and valves could be electronically or hydraulically controlled in a manner other than described herein and may be biased in other manners then those described herein. Still further, in some cases, various ones of the valves or actuator may be eliminated or the functionality may be combined into a single valve device. Still further, it will be understood that the controller  75  described herein includes one or more processors and a computer readable memory which stores one or more programs for performing the tripping, testing and monitoring functions described herein. When implemented, the programs may be stored in any computer readable memory such as on a magnetic disk, a laser disk, or other storage medium, in a RAM or ROM of a computer or processor, as part of an application specific integrated circuit, etc. Likewise, this software may be delivered to a user, a process plant, a controller, etc. using any known or desired delivery method including, for example, on a computer readable disk or other transportable computer storage mechanism or over a communication channel such as a telephone line, the Internet, the World Wide Web, any other local area network or wide area network, etc. (which delivery is viewed as being the same as or interchangeable with providing such software via a transportable storage medium). Furthermore, this software may be provided directly without modulation or encryption or may be modulated and/or encrypted using any suitable modulation carrier wave and/or encryption technique before being transmitted over a communication channel. 
     While the present disclosure has been described with reference to specific examples, which are intended to be illustrative only and not to be limiting of the disclosure, it will be apparent to those of ordinary skill in the art that changes, additions, or deletions may be made to the disclosed embodiments without departing from the spirit and scope of the disclosure.