Abstract:
The shut-off valve testing system provides for the testing of the main shut-off valve of a combustible gas supply line in such facilities as refineries, factories, or other plants utilizing such gaseous fuel. The system includes a combination hydraulic-pneumatic cylinder receiving pneumatic pressure from a suitable source, the cylinder communicating hydraulically with a hydraulic actuator for the main shut-off valve. The system provides for testing of the shut-off valve by actuating the valve through a portion of its full travel, thus confirming that the valve is free. This is accomplished by shutting off the pneumatic pressure to one side of the hydraulic-pneumatic cylinder, and opening the hydraulic line between the cylinder and the actuator. Thus, hydraulic pressure from the actuator can bleed to the cylinder, allowing the actuator to move to the extent of the limiting spring and/or pneumatic pressure to the opposite side of the cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of my prior application Ser. No. 13/304,602, filed Nov. 25, 2011 now pending. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to control valve systems, and particularly to a shut-off valve testing system for testing and operating the main shutdown valve that controls gas flow in a refinery, industrial plant or other facility. 
     2. Description of the Related Art 
     In the oil, gas, petroleum and power industries, natural gas or other combustible gas is often used to provide the required heat or combustion motive power for many operations in a processing refinery, plant, or other industrial facility. Various conditions may occur that necessitate immediate shut down of the operations of the facility. In those facilities, a majority of the final control elements of a shutdown system are in plemented with fast acting shut-off valves. In such industries, a majority of the shut-off valves remain open while the operation is operating safely in a nominal controlled state. Such shut-off valves are closed only upon actuation of the shutdown system of the facility arising from an out-of-control process or during a normal maintenance outage. 
     In practice, the testing of emergency shut-off valves is normally done during shut down of the facility operation. However, there is a tendency for such valves to stick or freeze due to corrosion or other reasons, which may lead to an unsafe condition where the valve cannot be closed during an emergency shutdown. This problem is exacerbated by economic conditions in the operation of the facility that have lead to a reduction in the frequency of valve shut-offs for maintenance or testing purposes. For example, some operations may run continuously for one or more years without shutting down the operation for maintenance. 
     State of the art emergency shut-off systems that control the shut-off valves have a number of features to detect system failures, and typically include redundancies for added reliability. However, such systems may not provide for the testing of a shut-off valve per se other than by operating the valve through its normal stroke or travel. The problem is that operating the valve through its full stroke or travel, i.e., completely closing the valve, causes an undesirable disruption in the operation of the facility. 
     Thus, a shut-off valve testing system solving the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The shut-off valve testing system uses a system of valves and other components for controlling the main shut-off valve installed in the combustible gas or fuel supply line in an industrial plant or facility. The testing system includes a combination hydraulic and pneumatic cylinder that receives pneumatic pressure from an appropriate source to regulate the system at times during the testing of the system. The hydraulic-pneumatic cylinder regulates the travel or stroke of a hydraulic actuator during testing. The actuator, in turn, operates the main shut-off valve, Hydraulic pressure to both sides of the actuator for the main shut-off valve is provided from a pressurized source of hydraulic fluid, some of that fluid being routed through one side of the actuator to the hydraulic portion of the hydraulic-pneumatic cylinder during some portions of the operation. 
     The hydraulic-pneumatic cylinder is closed relative to the actuator during normal operations, i.e., with the main shut-off valve open to allow gas flow through the gas delivery line. Partial Instrument Trip Testing (PITT) of the main shut-off valve by operating the valve through its partial stroke or travel is accomplished by relieving hydraulic pressure from one side of the actuator by opening a valve between the actuator and the hydraulic-pneumatic cylinder. This allows the actuator to relieve hydraulic pressure to the hydraulic-pneumatic cylinder to allow the actuator to move, thereby moving the shut-off valve through at least a portion of its full travel. Full travel of the shut-off valve (i.e., shut down of the system) is prevented by a differential pressure transmitter across the hydraulic-pneumatic cylinder. This transmitter provides a signal to the control system to reverse the positions of the various control valves before complete closure of the main shut-off valve occurs. As the operation of the shut-off valve requires some finite amount of time, partial travel of the valve may be determined, alternatively, by actuating the valve for a time period less than that required for full travel or shutoff. 
     When a complete shutoff of the fuel supply is demanded due to an emergency or other requirement in the plant or facility, the hydraulic actuator is cycled to its full travel to cause the shut-off valve to close completely. The combination hydraulic-pneumatic cylinder is not a factor during complete shutdown operations, as both hydraulic and pneumatic pressure is shut off to the hydraulic-pneumatic cylinder. However, other valves are actuated that result in hydraulic pressure being relieved in one side of the actuator, thereby causing the actuator piston to move to actuate the shut-off valve through its complete stroke or travel to completely shut off gas flow through the line. 
     The system further includes a control system for limiting the complete travel of the main shut-off valve during testing of the device, and for actuating the system in the event of an emergency requiring complete shutoff of flow through the combustible gas line controlled by the main shut-off valve. The control system is computerized for automatic operation, depending upon input from various conventional sensors of the fuel and valve control system. However, the system also provides for manual control when desired. 
     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a shut-off valve testing system according to the present invention, illustrating its general features. 
         FIG. 2  is a flowchart briefly listing the steps involved in the partial stroke testing of a shutdown valve in the shut-off valve testing system according to the present invention. 
         FIG. 3  is a flowchart describing the steps involved in operating various valves in the shutdown process of the shut-off valve testing system according to the present invention. 
         FIG. 4  is a flowchart describing the steps involved in operating various valves in the startup process of the shut-off valve testing system according to the present invention. 
         FIG. 5  is a schematic diagram of the major components of the control system for the shut-off valve testing system according to the present invention. 
     
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The shut-off valve testing system provides for the partial instrument trip testing (PITT) of a main shut-off valve in a combustive gas main fuel supply line, which are often installed to provide heat and combustive power for equipment found in refineries, factories, and similar industrial facilities. The system allows the main shut-off valve to be cycled through only a portion of its full travel or stroke, thus confirming that the valve is not stuck, while also allowing the valve to remain at least partially open to avoid disrupting the gaseous fuel supply for the operation of the facility. 
       FIG. 1  of the drawings is a schematic diagram of an exemplary shut-off valve testing system  10  according to the present invention, as it would be installed with a gaseous fuel supply line  12  and the main shut-off valve  14  installed in series in the line  12 . The main shut-off valve  14  is mechanically linked to a hydraulically operated actuator  16 . The actuator  16  has an internal piston  18  that separates the internal volume into a loading pressure side  20  and an opposite actuating pressure side  22 . The actuator  16  receives hydraulic pressure from a conventional hydraulic pressure source  24 . A loading pressure hydraulic line  26  extends from the pressure source  24  to the loading pressure side  20  of the actuator  16 , and an actuating pressure hydraulic line  28  extends from the pressure source  24  to the actuating pressure side  22  of the actuator  16 . 
     The loading pressure hydraulic line  26  may include a pressure regulator or reducer  30  to lower the pressure in the loading pressure side  20  of the actuator  16  to a level somewhat less than the opposite actuating pressure side  22 . This assures that the actuator  16  will remain in its normal operating condition, i.e., holding the main shut-off valve  14  open, so long as a higher hydraulic pressure is applied to the actuating pressure side  22  of the actuator  16 . The actuator  16  may also contain an internal mechanical spring  32  in the loading pressure side or volume  20  to assure positive shutdown in the event that all hydraulic pressure is lost. 
     The actuating pressure side  22  of the actuator  16  is connected hydraulically to the hydraulic side or volume of a combination hydraulic-pneumatic control cylinder  34 . A conventional source of pneumatic pressure  36  supplies pneumatic pressure to the opposite side or volume of the control cylinder  34 . The pneumatic pressure may comprise compressed air, or a cylinder of compressed nitrogen or other gas under pressure. A differential pressure transmitter  38  is connected across the control cylinder  34  and communicates with both the hydraulic side or volume  40  and the pneumatic side or volume  42  of the control cylinder  34  to provide information about the differential pressure across the control cylinder  34  to a control facility, discussed further below. An internal spring  44  is provided in the pneumatic volume side  42  of the hydraulic-pneumatic control cylinder  34  to bear against the piston  46  separating the two internal volumes  40  and  42  to assure proper operation in the event that pneumatic pressure is lost. The total volume of the two sides  40  and  42  of the control cylinder  34  is somewhat less than the total internal volumes of the two sides  20  and  22  of the actuator  16  to assure that the actuator  16  cannot travel to its limits during test actuation by the control cylinder  34 , thus limiting the main shut-off valve  14  to partial travel or stroke. 
     The shut-off valve testing system  10  includes a number of additional control valves that control hydraulic or pneumatic flow through the system. A three-way pneumatic valve  48  is disposed in the pneumatic pressure line between the source of pneumatic pressure  36  and the pneumatic side or volume  42  of the hydraulic-pneumatic control cylinder  34 , and serves to control pneumatic pressure to the pneumatic side  42  of the control cylinder  34 . This pneumatic valve  48  is normally closed between the pneumatic pressure source  36  and the control cylinder  34 , except during the brief time that the actuator  16  is being returned to its normally open condition to reopen the main shut-off valve  14  fully after testing, as explained in detail further below. The third port in this three-way pneumatic valve  48  comprises a vent, represented by the arrow extending from the valve  48  in  FIG. 1 . The valve  48  is preferably a solenoid operated electromechanical unit, the solenoid being indicated as component  48   a  of the valve  48 . This valve  48  preferably has a normally closed configuration, i.e., electrical power to the solenoid  48   a  is only required during the brief times that the valve  48  is open at the end of testing the main shut-off valve  14 . This is a safety factor to assure that this pneumatic valve  48  will remain in its desired state in the event that electrical power is lost. However, it will be seen that this pneumatic valve  48  may be configured to require electrical power during its normally closed state, opening only when power is removed, if desired. 
     A first hydraulic control valve  50  is installed in the hydraulic line between the actuating pressure side or volume  22  of the actuator  16  and the hydraulic side or volume  40  of the control cylinder  34 . This first hydraulic control valve  50  is also normally closed, opening only during the partial stroke or travel testing (PITT) of the main shut-off valve  14  by the actuator  16 , as explained further below. The first hydraulic control valve  50  is also operated by a solenoid  50   a . As in the case of the three-way pneumatic valve  48 , the first hydraulic valve  50  is preferably normally closed, requiring no electrical power for it to remain closed. Electrical power to the solenoid  50   a  is only required to open the valve  50  during the brief time of testing the main shut-off valve  14 , thus assuring that this valve  50  will remain in the desired closed condition in the event of loss of electrical power. However, this valve  50  may also be reconfigured to require electrical power to hold it in its closed condition, electrical power being removed to open the valve  50 , if desired. 
     A second hydraulic control valve  52  is disposed in the actuating pressure hydraulic line  28  between the hydraulic pressure source  24  and the actuating pressure side or volume  22  of the actuator  16 . This second hydraulic valve  52  is also operated by a solenoid  52   a , and is also normally closed when no electrical power is supplied to its solenoid  52   a . However, electrical power is normally provided to this solenoid  52   a  to hold this valve  52  in an open condition to provide hydraulic pressure to the actuating pressure side or volume  22  of the actuator  16 . This second valve  52  only closes when the actuator  16  is being cycled to close the main shut-off valve  14 , either partially during testing or completely during a shutdown event. The preferred state of this valve  52  is to require electrical power to hold it open, i.e., for normal operations. Thus, it will close if electrical power is lost, resulting in cycling of the actuator  16  and closure of the main shut-off valve  14 . As in the cases of the pneumatic control valve  48  and the first hydraulic control valve  50 , the second valve  52  may be reconfigured to require electrical power for closure, but the preferred configuration wherein the valve  52  closes when electrical power is lost is a safer configuration. 
     A hydraulic fluid reservoir  54  is provided in the system, and communicates hydraulically with the actuating pressure side or volume  22  of the actuator  16 . This reservoir  54  may comprise a hydraulic fluid supply tank for the hydraulic pressure source  24 , and would be connected conventionally to the pressure source  24  by a hydraulic line or passage (not shown). A third hydraulic control valve  56  is installed in the hydraulic line between the actuating pressure hydraulic line  28  and the hydraulic reservoir  54 , and an essentially identical fourth hydraulic control valve  58  is installed in the hydraulic line between the line connecting the actuating side or volume  22  of the actuator  16  and the hydraulic side or volume  40  of the control cylinder  34 . It will be seen that since there are no intervening components to affect the hydraulic pressure or flow between the third and fourth hydraulic control valves  56  and  58  and the components to which they attach, i.e., they both communicate hydraulically directly with the actuating pressure side or volume  22  of the actuator  16 , that either or both of these valves  56  and  58  may function to relieve pressure in the actuating pressure hydraulic line  28  and the actuating pressure side or volume  22  of the actuator  16 . This redundancy provides greater reliability for the emergency shutdown functions of the system. 
     The third and fourth hydraulic control valves  56  and  58  are also electromechanically actuated by their respective solenoids  56   a  and  58   a , as in the cases of the other solenoid-operated valves  48 ,  50 , and  52 . The third and fourth valves  56  and  58  are closed during all normal operations of the system, including partial stroke testing of the main shutoff valve  14 . The valves  56  and  58  are preferably configured to be normally open when no power is received, and are held in their closed states or conditions by power applied through their respective solenoids  56   a  and  58   a . These two valves  56  and  58  are only opened to relieve hydraulic pressure to the actuating side or volume  22  of the actuator  16  when a “trip” or emergency shutdown of the system occurs. When this occurs, electrical power is terminated to the two solenoids  56   a  and  58   a , allowing their valves  56  and  58  to open to release hydraulic pressure in the actuating portion of the system. It will be seen that these two valves  56  and  58  may be reconfigured to require electrical power to open, but it is preferred that they open when electrical power is terminated due to the additional safety factor provided by the likelihood that electrical power will be cut off in an emergency shutdown. 
     As the second, third, and fourth hydraulic control solenoid valves  52 ,  56 , and  58  are cycled during any emergency shutdown of the system, i.e., the complete closure of the main shut-off valve  14 , additional means may be provided for the operation of these three valves  52 ,  56 , and  58  to return the system to normal operation in the event that electrical power has not been restored by the operating system for the valves. Accordingly, each of the valves  52 ,  56 , and  58  includes a manual reset “latch,” shown respectively as components  52   b ,  56   b , and  58   b , allowing an operator(s) to close the valves  56  and  58  and reopen the valve  52  manually to restart the system in order to reopen the main shut-off valve  14 . 
     A number of additional manual valves are also provided in the system to remove hydraulic pressure and flow to various components for maintenance. A first manual valve  60  is installed in the hydraulic line between the actuating pressure side  22  of the actuator  16  and the first hydraulic control valve  50 . This valve  60  allows the first hydraulic valve  50  to be removed from the system for maintenance or replacement as required, without affecting the emergency shutdown capability of the system. A second manual valve  62  is provided in the hydraulic line between the actuating pressure hydraulic line  28  and the third hydraulic control valve  56 , and a third manual valve  64  is installed in the hydraulic line extending from the line between the actuating pressure side or volume  22  of the actuator  16  and the first hydraulic valve  50 . Either the second or the third manual valve  62  or  64  may be closed to allow the respective hydraulic control valve  56  or  58  to be removed from the system for maintenance or replacement, as required. As the two control valves  56  and  58  are redundant to one another, the operational retention of a single one of the valves  56  or  58  in the system still allows the emergency shutdown function of the system to perform as required in the event that it is needed, even if one of the two valves  56  or  58  is inoperative or removed. 
     Additional components are provided in the mechanical linkage that connects the actuator  16  to the main shut-off valve  14 . These components serve to indicate the position of the shut-off valve  14  during its operation. Main shut-off valve opening and closure limit switches  66  and  68 , respectively, serve to detect the fully opened and fully closed positions or states of the main shut-off valve  14  and to transmit those states to the control system. A third limit switch  70  serves to detect a predetermined partially open position or state for the main shut-off valve  14  during shut-off valve testing, and to transmit that data to the control system in order that the control system will stop the actuator  16  at that point to avoid excessive closure of the main shut-off valve  14  and subsequent reduction in gas flow through the line  12 . 
       FIG. 5  provides a schematic view of the control system for the shut-off valve testing system  10  of  FIG. 1 . The area to the lower right in  FIG. 5  indicates in a general manner some of the various components illustrated schematically in  FIG. 1  and described further above, i.e., the main shut-off valve  14 , its actuator  16 , the differential pressure transmitter or transducer  38  of the hydraulic-pneumatic control cylinder (not shown in  FIG. 5 ), and a single block representing the three limit switches  66 ,  68 , and  70  of the connection between the main shut-off valve  14  and the actuator  16 . This system is controlled by a computerized control system  100 . The system  100  comprises an emergency shutdown system (ESD) control center  102  that drives a series of transducers  102 . The transducers  102  interface with the differential pressure transmitter or transducer  38  across the two ends or volumes of the hydraulic-pneumatic cylinder  34  of  FIG. 1 . The ESD control center  102  normally carries out the operation of the shut-off valve system of  FIG. 1 , particularly for emergency shutdown operations. However, a computer and monitor  104  are provided to enable the human operator to command the ESD control center  102 , as may be required from time to time. The computer  104  may be hardwired to the ESD controller  102 , but may bypass the ESD controller to control and receive information from the transducers  102  via a remote communication interface  106 , if desired. 
       FIG. 2  of the drawings is a flowchart describing the basic steps in the Partial Instrument Trip Testing (PITT) of the main shut-off valve  14  of  FIG. 1 . Start position  200  represents the normal operational status of the system  10 , i.e., the main shut-off valve  14  is in its normal, fully opened state to allow gaseous fuel to flow therethrough. When the test is initiated, the second solenoid valve  52  installed in the actuating pressure hydraulic line  28  ( FIG. 1 ) is de-energized to allow the valve  52  to close, generally as indicated in the second step  202  of  FIG. 2 . At this point the system pauses for a two-second delay (more or less, depending upon programming) in order to confirm that the valve  52  is completely closed and will not allow any residual hydraulic fluid under pressure to continue to flow for a short period of time as the remainder of the sequence operates. This delay step is indicated as step  204  in  FIG. 2 . 
     After the delay has been completed, the first hydraulic shut-off valve  50  installed in the hydraulic line between the actuator  16  and the hydraulic-pneumatic cylinder  34  is actuated, i.e., opened, as indicated by step  206  of the flowchart of  FIG. 2 . This allows hydraulic pressure to flow from the actuating pressure side  22  of the actuator  16  to the hydraulic side  40  of the hydraulic-pneumatic cylinder  34 , where the increase in hydraulic pressure is cushioned by the pneumatic side of the cylinder  34 . The corresponding hydraulic flow from the actuating pressure side  22  of the actuator  16  allows its piston  18  to move, thereby mechanically moving the main shut-off valve  14  to a partially closed position. The Partial Instrument Trip Testing (PITT) timer of the control system of  FIG. 5  may also be initiated at this point, if travel of the main shut-off valve  14  is to be determined by time rather than by position as determined by the partial stroke limit switch  70  of  FIG. 1 . 
     The shut-off valve  50  remains energized (open), as indicated by step  208  in  FIG. 5 , until either the main shutdown valve  14  reaches a point close to its partial stroke limit as measured by the partial stroke limit switch  70 , or until the timer expires, as indicated by step  210  of  FIG. 5 . If neither of these conditions occurs, the shut-off valve  50  remains open. However, with normal main shut-off valve operation, it will reach its predetermined partial closure limit before the time limit expires, and the system will then energize (open) the pneumatic solenoid valve  48 , as indicated by step  212  of  FIG. 5 . 
     The opening of the pneumatic solenoid valve  48  allows pressurized gas (air, nitrogen, etc.) to flow from it source  36  ( FIG. 1 ) into the pneumatic side or volume  42  of the hydraulic-pneumatic cylinder  34 . This increase in pneumatic pressure drives the piston  46  toward the hydraulic side of the actuator, thereby pushing hydraulic fluid back into the actuating pressure side or volume  22  of the actuator  16 . This causes the actuator piston  18  to move in a direction to reopen the main shut-off valve  14 . This condition continues until the main shutdown or shut-off valve  14  ( FIG. 1 ) has completely reopened, as indicated by step  216  of  FIG. 2 . 
     Once the main shut-off valve  14  has reopened completely, the first hydraulic shut-off valve  50  is closed, as indicated by step  218  of  FIG. 2 . This prevents hydraulic pressure from flowing from the actuating pressure side or volume  22  of the actuator  16  to the hydraulic-pneumatic cylinder  34  once the system has returned to normal. Another two-second delay (or other time period as determined) is initiated immediately after closure of the valve  50  and before the operation of any other valves in order to be certain that the valve  50  is completely closed, as indicated by step  220  of  FIG. 2 . 
     When the time delay has elapsed and solenoid valve  50  is completely closed, the second solenoid valve  52  is reopened to allow hydraulic pressure to the actuating pressure side  22  of the actuator  16  to assure that the main shut-off valve  14  is held open. At the same time, the pneumatic solenoid valve  48  is closed. The closure of the hydraulic solenoid valve  50  and pneumatic solenoid valve  48  lock the hydraulic-pneumatic cylinder out of the system until the next operational check, as indicated by the final steps  222  and  224  of  FIG. 2 . 
       FIGS. 3 and 4  are flowcharts that respectively describe the basic steps involved in the emergency shutdown procedure and in the restart procedure. In  FIG. 3 , a signal indicating some other than nominal aspect of operation is sent to the control system  100  ( FIG. 5 ). The system  100  reacts by sending a shutdown signal to the second hydraulic solenoid valve  52  to close the actuating pressure hydraulic line  28  to the actuator  16  and to open the third and fourth hydraulic solenoid valves  56  and  58  to release hydraulic pressure in the actuating pressure side  22  of the actuator  16 . Although it is only necessary to open one of the two valves  56  or  58  to shut down the system due to the redundancy of these two valves, the operating system opens both valves to be absolutely certain that hydraulic pressure to the actuating pressure side  22  of the actuator is dumped in the event that one of the two valves  56  or  58  does not function. The regulated pressure through the loading pressure line  26  is, of course, greater than the essentially zero pressure in the actuating pressure side  22  of the actuator  16 . The spring  32  provides further pressure to drive the piston  18  to rapidly close the main shut-off valve  14 . The emergency shutdown process ends with the completion of the actuation of the three valves noted above, as indicated by the final step  304  of  FIG. 3 . 
       FIG. 4  is a flowchart briefly describing the steps in the restart process. Once the system has been determined to be ready to return to normal operation, as indicated by the initial step  400  of  FIG. 4 , the state or condition of the three hydraulic solenoid valves  52 ,  56 , and  58  is reversed, as indicated by the second step  402  of  FIG. 4 . However, the valves  52 ,  56 , and  58  may be set to remain in their system shutdown condition until their respective manual latches  52   b ,  56   b , and  58   b  ( FIG. 1 ) are reset (manually latched) to allow the valves to function normally, as indicated by step  402  of  FIG. 4 . This manual latch feature requires the operator(s) of the system to verify the proper state or condition of the system prior to restart of the system. Once this has been accomplished, the valves  52 ,  56 , and  58  are returned to their respective states or conditions for normal operation of the system, i.e., valve  52  is reopened and valves  56  and  58  are closed, to assure that the main shut-off valve  14  is open to supply a full delivery of combustive gas to the operation. 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.