Patent Abstract:
A hydraulic control circuit, comprising a control line connected to a device to be controlled by fluid pressure in the control line; a time-out valve on the control line, the time-out valve having a time-out period during which time-out period operation of the time-out valve is delayed after actuation of the time-out valve; a pump connected to the control line for pressurizing the control line with fluid; and an arming valve operated by pressure on an arming line connected to the control line and the arming valve being connected to the time-out valve to reduce the time-out period in response to pressure on the control line.

Full Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to hydraulic emergency shut-down systems (ESD) for actuating closure of valves.  
           [0002]    U.S. Pat. No. 6,276,135 issued Aug. 21, 2001, and Canadian application no. 2,266,806 published Sep. 23, 2001, describe a hydraulic control circuit for a hydraulic actuator, including a high-low pilot valve having a sensing port for connection to a flow line. When the sensed pressure from the flow line moves outside of a pre-set operating range, the hydraulic actuator is actuated and flow in the line is stopped. For initiating the operation of the high-low pilot, a time out valve is closed on the hydraulic control circuit to allow manual build up of pressure in the hydraulic control circuit to the operating range. This opens the hydraulic actuator and the high-low pilot maintains pressure on the hydraulic circuit to keep the hydraulic actuator open.  
           [0003]    A difficulty occurs with this hydraulic control circuit in that there may be a period in which the time-out valve is closed, but the hydraulic actuator is open, so that there is fluid flow in the flow line, with no way to monitor the pressure in the flow line.  
         SUMMARY OF THE INVENTION  
         [0004]    This invention is directed to providing increased safety of operation of a self-contained hydraulic emergency shut down system.  
           [0005]    Therefore, according to an aspect of the invention, there is provided a hydraulic control circuit, comprising a control line connected to a device to be controlled by fluid pressure in the control line; a time-out valve on the control line, the time-out valve having a time-out period during which time-out period operation of the time-out valve is delayed after actuation of the time-out valve; a pump connected to the control line for pressurizing the control line with fluid; and an arming valve operated by pressure on an arming line connected to the control line and the arming valve being connected to the time-out valve to reduce the time-out period in response to pressure on the control line.  
           [0006]    The hydraulic control circuit has particular utility for use with a flow line and the device to be controlled is a valve on the flow line.  
           [0007]    In a further aspect of the invention, the time-out valve includes a restrictor on a fluid return line that regulates the time-out period. The restrictor may comprise plural loops of continuous tubing arranged in plural layers, preferably spirally wound, the tubing having a smaller inner diameter than the fluid return line. In a further aspect of the invention, the arming valve operates a bypass around the restrictor. In a further aspect of the invention, the time-out valve is normally open, and is closed after actuation until expiry of the time-out period.  
           [0008]    In addition, this invention provides a novel configuration of bias restrictor for use on a control line on a hydraulic circuit. The restrictor comprises plural loops of continuous tubing arranged in plural layers, preferably spirally wound, the tubing having a smaller inner diameter than the control line.  
           [0009]    These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    There will now be described preferred embodiments of the invention, with reference to the drawings, by way of illustration only and not with the intention of limiting the scope of the invention, in which like numerals denote like elements and in which:  
         [0011]    [0011]FIG. 1 is a hydraulic schematic of a hydraulic control circuit according to the invention; and  
         [0012]    [0012]FIGS. 2A and 2B are sections through restrictors for use in hydraulic control circuits and particularly in the hydraulic control circuit of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0013]    In this patent document, a reference to “a connection”, “connected” or “connect(s)” is a reference to hydraulic connection unless the context otherwise requires. In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word in the sentence are included and that items not specifically mentioned are not excluded. The use of the indefinite article “a” in the claims before an element means that one of the elements is specified, but does not specifically exclude others of the elements being present, unless the context clearly requires that there be one and only one of the elements.  
         [0014]    Referring to FIG. 1, there is shown a hydraulic control circuit for an actuator  20 , which actuates a valve, not shown. A high-low pilot valve  10  is connected to a flow line  16  to be monitored through port  12  of valve  10  and line  14  through isolation valve  15 . A single pressure line or hydraulic manifold  18  connects the high-low pilot  10  to the hydraulic actuator  20 . The single pressure line  18  has a single pressure along its length, and thus forms a single pressure circuit. A second line  22  connects the high-low pilot  10  to a reservoir  24 . A normally closed relief valve  26  is connected to the single pressure line  18  through line  28  for relief of excessive pressure and drains through line  27  and line  22  to the reservoir  24 . A normally closed override valve  30  is connected to the single pressure line through line  28  and  29  for manual override of circuit controls. The line  28  connects to the line  18  between a time out valve  44  and actuator  20 . The override valve  30  drains through line  31  and  22  to the reservoir  24 . A pump  32  is connected to the single pressure line  18  via line  34  and line  28  for pressuring the single pressure line. The pump  32  is preferably a hand pump, and is separated from the line  28  by a filter  36  and a leak tight outlet check valve  38 , both on line  34 . The pump  32  is also connected via line  40  with inlet check valve  42  to reservoir  24 . A fusible plug  48  for relief of pressure eg during fires is also provided on line  18 .  
         [0015]    When the pump  32  is activated, fluid moves from reservoir  24  through lines  40 ,  34  and  28  into line  18 . The relief valve  26  and override valve  30  block return of fluid to reservoir  24 , and thus pressure builds up in line  18  when the pump  32  is activated. The time out valve  44  is normally open, and is set to close a pre-set time interval after being manually activated.  
         [0016]    The hydraulic control circuit works as follows. The high-low pilot  10  monitors pressure in the flow line  16  and is normally closed. When the pressure exceeds a high set point or is lower than a low set point, the pilot valve  10  opens, and hydraulic fluid drains from line  18  and  22  into reservoir  24 . Loss of pressure at the actuator  20  causes the actuator  20  to close its associated valve. If the pressure in lines  28  or  18  becomes too high itself, then relief valve  26  opens, until the pressure returns to normal. The actuator  20  can be activated manually by operation of the override valve  30 . If the temperature becomes too high, fusible plug  48  opens to allow line  18  to drain and activate the actuator  20 . Fusible plug  48  may be connected by a line (not shown) to discharge to the tank  24 .  
         [0017]    To set the actuator  20  initially, pressure must be built in line  18 . This is accomplished initially by manually closing time out valve  44 . High low pilot  10  is open with low line pressure being sensed. The time out valve  44  begins to count down towards opening. While time out valve  44  is closed, pump  32  is activated to increase the pressure in lines  18  and  28  until actuator  20  is activated. Activation of actuator  20  will lead to increase of pressure in flow line  16 , and if the line is working properly, pressure in line  16  will be in its intended operating range. Thus, when valve  44  opens, the high-low pilot  10  will have closed, thus maintaining pressure in line  18  and activating the actuator  20  with pressure in line  18 . The amount that the handle  50  is moved downward establishes the length of the time-out period, for example 90 seconds maximum at 20° C.  
         [0018]    The time out valve  44  has a manually operated handle  50  which when pushed downward lifts a piston  52  and loads a spring  54 . When the piston  52  is moved upward, fluid above the piston  52  flows through line  56  and piston O-ring valve  58  to the chamber  60  on the other side of the piston  52 . When the handle  50  is released, pressure of the spring  54  forces the piston  52  downward and fluid out of the chamber  60 . Flow through valve  58  is blocked, and so the fluid passes through flow restrictor  62  on line  64  back to the other side of the piston  52 . Line  64  may be a fitting on the valve  44 . The flow restrictor  62  therefore provides a regulated time out period that determines how long the time-out valve  44  remains closed while pressure is built up in line  18 .  
         [0019]    If the flow line pressure does not come within the high and low set points of the high-low pilot  10  before the end of the time-out period, the high-low pilot  10  will shut down the ESD system when the time-out period expires. If the flow line pressure does come within the high and low set points of the high-low pilot  10  before the end of the time-out period, a circuit is supplied to automatically end the time-out period and thus effectively reduce the time-out period. This circuit includes a control line  70  that senses pressure on the side of line  18  that is between the time-out valve  44  and the valve actuator  20 . The line  70  has a flow restrictor  72  and delivers pressure to a port  74  of an arming valve  76 . Arming valve  76  is provided on a line  78  that bypasses the restrictor  62 , so that when the arming valve  76  is armed, fluid in reservoir  60  bleeds rapidly through line  78  to the other side of the piston  52 , thus ending the time-out period. Pressure build-up sensed at port  74  of the arming valve  76  is regulated by bias restrictor  72 . The bias restrictor  72  allows pressure to build up in line  18  upon operation of the hand pump  32 , and allows the pressure at port  74  to operate arming valve  76  when the pressure in line  18  reaches the a low set point determined by the selection of a spring  80  on the arming valve  76 .  
         [0020]    Although any flow restrictor may be used as the flow restrictor  62  or  72  in the hydraulic control circuit disclosed here, according to a further inventive aspect disclosed here, the flow restrictor  62 ,  72  may be formed of plural loops of continuous tubing  84 A,  84 B arranged in plural layers as shown in FIGS. 2A and 2B. The tubing  84 A,  84 B has a smaller inner diameter than the inner diameter of the control line  70 ,  64 . Preferably, the tubing  84 A,  84 B is spirally wound around a spool  86 . The relative sizes of the inner diameters of the tubing  84 A,  84 B and control line  70 ,  64  are selected for a desired pressure differential across the restrictor  72 ,  62  respectively. The control line, as for example control line  64  in this case, may be a fitting on another part, for example a valve, in which the case the inner diameter of the control line is simply the inner diameter of the fitting. A restrictor of the type shown here is preferred over conventional orifice discs with a very small hole, since the small hole is subject to blockage, and the small filter mesh used to prevent blockage is subject to blockage. The elongated inner diameter of the plural loops of continuous tubing is four to six times larger than an orifice disc diameter to give the same amount of restriction to hydraulic oil flow. This larger inner diameter accommodates the bulk of the contaminants in the system, substantially reducing the requirement for cleaning, and maintaining free flow through the filters and restrictors.  
         [0021]    The sections in FIGS. 2A and 2B are characteristic of all sections through the axis of the spool, except that the connections appear as shown in only one section. For both restrictors  72 ,  62 , the tubing spools  86  are secured on a shaft  88  and protected by a cylindrical housing  90  and top cap  92  held on bolt  94 . At the opposite end to top cap  92 , the housing  90  is capped by a tubing connector spool  96 , as for example a swagelock fitting. In the case of the bias restrictor  72  of FIG. 2A, the fittings thread into a base plate  98  that has openings  100  for receiving the control line  70 . In the case of the arming restrictor  62  of FIG. 2B, the fittings thread directly into the valve  44  and themselves form the control line  64 . In an exemplary embodiment, the tubing  84 A,  84 B had an inner diameter of 0.020 inches, and the control lines had a diameter of 0.18 inches. The tubing  84 A in an exemplary embodiment is 88 inches long, while the tubing  84 B is 15 inches long.  
         [0022]    The pilot  10  is designed to bleed down an E.S.D. hydraulic circuit when high or low pressures are sensed, such as in an Oil/Gas production or pipeline facility. The high and low set points are independently adjustable to meet predetermined levels, in accordance with the desire of the operations personnel. The pilot may be used for high only or low only or both high and low in one unit. Several springs can be chosen to provide a broad range of set points, in both high and low categories. Standard high and low set points may range between 50 and 2000 PSI. Various conventional fluids may be used as the hydraulic fluid, depending on the temperature requirements, such as automatic transmission fluid and aircraft hydraulic oil. Various conventional filter discs (not shown here) are used within the hydraulic circuit disclosed here, in proximity to the time-out valve  44 , over-ride valve  30 , relief valve  26 , hydraulic pump  32 , arming valve  76 , restrictor  72  and high-low pilot  10  in conventional manner for protection of hydraulic circuits and valves.  
         [0023]    A person skilled in the art could make immaterial modifications to the invention described in this patent document without departing from the essence of the invention.

Technology Classification (CPC): 5