Abstract:
A pressure relief valve control system provides a method and apparatus for rapidly closing a relief valve in response to excess fluid pressure. The system uses a programmable controller to rapidly communicate pressure changes to a solenoid actuated valve and two control valves. The solenoid actuated valve has a dedicated accumulator and the two control valves have another dedicated accumulator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to pending U.S. Patent Application Ser. No. 61/403,131, filed Sep. 10, 2010 and entitled “System for Accelerating Relief Valve Opening.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for accelerating the opening of a relief valve. More particularly, the present invention relates to a method and apparatus for enhancing the rapidity of opening a relief valve in response to measured overpressure. 
     2. Description of the Related Art 
     Relief valves are used for processes involving flow to ensure that excessive system pressures will not cause major failures in the system. Typical relief valve control systems are used to control the relief valves associated with mud pumps on drilling rigs. These pumps are high powered and deliver fluids at high flow rates and delivery pressures. 
     Starting a pump against a closed valve or a plugged line will invariably result in major damage to the system unless the relief valve for the mud system opens extremely quickly. The currently available relief valves for mud systems are slow to open, so that failures often occur. 
     Currently used mud pumps accelerate rapidly and can quickly fill any damping accumulators and excessively pressurize the system before conventional relief valves can react to relieve the excessive pressures. Reaction times of less than 0.5 second are needed for mud pump relief valves. Even with the rapid measurement of system pressure, valve mechanical response times for existing valves are excessive. 
     A need exists for improved means to rapidly open mud system relief valves. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention relate to a pressure relief valve control system for rapidly closing a relief valve in response to excess fluid pressure. The system uses a programmable controller to rapidly communicate pressure changes to a solenoid actuated valve and two control valves. The solenoid actuated valve has a dedicated accumulator and the two control valves have another dedicated accumulator. 
     One embodiment includes a pressure relief valve control system comprising: (a) a normally closed relief valve having a selectably operable double acting cylinder with a first port and a second port, wherein the cylinder moves to a first position or a second position in response to changes in measured fluid pressure changes, wherein increased fluid pressure in the first port moves the cylinder to the first position to open the relief valve and increased fluid pressure in the second port moves the cylinder to the second position to close the relief valve; (b) a hydraulic pump and a hydraulic reservoir; (c) a first accumulator and a second accumulator charged by the hydraulic pump from fluid in the reservoir; and (d) a valve control system including (i) a pressure sensing device for monitoring the fluid pressure changes, (ii) a solenoid controlled valve responsive to the pressure sensing device and in fluid communication with the first accumulator, the reservoir, and a pilot pressure line; (iii) a first control valve connected to a first side of the cylinder, wherein the first control valve is in fluid communication with the second accumulator, the pilot pressure line, the reservoir, and the first port; and (iv) a second control valve connected to a second side of the cylinder, wherein the second control valve is in fluid communication with the second accumulator, the pilot pressure line, the reservoir, and the second port; whereby whenever the pressure sensing device senses a fluid pressure greater than a predetermined pressure an electronic signal is sent to the solenoid operated valve that opens the pilot pressure line to a fluid pressure in the second accumulator thereby activating the first and second control valves to open the relief valve. 
     Another embodiment includes a pressure relief valve control system comprising: (a) a normally closed relief valve having a selectably operable double acting cylinder with a first port and a second port, wherein the cylinder moves to a first position or a second position in response to changes in measured fluid pressure changes, wherein increased fluid pressure in the first port moves the cylinder to the first position to open the relief valve and increased fluid pressure in the second port moves the cylinder to the second position to close the relief valve; (b) a hydraulic pump and a hydraulic reservoir; (c) a first accumulator and a second accumulator charged by the hydraulic pump from fluid in the reservoir; and (d) a valve control system closely coupled to the relief valve, the hydraulic pump and reservoir, and the first and second accumulators, wherein the valve control system includes (i) a pressure sensing device for measuring fluid pressure changes, (ii) a programmable logic controller for monitoring the fluid pressure changes and sending out an electronic signal whenever the measured fluid pressure exceeds a predetermined desirable pressure, (iii) a solenoid controlled valve responsive to the electronic signal from the programmable logic controller and in fluid communication with the first accumulator and a pilot pressure line; (iv) a first control valve connected to a first side of the cylinder, wherein the first control valve is in fluid communication with the second accumulator, the pilot pressure line, the reservoir, and the first port; and (v) a second control valve connected to a second side of the cylinder, wherein the second control valve is in fluid communication with the second accumulator, the pilot pressure line, the reservoir, and the second port; whereby whenever the solenoid operated valve responds to the electronic signal to open the pilot pressure line to a fluid pressure in the second accumulator thereby activating the first and second control valves to open the relief valve. 
     Yet another embodiment includes a pressure relief valve control system comprising: (a) a normally closed relief valve having a selectably operable double acting cylinder with a first port and a second port, wherein the cylinder moves to a first position or a second position in response to changes in measured fluid pressure changes, wherein increased fluid pressure in the first port moves the cylinder to the first position to open the relief valve and increased fluid pressure in the second port moves the cylinder to the second position to close the relief valve; (b) a hydraulic pump and a hydraulic reservoir coupled to the pressure relief valve; and (c) a valve control system including (i) a pressure sensing device for monitoring the fluid pressure changes, (ii) a programmable logic controller in communication with the pressure sensing device, (iii) a solenoid controlled valve responsive to an electronic signal sent by the programmable logic controller in response to a detected pressure that exceeds a predetermined pressure, (iv) a first accumulator dedicated to the solenoid controlled valve, wherein the first accumulator is charged by the hydraulic pump from fluid in the reservoir, (v) a pilot pressure line, wherein whenever the solenoid controlled valve responds to excessive pressure the fluid in the first accumulator flows down the pilot pressure line, (vi) a first pilot operated control valve connected to a first side of the cylinder, wherein the first control valve is in fluid communication with a second accumulator, the pilot pressure line, the reservoir, and the first port; and (vii) a second pilot operated control valve connected to a second side of the cylinder, wherein the second control valve is in fluid communication with the second accumulator, the pilot pressure line, the reservoir, and the second port; whereby whenever the electronic signal is sent to the solenoid operated valve that opens the pilot pressure line to fluid flowing from the second accumulator thereby activating the first and second control valves to open the relief valve. 
     The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows an outlet end view of the relief valve on which the control system of the present invention is located. 
         FIG. 2  shows a longitudinal cross-sectional view, taken along the line  2 - 2  of  FIG. 1 . 
         FIGS. 3 ,  4 , and  5  are orthogonal views showing the intimate mounting of the hydraulic control system on the pressure relief valve. 
         FIG. 6  shows the control valve system hydraulic schematic. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A relief valve control and operator system  10  is described that consists of two intimately coacting subsystems. The first subsystem  100  is the relief valve with its operating hydraulic cylinder. The second subsystem  11  is the control and operating system. The relief valve control and operator system  10  is designed for high pressure service in abrasive drilling mud. 
     The Relief Valve and Operating Cylinder 
     The relief valve  101  has a hydraulic operating cylinder  110  directly mounted to the relief valve body  102 . The operating Cylinder  110  serves to both open and close the relief valve  101 . 
     The relief valve  101  is normally closed. Fast cycling of the relief valve  101  is not desirable, but fast opening is. With all hydraulic components located either directly on the relief valve  101  in a manifold block  24  or immediately adjacent the relief valve, response times are minimized. One exception to this principle is that it is unnecessary to locate the electronic pressure sensors or the electronic controller for the relief valve and its hydraulic control system  10  immediately adjacent the relief valve  101 , due to the rapid response time of electronics. 
     Referring to  FIGS. 1 and 2 , the relief valve and operating cylinder  100  consists of a valve body  102  and a sealing poppet  138  consisting of sealing plug  103  and carrier cylinder  122 . The rectangular prismatic body  102  is provided with an inlet port  104  on one side and has a cylindrical central cavity  126  with a coaxial central outlet port  105  at the first end of the body. 
     The outlet port  105  at the first end of the body  102  is provided with a concentric cylindrical seal groove  131  for a metallic annular sealing ring (not shown). The outlet port  105  also has a parallel concentric circular array of tapped holes  132  (seen in  FIG. 1 ) for mounting threaded studs used for connection to the outlet piping of the mud system. A cylindrical passage  136  coaxial with the central cavity  126  extends from the central cavity  126  to an opening in the opposed second end of the body  102 . A regular circular array of drilled and tapped holes (not shown) is concentric with the opening located on the second end of the body  102 . These tapped holes serve to mount threaded studs (not shown) to provide connecting means to the valve body  102  for the operating cylinder  110 . 
     Similarly to the outlet port  105 , the inlet port  104  of the relief valve body  102  is provided with a groove  134  for a metallic annular sealing ring (not shown) and a circular array of tapped holes for mounting threaded studs used for sealing structural connection to the inlet piping of the mud system (not shown). The cylindrical central cavity  126  of the body  102  has a pair of stepped counterbores  140 ,  141  at its outlet end. A thin wall cylindrical wear sleeve  120  is housed in the wear sleeve counterbore  141  closest to the first end of the body  102 , while the cylindrical valve seat  106  is housed in the larger, shorter seat counterbore  140  adjacent the outlet end of the cylindrical central cavity  126 . Typically, the wear sleeve  120  is made of a wear resistant material and is replaceable. 
     The valve seat  106  is a short cylindrical sleeve of hard wear resistant material having an annular external groove for a circumferential seal which seals between the outer diameter of the valve seat and the seat counterbore  140  of the body  102 . The valve seat  106  is pressed into its counterbore  140 . The interior edge of the valve seat  106  on its inlet side has a frustroconical taper sealingly comatable with a corresponding frustroconical face  107  on the sealing plug outlet end of the sealing plug  103 . 
     As seen in  FIG. 2 , the relief valve  101  utilizes a cylindrical poppet  138 , consisting of sealing plug  103  and carrier cylinder  122 , which is normally seated against its seat  106  so that the valve  101  is normally closed. The sealing plug  103  is a short cylindrical section having a frustroconical face  107  at its outer end, wherein the frustroconical face is comatable with the corresponding frustroconical face of the seat  106 . The sealing plug  103  has on its outlet end a through hole with a outwardly facing counterbore for the head of a retention screw  125 . The opposed transverse end to the of the sealing plug  103  has a shallow central counterbore and an annular face groove holding a seal near its outer periphery. 
     The carrier cylinder  122  of the cylindrical poppet  138  has coaxial opposed drilled and tapped holes on its transverse ends. The end of the carrier cylinder  122  abutting the sealing plug  103  has a short cylindrical extension which is a close fit to the counterbore on the inlet end of the sealing plug. A screw  125  engaged in the threaded hole on the outlet end of the carrier cylinder  122  retains the sealing plug  103 , while an O-ring mounted in the annular face groove of the sealing plug  103  seals between the two adjacent parts  103  and  122 . On the face of the relief valve body  102  opposed to the inlet port  104  is a drilled and tapped hole coaxial with the inlet port  104  and mounting a pressure port sealing plug assembly  121 . 
     The end of the relief valve body  102  opposed to the end having the outlet port  105  has a axially short counterbore at its outer end. The cylinder rod end  144  is a stepped cylinder having a substantially constant outer diameter except for a short transverse flange located in its central portion. Multiple external annular grooves on the first end of cylinder rod end  144  house annular seals which seal between the cylinder rod end outer diameter and the cylindrical passage  136  of the valve body  102 . The transverse flange of the cylinder rod end is sealingly engaged with the counterbore on the external end of the cylindrical passage  136  of the valve body  102 . 
     The cylinder rod end  144  has a through bore  146  which has a close fit to the outer diameter of the central portion of the cylinder rod  112 . A female annular groove housing an annular seal sealingly comatable with the outer diameter of the cylinder rod  112  is located in the through bore  146  of the cylinder rod end  144 . The end of the cylinder rod end  144  entered into the cylindrical passage  136  of the valve body  102  has a counterbore  145  having female annular seal grooves located on that end. The counterbore  145  is a close slip fit to the outer diameter of the inlet end of the of the carrier cylinder  122 , and annular female seals seal between the counterbore and the external cylindrical surface of the carrier cylinder  122 . 
     One or more radial vent holes  123  penetrate through the flange of the cylinder rod end  144  and intersect its counterbore  145 . The venting provided by the vent holes  123  prevent a hydraulic lock being formed by air trapped between carrier cylinder  122  and the counterbore  145  of the cylinder rod end  144 . 
     The cylinder body  111  of the relief valve operating cylinder  110  externally is a short stepped cylinder having at its first end a flange with a larger diameter adjacent where it is attached to the end of the relief valve body  102  opposed to the valve outlet end. The attachment of cylinder body  111  and the relief valve body  102  is made by threaded fasteners (not shown) inserted in a bolt hole circle (not shown) having the same pattern as the bolt hole circle in the adjacent end of the valve body. One or more shallow radial vent outlet grooves  124  are cut in the transverse face of the cylinder body on its first end. 
     The cylinder body  111  has a large bore  114  extending most of its length which is a close slip fit to the outer diameters of both the piston  113  and the upper cylindrical end of the cylinder rod end  144 . A short drilled and tapped through bore penetrates the reduced outer diameter portion of the cylinder body  111  at its second end. Radial ports  115  and  116  tapped at their external ends penetrate between the exterior of cylinder body  111  and the bore  114  respectively near the first and second ends of the cylinder body. 
     Opening port  115  admits fluid to urge the relief valve  101  open, while closing port  116  admits fluid to urge the relief valve  101  closed. Threaded fittings  147  are used to connect between ports  115  and  116  of the cylinder body  111  and supply lines  66  and  73  of the control and operator system  11 . These ports  115 ,  116  accommodate the hydraulic flows from the control and operator system  11 . These controllable flows through ports  115 ,  116  cause the relief valve assembly  101  to move reversibly between its closed and open positions. A male seal on the external second end of cylinder rod end  144  seals between the cylinder rod end and the large bore  114  of the cylinder body  111 . 
     The piston  113  of the relief valve operating cylinder is a short cylindrical disk which externally is a close slip to the bore  114  of the cylinder body  111 . An annular seal located in a male groove on the periphery of the piston  113  seals between the piston and the bore  114 . The piston  113  has a threaded section of its through bore and a short straight counterbore on its opposed end which faces the relief valve body  102 . 
     The cylinder rod  112  is an elongate cylinder having a first male thread located at a first end and a second male thread at its second end. A male seal groove is closely located inwardly from the interior end of the second male thread at its second end. The first male thread is threadedly engaged with the female thread on the end of the carrier cylinder  122  opposed to the end attached to the sealing plug  103 . The second male thread of the cylinder rod  112  is engaged with the thread of the piston  113 , and a male seal in the groove of the cylinder rod seals between the rod and the piston. The piston end of the cylinder rod  112  is tapped and threadedly engaged with elongated cylindrical tattletale rod  80 . 
     The tattletale guard  81  is a hollow externally threaded nut having a short external hex flange and an extended sleeve section on its end opposed to the threads. The extended sleeve section has multiple circumferentially spaced elongated slots, while the threaded end of the tattletale guard has a female seal groove and seal in its bore. The bore of the tattletale guard  81  is a close slip fit to the tattletale rod  80 , and the female seal in the tattletale guard seals therebetween. The thread of the tattletale guard  81  is sealingly engaged with the external end of the thread of the throughbore of the cylinder body  111  so that the sleeve section of the tattletale guard is externally visible. The length of the tattletale rod  80  is selected so that it is not visible in the slots of the tattle guard  81  when the relief valve  101  is closed, but becomes visible there when the relief valve  101  is open. 
     The cylindrical poppet  138  of the relief valve  101  is biased towards its closed, seated position against its seat  106  both by the retained mud system pressure while the valve is closed and by hydraulic pressure maintained on the piston side of a hydraulic cylinder  110 . The hydraulic relief valve operating cylinder  110  that operates the relief valve  101  has the first end of its cylindrical rod  112  externally threadedly attached to the drilled and tapped end of the carrier cylinder  122  on the end opposed to the sealing plug  103 . The opposed end of the rod  112  has a similar male thread and is threadedly attached to a drilled and tapped through hole in the cylindrical disk piston  113  of the operating cylinder  110 . 
     The Control and Operator System 
     An important element in achieving the rapid response time for the relief valve  101  is the choice of the configuration of the hydraulic circuit for the relief valve control and operator system  11  and the constituent elements of that hydraulic circuit. Referring to  FIG. 6 , the circuit is described using conventional hydraulic symbols. 
     The relief valve control and operator system  11  consists of an air supply system for providing a conditioned air supply, the integrated hydraulic pump and reservoir  16 , the manifold block  24  mounting the control valving and other system elements, and the accumulators  40 ,  50  which are directly mounted on the manifold block  24 . The relief valve control and operator system  11  is directly mounted on the body  102  of the relief valve assembly  101 . 
     Starting from the lower lefthand corner of the drawing and proceeding sequentially, rig air from a remote source (not shown) enters the control and operator system  11  through a quick connect fitting  12 , passes through a filter  13  and a pressure regulator  14  with an output pressure gauge  15  to an air-driven hydraulic pump system  16  via air delivery line  20 . The pneumatically driven hydraulic pump system  16  has its own integrally mounted tank or reservoir  19  and inlet filter  18 . 
     Output from the pneumatically driven pump  17  passes into the balance of the system  11  by way of pressure delivery line  25  having an intermediately positioned high pressure filter assembly consisting of parallel mounted components  27 ,  28 , and  29 . High pressure filter  28  has both an associated bypass check valve  27  and differential pressure gauge  29  for monitoring pressure losses in the filter  28 . A check valve  30  mounted downstream of the high pressure filter assembly prevents backflow towards the pump  17  through the pressure delivery line  25 . A system pressure relief valve  36  is located immediately downstream from the outlet check valve  30  for the high pressure filter assembly. Any relieved overpressure outflow from relief valve  36  is able to return to the reservoir  19  by way of flow return line  26 . 
     Normal conditioned flow from the pump  17  passes by way of pressure delivery line  25  to primary pressure supply header  39 . Primary pressure supply header  39  supplies both accumulators  40  and  50 , a first control valves  60  and a second control  70  both pilot operated directional valves, and also selectably operable manually operated system drain valve  43 . Drain valve  43  is used to bleed pressure from accumulator  40  whenever the mud pump system is either inoperative or being serviced. Valve  43  exhausts accumulator  40  through outlet line  44  which is in turn connected to the flow return line  26 . 
     The secondary accumulator  50 , typically the smaller accumulator, is isolated from primary accumulator  40  by check valve  42  located in the charging line for accumulator  50 . The charging pressure for the accumulators  40  and  50  is measured by pressure gauge  41  connected to primary pressure supply header  39 . Selectably operable manual ball valve  56  connected to smaller accumulator  50  by delivery line  51  and drain line  55  permits selective draining of accumulator  50 , with the draining flow from valve  56  through line  57  to flow return line  26  and the hydraulic system tank reservoir  19 . 
     Three way  2  position solenoid operated spring return directional valve  52  is shifted from its spring biased unactivated position by an integral solenoid, with the power applied to the solenoid over signal line  53  from the programmable electronic controller  210 . The electronic controller rapidly applies power within a few milliseconds to the solenoid of valve  52  in the event of electronically measured mud pump system overpressure. 
     Valve  52  has its two inlet ports and one outlet port. The normally connected inlet port is attached to vent line  54  which in turn is connected to the control valve drain line  47  and thence to flow return line  26 . The normally unconnected inlet port of valve  52  is connected to delivery line  51  from accumulator  50 . The single outlet side port of valve  52  is connected to pilot pressure line  58 , which is in turn connected to the pilot ports of both the first piloted control valve  60  and the second piloted control valve  70 . 
     Three way  2  position pilot operated spring return directional valve  60  is shifted from its spring biased unactivated position by pilot pressure delivered by pilot pressure line  58 , with the pressure valved by solenoid operated valve  52 . Valve  60  has its two inlet ports and one outlet port. The normally connected inlet port is attached to drain line  63  which in turn is connected to the control valve drain line  47  and thence to flow return line  26 . The normally unconnected inlet port of valve  60  is connected by line  61  to primary pressure supply line  39  from the accumulator  40 . 
     The single outlet side port of valve  60  is connected to opening pressure line  62 , which is bifurcated to supply parallel needle valve  64  and check valve&#39;65. Check valve  65  permits flow to pass from valve  60 , but stops reverse flow back towards valve  60  in its branch. The flow paths on the side of valves  64  and  65  away from valve  60  recombine into connection  66  which supplies opening port  115  on the relief valve control cylinder  110 . In its spring biased normal position, valve  60  drains fluid away from the opening side of the relief valve operating cylinder  110 . 
     Three way  2  position pilot operated spring return directional valve  70  also is shifted from its spring biased unactivated position by pilot pressure delivered by pilot pressure line  58 , with the pressure valved by solenoid operated valve  52 . Valve  70  has two inlet ports and one outlet port. The normally connected inlet port is attached to primary pressure supply line  39  which in turn is connected to accumulator  40 . The normally unconnected inlet port of valve  70  is connected to drain line  71  and thence to control valve drain line  47  and flow return line  26 . The outlet port of valve  70  is connected to supply line  73  which is in turn connected to closing port  116  on the valve closing piston side of relief valve operating cylinder  110 . 
     The preceding description describes a control system  10  wherein when the solenoid valve  52  is deenergized, the pressure relief valve  101  is closed. In the event that it is desired that the control system  10  maintains the pressure relief valve  101  closed whenever the solenoid valve  52  is energized and then opens the pressure relief valve  101  whenever the solenoid valve  52  is deenergized, this is achieved by interchanging the locations of directional valves  60  and  70 . If this is done, then energizing the solenoid of valve  52  applies pilot pressure to shift both interchanged valves  60  and  70 . For this situation, valve  70  then vents fluid from the rod end of cylinder  110  while valve  60  supplies fluid to the piston end of the cylinder  110 . This situation holds the pressure relief valve  101  closed until the signal to the solenoid of valve  52  is removed. 
     For some users of the present invention, this latter arrangement is preferable, since if electrical power to the system  10  fails, the rig mud pumps will be protected from overpressure. However, the venting of the mud system by the pressure relief valve does not allow for the circulation of mud until the power is restored. 
     Operation of the Invention 
     While the power source for creating the hydraulic pressure and flow to operate the relief valve and its control system is pressurized air provided by a remote outside source (the rig with the mud pump or pumps), the system utilizes the accumulators  40  and  50  to store the hydraulic pressure and flow necessary to operate the relief valve assembly  101  and its control and operator system  11 . This utilization of the two accumulators  40  and  50  makes the relief valve response time substantially independent of the pneumatic power transfer rate. This independence is in large part a result of the sizing of the accumulators  40  and  50  and the fact that the relief valve does not cycle quickly. 
     When the control and operator system  11  of the present invention is powered up, the mud pumps are temporarily shut down and venting ball valves  43  and  56  are closed. At that point, the air supply is turned on. Air passing through the quick connect  12  and conditioned by the filter  13  and the regulator  14  causes the pneumatically driven pump  17  to deliver hydraulic flow. The delivered hydraulic flow passes through pressure delivery line  25 . As the fluid passes through the delivery line  25  it is filtered by the high pressure filter  28  and has its pressure regulated by relief valve  36  before entering and fully charging both accumulators  40  and  50 . Once the accumulators  40  and  50  are fully charged, check valve  42  causes them to behave independently. 
     The accumulator  50  pressure and flow potential are used for piloting valves  60  and  70  which operate in parallel to control the position of the hydraulic cylinder  110  which opens and closes the relief valve  101 . Since the volumes required to simultaneously pilot both valves  60  and  70  are quite small, accumulator  50  is typically smaller than accumulator  40 , which must deliver higher flow volumes. The pressure and flow potential of accumulator  40  are used directly to shift the relief valve operating cylinder  110  that responds to flows passing through pilot operated valves  60  and  70  in response to piloting pressure from piloting valve  52 . 
     Following the charging of accumulators  40  and  50 , the relief valve assembly  101  is closed so that the mud pumps can be used for their intended purposes. An electronic pressure sensor continuously measures system pressure, which is monitored by a programmable logic controller (“PLC”)  210 . In the event that excessive pressure is determined by the PLC  210  through a comparison of a desired pressure and the actual measured pressure, the PLC  210  transmits a signal with sufficient power down the solenoid on/off power cable  53  to the solenoid of valve  52 . Such a signal on power cable  53  causes the solenoid valve  52  to quickly shift so that the pressure and flow from accumulator  50  passes through valve  52  and into the pilot pressure line  58 . 
     Pilot pressure from valve  52  on line  58  causes both valves  60  and  70  to shift from their normal positions. When valves  60  and  70  shift from their normal positions, pressure and flow from larger accumulator  40  passes through valve  60  and through supply line  62 , both needle valve  64  and check valve  65 , and then through connecting line  62  and into the opening port  115  of cylinder  110  to urge cylinder  110  to retract rod  112  and open the relief valve  101 . 
     At the same time, pressure from accumulator  40  is removed from its previous connection through valve  70  and supply line  73  to closing port  116  of cylinder  110 . The hydraulic fluid on the piston side of cylinder  110  is vented from cylinder  110  through valve  70  to tank  18  through lines  71 ,  47 , and  26  as the piston  113  of cylinder  110  is urged to open the valve  101  by the higher pressure fluid entering the cylinder  110  on its rod end. When the sealing plug  103  of the valve  101  is lifted from its seat  106 , the mud pump system fluid is vented through outlet port  105  of the relief valve  101 . 
     Normally, it is desirable for the mud pumps to be shut off following system venting by the relief valve  101  so that the problem can be determined and rectified. During such a waiting period, the hydraulic pump  17  will fully recharge the accumulators  40  and  50 . Reclosing the relief valve  101  is accomplished by having the PLC remove the signal on power cable  53 . This permits the spring of valve  52  to shift valve  52  to its normal position so that the piloting pressure on pilot pressure line  58  is vented through valve  52  to tank  19 . 
     When the pilot pressure on line  58  is vented, the springs on valves  60  and  70  return those valves to their normal positions so that pressure is removed from the rod side of cylinder  110  and applied to the piston side of cylinder  110 . Consequentially, rod  112  of cylinder  110  is urged forward. The flow coming out of the rod end of cylinder  110  cannot pass through check valve  65 , so the flow is restricted during passage through restrictor needle valve  64  as the flow is returned to tank  18 . This slows reclosure of relief valve  101  so that the sealing plug  103  and the seat  106  are not damaged during valve reseating. 
     Advantages of the Invention 
     The provision of operating fluid supplies for achieving quick relief valve opening from close coupled accumulators, flow connections, and control valves markedly decreases relief valve response times. This avoidance of reliance on typically remote and slowly responding pumps to provide the most significant part of the actuation oil during the actual relief valve opening reduces relief valve opening times more than enough (i.e., by more than halving of response time) to reliably avoid mud system damage even when the system pumps are deadheaded into a closed system. 
     Utilization of a close coupled design based on a manifold block for housing most of the flow paths and hydraulic system valves markedly improves hydraulic system response time. Use of a rapid response solenoid controlled valve to pilot the main piloted three way two position flow control valves further improves system response time. Use of two separate piloted three way valves, one for each side of the relief valve operating cylinder, reduces flow restrictions to also improve relief valve response time. 
     System construction using cartridge valves and a manifold block reduces leakage and the probability of in service damage. Other system advantages may be obvious to those skilled in the art. 
     It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.