Abstract:
A dual filter isolation block for isolating a fluid stream between a fluid source and a user device and including a main body, a first fluid path provided in the main body between the source and the user device and a first filter provided in the first fluid path. A second fluid path is also provided in the main body between the source and the user device and a second filter is included in the second fluid path. A pair of spools are slidably disposed in the main body and intersect the first fluid path and the second fluid path, respectively, for selectively isolating the first fluid path and the first filter from the second fluid path and the second filter. In a specific application the dual filter isolation block selectively isolates a pair of filters for filteringg an operating fluid such as hydraulic oil or fluid between an actuator and a servo valve to protect the servo valve from contaminants in the operating fluid. The filters are each designed for separate removal and replacement while the hydraulic fluid flows through the other filter, to avoid interrupting operation of the user device. A method for maintaining a flow of operating fluid between a fluid source and a user device while continuously filtering the operating fluid is also included.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the protection of control devices and mechanisms such as servo valves from contaminated operating fluid and more particularly, to a dual filter isolation block for positioning between a source of operating fluid such as hydraulic fluid or oil and the user mechanism or device receiving the operating fluid, wherein the dual filter isolation block includes a main body having a pair of fluid paths, a pair of filters provided in the fluid paths, respectively, and a pair of spools disposed for sliding operation in the main body of the isolation block and intersecting the fluid paths, respectively, such that the operating fluid is selectively diverted through one of the fluid paths and the associated filter, while the remaining fluid path and filter remain free of operating fluid. The latter filter can then be removed and replaced without interrupting operation of the user device because of the constant flow of operating fluid through the first fluid path and filter to the user device. 
     In a specific embodiment the dual filter isolation block of this invention is designed to isolate hydraulic oil or fluid flowing between an actuator and a servo valve, which actuator operates steam valves on a turbine and the servo valve serves to control operation of the actuator. A pair of distinct fluid paths are provided in the main body of the isolation block to selectively receive operating hydraulic oil or fluid flowing under pressure from a storage tank through the actuator and the isolation block, into the servo valve. Each of these fluid paths includes a removable filter and a pair of spool valves operate in sliding concert in the isolation block and intersect the respective fluid paths, such that the hydraulic operating oil or fluid can be directed from a tank through the actuator and through a selected one of the fluid paths and filters into the servo valve and back from the servo valve through the isolation block and the actuator to the tank, while the other filter is removed and replaced. This operation eliminates the necessity for discontinuing or disrupting operation of the servo valve while typically removing a conventional filter which serves the conventional single fluid path between the actuator and the servo valve. 
     2. Description of the Prior Art 
     Various mechanisms are known in the art for diverting fluid flow from one point to another in various types of devices. U.S. Pat. No. 3,521,673, dated Jul. 28, 1970, to Gruner, et al, details a constant flow fluid diverting valve which has six fluid ports and is used in four pipe temperature conditioning systems, with a cylindrical plunger longitudinally movable in a valve body to selectively connect to the appropriate ports. U.S. Pat. No. 4,271,020, dated Jun. 2, 1981, to Van Meter, details a valve for a filter device, wherein the valve assembly includes a rotatable valve spindle removable with respect to a valve housing and having first and second channels communicating with the filter. A bypass channel is also provided to bypass the fluid filter. Fluid may flow through the respective channels, including the bypass channel, responsive to rotation of the spindle into a selected position. U.S. Pat. No. 4,469,131, dated Sep. 4, 1984, to Paul L. Traylor, details a spool valve including a valve stem mounting a pair of valve heads removable in a body and cooperating with various valve seats to direct fluid along respective paths through the fluid body. U.S. Pat. No. 4,501,295, dated Feb. 26, 1985, to Williams, details a transfer valve having a valve casing with a closed bottom, a closed top and a separator plate dividing the interior of the valve casing into an upper chamber and a lower chamber. Inlet and outlet ports communicate with the upper and lower chambers and two additional ports open into both the upper chamber and the lower chamber. Valves are provided in the upper and lower chamber and a control rod extends through the device to simultaneously rotate the valve and channel fluid through the respective ports. U.S. Pat. No. 4,683,914, dated Aug. 4, 1987, to Brisland, details a slide valve having a valve body with a slide mounted therein for controlling opening interconnection and closing of various valve ports in the body. U.S. Pat. No. 5,152,320, dated Oct. 6, 1992, to Zimmerly, details a diverter valve which includes a valve body with two identical sections having valve seats and a valve stem extending through the valve body. A valve actuator lifts the valve stem, closing a pair of plugs in the valves and selectively allowing fluid to flow from various ports communicating with the valve body. U.S. Pat. No. 5,184,643, dated Feb. 9, 1993, to Raymond, details a valve sleeve assembly, typically having a valve sleeve defining a generally truncated, triangular, upraised land formed by complimentary shaped, adjacent recesses, when the sleeve is used as shown in a section taken along a radial plane perpendicular to the axis of the spool bore. 
     It is an object of this invention to provide a new and improved dual filter isolation block or selectively filtering an operating fluid from a source to a user apparatus or device and facilitating removal and replacement of one of the filters in the isolation block without discontinuing or interrupting operation of the user device. 
     Another object of the invention is to provide a dual filter isolation block for sandwiching between a source of operating fluid and a user or control device receiving that fluid, which isolation block includes a pair of distinct fluid paths extending through the isolation block and serving a pair of filters, respectively, with a pair of spools operating in sliding concert in the isolation block and extending through the fluid paths, respectively, such that the operating fluid can be selectively diverted through one of the fluid paths and its corresponding filter into the user or control device, thus leaving the second fluid path and filter free of operating fluid to facilitate changing the second filter without the necessity of interrupting the flow of operating fluid from the source to the user or control device. 
     Still another object of the invention is to provide a dual filter isolation block and method of use for protecting a user device or mechanism from contaminants in operating oil or fluid flowing from a source, which dual filter isolation block is inserted between the source and the user device. The dual filter isolation block is characterized by a pair of fluid paths, each fitted with a filter and a pair of slidably disposed spools intersecting the respective fluid paths to facilitate selective isolation of one of the fluid paths and the filter from the other fluid path and filter by slidable operation of the spools in the isolation block. 
     Yet another object of this invention is to provide dual filter isolation block and method for isolating an operating oil or fluid such as hydraulic fluid between an actuator and a control device such as a servo valve in order to protect the servo valve from contaminants in the hydraulic fluid. The isolation block includes a main body; a pair of separate fluid paths provided in the main body extending from the actuator to the servo valve and a pair of filters provided in the fluid paths, respectively; and a pair of spools having areas of reduced diameter for fluid flow, the spools slidably disposed in the main body of the isolation block and intersecting the respective fluid paths, such that the flow of hydraulic fluid from the actuator into the servo valve is isolated in and directed through a selected one of the fluid paths, the areas of reduced diameter in the spools and the associated filter and the opposite filter can be replaced without interrupting the flow of hydraulic fluid between the actuator and the servo valve. 
     still further object of the invention is to provide a method for protecting an end user mechanism or device such as a servo valve from contaminants in an operating fluid flowing from a source to the end user device, which method includes providing a dual filter isolation block between the operating fluid source and the end user device; providing a pair of fluid paths in the isolation block, both of which fluid paths include a removable filter; providing a pair of slidably-operated spools having areas of reduced diameter in the isolation block for intersecting the fluid paths, respectively; and operating the spools in concert to direct a flow of operating fluid from the fluid source through one of the fluid paths and its associated filter and spool in the isolation block, to the user device, thus facilitating removal and replacement of the second filter without interrupting the flow of operating fluid from the source to the user device. 
     SUMMARY OF THE INVENTION 
     These and other objects of the invention are provided in a new and improved new filter isolation block and method for isolating an operating fluid such as hydraulic fluid between a control device such as an actuator and an end user control mechanism or device such as a servo valve, as in a turbine electricity generating system, which isolation block includes a pair of fluid paths and a pair of filters provided in the fluid paths, respectively, along with a pair of spool valves having fluid flow cavities, slidably seated in the isolation block and intersecting the fluid paths, respectively, wherein operating hydraulic fluid is allowed to flow through the actuator and through a selected one of the fluid paths and the spool cavities in the filter isolation block, into the servo valve for operating the servo valve responsive to first and second selected positions of the spool valve, and the opposite filter is isolated from the flow of the operating fluid and may be removed from the opposite or second fluid path without interrupting the flow of operating fluid to and from the servo valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by reference to the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a conventional actuator and servo valve combination for operating the steam valves (not illustrated) of a turbine (not illustrated); 
     FIG. 2 is a perspective view of the actuator and servo valve illustrated in FIG. 1, with the dual filter isolation block of this invention inserted therebetween; 
     FIG. 3 is an enlarged view of the servo valve illustrated in FIGS. 1 and 2 and a portion of the actuator, illustrated in phantom, with the dual filter isolation block inserted therebetween; 
     FIG. 4 is a perspective view of the actuator, servo valve and dual filter isolation block illustrated in FIG. 3, more particularly illustrating removal of a filter from the isolated one of the fluid paths provided in the dual filter isolation block; 
     FIG. 5 is a perspective view, including the servo valve face of the dual filter isolation block illustrated in FIGS. 2-4, more particularly illustrating a fluid inlet port, fluid return port and a pair of operating or shifting ports provided therein; 
     FIG. 6 is a perspective view of the opposite side of the dual filter isolation block illustrated in FIG. 5, more particularly illustrating the actuator face of the dual filter isolation block; 
     FIG. 7 is an exploded view of the dual filter isolation block illustrated in FIGS. 5 and 6, more particularly illustrating the internal main body components, including a pair of spool valves and filters that correspond to specific flow paths through the dual filter isolation block; 
     FIG. 8 is a sectional view taken along line  8 — 8  in FIG. 5, more particularly illustrating typical respective flow paths and corresponding filters and spool valves provided in the isolation block main body, wherein the bottom flow path is illustrated as filled with operating fluid responsive to downward shifting and locking of the spool valves in the main body; 
     FIG. 9 is a sectional view taken along line  8 — 8  of the dual filter isolation block illustrated in FIG. 5, more particularly illustrating the flow of operating fluid through the upper fluid path and filter responsive to shifting and locking of the spool valves in an upward operating configuration; 
     FIG. 10 is a sectional view taken along line  10 — 10  of the dual filter isolation block illustrated in FIG. 6, more particularly illustrating a typical inlet pressure port communicating with a fluid inlet port in the main body of the dual filter isolation block; 
     FIG. 11 is a sectional view taken along line  11 — 11  in FIG. 5, more particularly illustrating fluid flow paths intersecting the spool valves in the main body; 
     FIG. 12 is a sectional view taken along line  12 — 12  of the dual filter isolation block illustrated in FIG. 5, more particularly illustrating additional flow paths intersecting the spool valves therein; 
     FIG. 13 is a sectional view and flow diagram of the conventional actuator and servo valve combination illustrated in FIG. 1, more particularly illustrating a typical hydraulic oil or fluid flow from the actuator to the servo valve and from the servo valve back to the actuator, in a typical actuator-servo valve system; and 
     FIG. 14 is a sectional view of the actuator, dual filter isolation block and servo valve, with a flow diagram, more particularly illustrating the dual filter isolation block inserted between the actuator and servo valve. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 13 of the drawings illustrate a conventional turbine operating system wherein steam valves (not illustrated) are used to control the speed of a turbine (not illustrated) and an actuator-servo valve combination is used to control the steam valves. A servo valve  28  is connected to an actuator  30  in functional configuration. The actuator  30  controls the steam valve (not illustrated), which in turn controls the speed of a turbine (not illustrated) in an electricity-generating system, according to the knowledge of those skilled in the art. The servo valve  28  is typically attached directly to the actuator  30  such that an inlet fluid flow  47  flows from the actuator  30  into the servo valve  28  and returns by means of a return fluid flow  48 , as illustrated in FIG. 13. A control fluid flow  49  serves to control operation of the actuator  30  responsive to a pilot fluid flow  50  through the actuator  30  and into the servo valve pilot mechanism  28   a  of the servo valve  28 , further according to the knowledge of those skilled in the art. A servo valve filter  28   b  is typically provided in the pilot fluid flow  50  for filtering the pilot fluid prior to entry into the servo valve pilot mechanism  28   a.    
     Referring now to FIGS. 2 and 14 of the drawings, a dual filter isolation block  1  is inserted between the servo valve  28  and the actuator  30  and includes a valve  42 , illustrated in schematic form in FIG. 14, which represents in schematic a pair of spool valves  5  and  6  (FIG. 3) which control the flow of control fluid through the main body  2  of the dual filter isolation block  1  and selectively, through a top filter  15  and a bottom filter  31 , as hereinafter more particularly described. As in the case of the conventional servo valve  28 -actuator  30  combination illustrated in FIG. 13, a control fluid flow  49  is provided from the actuator  30  through the main body  2  of the dual filter isolation block  1  and into the servo valve  28 . Similarly, an inlet fluid flow  47  extends from a storage tank or vessel (not illustrated) through the actuator  30  and the main body  2  of the dual filter isolation block  1  and into the servo valve  28 , while a return fluid flow  48  extends from the servo valve  28  through the main body  2  of the dual filter isolation block, into the actuator  30  and back to the storage tank or vessel. 
     Referring to FIGS. 3-6 of the drawings, the dual filter isolation block  1  is characterized in a preferred embodiment by a generally rectangular main body  2 , having a flat servo valve face  2   a  and actuator face  2   b  (FIG. 6) for receiving and mounting the servo valve  28  and the actuator  30 , respectively. A bar slot  34   a  is provided on each end of the main body  2  and a bar slot opening  34   b  extends from the bottom of the bar slot  34   a  downwardly through the main body  2 . A spool lock bar  34  element of a lock assembly  39  is designed to removably and selectively seat in the respective bar slots  34   a  and extend beneath a synchronizing bar or plate  12 , attached to the ends of the inlet spool  5  and outlet spool  6  by means of clips  40 , as illustrated in FIGS. 5 and 6. Accordingly, the lock assembly  39  serves to secure the spool lock bar  34  in place in the respective bar slots  34   a  for a purpose which is hereinafter described. A filter access plug  19  is threaded in a corresponding top filter cavity  14  and is sealed therein by means of a sealing washer  19   a  that fits in a sealing washer seat  19   b , as further illustrated in FIG. 4. A top filter  15  is inserted in the top filter cavity  14 , and the sealing washer  19   a  is fitted in the sealing washer seat  19   b  as the filter access plug  19  is threaded into the top segment of the top filter cavity  14 . As further illustrated in FIGS. 5 and 6, a fluid inlet port  22  and a fluid return port  23 , as well as a first shifting port  44  and a second shifting port  45  are typically provided in both the servo valve face  2   a  and the actuator face  2   b  of the main body  2 . It will be appreciated by those skilled in the art that either three or four of these ports may be used in any typical installation, depending upon the design of the servo valve  28  and the actuator  30 . For example, as illustrated in FIG. 14, three of the four ports, the fluid inlet port  22 , the fluid return port  23  and either the first shifting port  44  or the second shifting port  45 , are utilized to accommodate the inlet fluid flow  47 , return fluid flow  48  and the control fluid flow  49  in the main body  2  and connecting with the servo valve  28  and the actuator  30 , with the unused one of the shifting port  44  or the shifting port  45  closed or “blinded” against the servo valve  28  and the actuator  30 . Mount bolt holes  20  extend through the main body  2  from the servo valve face  2   a  to the actuator lace  2   b  for receiving mount bolts (not illustrated) and mounting the dual filter isolation block  1  between the servo valve  28  and the actuator  30 . 
     Referring now to FIG. 7 of the drawings the dual filter isolation block  1  is illustrated in exploded view and it will be appreciated that the spool lock bar  34  can be slidably inserted in the corresponding bar slot  34   a  on either the top or bottom of the main body  2 , depending upon whether the top filter  15  or the bottom filter  31  is to be locked inside the main body  2 . When the spool lock bar  34  is slidably inserted in the selected bar slot  34   a , the corresponding filter access plug  19  is blocked and the grip lock pin  36  of a lock bar grip  35  in the lock assembly  39  is extended through a bar opening  34   c  provided in the spool lock bar  34 , and further into the underlying and registering bar slot  34   b  in the bar slot  34   a , to secure the spool lock bar  34  in the bar slot  34   a  over the filter access plug  19 . In a preferred embodiment a spring-loaded ball  37  is provided in the bottom end of the grip lock pin  36  and is caused to extend from and recess into the grip lock pin  36  by depression and release, respectively, of the push button  38  fitted in the lock bar grip  35 . Accordingly, the spring-loaded ball  37  can be caused to retract in the grip lock pin  36  upon application of pressure to the push button  38 , and the grip lock pin  36  then extended through the bar opening  34   c  in the spool lock bar  34  and into the bar slot  34   b , where it is locked in place by release of pressure from the push button  38  as the spring-loaded ball  37  extends into a slot or depression (not illustrated) provided in the main body  2  at the base of the bar slot  34   b . Similarly, in the lock assembly  39  can be assembled on the bottom side of the main body  2  in a corresponding bar slot  34   a  (not illustrated) as illustrated in phantom in FIG. 7, under circumstances where it is desired to facilitate operation of the dual filter isolation block  1  with the inlet spool  5  and the outlet spool  6  locked in a selected alternative operational mode, as hereinafter further described. 
     Referring again to FIG. 7 of the drawings the inlet spool  5  and outlet spool  6  are each characterized by clip seats  41  at each end that receive clips  40  to facilitate mounting of the respective synchronizing bars  12  on each end of the inlet spool  5  and outlet spool  6 , as illustrated. Additionally, corresponding sets of O-ring grooves  27  are provided in the inlet spool  5  and outlet spool  6  inwardly of the clip seats  41 , for accommodating wiper O-rings  8  and sealer O-rings  9 , respectively. Moreover, an inlet spool cavity  5   a  is provided near the center of the inlet spool  5  and a corresponding, somewhat longer, outlet spool cavity  6   a  is provided near the center of the corresponding outlet spool  6 . The inlet spool  5  is slidably seated in a corresponding inlet spool cavity bore  5   b , while the outlet spool  6  is similarly slidably mounted in a parallel outlet spool cavity bore  6   b , each provided in the main body  2 , as illustrated. It will be appreciated that the inlet spool  5  and outlet spool  6  are constrained to slide in concert in the respective inlet spool cavity bore  5   b  and outlet spool cavity bore  6   b , by operation of the two synchronizing bars  12 , each having bar openings  12   a  and seated on each end of the inlet spool  5  and outlet spool  6  by means of the clips  40 . As further illustrated in FIG. 7, each of the top filter  15  and bottom filter  31  are seated and sealed in the corresponding top filter cavity  14  and bottom filter cavity  31   a , respectively, by means of top and bottom filter seal O-rings  13 , respectively. 
     Referring now to FIGS. 8 and 9 of the drawings, the main body  2  is characterized by a pair of fluid paths, one of which accommodates the top filter  15  and the other, the bottom filter  31 . As illustrated in FIG. 8, the top filter inlet port  16  is typically created by drilling a hole transversely through the main body  2  from the actuator face  2   b  and terminating at the top filter cavity  14 . A weld  18  is provided in the main body  2  at the top filter inlet port  16  to seal the top filter inlet port  16  and a top filter inlet port leg  16   a  extends from the top filter inlet port  16  and terminates at the outlet spool  6 . A top filter outlet port  17  is drilled from the servo valve face  2   a  of the main body  2  downwardly at an angle and connects to the bottom of the top filter cavity  14 . Another weld  18  closes the entrance end of the top filter outlet port  17  and a top filter outlet port leg  17   a  extends from the top filter outlet port  17  to the inlet spool  5 . 
     Similarly, as further illustrated in FIG. 9, a bottom inlet port  32  extends from the actuator face  2   b  of the main body  2  to the bottom filter cavity  31   a , which houses the bottom filter  31 . Another weld  18  closes the entrance end of the bottom filter inlet port  32 . A bottom filter inlet port leg  33   a  joins the bottom filter inlet port  32  to the outlet spool cavity  6   a  of the outlet spool  6 . A bottom filter outlet port  33  extends from the top end of the bottom filter cavity  31   a  to the servo valve face  2   a  face of the main body  2  and is typically drilled from that face in upwardly angular relationship into the bottom filter cavity  31   a , as illustrated. A weld  18  closes the entrance drill bore of the bottom filter outlet port  33  and a bottom filter outlet port leg  33   a  extends from the bottom filter outlet port  33  to the inlet spool cavity  5   a  of the inlet spool  5 . 
     Referring again to FIG. 8 of the drawings, an O-ring seat  7  is typically provided in the outlet pilot pressure port  26   a , provided in the actuator face  2   b  of the main body  2 , to seal this port against a corresponding fluid flow aperture in the actuator  30 . The inlet pilot pressure port  26  extends to the outlet spool cavity  6   a  of the outlet spool  6 , while the outlet pilot pressure port  26   a  extends to the inlet spool cavity  5   a  of the inlet spool  5 , as illustrated. Accordingly, when the dual filter isolation block  1  is in the configuration illustrated in FIG. 8, an operating fluid such as hydraulic oil or fluid introduced under pressure from the actuator  30  into the inlet pilot pressure port  26  at the actuator face  26 , flows downwardly through the annulus created by the outlet spool cavity  6   a  and the outlet spool bore  6   b , to the bottom filter inlet port leg  32   a  and from there into the bottom filter inlet port  32  and through the bottom filter  31  and the top of the bottom filter cavity  31   a , to the bottom filter outlet port  33 . The hydraulic fluid then flows from the bottom filter outlet port  33  through the bottom filter outlet port leg  33   a , to the annulus created between the inlet spool cavity  5   a  and the inlet spool bore  5   b  and from there upwardly, to the pilot pressure port  26   a  at the servo valve face  2   a  and into the servo valve  28 . 
     It will be understood that while the working oil or fluid is constrained to flow through the bottom filter  31  as indicated above in the flow configuration illustrated in FIG. 8, it is not permitted to flow simultaneously through the top filter  15 , since the top filter inlet port leg  16   a  is closed against the outlet spool  6  at the outlet spool bore  6   b  above the outlet spool cavity  6   a , to prevent hydraulic fluid from flowing past that point. Accordingly, since hydraulic working oil or fluid is not introduced into the top filter inlet port  16 , the top filter  15  is isolated from the operating hydraulic fluid and can be removed and replaced by simply unthreading the top filter access plug  19  and removing and replacing the top filter  15 . It is further significant that this operation in no way hinders the flow of operating hydraulic fluid through the bottom filter  31  and to the servo valve  28 , as above described. The inlet spool  5  and outlet spool  6  are locked into the filter  31  flow configuration illustrated in FIG.  8  and access to the bottom access plug  19  is blocked by means of the spool lock bar  34  and the lock bar grip  35  elements of the lock assembly  39 . 
     Referring now to FIG. 9 of the drawings, under circumstances where it is desired to isolate the bottom filter  31  and facilitate a flow of operating hydraulic fluid through the top filter  15 , the lock assembly  39  is removed from the bottom end of the inlet spool  5  by depressing the push button  38  on the lock bar grip  35  and the inlet spool  5  and outlet spool  6  are shifted upwardly in concert to the position illustrated in FIG. 9, thereby also shifting the relative positions of the inlet spool cavity  5   a  and outlet spool cavity  6   a  internally in the main body  2 . The lock assembly  39  is then replaced on the top end of the inlet spool  5  and outlet  5  spool  6 , to block access to the top filter access plug  19 , as illustrated. Consequently, operating hydraulic fluid introduced into the inlet pilot pressure port  26  extends to the annulus created between the outlet spool cavity  6   a  and the corresponding outlet spool bore  6   b  and the hydraulic fluid is caused to flow through that annulus into the top filter inlet port leg  16   a  and from there into the top filter inlet port  16 , through the top filter  15  and from the bottom end of the top filter cavity  14 , through the top filter outlet port  17  and the top filter outlet port leg  17   a , to the annulus created by the inlet spool cavity  5   a  and the inlet spool bore  5   b . From that annulus, the operating hydraulic fluid flows through the servo valve  28  from the outlet pilot pressure port  26   a . While the hydraulic operating fluid is flowing through the top filter  15  as described above, it will be appreciated that it is unable to flow through the isolated bottom filter  31 , since the bottom filter inlet port leg  32   a  is blinded against the inlet spool  5  at the inlet spool bore  5   b  and is not in alignment with the outlet spool cavity  6   a . Furthermore, the bottom filter outlet port leg  33   a  is similarly blinded or closed against the inlet spool  5 . Accordingly, the hydraulic fluid cannot flow through the bottom filter  31  and the bottom filter  31  may be quickly and easily removed from the bottom filter cavity  31   a  by removing the bottom filter access plug  19  as described above with respect to the top filter  15 , without interrupting the flow of hydraulic fluid from the actuator  30  to the servo valve  28  through the top filter  15 . 
     Referring now to FIGS. 8,  9  and  10  of the drawings, hydraulic oil or fluid is caused to enter the inlet pilot pressure port  26  under pump pressure from a tank (not illustrated) and from the actuator  30 , typically by means of a pilot service line  29  (FIG. 10) which extends from the fluid inlet port  22  to the inlet pilot pressure port  26 . Furthermore, FIG. 10 also illustrates the bar slot  34   a  in both the top and bottom ends of the main body  2  for accommodating the spool lock bar  34  element of the lock assembly  39 , as heretofore described, and the mount bolt holes  20  are also illustrated for mounting the main body  2  to the servo valve  28  and the actuator  30  using suitable mount bolts  21 , as illustrated in FIGS. 2-4. 
     Referring now to FIGS. 8,  9  and  11  of the drawings, the inlet spool  5  and outlet spool  6  are shown in section, more particularly illustrating the inlet spool cavity  5   a  and corresponding outlet spool cavity  6   a , as well as the inlet pilot pressure port  26  and the outlet pilot pressure port  26   a . The welds  18  serve to blind off the top filter outlet port  17  and the outlet pilot pressure port  26   a , as further heretofore described. 
     Referring to FIGS. 8,  9  and  12  of the drawings, in similar fashion the inlet spool  5  and outlet spool  6  with accompanying inlet spool cavity  5   a  and outlet spool cavity  6   a  are illustrated, with the connecting bottom filter inlet port  32  and the bottom filter inlet port leg  32   a , as well as the bottom filter outlet port  33  and the bottom filter outlet port leg  33   a , one end of each of which bottom filter inlet port  32  and bottom filter outlet port  33  is terminated by welds  18  to facilitate a flow of hydraulic fluid through the respective ports as described above. 
     In operation, and referring again to the drawings, under circumstances where it is desired to facilitate a flow of operating hydraulic oil or fluid from the actuator  30  to the servo valve  28  and back to the actuator  30  through the main body  2  of the dual filter isolation block  1 , with the flow path extending through the bottom filter  31 , the inlet spool  5  and outlet spool  6  are initially shifted downwardly in the main body  2 , as illustrated in FIG.  8 . Secure positioning of the inlet spool  5  and outlet spool  6  in the configuration illustrated in FIG.  8  and blocking of the bottom filter access plug  19  is assured by sliding the spool lock bar  34  into the corresponding bar slot  34   a  in the bottom side of the main body  2 , depressing the push button  38  and projecting the grip lock pin  36  through the corresponding bar opening  34   c  in the spool lock bar  34  and into the bar slot  34   b  provided in the bottom of the bar slot  34   a . The push button  38  is then released to facilitate extension of the spring-loaded ball  37  outwardly into a slot (not illustrated) provided in the main body  2  to lock the spool lock bar  34  securely in the bar slot  34   a  beneath the lower synchronizing bar  12 . This action prevents shifting of the inlet spool  5  and outlet spool  6  from the position illustrated in FIG. 8 to the position illustrated in FIG.  9 . Accordingly, hydraulic oil or fluid introduced from the actuator  30  into the fluid inlet port  22  illustrated in FIGS. 7 and 10, also flows under pressure through the pilot service line  29  into the inlet pilot pressure port  26  and through the bottom filter  31  as heretofore described, where it exits the outlet pilot pressure port  26   a  and flows into the servo valve  28 . In this flow configuration, as heretofore described, access to the bottom filter  31  is blocked and the hydraulic oil or fluid cannot flow through the top filter  15  and the top filter  15  may therefore be removed and replaced, as further heretofore described. 
     Under circumstances where it is desired to facilitate a flow of hydraulic oil or fluid through the newly installed top filter  15  and change the bottom filter  31 , the push button  38  on the lock bar grip  35  is depressed and the lock bar grip  35  removed from contact with the spool lock bar  34  to facilitate sliding the spool lock bar  34  from beneath the bottom synchronizing bar  12  and from the bottom bar slot  34   a . This action facilitates shifting of the inlet spool  5  and the outlet spool  6  in concert to the position illustrated in FIG. 9, where the spool lock bar  34  is again slipped into position in the top bar slot  34   a  beneath the top synchronizing bar  12  and the spool lock bar  34  again locked into position to block access to the top filter  15  by operation of the push button  38  and spring-loaded ball  37 , as heretofore described. The inlet spool  5  and outlet spool  6  cannot therefore be inadvertently shifted back into the position illustrated in FIG. 8 due to the presence of the spool lock bar  34 . Under these circumstances, hydraulic oil or fluid introduced into the fluid inlet port  22  is also introduced under pressure into the inlet pilot pressure port  26  as heretofore described and flows through the top filter  15  and from the outlet pilot pressure port  26   a , into the servo valve  28 . The isolated bottom filter  31  can then he removed and exchanged as desired and as heretofore described. 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.