Abstract:
A quick disconnect female coupler comprises, inter alia, a wiper seal retained in a radially opening annular groove and including at its rear side an annular recess that allows rearward rolling of the wiper seal in the annular groove when the wiper seal is subjected to a surge of high pressure fluid from the main cavity to the back side of the piston, whereby the wiper seal moves out of the way of the high pressure fluid surge to avoid being forced out of the annular groove; a tubular spacer in the female housing bore the forms therewith an outer flow passage and which serves as a guide for an axially movable valve body, the spacer having an annular land and a rear end post press-fitted in the housing bore and a housing counterbore, respectively, for retaining and aligning the spacer in the housing; a poppet valve provided with orifices in an angled shoulder thereof for avoiding interference with flow previously caused by coil springs used to bias the poppet valve; and an annular protection shield which performs the dual functions of retaining a collar spring in a locking collar chamber and providing a barrier to entry of foreign material into the locking collar chamber.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/247,278 filed Nov. 10, 2000, which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to quick disconnect couplings and, more particularly, to a female quick disconnect coupler which provides for quick disconnect and preferably also quick connect. 
     BACKGROUND OF THE INVENTION 
     Quick disconnect couplings are used, for example, to connect hoses in hydraulic fluid lines. A typical application is on agricultural tractors to connect the tractor hydraulic system with attachable implements. The tractor typically includes one or more female coupler sockets, while the implements include one or more male coupler nipples. Pneumatic and other applications for such couplings are also well known. 
     Over the years changes have occurred in these systems which have required changes and performance improvements in the couplings. One early coupling design is shown in U.S. Pat. No. 4,077,433 where the female coupler includes a valve body slidable within the housing and a poppet valve internal to the valve body. The poppet valve is axially movable to engage a check valve in a male coupler when the male coupler is inserted into the female coupler. When low pressure is present in the male coupler, the poppet valve moves the check valve (ball valve) off its valve seat to allow flow from the female coupler to pass to the male coupler. When higher pressures are present in the male coupler, an internal passage in the poppet valve provides incoming fluid pressure to the rear surface of the poppet valve. Due to the differences in effective surface areas, the fluid pressure assists in driving the poppet valve against the check valve to move the check valve into an open position. 
     An improvement in this coupling is shown in U.S. Pat. No. 4,598,896, where a separate piston is located around the poppet valve. The piston can engage the poppet valve when moved forwardly. An internal passage in the poppet valve provides fluid pressure to the rear surface of the piston, which assists in driving the poppet valve against the check valve in the male coupler in high pressure situations. A spool is also provided around the piston and poppet valve in this coupling. The spool is fixed to the valve body and includes a port for exhausting pressure within the poppet valve. A retainer sleeve with a seal surrounds the port on the spool, and when the valve body slides within the housing (when the male coupler is inserted or removed), the port relieves the internal pressure in the female coupler to atmosphere. 
     In some cases, particularly when a pair of couplers are used to direct fluid to and from a hydraulic cylinder in an implement, a check valve mechanism is also provided in the female coupler to prevent the rapid backflow of pressure out of the female coupler when a pressure imbalance occurs within the system, such as during thermal expansion of the fluid caused by severe operating conditions, or when the implement is dragged over an uneven surface. In these situations, one of the female couplers can allow the check valve in an associated male coupler to close, which can cause a block in the system when the flow through the female coupler is desired. 
     To remedy this problem, some female couplers include a check valve mechanism which allows fluid to flow relatively unimpeded rearwardly to the rear surface of the piston, but which restricts or prevents fluid flow forwardly out of the female coupler. One known check valve mechanism includes a valve ball located within the internal bore of the piston which is spring-biased in both directions to allow fluid to flow rearwardly through the piston at a higher flow rate than forwardly through the piston. 
     The above couplings have received wide-spread acceptance in the marketplace for providing reliable, serviceable and effective components which operate under a variety of conditions. Some of these couplings direct the fluid internally through the poppet valve to the rear surface of the piston. The flow path includes a radial hole formed in the side of the poppet valve, and a central bore extending axially through the poppet valve. A spring is commonly disposed within the central bore of the poppet valve for biasing the poppet valve against the valve seat. As the spring flexes, the spring can interfere with the flow through the radial hole, which can reduce or even temporarily interrupt the flow through the poppet valve. This can cause an uneven driving force of the piston against the poppet valve, which can be undesirable in certain applications. 
     Towards providing a direct and uninterrupted flow path to the rear surface of the piston to facilitate moving the poppet valve against the check valve in the male coupler, U.S. Pat. No. 6,016,835 discloses a quick disconnect coupling wherein the female coupler includes a housing adapted to receive a male coupler. The housing includes a valve body slidable within the housing, and a poppet valve internal to the valve body. A piston surrounds the poppet valve to assist in moving the poppet valve against the check valve in the male coupler. Unlike prior female couplers, the flow passage to the rear surface of the piston is provided internally of the piston, rather than the poppet valve, which provides a direct and uninterrupted flow path to the rear surface of the piston to facilitate moving the poppet valve against the check valve in the male coupler. In one design, the flow path extends axially through a tubular main portion of the piston closely surrounding the poppet valve to an internal cavity bounded by an enlarged end portion of the piston, and then to the rear surface of the piston. The flow path can be provided through one or more bores formed axially through the tubular main portion of the poppet valve. 
     According to second design of quick disconnect coupling disclosed in the &#39;835 patent, a check valve is provided to prevent fluid rapidly flowing from the female coupler during pressure imbalances in the system. The check valve includes an annular wiper seal supported on the rear surface of the piston, and projecting radially inward therefrom. A poppet guide and relief poppet assembly is provided in the rear end of the valve body and extends axially forward internally of the piston and poppet valve. The poppet guide and relief poppet assembly includes a circumferential ridge along an exterior surface thereof. The wiper seal on the piston seals against the annular ridge on the assembly when the pressure drops in the female coupler and the piston moves forwardly within the coupler body. In this position, the wiper seal, also referred to as a trap seal, allows fluid to pass only rearward through the female coupler to the rear surface of the piston, and prevents a vacuum in the female coupler from allowing the male check valve to close. The fluid pressure behind the wiper seal is relieved to ambient only during connect and disconnect to allow the piston to move rearwardly. 
     In the past, the trap seal sometimes would be “blown out” when a surge of pressurized fluid would pass through the trap seal. This obviously negatively impacts the performance of the coupling and may necessitate repair or replacement of the female coupler. 
     Other problems have been encountered in female couplers which have an axial end port. Heretofore, a spacer has been used in the housing to provide a flow path for pressurized fluid around the piston and also to isolate the pressurized flow path from a vent port. One end of the spacer is supported by a tubular extension of a housing end plug which is threaded into the end of a cylindrical portion of the housing opposite the flow port. The other end of the sleeve is radially supported in the housing at an annular land including an annular seal which seals against the inner diameter surface of the housing. The annular seal separates high pressure flow from the usually zero pressure in the vent port. The high pressure acting on the seal may cause the seal to be extruded between the spacer and housing. 
     Still another problem area in prior art female couplers has been contamination of the region containing locking balls that lock the male coupler in the female coupler. Various attempts have been made in the past to prevent sand or other foreign material from entering the locking ball region, but each has had one or more drawbacks associated therewith. 
     In any case, a constant demand exists in the industry for novel and unique couplings which overcome one or more of the aforesaid problems, and which preferably are reliable, easily serviceable, and operate under a variety of conditions. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides improvements in female couplers which overcome one or more of the aforesaid problems encountered with prior art female couplers. 
     According to one aspect fo the invention, a quick disconnect female coupler comprises a housing and a valve body axially movable in the housing. The valve body has a main cavity and a poppet valve seat at the forward end of the main cavity. A poppet valve is axially movable in the valve body toward and away from the poppet valve seat, and a piston is provided for forwardly urging the poppet valve toward the poppet valve seat upon application of pressurized fluid to the rear side of the piston. A flow passage for supplying pressurized fluid from the main cavity to the back side of the piston has associated therewith a trap seal valve seat and a resilient wiper seal engageable with the trap seal valve seat to block reverse flow of pressurized fluid from behind the piston to the main cavity while permitting flow of pressurized fluid from the main cavity to the rear side of the piston. The wiper seal is retained in a radially opening annular groove and includes at its rear side an annular recess that allows rearward rolling/flaring of the wiper seal in the annular groove when the wiper seal is subjected to a surge of high pressure fluid from the main cavity to the back side of the piston, whereby the wiper seal moves out of the way of the high pressure fluid surge to avoid being forced out of the annular groove. 
     In a preferred embodiment, the annular recess defines a web joining an annular base portion and an annular sealing portion of the wiper seal, and the wiper seal is radially elongated in cross-section. The annular base portion preferably is larger in cross-section than the annular sealing portion and is retained in the annular groove that preferably is located in a radially inner surface of the poppet valve piston. As will be appreciated, the annular relief preferably functions as a catch for rear side wall of the annular groove when the wiper seal is rotated thereover to aid in holding the wiper seal in the annular groove when a surge of high pressure fluid passes from the main cavity to the back side of the piston. 
     According to another aspect of the invention, a female coupler comprises a housing having an internal bore with an open forward end adapted to receive a male coupler, and a flow port for supplying pressurized fluid to the internal bore. A tubular spacer is inserted in the housing bore and forms therewith an outer flow passage isolated from an internal bore in the spacer. The spacer has an open forward end and a rear end wall closing the rear end of the spacer. A valve body, which is axially slidable in the spacer bore, includes a main cavity opening to the forward end of the housing bore and a peripheral inlet passage through the valve body communicating the outer flow passage with the main cavity. The valve body and the rear end wall of the spacer define therebetween a vent cavity; and the spacer has an annular land press-fitted in the housing bore and located axially between the outer flow passage and a vent chamber within the housing bore, which vent chamber communicates with the vent cavity via a passage in the spacer. The annular land has an annular groove retaining an annular seal for sealing against the side wall of the housing bore to prevent leakage flow from the outer flow passage to the vent chamber. The press-fitted land protects against extrusion of the seal between the spacer and the housing wall. 
     In a preferred embodiment, the housing has a rear end wall including a counterbore opening to the housing bore, and the rear end wall of the spacer has an axially rearwardly extending post press-fitted in the counterbore. The annular land and the post preferably are coaxial, and the post may include an annular groove retaining an annular seal for sealing against the housing which may include the flow port in a rear end wall thereof. As will be appreciated, the two-point press-fit securement of the spacer enables elimination of the prior art tubular extension of the end plug that is threaded into the end of the cylindrical portion of the housing opposite the flow port. Consequently the overall length and weight of the female coupler can be reduced if desired. 
     According to a further aspect of the invention, a female coupler, comprises a housing having an internal bore with an open forward end adapted to receive a male coupler, and a flow port for supplying pressurized fluid to the internal bore. A valve body is disposed in the bore and axially moveable in the housing. The valve body includes a main cavity opening to the forward end of the housing bore, a peripheral inlet passage through the valve body communicating with the main cavity, and an interior valve seat forwardly of the inlet passage. A piston is axially movable in the valve body and includes a central bore in which a poppet valve is slidably guided. The poppet includes a valve portion disposed in the main cavity of the valve body, a forward projection adapted to engage a check valve in the male coupler when the male coupler is received in the housing, and a rearward tubular portion radially stepped to form a annular shoulder portion joining a front wall section to a rear wall section. At least one coil spring is provided to forwardly bias the poppet valve against the valve seat to normally prevent fluid flow through the valve body. A forward portion of the coil spring is radially constrained by a radially inner surface of the front wall section of the rearward portion of the poppet valve, while the rear wall section has a radially inner surface spaced radially outwardly from the coil spring to form interiorly of the poppet valve a flow path for pressurized fluid passing form the main cavity to a back side of the piston. The annular shoulder portion includes one or more orifices for connecting the main cavity to the flow path without any interference of the coil spring. 
     According to yet another aspect of the invention, a female coupler comprises a housing having an internal bore with an open forward end adapted to receive a male coupler, a flow port for supplying pressurized fluid to the internal bore, and a locking collar chamber at the open forward end. A valve body, which is disposed in the bore and axially moveable in the housing, includes a main cavity opening to the forward end of the housing bore, and a peripheral inlet passage through the valve body communicating with the main cavity, and a tubular front end socket portion including at least one radial bore which retains a locking element for radially inward and outward movement. A locking collar is axially movable in the collar chamber between locking and release positions, the collar in its locking position being operative to hold the locking element at a locking position such that it protrudes radially inwardly of a radially inner surface of the socket portion for engaging a locking groove in the male coupler, and the collar in its release position enabling radial outward movement of the locking element for disengagement from the locking groove in the male coupler. A coil spring circumscribes the locking collar for biasing the locking collar against a stop, and an annular protection shield is interposed between a front end of the coil spring and a retainer at the front end of the locking collar chamber to hold the coil spring in the collar chamber. The protection shield has a radially inner edge adjacent and surrounding the socket portion of the valve body, thereby to prevent debris from entering the locking collar chamber. 
     Further features and advantages of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view, partially in section, of a female coupler according to the present invention, with a male coupler fully inserted and latched in the female coupler, and the male check valve closed. 
     FIG. 2 is a view similar to FIG. 1, but showing the female coupler pressurized and the male check valve open. 
     FIG. 3 is an enlarged portion of FIG. 1, showing a trap seal in its normal position. 
     FIG. 4 is a portion of FIG. 3, but showing the trap seal rolled out of the way by a surge of high pressure fluid passing through the inner diameter of the trap seal from right to left in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in detail to the drawings, and initially to FIG. 1, a quick disconnect coupling of the present invention is indicated generally at  15 , and includes a female coupler  16  and a male coupler  17 , which are commonly referred to as a socket and nipple, respectively. The quick disconnect coupling was designed for use on agricultural tractors to connect the tractor hydraulic system with attachable implements, and therefore will be chiefly described in this context. However, those skilled in the art will appreciate that the coupling may be used advantageously in other applications. 
     The male coupler  17 , which is typically mounted on an agricultural implement, is a conventional, commercially-available male coupler and includes an outer tubular housing  19  which is also herein referred to as the nipple housing to differentiate it from the housing of the female coupler. The nipple housing has an internal bore  20  and a valve closure or ball  21  that is biased by a spring  22  to a closed position against a valve seat  23  at the forward end of the nipple housing. The spring  22  is retained within a shroud or cup portion  24  of a guide  25 . The guide  25  is mounted within the nipple housing by a radially outwardly flared skirt portion thereof that is captured in an annular groove formed in the radially inner surface of the nipple housing. The nipple housing also is provided with an exterior annular groove  28  for receiving the locking balls  30  of the female coupler  16 . 
     The female coupler  16 , which is typically mounted on the tractor, includes a housing  30  which for convenience is also referred to herein as the socket housing. In the illustrated embodiment the socket housing  30  is composed of a tubular main portion  31  and a tubular plug end portion  32  threaded into one end of the main portion  31  and sealed thereto by a fitting seal  33 . At a rear end wall  34  of the main housing portion  31  opposite the plug  32  there is provided a flow port  35  and a threaded fitting portion  36  for connection of the female coupler to a hydraulic supply hose or other fluid conveyance means on the tractor. 
     The socket housing  30  houses the internal components of the female coupler  16  which generally comprise, going from left to right in FIG. 1, a spacer  40 , a spool guide  41 , a spool  42 , an axially slidable valve body  43 , a piston  44 , a relief poppet  45 , a poppet assembly  46  and a locking assembly  47 . The details, functions and operation of these components are discussed below. 
     The spacer  40  has a tubular wall portion  50  which is closed by a rear end wall  51  adjacent the flow port  35  and which is open at its opposite or front end. The tubular wall portion  50  has intermediate its ends a radially outwardly protruding annular land  52  which is press-fitted into the interior bore  53  of the socket housing  30  to secure the spacer in the socket housing. The spacer is further secured in the socket housing by a tubular rear end projection or post  55  extending axially from the end wall  51  of the spacer. The post  55  is press-fitted in a counterbore  56  in the end wall  34  of the socket housing  30  coaxially with the socket housing bore  53 . Together the land and post secure the spacer in place in the socket housing and further combine to precisely align and hold the spacer in place for proper operation of the coupling. This arrangement obviates the need for an axial extension on the plug fitting  32  previously used in prior art couplers to support and locate the open end of the spacer. The omission of the axial extension in turn enables the overall length of the female coupler to be reduced with a corresponding reduction in material and weight, but without sacrificing performance and durability. 
     The land  52  on the spacer  40  separates radially reduced portions of the spacer which define with the housing a main flow passage  58  forwardly of the land and a vent flow passage/chamber  59  rearwardly of the land. One or more bores/passages  60  are provided in the spacer to connect the main flow passage  58  to the flow port  35 , while one or more other bores/passages  61  are provided in the spacer to connect the vent flow passage/chamber  59  to an interior cavity  62  of the spacer rearwardly of the valve body  43 . The rear end post  55  of the spacer  40  has an annular corner groove for retaining an annular seal  64  which seals against leakage from the flow port  35  to the vent chamber  59 . The land  52  also has an annular groove for retaining a seal  66  that seals against leakage from the main flow passage  58  to the vent chamber  59 . As will be appreciated, the press fit between the land and the interior surface of the housing eliminates any space between the spacer and housing into which the seal  66  might otherwise be extruded due to high pressure fluid in the main flow passage  58 . Also, the end of the post  55  is butted up against the end wall  34  of the housing  30  to eliminate any space into which the seal  64  might otherwise be extruded due to high pressure fluid in the flow port  35 . However, the interface between the end of the rear end of the post and the bottom wall of the counterbore  56  may be connected to the vent chamber  59  to prevent pressure buildup at such interface if leakage were to occur at the seal  64 . The connection may be provided by suitable means, such as by providing one or more flats or axial grooves on the outer diameter surface of the post or on the side wall of the counterbore  56  into which the post is press-fit. 
     The valve body  43  has a tubular rear end portion  70  that is axially slidable in the spacer  40  and a front tubular portion  71  that is radially supported in the housing plug  32  for axial sliding movement. Between the rear and front end portions, the valve body has passing through an intermediate portion thereof one or more ports  73  for connecting the main flow passage  58  to a main flow cavity  74  within the valve body. A slipper seal  75  or other suitable seal is provided in a groove in the spacer to seal against leakage between the main flow passage  58  and the interior cavity  62  formed at the rear end of the spacer  40 , and a slipper seal  77  or other suitable seal is provided in a groove in housing plug to seal against leakage from the main flow passage to the exterior of the female coupler. 
     The valve body is normally biased to a center position shown in FIG. 1 by a centering spring  80 . The centering spring preferably is a coil spring that encircles the valve body  43  and is positioned partway in an annular groove  81  in the outer diameter surface of the valve body. That is, the spring is positioned between oppositely facing shoulder surfaces  82  and  83  (FIG. 2) on the valve body. The spring also is positioned between the forward end face  84  (FIG. 2) of the spacer  40  and a rear end surface  85  (FIG. 2) of the housing plug  32 . Preferably, the axial spacing between the shoulder surfaces is equal the axial spacing between the end surfaces of the spacer and housing plug such that the centering spring functions to locate the valve body in the center position shown in FIG. 1 when no fluid pressure or external forces are acting on the valve body. 
     With particular reference to FIG. 2, the spool  42  has a tubular front portion  88  threaded into the rear end of the valve body  43  and thus is axially movable with the valve body. The tubular front portion of the spool includes a piston bore  89  for the axially movable piston  44 . The piston has a tubular extension  90  which is guided for axial movement in the valve body, and the poppet assembly  46  includes a poppet valve  91  which is guided for axial sliding movement in the tubular extension  90  of the piston. As shown, the piston has an annular groove for a seal  92  that seals against the piston bore  89  and the valve body has an annular groove for a suitable seal  93  that seals against the an outer surface of the extension  90  to close off the rear end of the main cavity  74  at a point rearwardly of the ports  73  in the valve body. 
     The poppet valve  91  includes a tubular wall  96  that is closely and slidably received within the interior central bore of the piston extension  90 , and a front end wall  97  that closes the front end of the poppet valve and which projects forwardly for engaging the check valve ball  21  in the male coupler  17 . The front end wall has a radially enlarged, conical outer surface which is engageable with a conical seat  99  on the valve body  43 . A seal  100  on the poppet valve provides a seal between the poppet valve and the valve seat  99 . A set of concentric coil springs, three such springs  102 - 104  being shown for example, are located within the poppet valve between the front end wall and a stepped front surface of the relief poppet  45 . The springs function to bias the poppet valve toward the valve seat. The springs also function to bias the relief poppet  45  against a stop formed on the spool  42 . 
     With reference to FIGS. 1 and 3, the tubular wall  96  of the poppet valve  91  is radially stepped along its axial length by an angled shoulder portion  107 . The shoulder portion  107  is located between a smaller diameter front wall portion  96   a  and a larger diameter rear wall portion  96   b . The inner cylindrical surface of the smaller diameter portion  96   a  radially constrains the front end portion of the larger diameter coil spring  102 . The larger rear wall portion  96   b  is radially outwardly spaced from the larger diameter coil spring  102  to form therebetween an axially extending, cylindrical flow passage  108  between the shoulder portion  107  and relief poppet  45  which is not obstructed by the coil springs  102 - 104 . This flow passage  108  is connected to the main cavity  74  by one or more orifices  110  in the shoulder portion  107  for flow of pressurized fluid from the main cavity  74  into and through the poppet valve  91  and past a trap seal valve seat  112  on the relief poppet  45 . Locating the poppet orifices in the shoulder portion avoids the interference with flow caused by the springs in similar prior art couplers. As a further aid to venting flow, the rear wall portion may have the radially inner surface thereof radially outwardly stepped in the region that surrounds the trap seal valve seat  112  on the relief poppet, the trap seal valve seat being formed by a radially outwardly protruding ridge or bead on the relief poppet. 
     As discussed further below, the trap seal valve seat  112  is engageable on its rear side by a trap seal  118  carried in an annular groove  119  formed in the radially inner surface of the piston  42 , as is shown in FIG.  3 . The trap seal preferably is a unitary elastomeric annular structure that functions as a wiper seal. The trap seal is radially elongated in cross-section and is provided at is rear side with an annular groove  121 . The annular groove  121  defines a reduced thickness, radially extending web  122  that connects a radially outer and larger base ring portion  123  to a radially inner and smaller wiper ring portion  124 . The outer ring portion  123  is fully retained within the groove  119  which is sized to allow a rolling or flaring movement of the trap seal from its position shown in FIG. 3 to its position shown in FIG.  4 . The annular groove  121  at the rear side of the trap seal provides a relief which allows adequate rolling/flaring movement of the trap seal to an out of the way position. In addition, the groove  119  provides for a mechanical interlock between the radially inner side of the outer ring  123  and the rear side wall  127  of the groove which aids in holding the seal in the groove when a surge of high pressure fluid passes from the main cavity to the back side of the piston. If desired, the radially inner edge  128  of the rear side wall of the groove may be offset radially outwardly from the radially inner edge  129  of the front side wall of the groove by at least about the thickness of the web  122  that moves over the rear side wall. Thus, upon a full 90° rotation clockwise in FIGS. 3 and 4, the front surface of the seal will be substantially aligned with or spaced radially outwardly of the inner edge surface  129  of the front side wall of the groove. 
     As will be appreciated, the inherent resilience of the trap seal  118  will cause the seal to return to its normal un-rolled condition shown in FIG.  3 . In addition, it will be appreciated from the following description that pressure fluid on the rear side of the piston may also assist and/or cause the seal to roll back to its FIG. 3 position. 
     Reverting to FIG. 2, the piston bore  82  forwardly of the piston  42  is vented to the vent cavity  62  behind the spool  42  via one or more passages (not shown) between or in the spool and/or valve body, for example by providing one or more axial grooves in the threads securing the spool to the valve body. The piston bore to the rear of the piston is connected via one or more passages  122  in the spool to an interior spool chamber  123  which is controllably connected to the vent cavity  62  by axial movement of the spool relative to a cylindrical spool seal  125 . The spool seal  125  is retained in an annular groove on a tubular spool guide  41  which is fixed at an end flange  128  to the spacer end wall by a retaining clip  129 . The spool seal has radially outwardly protruding sealing portions which are axially spaced apart such that they can seal against the inner diameter surface of the spool on opposite sides of the spool chamber  123 . Axial movement of the spool relative to the spool seal in either direction will connect the spool chamber  123  to the vent cavity  62 . The tubular guide  41  includes one or more passages  130  to connect the interior thereof to the vent cavity for venting when the spool moves rearwardly relative to the spool seal, as occurs during insertion of the male coupler  17  into the female coupler  16  prior to engagement of the locking assembly  47 . 
     Still referring to FIG. 2, the locking assembly  47  includes one or more locking balls  135  in the forward end of the valve body  43 . The locking balls are retained by a collar  136  which surrounds the locking balls and which can slide axially between a radially-extending shoulder  138  at the bottom of a locking collar chamber  140  in the female housing and a protection shield  142  which functions as a stop. The protection shield is captured between a retaining ring  145  in an annular groove in the socket housing  30  and the front end of a coil spring  146  that circumscribes the collar. The other end of the coil spring engages a shoulder flange  147  on the collar via a washer  148 . Accordingly, the coil spring biases the collar rearwardly (to the left in FIG.  2 ). A nipple seal  150  is positioned in an annular groove on the inside of the valve body and is engageable with the male housing  19  when the male coupler  17  is inserted into the female coupler  16 . 
     In accordance with the invention, the protection shield  142  not only functions as a stop for the collar  136 , but it also functions as a seal or shield to prevent dirt and other contaminants from entering into the collar chamber  140  and fouling operation of the locking mechanism. To this end, the shield preferably spans the annular gap between the valve body and the socket housing at the front end of the socket housing. The seal may be made of a stiff material, or of a resilient and/or elastomeric material that may wipingly engage the outer surface of the axially shiftable valve body, if desired. 
     The operation of the quick disconnect coupling will now be described. FIG. 1 shows the male coupler  17  after it has been fully inserted into the female coupler  16  and with the female coupler at zero pressure, i.e., fully vented, and the male coupler pressurized. As shown, the poppet valve  91  has been moved away from the valve seat  99  (FIG. 2) by the projecting end of the ball  21  of the male coupler  17 . Also, the locking balls  135  are held engaged in the locking groove  28  in the nipple housing  19  of the male coupler by the locking collar  136 . 
     In the context of a coupling for connecting a tractor to an attachable tractor implement, the tractor operator may pressurize the flow port  35  and the main cavity  74  of the valve body  43  by operating a control valve on the tractor. High pressure within the main cavity  74  forces the ball  21  of the male coupler away from its seat  23  and opens the male coupler to the tractor hydraulic pressure. At the same time, high pressure fluid will be communicated with the rear side of the piston  44  via the poppet orifices  110  (FIG. 3) and past the check valve formed by the trap seal  118  and seat  112 . This may occur in some instances with a surge of high pressure fluid passing through the trap seal. In accordance with the invention, the trap seal will be caused by such flow to roll/flare to an out of the way position thereby preventing it from being “blown out” of its retaining groove  119 . 
     High pressure fluid acting on the rear side of the piston  42  will cause the piston to shift to the right and against a shoulder surface in the valve body  43 . In this position shown in FIG. 2, the piston operates to hold the poppet valve  91  at a position which will prevent the ball  21  of the male coupler  17  from closing against the valve seat  23  in the male coupler, should a situation arise where the forces acting on the ball of the male coupler are insufficient to hold it open. 
     When the piston  44  has been shifted forwardly as shown in FIG. 2, the trap seal  118  will seal against the trap seal valve seat  112  to retain pressurized fluid at the rear side of the piston when pressure in the main cavity  74  drops below that necessary to maintain the piston in a position that keeps open the ball of the male coupler. That is, the trap seal prevents back flow of pressurized fluid from the piston chamber to the main cavity  74 , i.e., it traps pressurized fluid behind the piston, while allowing fluid flow rearward through the coupling. In essence, the trap seal functions as a wiper seal that operates as a simple one-way check valve when in engagement with valve seat on the relief poppet. As a result, a loss of pressure in the valve body cavity will not result in closure of the ball of the male coupler. 
     If the trapped pressure in the male coupler  17  exceeds the tractor pressure applied at port  35 , the piston  44  will still force open the ball  21  of the male coupler since the diameter of the piston is greater than the diameter of the ball. As a result, the ball can be forced open even if the pressure within the female coupler is less than the trapped pressure within the male coupler. 
     During use the pressure of fluid passing through the coupling will fluctuate, typically from a high value when tractor pressure is being supplied for example to extend a hydraulic actuator to a lower pressure such as when the hydraulic actuator is connected to return for retraction. To alleviate unneeded/excess pressure behind the piston  44  under low or atmospheric pressure in the hydraulic line, in a known manner the relief poppet  45  will be caused to be unseated from the trap seal by a pressure difference thereacross to allow pressure to bleed back into the main cavity. 
     When the couplers are to be disconnected, the control valve to the flow port  35  is closed, and a pull force is applied to the male coupler  17  which will shift the male coupler and the slidable internal components of the female coupler  16  to the right from the FIG. 2 position. The locking collar  136  remains in locking engagement with the locking balls  135 . As the locking collar moves to the right with the male coupler, the spring  146  is compressed. The movement to the right of the valve body  43  and the spool is sufficient to open the seal between the spool  42  and the spool seal  125 . The pressure within spool chamber  123  and that acting on the rear side of the piston  44  will be dumped to atmospheric pressure and the ball  21  of the male coupler  17  will close by virtue of the trapped pressure within the male coupler and/or by the action of the return spring  22 . 
     As the valve body  43  is further moved forwardly, the locking balls  135  will align with the front ramp surface on the collar  136  and thus will be free to move radially outwardly to release the male coupler  17 . As the male coupler is pulled away from the female coupler, the poppet valve  91  will be allowed to return to its closed position engaging the poppet valve seat  99 . Also, the spring force acting on the locking collar  136  will cause the balls to move radially inwardly and the locking collar to return to its normal position. Finally, the centering spring  80  will cause the valve body to return to its centered position shown in FIG. 1, whereupon the spool valve  125  will once again block communication between the back side of the piston and the vent cavity  62 . 
     To couple the couplers, the male coupler  17  is inserted into the female coupler  16 . As the male coupler is being inserted, the nipple housing  19  will engage the nipple seal  150  in the valve body  43  and the nipple housing will engage the balls  135 . The balls will initially be precluded from moving radially outwardly because of the collar  136 , and consequently the valve body  43  will be caused to be shifted rearwardly in the socket housing  30 . In addition, if the male coupler is pressurized the ball  21  of the male coupler will engage the poppet valve  91  and move it rearwardly away from the poppet valve seat  99 . In addition, the spool  42  will be shifted rearwardly to release any pressurized fluid behind the piston  44  so that the poppet valve can be opened. Also, the locking balls  135  will align with the rear ramp surface of the locking collar  136  whereupon they will be forced radially outwardly with the retaining collar being cammed forwardly against the biasing force of the collar spring  146 . As the male coupler reaches its fully inserted position, the locking balls will align with the locking groove  28  in the male coupler, whereupon the collar will cam the locking balls radially inwardly into the locking groove and then move to hold the locking balls in the locking groove. Also, the centering spring  80  will shift the valve body  43  back to its position shown in FIG. 1, whereupon the female and male couplers will be ready for application of pressure in the above-described manner. 
     As described above, the present invention provides a novel and unique quick disconnect coupling which is particularly useful for hydraulic and pneumatic fluid lines. The disconnect coupling is reliable, serviceable and operates under a variety of conditions. 
     The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein should not, however, be construed as limited to the particular form described as it is to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims.