Patent Publication Number: US-11648996-B2

Title: Portable trailer stabilizers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application 63/303,393, filed Jan. 26, 2022, and U.S. Provisional Patent Application 63/188,482, filed May 14, 2021, which are incorporated by reference. 
    
    
     INTRODUCTION 
     The present disclosure is directed to supporting devices utilized to stabilize and/or support parked trailers and, more particularly, to portable trailer stabilizers that may be used, for example, with semi-trailers parked at loading docks while loading and/or unloading cargo, and related methods. 
     The present disclosure contemplates that distribution warehouses and facilities having semi-trailer loading/unloading capabilities (e.g., facilities with loading/unloading docks) are a necessary component of commerce in the twenty-first century. These warehouses may act as clearinghouses for shipments from various product suppliers and centralize the distribution of goods. Large chain retailers utilize warehouses to generate shipments to particular points of sale that are specific to the needs of consumers in that area, without requiring the original manufacturer of the goods to identify consumer demand at each point of sale and correspondingly deliver the particular goods to each point of sale. 
     The present disclosure contemplates that an example distribution warehouse (or similar facility) may include fifteen or more loading dock bays, with each loading dock bay adapted to receive a single freight trailer of a semi-truck. A loading dock door selectively closes off an opening of the loading dock bay elevated above ground level (e.g., a mezzanine) matching a height of the floor of the freight trailer. Alternatively, for liquid contents of a semi-trailer, a loading dock may comprise a horizontal or angled floor teamed with piping to allow egress of liquids to and from the semi-trailer. In the context of a warehouse, the relatively equal height between the floor of the loading dock and the floor of the trailer enables lift trucks (e.g., forklifts) and other material handling devices to move freely back and forth between the warehouse and interior of the freight trailer. 
     The present disclosure contemplates that in an example sequence, a loading dock bay at a warehouse or similar facility is initially unoccupied by a freight trailer. Thereafter, a semi-trailer driver or terminal tractor driver (or autonomous vehicle) backs a semi-trailer into alignment with the loading dock bay. In the context of a box semi-trailer, this includes backing the rear of the trailer to overlap with the loading dock door. After the semi-trailer is properly aligned and positioned adjacent to the loading dock door, engagement between the terminal truck and trailer will be continued or discontinued, where discontinuing allows the truck or autonomous vehicle to engage another trailer and/or relocate to a different location. As used herein, the term “terminal tractor” includes manned and autonomous vehicles utilized to engage and reposition semi-trailers. In the context of terminal tractors, a usual practice is to maintain engagement between such a vehicle and the freight trailer only long enough to position or reposition the freight trailer with respect to the loading dock bay. In an example day, a terminal tractor may connect to and disconnect from one hundred or more freight trailers. 
     The present disclosure contemplates that, in summary fashion, a terminal tractor (also known as a spotter truck or yard truck) is a dedicated tractor that stays at the dock facility and is only used to reposition freight trailers (e.g., not to tow the trailers on the open highways). By way of example, a facility may have ten loading dock bays, but may have fifty trailers waiting to be unloaded and/or unloaded. In order to expedite unloading and loading of contents with respect to each semi-trailer, as well as the convenience of the semi-truck drivers that deliver to or pick up the trailers from the facility, the trailers may need to be shuffled. This means that trailers do not include dedicated semi-tractors continuously connected to them. Instead, because no semi-tractor is connected to many, if not all, of the trailers at a facility, a terminal tractor may be used to shuffle the trailers at the facility. 
     The present disclosure contemplates that an exemplary process for engaging between the terminal tractor and the freight trailer includes backing the terminal tractor under a front end of the semi-trailer so a hydraulic fifth wheel of the terminal tractor engages a king pin of the semi-trailer, followed by initially raising the hydraulic fifth wheel to raise the front end of the trailer above its normal ride height. While the front end is raised, the landing gear of the freight trailer, which comprises a pair of equal length jacks permanently mounted to the trailer, are also elevated off the ground to allow repositioning of the trailer via its rear axle(s) engaged with the ground. The hydraulic fifth wheel allows the terminal tractor to reposition trailers without ever adjusting or otherwise repositioning the trailer&#39;s landing gear. As is customary, associated pneumatic and electrical connections between the terminal tractor and trailer are connected so that the brakes of the trailer are able to be unlocked. Conversely, to disengage the terminal tractor from the trailer, the hydraulic fifth wheel may be lowered so that lowering of the fifth wheel is operative to lower the front of the trailer and contact the ground with the landing gear. When the trailer is set down on its landing gear, the trailer is freestanding. After the trailer is freestanding, associated pneumatic and electrical connections between the terminal tractor and trailer are disconnected so that the brakes of the trailer are locked. Thereafter, the terminal tractor pulls out from under the front of the trailer, thereby leaving the trailer adjacent to the loading dock door and being supported at the front end using only the trailer&#39;s landing gear. 
     The present disclosure contemplates that when loading and unloading contents from a freestanding trailer, movement of the contents themselves and/or a lift truck along the floor of the trailer can impart considerable motion to the trailer. While some movement of the trailer is inevitable, considerable movement can result in the trailer becoming separated from the dock and/or possibly tipping over. More importantly, the landing gear of the trailer are generally not designed to hold up the weight of a fully loaded trailer, let alone the dynamic forces generated by contents and a lift truck moving through a trailer. In cases where these forces are great enough, the landing gear of the trailer can fail, leading the front end of the trailer to collapse or tip over. The obvious implications of a trailer collapsing or tipping over include damage to the goods within the trailer, the trailer itself, and the lift truck, not to mention the possible serious injury to or death of the lift truck operator. 
     While known devices have been used to support parked semi-trailers, there is a need in the industry for improved trailer stabilizers for use with parked semi-trailers. In addition, there is a need in the industry for a trailer stabilizer that utilizes a closed hydraulic system to potentially support the freight trailer. Moreover, there is a need in the industry for a trailer stabilizer that utilizes a closed hydraulic system that can be repositioned underneath a parked semi-trailer and operates to support the semi-trailer if the landing gear of the trailer fail. Further, there is a need in the industry to provide a trailer stabilizer that may be repositioned by engaging the front of a terminal tractor and deployed by the terminal tractor driving forward and toward a front of the semi-trailer, rather than backing the terminal tractor to reposition a trailer stabilizer. Still further, there is a need in the industry to provide a trailer stabilizer that can support the weight of a fully loaded front end of a semi-trailer, upon landing gear failure, that dampens the abrupt forces otherwise present from an undampened collision between the semi-trailer and a stabilizer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a simplified schematic view of an example portable trailer stabilizer system, according to at least some aspects of the present disclosure. 
         FIG.  2    is a schematic view of an example towable portable trailer stabilizer engaged with a trailer, according to at least some aspects of the present disclosure. 
         FIG.  3    is a front elevated perspective views showing various aspects of an example portable trailer stabilizer according to at least some aspects of the present disclosure. 
         FIG.  4    is a partial profile elevated perspective view showing various aspects of the example portable trailer stabilizer of  FIG.  3    according to at least some aspects of the present disclosure. 
         FIG.  5    is a partial front elevated perspective view showing various aspects of the example portable trailer stabilizer of  FIG.  3    according to at least some aspects of the present disclosure. 
         FIG.  6    is a narrowed partial profile elevated perspective view showing various aspects of the example portable trailer stabilizer of  FIG.  3    according to at least some aspects of the present disclosure. 
         FIG.  7    is a narrowed partial rear profile elevated perspective view showing various aspects of the example portable trailer stabilizer of  FIG.  3    according to at least some aspects of the present disclosure. 
         FIG.  8    is a front perspective view of a further example portable trailer stabilizer, depicted with signaling in the notification position according to at least some aspects of the present disclosure. 
         FIG.  9    is a rear perspective view of the portable trailer stabilizer of  FIG.  8    with signaling in the notification position. 
         FIG.  10    is a front perspective view of the portable trailer stabilizer of  FIG.  8    with signaling in the transport position. 
         FIG.  11    is a rear elevation view of the portable trailer stabilizer of  FIG.  8    with signaling in the transport position. 
         FIG.  12    is a perspective view of another example portable trailer stabilizer showing various aspects of an example portable trailer stabilizer according to at least some aspects of the present disclosure. 
         FIG.  12 A  is a plan view of the portable trailer stabilizer of  FIG.  12    shown with a wheeled configuration. 
         FIG.  13    is a plan view of the portable trailer stabilizer of  FIG.  12   . 
         FIG.  14    is a side elevation view of the portable trailer stabilizer of  FIG.  12   . 
         FIG.  15    is a rear elevation view of the portable trailer stabilizer of  FIG.  12   . 
         FIG.  16    is a simplified side elevation view of a first example terminal tractor including a trailer stabilizer positioning element separate from the terminal tractor&#39;s fifth wheel, all according to at least some aspects of the present disclosure. 
         FIG.  17    is a simplified side elevation view of a second example terminal tractor including a trailer stabilizer positioning element separate from the terminal tractor&#39;s fifth wheel, all according to at least some aspects of the present disclosure. 
         FIG.  18    is a front elevation view of a third example terminal tractor including a trailer stabilizer positioning element separate from the terminal tractor&#39;s fifth wheel, all according to at least some aspects of the present disclosure. 
         FIG.  19    is a simplified side elevation view of yet another exemplary terminal tractor including a trailer stabilizer positioning element separate from the terminal tractor&#39;s fifth wheel, all according to at least some aspects of the present disclosure. 
         FIG.  20    is a front elevation view of the exemplary terminal tractor of  FIG.  19   . 
         FIG.  21    is a perspective view of an example indicator according to at least some aspects of the present disclosure. 
         FIG.  22    is an exemplary diagram for a closed hydraulic system in accordance with the instant disclosure. 
         FIG.  23    is a further exemplary diagram for a closed hydraulic system in accordance with the instant disclosure. 
         FIG.  24    is still a further exemplary diagram for a closed hydraulic system in accordance with the instant disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments according to the present disclosure are described and illustrated below to encompass devices, methods, and techniques relating to supports utilized to stabilize and/or support parked trailers, such as portable stabilizers and/or stabilizing systems that may be used, for example, with semi-trailers parked at loading docks while loading and/or unloading contents. Of course, it will be apparent to those of ordinary skill in the art that the embodiments discussed below are examples and may be reconfigured without departing from the scope and spirit of the present disclosure. It is also to be understood that variations of the example embodiments contemplated by one of ordinary skill in the art shall concurrently comprise part of the instant disclosure. However, for clarity and precision, the example embodiments as discussed below may include optional steps, methods, and features that one of ordinary skill should recognize as not being a requisite to fall within the scope of the present disclosure. Various example embodiments are described and, unless specifically excluded, any element, feature, aspect, or operation described in connection with any example embodiment may be utilized in any combination in connection with any other embodiment. Moreover, in the example embodiments described herein, unless specifically noted as being necessary or indispensable, any element, feature, aspect, or operation described in connection with any example embodiment or in any combination may be omitted in connection with that embodiment or any other embodiment or combination of embodiments. 
       FIG.  1    depicts an example portable trailer stabilizer system  10  that may include and/or may be used in connection with one or more semi-trailers  100 , which may be parked on a support surface  102 , such as in a parking location proximate a building  104 . For example, the building  104  may include a loading dock having one or more loading dock bays  104 A, with each bay having a loading dock opening that may be selectively opened and closed by an overhead door. The trailer  100  may be transported relatively long distances by an over-the-road tractor  106  and/or the trailer may be transported relatively short distances by a terminal tractor  108 ,  110 . When the trailer  100  is parked, a portable trailer stabilizer  200 ,  300  may be positioned proximate the trailer  100  and ready to stabilize and/or support at least a portion of the trailer  100 . For example, the terminal tractor  108 ,  110  may be used to position the portable trailer stabilizer  200 ,  300  proximate a forward end portion  118  of the trailer  100 , such as beneath the forward end portion  118  of the trailer  100  and between the trailer  100  and the support surface  102 . Generally, as used herein, “tractor” may refer to a vehicle that is configured to pull, push, carry, and/or reposition another piece of equipment and includes over-the-road tractors  106 , terminal tractors  108 ,  110 , lift trucks, and/or other vehicles suitable for performing similar functions. For brevity, the following description focuses on tractors  106 ,  108 ,  110 ; however, it will be understood that other tractors may be utilized in similar manners in accordance with the instant disclosure. 
     In some example embodiments, a tractor such as the terminal tractor  108 ,  110  may be used to reposition the portable trailer stabilizer  200 ,  300  proximate the trailer  100 . Some example portable trailer stabilizers  200  may be configured to be repositioned by towing (e.g., pulling and/or pushing) by a terminal tractor  108 ,  110  using the terminal tractor&#39;s fifth wheel  112 ,  114 , which it may also use for repositioning trailers  100 . Some example portable trailer stabilizers  300  may be configured to be repositioned by lifting and carrying by a terminal tractor  110  using a trailer stabilizer positioning element  116  separate from the terminal tractor&#39;s fifth wheel  114 . 
     Turning to  FIG.  2   , the portable trailer stabilizer  200  may be configured to extend between the support surface  102  (e.g., ground) and the underside of the forward end portion  118  of the trailer  100 , such as to stabilize and/or support the forward end portion  118  of the trailer  100 . Alternatively, as discussed hereafter, the trailer stabilizer  200  may be positioned not to contact the trailer  100  unless the landing gear of the trailer fails or significantly sags, or the trailer frame bends under load. While  FIG.  2    depicts the portable trailer stabilizer  200  as concurrently contacting the support surface  102  and the underside of the forward end portion  118 , it is within the scope of the disclosure for there to be a gap between the portable trailer stabilizer  200  and at least one of the support surface  102  and the underside of the forward end portion  118  of the trailer  100 . 
     The portable trailer stabilizer  200  may include a support surface engagement element, such as a ground pad  202 , which may be configured to selectively engage the support surface  102 . The portable trailer stabilizer  200  may include a trailer engagement element, such as a trailer engagement bar  204 , which may be configured to selectively engage the trailer  100 . The trailer engagement bar  204  may be arranged to extend generally horizontally and/or generally laterally (e.g., side-to-side) beneath the forward end portion  118  of the trailer  100 . In some example embodiments, the trailer engagement bar  204  may be constructed from a section of metal channel or tube, such as round tube. 
     In some example embodiments, the support surface engagement element  202  and the trailer engagement element  204  may be operatively connected by one or more structural elements  206 ,  208  and/or one or more actuators, such as one or more hydraulic cylinders  210 . In other example embodiments, alternative actuators may be used, such as pneumatic or electrical actuators, electromechanical jacks, and/or a spring lifting apparatus with a ratchet and pawl mechanism to vertically reposition the trailer engagement element  204  with respect to the support surface engagement element  202 . The actuators  210  may be configured to facilitate vertical repositioning, such as extension and/or retraction, of the trailer engagement element  204  relative to the support surface engagement element  202 . For example, when pressurized hydraulic fluid is directed to the hydraulic cylinder  210 , the hydraulic cylinder  210  may extend to extend the trailer engagement element  204  relative to the support surface engagement element  202 . As used herein, “pressurized” may refer to a pressure greater than ambient atmospheric pressure. 
     In some example embodiments, the trailer engagement element (e.g., trailer engagement bar  204 ) may be coupled to the structural elements  206 ,  208  and/or the actuators (e.g., hydraulic cylinders  210 ) by one or more pivot connections  210 A (see  FIG.  4   ). For example, some pivot connections may allow the trailer engagement bar  204  to tilt side-to-side with respect to the trailer. Accordingly, the portable trailer stabilizer  200  may accommodate uneven support surfaces  102 , support surfaces  102  having debris thereon, and/or tilted semi-trailers  100 , for example. 
     In some example embodiments, the actuator  210  may be powered by an on-board, self-contained energy source. For example, the hydraulic cylinder  210  may be operatively connected to an on-board, self-contained hydraulic system  212 . As used herein, “on-board” may refer to a component or clarity, as used herein, an energy source may be “self-contained” even if it stores energy resulting from externally applied forces, provided that the application of the externally applied forces is incidental to operation of the portable trailer stabilizer. 
     In some example embodiments, the hydraulic system  212  may include one or more hydraulic accumulators  214 , one or more isolation valves  216  (e.g., ball valves), one or more relief valves  217 , and/or one or more hydraulic conduits  218  in selective fluid communication with the accumulator  214  and the cylinder(s)  210 . The hydraulic system  212  may comprise a closed hydraulic system. As used herein, “closed hydraulic system” may refer to operatively connected hydraulic components that are configured for normal operation without supplying hydraulic fluid to and/or receiving hydraulic fluid from an external component. For example, the hydraulic system  212  may be configured so that hydraulic fluid flows between the accumulator  214  and the cylinder(s)  210  via the conduits  218  and valves  216 ,  217  without external connections (during normal use). As used herein, “closed hydraulic system” may include a hydraulic system that occasionally receives supplemental hydraulic fluid, such as to replace hydraulic fluid lost due to leakage. 
     In some alternative example embodiments, a hydraulic system may utilize an external pump (e.g., located on board the stabilizer  200 ,  300  and/or on a tractor), such as to raise and/or lower the trailer engagement element  204 . Some example on board pumps may utilize a battery with a solar charger and/or may be configured for charging from an external charger or dedicated power supply such as a corded outlet. In some example embodiments, limit and/or pressure switches may limit the travel of the trailer engagement element  204 . 
     In some example embodiments, the hydraulic fluid throughout the closed hydraulic system may be pressurized, such as at all times during normal operation. For example, some example closed hydraulic systems may not include a vented reservoir (e.g., at about atmospheric pressure). Although  FIG.  2    schematically illustrates one hydraulic cylinder  210  coupled to one accumulator  214  via one isolation valve  216  for clarity, some example embodiments may include one or more (e.g., two) hydraulic cylinders  210 , one or more accumulators  214 , one or more relief valves  217 , and/or one or more (e.g., two) isolation valves  216  (or other flow control devices) interconnected by any number of conduit  218  segments. 
     In some example embodiments, the isolation valve  216  may be operated (e.g., opened and/or shut) by an isolation valve operator mechanism, such as a valve operator element  220  and/or a cable  222  operatively connecting the valve operator element  220  to the isolation valve  216 . In other example embodiments, isolation valve operator mechanisms may include mechanical linkages, electrical actuators, and/or hydraulic actuators arranged to open and/or shut the isolation valve  216 . 
     In some example embodiments, the isolation valve operator mechanism (e.g., valve operator element  220 ) may be configured for operation in connection with coupling the portable trailer stabilizer  200  to a tractor  106 ,  108  and/or uncoupling the portable trailer stabilizer  200  from a tractor  106 ,  108 . For example, the isolation valve operator mechanism may be configured so that it is actuated by the act of coupling the portable trailer stabilizer  200  to a tractor  106 ,  108  and/or the act of uncoupling the portable trailer stabilizer  200  from a tractor  106 ,  108  (e.g., without additional action by an operator). For example, the valve operator element  220  may comprise a valve operator plate coupled to a positioning element engagement element, such as a fifth wheel plate  224 , via a pivot  226 . In operation, the valve operator element  220  may be configured so that when a terminal tractor&#39;s trailer stabilizer positioning element, such as a fifth wheel  112 ,  114 , engages or disengages the fifth wheel plate  224  of the portable trailer stabilizer  200 , the valve operator element  220  is pivoted. Repositioning, such as by pivoting, the valve operator element  220  may operate (e.g., open and/or shut) the isolation valve  216  via the cable  222 . For example, the isolation valve operator mechanism may be configured so that when the fifth wheel plate  224  of the portable trailer stabilizer  200  is disengaged from the terminal tractor&#39;s fifth wheel  112 ,  114 , the isolation valve  216  may be shut and/or when the fifth wheel plate  224  of the portable trailer stabilizer  200  is engaged with the terminal tractor&#39;s fifth wheel  112 ,  114 , the isolation valve  216  may be open. Some example embodiments may include one or more wheels  228  configured to support the portable trailer stabilizer  200  on the support surface  102  during repositioning. The wheels  228  may facilitate repositioning of the portable trailer stabilizer  200  by towing (e.g., pulling and/or pushing), such as when the portable trailer stabilizer&#39;s fifth wheel plate  224  is coupled to the terminal tractor&#39;s fifth wheel  112 ,  114 . 
     Referring to  FIGS.  3  and  4   , in some example embodiments, the trailer engagement element  204  may be pivotably disposed with respect to one or more of the structural elements  206 ,  208 . For example, the trailer engagement bar  204  may be coupled to the structural element  206  by a pivot  206 A that may include a pivot pin, which may allow the trailer engagement bar  204  to move generally upward and downward (e.g., at a radius from the pivot  206 A) while extending and/or compressing the hydraulic cylinder  210 . 
     In some example embodiments, the trailer engagement element (e.g., trailer engagement bar  204 ) may comprise a sloped engagement surface  204 A. The engagement surface  204 A may be arranged to contact the forward end portion  118  of the trailer  100  when the portable trailer stabilizer  200  is positioned beneath the forward end portion  118 . When the trailer engagement bar  204  is higher than the underside of the forward end portion  118  of the trailer  100 , the engagement surface  204 A may contact and slide beneath and along the forward end portion  118  underside as the portable trailer stabilizer  200  is moved underneath the forward end portion  118 . Accordingly, contact between a forward edge and the underside of the trailer  100  and the engagement surface  204 A and/or the trailer engagement bar  204  may press the trailer engagement bar  204  downward, thus compressing the hydraulic cylinder  210 . 
       FIG.  8    is a front perspective view of a further example portable trailer stabilizer  1200 , depicted with signaling in the notification position.  FIG.  9    is a rear perspective view of the portable trailer stabilizer  1200  with signaling in the notification position,  FIG.  10    is a front perspective view of the portable trailer stabilizer  1200  with signaling in the transport position, and  FIG.  11    is a rear elevation view of the portable trailer stabilizer  1200  with signaling in the transport position, all according to at least some aspects of the present disclosure. Generally, portable trailer stabilizer  1200  may be similar in construction and operation to portable trailer stabilizer  200  described above. Repeated description of some similar features and operations is omitted for brevity. 
     Referring to  FIGS.  8 - 11   , generally, the portable trailer stabilizer  1200  may be configured to extend between the support surface  102  and the underside of the forward end portion  118  of the trailer  100  ( FIG.  1   ), such as to stabilize and/or support the forward end portion  118  of the trailer  100 . 
     The portable trailer stabilizer  1200  may include a support surface engagement element, such as a ground pad  1202 , which may be configured to selectively engage the support surface  102 . The portable trailer stabilizer  1200  may include a trailer engagement element, such as a trailer engagement bar  1204 , which may be configured to selectively engage the trailer  100  ( FIG.  1   ). The trailer engagement bar  1204  may be arranged to extend generally horizontally and/or generally laterally (e.g., side-to-side) beneath the forward end portion  118  of the trailer  100 . In some example embodiments, the trailer engagement bar  1204  may be constructed from a section of metal channel or tube, such as round tube. 
     In some example embodiments, the support surface engagement element  1202  and the trailer engagement element  1204  may be operatively connected by one or more structural elements  1206 ,  1208  and/or one or more actuators, such as one or more hydraulic cylinders  1210 . In other example embodiments, alternative actuators may be used, such as pneumatic or electrical actuators, electromechanical jacks, and/or a spring lifting apparatus with a ratchet and pawl mechanism to lift the trailer engagement element and secure it in place. The actuators may be configured to facilitate extension and/or retraction of the trailer engagement element relative to the support surface engagement element. For example, when pressurized hydraulic fluid is directed to the hydraulic cylinder  1210 , the hydraulic cylinder  1210  may extend to extend/raise the trailer engagement element  1204  relative to the support surface engagement element  1202 . 
     In some example embodiments, the trailer engagement element (e.g., trailer engagement bar  1204 ) may be coupled to the structural elements  1206 ,  1208  and/or the actuators (e.g., hydraulic cylinders  1210 ) by one or more pivot connections  1210 A. For example, some pivot connections may allow the trailer engagement bar  1204  to tilt side-to-side with respect to the trailer  100 . Accordingly, the portable trailer stabilizer  1200  may accommodate uneven support surfaces  102 , support surfaces  102  having debris thereon, and/or tilted semi-trailers  100 , for example. 
     In some example embodiments, the actuator may be powered by an on-board, self-contained energy source. For example, the hydraulic cylinders  1210  may be operatively connected to an on-board, self-contained hydraulic system  1212 . In some example embodiments, the hydraulic system  1212  may include one or more hydraulic accumulators  1214 , one or more isolation valves  1216  (e.g., ball valves), and/or one or more hydraulic conduits  1218  fluidically connecting the accumulator  1214  to the cylinders  1210  via the isolation valves  1216 . The hydraulic system  1212  may comprise a closed hydraulic system. The hydraulic system  1212  may be configured so that hydraulic fluid flows between the accumulator  1214  and the cylinders  1210  via the conduits  1218  and isolation valves  1216  without external connections (during normal use). 
     In some example embodiments, the isolation valves  1216  may be operated (e.g., opened and/or shut) by an isolation valve operator mechanism, such as a valve operator element  1220  and/or one or more rods  1222  operatively connecting the valve operator element  1220  to the isolation valves  1216 . In other example embodiments, isolation valve operator mechanisms may include cables, electrical actuators, and/or hydraulic actuators arranged to open and/or shut the isolation valves  1216 . 
     In some example embodiments, the isolation valve operator mechanism (e.g., valve operator element  1220 ) may be configured for operation in connection with coupling the portable trailer stabilizer  1200  to a tractor  106 ,  108  ( FIG.  1   ) and/or uncoupling the portable trailer stabilizer  1200  from a tractor  106 ,  108 . For example, the isolation valve operator mechanism may be configured so that it is actuated by the act of coupling the portable trailer stabilizer  1200  to a tractor  106 ,  108  and/or the act of uncoupling the portable trailer stabilizer  1200  from a tractor  106 ,  108  (e.g., without additional action by an operator). For example, the valve operator element  1220  may comprise a valve operator plate coupled to a positioning element engagement element, such a fifth wheel plate  1224 , via a pivot  1226 . In operation, the valve operator element  1220  may be configured so that when a terminal tractor&#39;s trailer stabilizer positioning element, such as fifth wheel  112 ,  114 , engages or disengages the fifth wheel plate  1224  of the portable trailer stabilizer  1200 , the valve operator element  1220  is pivoted. Pivoting the valve operator element  1220  may operate (e.g., open and/or shut) the isolation valve  1216  via the rod  1222 . For example, the isolation valve operator mechanism may be configured so that when the fifth wheel plate  1224  of the portable trailer stabilizer  1200  is disengaged from the terminal tractor&#39;s fifth wheel  112 ,  114 , the isolation valves  1216  may be shut and/or when the fifth wheel plate  1224  of the portable trailer stabilizer  1200  is engaged with the terminal tractor&#39;s fifth wheel  112 ,  114 , the isolation valves  1216  may be open. Some example embodiments may include one or more wheels  1228 , which may facilitate repositioning the portable trailer stabilizer  1200 , such as when the portable trailer stabilizer&#39;s fifth wheel plate  1224  is coupled to the terminal tractor&#39;s fifth wheel  112 ,  114 . 
     In some example embodiments, the trailer engagement element  1204  may be pivotably disposed with respect to one or more of the structural elements  1206 ,  1208 . For example, the trailer engagement bar  1204  may be coupled to the structural element  1206  by a pivot  1206 A, which may allow the trailer engagement bar  204  to move generally upward and downward (e.g., at a radius from the pivot  1206 A) while extending and compressing the hydraulic cylinder  1210 . 
     In some example embodiments, the trailer engagement element (e.g., trailer engagement bar  1204 ) may comprise a sloped engagement surface  1240 A. The engagement surface  1240 A may be arranged to contact the forward end portion  118  of the trailer  100  ( FIG.  1   ) when the portable trailer stabilizer  1200  is positioned beneath the forward end portion  118 . When the trailer engagement bar  1204  is higher than the underside of the forward end portion  118  of the trailer  100 , the engagement surface  1240 A may contact a leading forward edge of the trailer and/or a front face of the trailer and thereafter slide along and underneath the forward end portion  118  as the portable trailer stabilizer  1200  is moved underneath the forward end portion  118 . Accordingly, the contact between the trailer  100  and at least one of the engagement surface  1240 A and the trailer engagement bar  1204  may press the trailer engagement bar  1204  downward, thus compressing the hydraulic cylinder  1210 . 
     In some example embodiments, the trailer stabilizer  1200  may include one or more signal elements  1250 ,  1252 . For example, a flag rod  1250  may pivot between a generally horizontal travel position and a generally vertical notification position to indicate whether the isolation valves  1216  are open or shut. In the illustrated embodiment, the flag rod  1250  is pivoted by a mechanical linkage (e.g., rod) operatively coupled to the valve operator element  1220 . When the isolation valves  1216  are shut, the flag rod  1250  is in the generally horizontal travel or stowed position. When the isolation valves are open, the flag rod  1250  is in the generally vertical notification position. Those skilled in the art will understand that the horizontal and vertical positions of the flag rod  1250  may be switched so that a horizontal position reflects the isolation valves are open, whereas a vertical position reflects that the isolation valves are closed. Accordingly, an operator of a tractor  106 ,  108  can readily determine whether the isolation valves  1216  are open or shut using the position of the flag rod  1250 . In addition, when the flag rod  1250  is in the generally horizontal notification position, a dock attendant inside the loading dock may view or verify the position of the flag rod using a camera image of a video camera on the outside of the loading dock to provide a form of physical sight verification. 
     As another example, a full up indicator  1252  may pivot between a “full up” position and a not “full up” position. In the illustrated embodiment, the full up indicator displays a flag to the operator of a tractor  106 ,  108  (e.g., in a generally vertical position) when the trailer engagement element  1204  is at or near its fully raised position. When the trailer engagement element  1204  is below its fully raised position, the flag of the full up indicator  1252  drops to a generally horizontal position. In the illustrated embodiment, the full up indicator  1252  is pivotably disposed on the trailer engagement element  1204  and is operated by a connector (e.g., cable), which is coupled to another portion of the trailer stabilizer  1200  that does not move with the trailer engagement element  1204 . Accordingly, the operator of the tractor  106 ,  108  can readily determine whether the trailer engagement element  1204  is at or near its fully raised position. 
     Referring to  FIGS.  12 - 16   , a further example portable trailer stabilizer  300  may be configured to extend between a support surface  102  and the underside of the forward end portion  118  of the trailer  100 , such as to stabilize and/or support the forward end portion  118  of the trailer  100 . Alternatively, as discussed hereafter, the trailer stabilizer  300  may be positioned to not contact the trailer  100  unless the landing gear of the trailer fails or significantly sags, or the trailer frame bends under load. Portable trailer stabilizer  300  may be similar to portable trailer stabilizer  200 ,  1200  in construction and operation except that portable trailer stabilizer  300  may be configured to be repositioned by lifting and carrying using a trailer stabilizer positioning element  116  separate from the fifth wheel  112 ,  114  of the tractor  108 ,  110  as shown in  FIG.  1    and described in more detail below. Repeated description of elements in common may be omitted for brevity. 
     The portable trailer stabilizer  300  may include a support surface engagement element, such as a ground pad  302 , which may be configured to selectively engage the support surface  102 . The portable trailer stabilizer  300  may include a trailer engagement element, such as a trailer engagement bar  304  arranged to extend generally horizontally and/or generally laterally (e.g., side-to-side) beneath the forward end portion  118  of the trailer  100 . In some example embodiments, the trailer engagement bar  304  may be constructed from a section of metal channel or tube, such as round tube. 
     In some example embodiments, the support surface engagement element  302  and the trailer engagement element  304  may be operatively connected by one or more structural elements  306 ,  308  and/or one or more actuators, such as one or more hydraulic cylinders  310 . In other example embodiments, alternative actuators may be used, such as pneumatic or electrical actuators and/or electromechanical jacks, and/or springs, and/or ratchets, and/or pawls. The actuators may be configured to facilitate extension and/or retraction of the trailer engagement element  304  relative to the support surface engagement element  302 . 
     In some example embodiments, the trailer engagement element (e.g., trailer engagement bar  304 ) may be coupled to the structural elements  306 ,  308  and/or the actuators (e.g., hydraulic cylinders  310 ) by one or more pivot connections  310 A that may include a pivot pin. For example, some pivot connections may allow the trailer engagement bar  304  to tilt side-to-side with respect to the trailer, in addition to pivoting front-to-rear. Accordingly, the portable trailer stabilizer  300  may accommodate debris and uneven support surfaces  102  and/or tilted semi-trailers  100 , for example. 
     In some example embodiments, the actuators may be powered by one or more on-board, self-contained energy sources. For example, the hydraulic cylinders  310  may be operatively connected to an on-board, self-contained hydraulic system  312 . In some example embodiments, the hydraulic system  312  may include one or more hydraulic accumulators  314 , one or more isolation valves  316  (e.g., ball valves), one or more relief valves  317 , and/or one or more hydraulic conduits  318  fluidically connecting the accumulator  314 , the cylinders  310 , and valves  316 ,  317 . Although the example embodiment of  FIGS.  12 - 15    is shown with two hydraulic cylinders  310  coupled to one accumulator  314  via respective isolation valves  316 , some example embodiments may include one or more hydraulic cylinders  310 , one or more accumulators  314 , and/or one or more isolation valves  316  (or other flow control devices). In some example embodiments, the isolation valves  316  may be operated (e.g., opened and/or shut) by an isolation valve operator mechanism, such as valve operator elements  320  and/or cables  322  operatively connecting the valve operator elements  320  to the isolation valves  316 . In other example embodiments, isolation valve operator mechanisms may include mechanical linkages, electrical actuators, and/or hydraulic actuators arranged to open and/or shut the isolation valves  316 . 
     In some example embodiments, the isolation valve operator mechanism (e.g., valve operator elements  320 ) may be configured for operation in connection with coupling the portable trailer stabilizer  300  to a tractor  108  and/or uncoupling the portable trailer stabilizer from a tractor  108 . For example, the isolation valve operator mechanism  320  may be configured so that it is actuated by the act of coupling the portable trailer stabilizer  300  to a tractor  108  and/or the act of uncoupling the portable trailer stabilizer from a tractor  108 . For example, the portable trailer stabilizer  300  may include one or more positioning element engagement elements, such as conduits  324 , configured to receive respective arms  120  of the trailer stabilizer positioning element  116  (described below). The conduits  324  of the portable trailer stabilizer  300  may be spaced apart a distance corresponding to a distance between the arms  120  of the trailer stabilizer positioning element  116 . In some example embodiments, the conduits  324  may include respective bell mouths  326  to facilitate engagement of the arms  120  with the conduits  324 . 
     In some example embodiments, the valve operator elements  320  may be configured so that when the arms  120  of the trailer stabilizer positioning element  116  engage or disengage the conduits  324  of the portable trailer stabilizer  300 , the valve operator elements  320  are moved (e.g., pivoted). Moving the valve operator elements  320  may operate (e.g., open and/or shut) the isolation valves  316  via the cables  322 . For example, the isolation valve operator mechanism may be configured so that when the conduits  324  of the portable trailer stabilizer  300  are disengaged from the arms  120  of the trailer stabilizer positioning element  116 , the isolation valves  316  are shut and/or when the conduits  324  of the portable trailer stabilizer  300  are engaged with the arms  120  of the trailer stabilizer positioning element  116 , the isolation valves  316  are opened. 
     In some example embodiments, the trailer engagement element  304  may be pivotably disposed with respect to one or more of the structural elements  306 ,  308 . For example, the trailer engagement bar  304  may be coupled to the structural element  306  by a pivot  306 A that may include a pin, which may allow the trailer engagement bar  304  to move generally upward and downward (e.g., at a radius from the pivot  306 A) while extending and compressing the hydraulic cylinder  310 . In some example embodiments, the trailer engagement element (e.g., trailer engagement bar  304 ) may comprise one or more sloped engagement surfaces  304 A. The engagement surfaces  304 A may be arranged to contact a forward edge of the forward end portion  118  of the trailer  100  when the portable trailer stabilizer  300  is positioned beneath the forward end portion  118 . When the trailer engagement bar  304  is higher than the underside of the forward end portion  118  of the trailer  100 , the engagement surfaces  304 A may contact and be forced downward to slide below and along the forward end portion  118  as the portable trailer stabilizer  300  is moved underneath the forward end portion  118 . Accordingly, the contact between the engagement surfaces  304 A and/or the trailer engagement bar  304  may press the trailer engagement bar  304  downward, thus shortening the hydraulic cylinders  310 . 
     As depicted in  FIG.  12 A , the exemplary portable trailer stabilizer  300  may include extended rails  336  to which are mounted an axle  330 . Opposing ends of the axle  330  are mounted to respective wheel and tire combinations  340 . By incorporating the axle  330  and the wheel and tire combinations  340 , the exemplary portable trailer stabilizer  300  may be repositioned without requiring the entire stabilizer  300  to be lifted off the ground. 
     Looking to  FIG.  16   , the arms  120  of the trailer stabilizer positioning element  116  may be pivotable, such as about a pivot  122 , so that the arms  120  may be pivoted between a generally horizontal extended configuration and a generally vertical retracted configuration. In the extended configuration, the arms  120  may be pivotable above and/or below generally horizontal, such as to facilitate engagement of the arms  120  with a portable trailer stabilizer  300  that may be positioned on an even support surface  102  or on a tilted and/or uneven support surface  102 . In some example embodiments, the arms  120  may be pivoted by one or more actuators, such as a hydraulic cylinder  124 . 
     In some example embodiments, the trailer stabilizer positioning element  116  may be vertically repositionable relative to the terminal tractor, such as to vary the height of the arms  120  above the support surface  102 . In some example embodiments, the trailer stabilizer positioning element  116  may include one or more actuators, such as a hydraulic cylinder  126 , which may be arranged to raise and/or lower the arms  120 . 
     In some example embodiments, the trailer stabilizer positioning element  116  may be horizontally repositionable relative to the terminal tractor, such as to vary the horizontal length of the arms  120  above the support surface  102 . In some example embodiments, the trailer stabilizer positioning element  116  may include one or more actuators, such as a hydraulic cylinder  124 , which may be arranged to extend and contract the arms  120  and change the longitudinal length thereof. 
     Some example arms  120  may include an engagement element, such as a hook  128 , which may be disposed proximate a distal end portion of the arm  120 . Some example engagement elements may be configured to selectively retain a portable trailer stabilizer  300  on the arms  120 . In some example embodiments, one or more of the engagement elements (e.g., hooks  128 ,  1120 ,  2120 ) may be arranged to move the isolation valve operator mechanism (e.g., by contacting the valve operator elements  320 ,  2320 ,  1320 ) of the portable trailer stabilizer  300 . 
     Turning to  FIGS.  17  and  18   , an example terminal tractor  1110  may include a fifth wheel (which may be used to couple to semi-trailers), a trailer stabilizer positioning element  1116  (which may be used to couple to portable trailer stabilizers), and/or an operator cab  1130 . In the context of a remote or autonomous tractor  1110 , the operator cab  1130  may be optional. In some example embodiments, the trailer stabilizer positioning element  1116  may comprise one or more generally laterally oriented hooks  1120 , which may be arranged on a forward portion of the terminal tractor  1110 . For example, each hook  1120  may be generally elongated and/or may have a generally upwardly facing opening. In some alternative example embodiments, one or more trailer stabilizer positioning elements (e.g., one or more hooks  1120 ) may be arranged to operate on one or multiple sides of the tractor  1110  (e.g., for side deployment of the stabilizer) and/or from the rear of the tractor  1110  (e.g., for rearward deployment of the stabilizer). 
     In some example embodiments, the trailer stabilizer positioning element  1116  may be vertically repositionable relative to the terminal tractor  1100 , such as to vary the height of the hooks  1120  above the support surface  102 . In some example embodiments, the trailer stabilizer positioning element  1116  may include one or more actuators, such as a hydraulic cylinder  1126 , which may be arranged to raise and/or lower the hooks  1120 . It should be noted that in lieu of hooks  1120 , the trailer stabilizer positioning element may comprise an elongated trough. 
     In some example embodiments, the trailer stabilizer positioning element  1116  may be horizontally repositionable relative to the terminal tractor  1100 , such as to vary the horizontal position of the device with respect to the terminal tractor. In some example embodiments, the trailer stabilizer positioning element  1116  may include one or more actuators, such as a hydraulic cylinder, which may be arranged to extend and contract the horizontal position of the hook(s)  1120 . 
     The terminal tractor  1100  including the trailer stabilizer positioning element  1116  may be used with a further exemplary portable trailer stabilizer  1300  (see  FIG.  17   ). The portable trailer stabilizer  1300  may be generally similar to the earlier portable trailer stabilizer  300 , and repeated description of elements in common may be omitted for brevity. The portable trailer stabilizer  1300  may include one or more positioning element engagement elements, such as inverted hooks or an inverted trough  1324 , which may be configured to selectively engage the hooks/trough  1120  of the trailer stabilizer positioning element  1116 . In some example embodiments, the hooks/trough  1324  of the portable trailer stabilizer  1300  may be generally laterally oriented and/or may include a generally downwardly facing opening. One or more valve operator elements  1320 , which may be movably disposed within an opening defined by the hooks/trough  1324 , may be configured so that engagement of the hooks/trough  1120  of trailer stabilizer positioning element  1116  of the terminal tractor  1110  with the hooks/trough  1324  of the portable trailer stabilizer  1300  may operate isolation valves in the manner described above. For example, engaging the hooks/trough  1324  with the hooks/trough  1120  may move the valve operator element  1320 , which may operate the isolation valves via an isolation valve operator mechanism  1322 . 
     Referencing  FIGS.  19  and  20   , another example exemplary terminal tractor  2110  is depicted that includes a trailer stabilizer positioning element  2116  separate from the terminal tractor&#39;s fifth wheel. In exemplary form, the terminal tractor  2110  may include a fifth wheel (which may be used to couple to semi-trailers), the trailer stabilizer positioning element  2116  (which may be used to couple to portable trailer stabilizers), and/or an operator cab  2130 . In some example embodiments, the trailer stabilizer positioning element  2116  may comprise one or more hooks  2120  (or a trough), which may be arranged on a forward portion of the terminal tractor  2110 . For example, the hooks  2120  may be laterally spaced apart and/or may have generally upwardly facing openings. In some alternative example embodiments, one or more trailer stabilizer positioning elements (e.g., one or more hooks  2120 ) may be arranged to operate on one or multiple sides of the tractor  2110  (e.g., for side on deployment of the stabilizer) and/or from the rear of the tractor  2110  (e.g., for rearward deployment of the stabilizer). 
     In some example embodiments, the trailer stabilizer positioning element  2116  may be vertically repositionable relative to the terminal tractor  2110 , such as to vary the height of the hooks  2120  above the support surface  102 . In some example embodiments, the trailer stabilizer positioning element  2116  may include one or more actuators, such as a hydraulic cylinder  2126 , which may be arranged to raise and/or lower the hooks  2120 . 
     In some example embodiments, the trailer stabilizer positioning element  2116  may be horizontally repositionable relative to the terminal tractor  2110 , such as to vary the horizontal spacing of the hooks  2120  relative to a side (e.g., front, rear, left, right) of the terminal tractor. In some example embodiments, the trailer stabilizer positioning element  2116  may include one or more actuators, such as a hydraulic cylinder, which may be arranged to extend and contract to vary the horizontal position of the hooks  2120  with respect to a side of the tractor. 
     The terminal tractor  2100  including the trailer stabilizer positioning element  2116  may be used with a further example exemplary portable trailer stabilizer  2300 . The portable trailer stabilizer  2300  may be generally similar to portable trailer stabilizers  300 ,  1300 , and repeated description of elements in common may be omitted for brevity. The portable trailer stabilizer  2300  may include one or more positioning element engagement elements, such as a bar  2324 , which may be configured to selectively engage the hooks  2120  of the trailer stabilizer positioning element  2116 . In some example embodiments, the bar  2324  of the portable trailer stabilizer  2300  may be generally laterally oriented and/or generally horizontal. One or more valve operator elements  2320 , which may be movably disposed relative to the bar  2324 , may be configured so that engagement of the trailer stabilizer positioning element  2116  of the terminal tractor  2110  with the bar  2324  of the portable trailer stabilizer  2300  may operate isolation valves in the manner described above. For example, the trailer stabilizer positioning element  2116  of the terminal tractor  2110  may include a tractor valve operator element  2118 , which may be configured to engage a stabilizer valve operator element  2320 , such as a pivotable plate. The stabilizer valve operator element  2320  may operate the isolation valves via an isolation valve operator mechanism  2322 . 
     Referring back to  FIGS.  12 A and  12 - 15   , some example portable trailer stabilizers  300  according to at least some aspects of the present disclosure may be configured in consideration of trailers having undersides with varied spacings from the ground or a support surface. For example, some portable trailer stabilizers  300  may be configured to accommodate trailers  100  with an undersurface at a given height  450  (see  FIG.  14   ). Some portable trailer stabilizers  300  may have a minimum height  452 , which may be less than the given trailer height  450 , to facilitate positioning of the portable trailer stabilizer  300  beneath an underside of the trailer  100 . For example, the minimum height  452  may be the height of the portable trailer stabilizer  300  when the trailer engagement tube  304  is fully retracted relative to the ground pad  302 . Some portable trailer stabilizers  300  may have a maximum height  454 , which may be greater than or equal to the highest height of the undersurface of a trailer. For example, the maximum height  454  may be the height of the portable trailer stabilizer  300  when the trailer engagement tube  304  is fully spaced relative to the ground pad  302 . In some example embodiments, the maximum height  454  of the stabilizer  300  may comprise the minimum height  452  plus a travel range  456 . For example, the travel range  456  may be the height above the minimum height  452  that the trailer engagement tube  304  may be configured to occupy by operation of the hydraulic cylinder  310 . Although these height parameters have been described in connection with the embodiment shown in  FIGS.  12 A and  12 - 15   , similar height parameters may be applicable to other example stabilizer embodiments according to at least some aspects of the present disclosure, such as the portable trailer stabilizers  200 ,  1200 ,  1300 ,  2300  as described herein. 
     In some example embodiments according to at least some aspects of the present disclosure, the minimum height  452  may be about 40 inches to about 42 inches. In some circumstances, such a minimum structure height may provide support for the semi-trailer should the repositioning mechanism of the trailer stabilizer bar  304  (e.g., hydraulics) fail. In some example embodiments, the maximum height  454  may be about 52 inches. In some example embodiments, the structure of the stabilizer may be height adjustable to facilitate use with trailer heights  450  out of the normal travel range  456 . In some such embodiments, adjusting the height-adjustable structure may allow the structure to be reconfigured to have lower or higher minimum heights  452  and maximum heights  454 . Generally, stabilizers according to at least some aspects of the present disclosure may be constructed to operate at any heights necessary to facilitate use with trailers of a particular height or range of heights. 
     Referring to  FIG.  21   , an indicator  400  may be included as part of any one of the foregoing portable trailer stabilizers  200 ,  300 ,  1200 ,  1300 ,  2300 . The indicator  400  may include a signal element, such as a pivotably disposed flag  402 , which may be arranged to visually indicate whether a portable trailer stabilizer is positioned to support a parked trailer. For example, when a trailer engagement bar  404  (equivalent to the stabilizer bars  204 ,  304 ,  1204 ) of a portable trailer stabilizer is not engaged with the underside of a trailer, the flag  402  may be in the generally vertical, generally downward position shown in  FIG.  21   . When the trailer engagement bar  404  of the portable trailer stabilizer approximates or is in contact with the underside the trailer, the flag  402  may extend generally horizontally and/or laterally outward from the stabilizer to evidence the stabilizer is in a support position with respect to the parked trailer. For example, the indicator  400  may include a linkage and roller  406  operatively coupled to the flag  402  so that contact between the roller  406  and the undersurface of the parked trailer may result in repositioning of the flag  402 . Accordingly, the stabilizer status of the portable trailer stabilizer may be determined by individuals viewing the position of the indicator flag  402 . In some circumstances, the indicator flag  402  may be viewed directly by individuals with a direct line of sight thereto, such as individuals in the area of the portable trailer stabilizer. In some circumstances, the indicator flag  402  may be viewed indirectly by individuals utilizing a remote viewing device, such as individuals inside a warehouse viewing the indicator flag  402  position on a screen displaying an image obtained by a camera outside of the warehouse. In some example embodiments, the flag  402  may include reflective elements and/or other visibility enhancing features to allow visual differentiation between the flag&#39;s position  402  reflecting the stabilizer in a stabilizing position versus a non-stabilizing position. 
     Some example methods of operating a portable trailer stabilizer are described below. Various example methods according to at least some aspects of the present disclosure may include any combination of any one or more of the steps or operations discussed below. 
     Some example methods of supporting or providing support for a trailer using a portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may include parking a trailer  100  in a desired location using a tractor  106 ,  108 ,  110  and disconnecting the tractor  106 ,  108 ,  110  from the trailer  100  (e.g., disconnecting the fifth wheel plate of the trailer from the fifth wheel of the tractor  106 ,  108 ,  110 ). For example, the tractor  106 ,  108 ,  110  (e.g., while operatively coupled to the trailer  100 ) may be driven rearward to reposition the trailer  100  at a loading dock bay  104 A. Upon termination of the repositioning, the trailer  100  may be decoupled from the tractor  106 ,  108 ,  110 , leaving the trailer  100  parked in position. The tractor  106 ,  108 ,  110  (e.g., while operatively decoupled from the trailer) may be driven forward to vacate the position immediately in front of the forward end portion  118  of the parked trailer  100 . 
     A tractor  108 ,  110  may be coupled to a portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 , which may be operative to open the isolation valves  216 ,  1216 ,  316  of the portable trailer stabilizer. In particular, engagement of the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  by the tractor  108 ,  110  may be operative to reposition the isolation valves  216 ,  1216 ,  316  so that fluid can flow between the actuators  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 , as will be discussed in more detail hereafter. Repositioning the isolation valves  216 ,  1216 ,  316  may direct hydraulic fluid to or from the hydraulic accumulator  214 ,  1214 ,  314  to or from the hydraulic cylinders  210 ,  1210 ,  310 , thus varying the effective length of the hydraulic cylinders  210 ,  1210 ,  310  (if not already fully extended or fully retracted). By way of example, higher pressurized fluid from the hydraulic accumulator  214 ,  1214 ,  314  flowing to the hydraulic cylinders  210 ,  1210 ,  310  would be operative to extend the hydraulic cylinders where the fluid pressure within the cylinders is less than that of the accumulator. Conversely, higher pressurized fluid from the hydraulic cylinders  210 ,  1210 ,  310  flowing to the accumulator  214 ,  1214 ,  314  would be operative to retract the hydraulic cylinders where the fluid pressure within the cylinders is greater than that of the accumulator. 
     Coupling the tractor  108 ,  110  to the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may include coupling a trailer stabilizer positioning element (e.g., fifth wheel  112 ,  114  and/or trailer stabilizer positioning element  116 ) of the tractor  108 ,  110  to a positioning element engagement element (e.g., fifth wheel plate  224  and/or conduits  324 ) of the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 . In this fashion, the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may be repositioned by the tractor  108 ,  110  at least partially beneath and/or in contact with the underside of a forward end portion  118  of the parked trailer  100 . For example, a tractor  108 ,  110  (e.g., operatively coupled to the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 ) may be driven forward to position the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  at least partially beneath the forward end portion  118  of the parked trailer  100 . If the portable trailer stabilizer  200 ,  1200  includes a fifth wheel plate  224 ,  1224  and the tractor  108 ,  110  includes a fifth wheel  112 ,  114  disposed on a rear portion of the tractor  108 ,  110 , positioning the portable trailer stabilizer  200 ,  1200  may include driving the tractor  108 ,  110  in a rearward direction. If the portable trailer stabilizer  300  includes at least one conduit  324  and the tractor  110  includes at least one extended arm  120  disposed at a front end portion of the tractor  110 , positioning the portable trailer stabilizer  300  may include driving the tractor  110  in a forward direction. If the portable trailer stabilizer  1300 ,  2300  includes at least one hook or trough  1324 , or bar  2324  and the tractor  1110  includes at least one hook or trough  1324  disposed at a front end portion of the tractor  1110  or the tractor  2110  includes at least one hook  2120  disposed at a front end portion of the tractor  2110 , positioning the portable trailer stabilizer  1300 ,  2300  may include driving the tractor  110  in a forward direction. 
     A vertical surface of the forward end portion  118  of the trailer  100  (and/or possibly the underneath surface of the trailer  100 ) may be contacted by the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A) while the trailer engagement element is in a partial or fully extended configuration. While at least a portion of the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is being positioned beneath the forward end portion  118  of the trailer  100 , the trailer engagement element  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A may be pressed against a bottom edge of the vertical surface of the forward end portion  118  of the trailer  100 , which may move the trailer engagement element from a partial or fully extended configuration to a lesser extended configuration that may include compressing the hydraulic cylinders  210 ,  1210 ,  310 . Compressing the hydraulic cylinders  210 ,  1210 ,  310  may direct pressurized hydraulic fluid from the hydraulic cylinders  210 ,  1210 ,  310  to the hydraulic accumulator  214 ,  1214 ,  314  via the open isolation valves  216 ,  1216 ,  316 , where the pressurized hydraulic fluid may be stored in the accumulator  214 ,  1214 ,  314 . 
     While repositioning the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  partially underneath the trailer  100 , the support surface engagement elements (e.g., ground pad  202 ,  1202 ,  302 ) may be repositioned to contact the support surface  102 . Contact between the ground pads  202 ,  1202 ,  302  and the support surface  102  may occur as the stabilizer is being repositioned horizontally or may occur after the horizontal position of the stabilizer is established. In either of the foregoing instances, at least a portion of the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may be vertically repositioned toward the support surface  102  to establish or at least increase the contact between grounds pads  202 ,  1202 ,  302  and the support surface. During this vertical repositioning (i.e., lowering) operation, the isolation valves  216 ,  1216 ,  316  may remain open, thereby allowing hydraulic fluid to flow between the accumulator  214 ,  1214 ,  314  and the hydraulic cylinders  210 ,  1210 ,  310 . Accordingly, the trailer engagement element  204 ,  1204 ,  304  may remain in contact with an underside of the trailer  100  due to pressurized hydraulic fluid flowing from the accumulator  214 ,  1214 ,  314  to the hydraulic cylinders  210 ,  1210 ,  310  and extending the hydraulic cylinders  210 ,  1210 ,  310 . 
     In this manner, when the hydraulic system is closed, pressurized, and the isolation valves  216 ,  1210 ,  316  are open, an equilibrium is established between the fluid within the hydraulic cylinders  210 ,  1210 ,  310  and the fluid within the accumulator  214 ,  1214 ,  314  (as well as the fluid flowing throughout the system). Prior to reaching this equilibrium, forces pushing down on the engagement element  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A may be operative to increase the hydraulic pressure within the hydraulic cylinders  210 ,  1210 ,  310  and, if this increased pressure is greater than that of the hydraulic pressure within the accumulator  214 ,  1214 ,  314 , fluid will flow from the hydraulic cylinders  210 ,  1210 ,  310  and toward the accumulator  214 ,  1214 ,  314  until pressure within the system equilibrates, presuming the isolation valves  216 ,  1210 ,  316  are open. In this manner, active loads on the engagement element  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A may be operative to increase the hydraulic pressure within the system after equilibration. Conversely, if forces pushing down on the engagement element  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A are not operative to increase or maintain the hydraulic pressure within the hydraulic cylinders  210 ,  1210 ,  310  to a pressure at or above that of hydraulic fluid within the accumulator  214 ,  1214 ,  314 , then fluid will flow from the accumulator  214 ,  1214 ,  314  toward the hydraulic cylinders  210 ,  1210 ,  310  (presuming the isolation valves  216 ,  1210 ,  316  are open), thus causing the hydraulic cylinders to extend or increase in length. In this manner, the absence of or lesser active loads on the engagement element  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A may be operative to decrease the hydraulic pressure within the system after equilibration. And when the pressure within the system reaches equilibrium again, the hydraulic pressure of the cylinders  210 ,  1210 ,  310  is approximately equal to the hydraulic pressure within the accumulator  214 ,  1214 ,  314 , which maintains the position of the cylinders  210 ,  1210 ,  310  (i.e., no contraction or extension) presuming the isolation valves  216 ,  1210 ,  316  are open. 
     In exemplary application, when the hydraulic system is closed, pressurized, and the isolation valves  216 ,  1216 ,  316  are open, the hydraulic pressure of the system is operative to cause the hydraulic cylinders  210 ,  1210 ,  310  to extend to a maximum or near maximum length (unless otherwise governed). This maximum or near maximum length results in the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ) being positioned at a maximum height or near maximum height (unless otherwise governed). In this fashion, as the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is positioned underneath the trailer  100 , the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A) may make contact with a portion of the trailer (such as the lower leading edge, a forward vertical surface, or a horizontal underneath surface) as the stabilizer is vertically and/or horizontally repositioned. In cases where the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A) needs to have its vertical positioned lowered to fit underneath the trailer  100 , the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may be wedged with respect to the trailer  100  so that the trailer exerts downward force on the trailer engagement element. Downward force on the trailer engagement element is resultantly transferred to the hydraulic cylinders  210 ,  1210 ,  310  and the pressure of the fluid therein. In this manner, the downward force on the trailer engagement bar  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A (exerted by the trailer  100 ) is operative to increase the hydraulic pressure and compress the hydraulic cylinders  210 ,  1210 ,  310  to lower the trailer engagement element and allow it to pass underneath the trailer, while the higher pressure fluid flows from the cylinders  210 ,  1210 ,  310  toward the accumulator  214 ,  1214 ,  314  as the isolation valves  216 ,  1216 ,  316  are open. But because the hydraulic system is pressurized, the fluid reaches equilibrium and the upward and downward forces acting on the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304  and/or sloped engagement surface  204 A,  304 A,  1240 A) are equalized with respect to the hydraulic pressure of the fluid within the accumulator  214 ,  1214 ,  314  to maintain contact between the underside of the trailer  100  and trailer engagement element. Upon reaching the final horizontal position of the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 , underneath the trailer  100 , at least a portion of the stabilizer may be repositioned (i.e., vertically lowered) so that the support surface engagement elements (e.g., ground pad  202 ,  1202 ,  302 ) thoroughly contact the support surface  102 . In circumstances where at least a portion of the stabilizer is vertically lowered so that the support surface engagement elements thoroughly contact the support surface, the trailer forces acting on the trailer engagement element effectively decrease during this vertical repositioning of the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 . As a result, the pressurized hydraulic fluid within the system would be the dominant force, thus causing the hydraulic cylinders  210 ,  1210 ,  310  to extend (i.e., increase in length) until reaching a maximum length or until the trailer engagement element contacts the undersurface of the trailer so that the downward trailer forces are sufficient to oppose further extension of the hydraulic cylinders  210 ,  1210 ,  310 . 
     After at least a portion of the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is positioned appropriately (vertically, laterally, and horizontally) underneath a forward end  118  of the trailer  100 , the tractor  108 ,  110  may disengage from the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 . Disengagement between the tractor  108 ,  110  and the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may coincide with shutting the isolation valve  216 ,  1216 ,  316 . More specifically, if the trailer stabilizer positioning element includes a fifth wheel  112 ,  114  and the positioning element engagement element includes a fifth wheel plate  224 ,  1224 , disengaging the tractor  108 ,  110  from the portable trailer stabilizer  200 ,  1200  may include uncoupling the fifth wheel plate  224 ,  1224  of the portable trailer stabilizer from the fifth wheel  112 ,  114  of the tractor  108 ,  110 . Disengaging the tractor  108 ,  110  from the portable trailer stabilizer  200 ,  1200  may include repositioning the valve operator element  220 ,  1220  to shut the isolation valve  216 ,  1216 . If the trailer stabilizer positioning element includes an extended arm  120  and the positioning element engagement element includes a conduit  324  configured to receive the arm  120 , disengaging the tractor  110  from the portable trailer stabilizer  300  may include disengaging the conduit  324  of the portable trailer stabilizer  300  from the arm  120  of the tractor  110 . Disengaging the tractor  110  from the portable trailer stabilizer  300 ,  1300 ,  2300  may include moving the valve operator element  320 ,  1320 ,  2320  to shut the isolation valves  316 . Post disengagement, the tractor  108 ,  110  (e.g., operatively decoupled from the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 ) may be repositioned to vacate a position immediately in front of the forward end portion  118  of the parked trailer  100 . In cases where the tractor  108 ,  110  disengages from a portable trailer stabilizer  200 ,  1200 , the tractor may be driven forward to finalize the tractor repositioning. Conversely, in cases where the tractor  108 ,  110  disengages from a portable trailer stabilizer  300 ,  1300 ,  2300 , the tractor may be driven backwards to finalize the tractor repositioning. 
     As mentioned, when the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is in a stabilized position having at least a portion of the stabilizer underneath the forward end  118  of a parked trailer  100 , the stabilizer may be operative to provide stabilization to the parked trailer during loading and/or unloading of material/goods/contents to or from the trailer. In one example, the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may be actively in contact with an underside of the trailer  100 . In another example, the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  may be spaced apart from the underside of the trailer  100 . Both examples will be explained hereafter. 
     In an instance where the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is in a stabilization position that involves the stabilizer initially and thereafter being in contact with the underside of the trailer  100 , the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ) will most generally be the portion of the stabilizer contacting the trailer. For purposes of discussion, it may be presumed that the tractor  108 ,  110  is disengaged from the portable trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  and that the isolation valve  216 ,  1216 ,  316  is closed, thereby discontinuing fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 . As a result, the hydraulic fluid within the hydraulic cylinders  210 ,  1210 ,  310  and conduits leading to the isolation valve  216 ,  1216 ,  316  is held within a fixed volume and the hydraulic fluid generally embodies an incompressible fluid. 
     In a case where material/goods/contents are loaded onto the trailer  100 , particularly at the forward end portion  118  of the trailer  100 , and the trailer engagement element contacts an underside of the trailer, the downward force imparted by the trailer  100  upon the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  increases as more goods are loaded within the front of the trailer. This increase in downward force is ultimately borne by the hydraulic cylinders  210 ,  1210 ,  310  and operates to increase the pressure of the hydraulic fluid therein. But given that the hydraulic fluid is trapped, and is nearly incompressible, the increased hydraulic pressure does not lead to appreciable retraction of the hydraulic cylinders  210 ,  1210 ,  310  given that the hydraulic fluid is trapped in a fixed volume. As a result, even if the landing gear of the trailer  100  was to fail, the hydraulic cylinders  210 ,  1210 ,  310  are operative to support the entire weight of the forward end portion  118  of the trailer  100 , thus avoiding roll-over or tip-over of the trailer  100  in an instance of landing gear partial or complete failure. A similar sequence applies to a trailer  100  unloaded with the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  in a stabilized position. 
     Where material/goods/contents are unloaded from the trailer  100 , particularly from the forward end portion  118  of the trailer  100 , and the trailer engagement element contacts an underside of the trailer, the downward forces imparted by the trailer  100  upon the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  decrease. This decrease in downward forces when the hydraulic cylinders  210 ,  1210 ,  310  are fully extended may lead to a vertical gap being created between the underside of the trailer  100  and the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ) as sag associated with the trailer frame at the forward end portion  118  of the trailer is lessened. Conversely, a decrease in downward forces when the hydraulic cylinders  210 ,  1210 ,  310  are not fully extended may lead to no extension or a minimal extension of the hydraulic cylinders by lessening the downward forced applied to the stabilizer by the trailer while the hydraulic fluid continues to remain within a fixed volume as a result of the isolation valve  216 ,  1216 ,  316  being closed and inhibiting fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 . In either instance, however, the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  maintains itself in a stabilizing position so that if the landing gear of the trailer  100  fails, the entire weight of the forward end portion of the trailer is able to be held up by the stabilizer. Those skilled in the art are aware of the dynamic forces imparted upon trailers by forklifts moving therein, as well as pumping fluids within on-board tanks of a semi-trailer, which can cause landing gear failure even when a trailer is being unloaded or is near empty. Consequently, stabilization of trailers is important in both loading and unloading operations. 
     Conversely, in an instance where the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is in a stabilization position that involves the stabilizer initially being spaced apart from the underside of the trailer  100 , the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ) will most generally be the portion of the stabilizer nearest to the underside of the trailer. For purposes of discussion, it may be presumed that the tractor  108 ,  110  is disengaged from the portable trailer stabilizer  200 ,  1200 ,  300  and that the isolation valve  216 ,  1216 ,  316  is closed, thereby discontinuing fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 . As a result, the hydraulic fluid within the hydraulic cylinders  210 ,  1210 ,  310  and conduits leading to the isolation valve  216 ,  1216 ,  316  is held within a fixed volume and the hydraulic fluid generally embodies an incompressible fluid. 
     In a case where material/goods/contents are loaded onto the trailer  100 , particularly at the forward end portion  118  of the trailer  100 , the downward forces imparted by the trailer increase. This increase in forces on the trailer  100  may result in the trailer sagging, which may or may not close the original spacing between the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  and the underside of the trailer, which may result in contact between the stabilizer and the underside of the trailer  100 . Contact by the trailer  100  onto the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  results in some of the downward forces of the trailer being ultimately borne by the hydraulic cylinders  210 ,  1210 ,  310  and operates to increase the pressure of the hydraulic fluid therein. But given that the hydraulic fluid is trapped, and is nearly incompressible, the increased hydraulic pressure does not lead to appreciable retraction of the hydraulic cylinders  210 ,  1210 ,  310  given that the hydraulic fluid is trapped in a fixed volume. As a result, even if the landing gear of the trailer  100  was to fail, the hydraulic cylinders  210 ,  1210 ,  310  are operative to support the entire weight of the forward end portion  118  of the trailer  100 , thus avoiding roll-over or tip-over of the trailer  100  in an instance of landing gear failure. Conversely, if a gap is maintained between the trailer  100  and the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300 , and forces acting on the trailer cause the landing gear to fail, the underside of the trailer will immediately contact the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ) in order to support the trailer. Given that the hydraulic fluid is trapped in a fixed volume, and is nearly incompressible, the increased hydraulic pressure that results on the hydraulic fluid trapped within the cylinders  210 ,  1210 ,  310  from the forward weight of the trailer being borne by the stabilizer does not lead to appreciable retraction of the hydraulic cylinders  210 ,  1210 ,  310 . As a result, even if the landing gear of the trailer  100  fails, the hydraulic cylinders  210 ,  1210 ,  310  are operative to support the entire weight of the forward end portion  118  of the trailer  100 , thus avoiding roll-over or tip-over of the trailer  100  in an instance of landing gear failure. A similar sequence applies to a trailer  100  unloaded with the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  in a stabilized position. 
     In a circumstance where the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is positioned underneath the trailer  100  prior to the trailer being unloaded, and a gap exists between the underside of the trailer and the stabilizer, this gap will generally be maintained or slightly increased during unloading of material/goods/contents from the trailer  100 . By way of example, particularly at the forward end portion  118  of the trailer  100 , the downward forces imparted upon the trailer  100  decease as material is unloaded from the front of the trailer, which may result in a lesser sag associated with the trailer frame at the forward end portion  118  of the trailer. If this lessening of sag occurs, the spacing/gap between the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  and the trailer may increase. Nevertheless, the spacing between the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  and the trailer does not negate the stabilization provided if the landing gear of the trailer  100  fails during unloading. In a case of landing gear failure, the forward end portion  118  of the trailer  100  would be repositioned downward and negate any gap between the trailer and stabilizer, thereby coming to rest upon the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ). Given that the hydraulic fluid is trapped in a fixed volume, and is nearly incompressible, the increased hydraulic pressure that results from the stabilizer bearing at least a portion of the weight of the trailer is trapped within the cylinders  210 ,  1210 ,  310  and does not lead to appreciable retraction of the hydraulic cylinders  210 ,  1210 ,  310 . As a result, even if the landing gear of the trailer  100  fails, the hydraulic cylinders  210 ,  1210 ,  310  are operative to support the entire weight of the forward end portion  118  of the trailer  100 , thus avoiding roll-over or tip-over of the trailer  100  in an instance of landing gear partial or complete failure. 
     Turning to  FIG.  22   , a closed hydraulic system in accordance with the instant disclosure that may be used with any of the stabilizers  200 ,  1200 ,  300 ,  1300 ,  2300  may include a pair of hydraulic cylinders  210 ,  1210 ,  310  are in selective fluid communication with an accumulator  214 ,  1214 ,  314  via hydraulic lines  218 ,  1218 ,  318  and a pair of isolation valves  216 ,  1216 ,  316 . As discussed herein, when the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is being repositioned from or to a stabilized position, the isolation valves  216 ,  1216 ,  316  may be open to allow fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 . But when the stabilizer is in a stabilized position, the isolation valves  216 ,  1216 ,  316  may be closed to discontinue fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 . Thus, when the stabilizer is in a stabilized position, the hydraulic fluid in the cylinders and downstream from the isolation valve in fluid communication with the cylinders occupies a fixed volume. In this manner, the stabilizer can hold up the load of the front portion of a trailer using a locked column or volume of fluid. Conversely, when the isolation valves  216 ,  1216 ,  316  are open to allow fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 , weight applied to the stabilizers  200 ,  1200 ,  300 ,  1300 ,  2300  results in increased pressure of the hydraulic fluid at the hydraulic cylinders  210 ,  1210 ,  310 , which causes the cylinders to retract and fluid to flow from the cylinders, through the isolation valves, and into the accumulator  214 ,  1214 ,  314  until reaching an equilibrium. It should be noted that the accumulator  214 ,  1214 ,  314  comprises a variable volume chamber to accommodate different amounts of hydraulic fluid, while the chamber is pressurized to maintain at least a minimum pressure on the hydraulic fluid. As discussed herein, this minimum pressure may be sufficient to cause the hydraulic cylinders  210 ,  1210 ,  310  to fully extend or at least partially extend, rather than being fully retracted at a minimum length. 
     Looking at  FIG.  23   , a further exemplary closed hydraulic system in accordance with the instant disclosure that may be used with any of the stabilizers  200 ,  1200 ,  300 ,  1300 ,  2300  may include a pair of hydraulic cylinders  210 ,  1210 ,  310  in selective fluid communication with an accumulator  214 ,  1214 ,  314  via hydraulic lines  218 ,  1218 ,  318 , a pair of isolation valves  216 ,  1216 ,  316 , and a pair of relief valves  217 ,  1217 ,  317 . As discussed herein, when the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is being repositioned from or to a stabilized position, the isolation valves  216 ,  1216 ,  316  may be open to allow fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 . But when the stabilizer is in a stabilized position, the isolation valves  216 ,  1216 ,  316  may be closed to discontinue fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314  along a first path. Likewise, when the stabilizer is in a stabilized position, the relief valves  217 ,  1217 ,  317  may be closed to discontinue fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314  along a second path. Thus, when the stabilizer is in a stabilized position, the hydraulic fluid in the cylinders and downstream from the isolation valve in fluid communication with the cylinders occupies a fixed volume. In this manner, stabilizer can hold up the load of the front portion of a trailer using a locked column or volume of fluid until a pressure exerted by the hydraulic fluid reaches a predetermined pressure. This predetermined pressure may be the result of an abrupt landing gear failure or abrupt forces occurring as a result of loading/unloading of the trailer, thereby amplifying the force exerted upon the stabilizer (resulting from the dynamic forces being greater than the static forces), and causing an abrupt spike in the hydraulic fluid pressure within the cylinders. Upon reaching the predetermined relief pressure, which may result from the forward portion of the trailer  100  crashing downward onto the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ), the relief valves  217 ,  1217 ,  317  may automatically open to bleed off hydraulic pressure from the cylinders and to the accumulator  214 ,  1214 ,  314  via the second path. In such a case, the bleeding action of the hydraulic fluid from the cylinders  210 ,  1210 ,  310  causes the cylinders to gradually retract until reaching a minimum length or until the hydraulic fluid within the cylinders is below the predetermined relief pressure—whichever occurs first. In either circumstance, the result may include the trailer stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  continuing to function as a support or functioning anew as a support with the stabilizer being in contact with the trailer. Accordingly, the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  operates to dampen the descent of the forward portion of the trailer  100  in cases of landing gear partial or total failure or dynamic forces tending to sag the trailer from loading/unloading of materials. Conversely, when the isolation valves  216 ,  1216 ,  316  are open to allow fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 , such as when the stabilizer is being repositioned, hydraulic fluid pressure between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314  along the first path may be equalized and correspondingly vary the length of the cylinders depending upon forced applied to the cylinders to counteract the hydraulic fluid pressure. 
     With reference to  FIG.  24   , a still further exemplary closed hydraulic system in accordance with the instant disclosure that may be used with any of the stabilizers  200 ,  1200 ,  300 ,  1300 ,  2300  may include a pair of hydraulic cylinders  210 ,  310  are in selective fluid communication along a first path with an accumulator  214 ,  1214 ,  314  via hydraulic lines  218 ,  1218 ,  318  and a pair of one-way valves  219 ,  1219 ,  319 . These same hydraulic cylinders  210 ,  1210 ,  310  are in selective fluid communication along a second path with the accumulator  214 ,  1214 ,  314  via hydraulic lines  221 ,  1221 ,  321  and a second set of valves  223 ,  1223 ,  323 . When the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is being repositioned from or to a stabilized position, the one-way valves  219 ,  1219 ,  319  allow fluid communication between the hydraulic cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314  such that higher pressure fluid in the accumulator is able to flow to the cylinders via the hydraulic lines  218 ,  1218 ,  318 , but higher pressure fluid in the cylinders is precluded from flowing through the one-way valves via the hydraulic lines  218 ,  1218 ,  318  to the accumulator. When the stabilizer is in a stabilized position, the one-way valves  219 ,  1219 ,  319  remain able to be opened when the hydraulic pressure within the accumulator  214 ,  1214 ,  314  is higher than the hydraulic pressure within the cylinders  210 ,  1210 ,  310 . Similarly, the set of valves  223 ,  1223 ,  323  are normally closed when the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is being repositioned from or to a stabilized position, as well as when the stabilizer is in a stabilized position. When the release valves  223 ,  1223 ,  323  are closed, fluid communication between the cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314  is precluded within the hydraulic lines  221 ,  1221 ,  321 . 
     When the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is in a stabilized position, the hydraulic fluid in the cylinders  210 ,  1210 ,  310  and downstream from the one-way valves  219 ,  1219 ,  319  occupies a fixed volume. In this manner, stabilizer can hold up the load of the front portion of a trailer using a locked column of fluid as the downward force exerted by the trailer on the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  increases, without appreciable compression of the overall height of the stabilizer, because the one-way valves  219 ,  1219 ,  319  inhibit higher pressure fluid from traveling to the accumulator  214 ,  1214 ,  314 . Conversely, in cases where the downward force on the front of the trailer is reduced, such as when material is unloaded from the trailer, sag associated with the trailer may decrease, thereby causing the underneath surface of the trailer to rise. This increase in height of the underside of the trailer may create a gap between the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  and the underneath surface of the trailer. Unlike the prior exemplary diagrams, the instant configuration allows the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  to automatically react to increases in height of the underside of the trailer, post location in a stabilization position. In particular, as the downward force applied to the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  by the trailer decreases or is eliminated (e.g., resulting from unloading of materials from the trailer), the pressure of the hydraulic fluid within the cylinders decreases, which means that the hydraulic fluid pressure on the accumulator  214 ,  1214 ,  314  side of the one-way valves  219 ,  1219 ,  319  is greater than the hydraulic fluid pressure on the cylinder side of the one-way valves  219 ,  1219 ,  319 . This pressure differential allows the one-way valves  219 ,  1219 ,  319  to open and push additional hydraulic fluid into the cylinders  210 ,  1210 ,  310 , which causes the cylinders to extend until reaching a maximum extension or until contacting the undersurface of the trailer and reaching an equilibrium between the downward force of the trailer and the hydraulic fluid pressure. In this manner, the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is able to actively react to decreases in downward pressure coming from the trailer to reduce or eliminate any gap between the stabilizer and the underside of the trailer. 
     Similarly, when the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  is in a stabilized position, the hydraulic fluid in the cylinders  210 ,  1210 ,  310  and upstream from the release valves  223 ,  1223 ,  323  occupies a fixed volume. In this manner, stabilizer can hold up the load of the front portion of a trailer using a locked column of fluid as the downward force exerted by the trailer on the stabilizer  200 ,  1200 ,  300 ,  1300 ,  2300  increases, without appreciable compression of the overall height of the stabilizer. In a circumstance where the release valves  223 ,  1223 ,  323  are relief valves, the valves will maintain a fixed volume until the hydraulic pressure exceeds a predetermined threshold pressure, which when reached allows the valves to open and release the higher pressure hydraulic fluid to the accumulator  214 ,  1214 ,  314 . Moreover, the relief valves may have a manual override that allows the valves to open when the stabilizer is  200 ,  1200 ,  300 ,  1300 ,  2300  engaged by a tractor  108 ,  110  for repositioning of the stabilizer. Alternatively, the release valves  223 ,  1223 ,  323  may comprise any type of valve that allows selective communication between the cylinders  210 ,  1210 ,  310  and the accumulator  214 ,  1214 ,  314 , such as, without limitation, isolation valves that are opened upon engaged by a tractor  108 ,  110  for repositioning of the stabilizer. In this fashion, higher pressure fluid within the cylinders  210 ,  1210 ,  310  may be routed to the accumulator  214 ,  1214 ,  314  via manual control over the valves  223 ,  1223 ,  323  or automatic opening of the valves when the stabilizer is  200 ,  1200 ,  300 ,  1300 ,  2300  engaged by a tractor  108 ,  110  for repositioning of the stabilizer. 
     Returning to  FIGS.  1 - 20   , when it is desired to discontinue use of the portable trailer stabilizer  200 ,  1200 ,  300  with the trailer  100  (e.g., when the trailer  100  no longer requires stabilization), the portable trailer stabilizer  200 ,  1200 ,  300  may be moved from at least partially beneath and/or in contact with the forward end portion  118  of the trailer  100  to a different location. Some example methods of moving a portable trailer stabilizer  200 ,  1200 ,  300  may include coupling a tractor  108 ,  110  to a portable trailer stabilizer  200 ,  1200 ,  300 , which may be positioned at least partially beneath and/or in contact with a forward end portion  118  of a parked trailer  100 . Coupling the tractor  108 ,  110  to the portable trailer stabilizer  200 ,  1200 ,  300  may be operative to open the isolation valves  216 ,  1216 ,  316 , such as by moving the valve operator element  220 ,  1220 ,  320 . Coupling the tractor  108 ,  110  to the portable trailer stabilizer  200 ,  1200 ,  300  may include coupling a trailer stabilizer positioning element (e.g., fifth wheel  112 ,  114  and/or trailer stabilizer positioning element  116 ) of the tractor  108 ,  110  to a positioning element engagement element (e.g., fifth wheel plate  224 ,  1224  and/or conduits  324 ) of the portable trailer stabilizer  200 ,  1200 ,  300 . 
     If the trailer stabilizer positioning element includes a fifth wheel  112 ,  114  and the positioning element engagement element includes a fifth wheel plate  224 ,  1224 , coupling the tractor  108 ,  110  to the portable trailer stabilizer  200 ,  1200  may include coupling the fifth wheel plate  224 ,  1224  of the portable trailer stabilizer  200 ,  1200  to the fifth wheel  112 ,  114  of the tractor  108 ,  110 . Coupling the tractor  108 ,  110  to the portable trailer stabilizer  200 ,  1200  may include pivoting the valve operator element  220 ,  1220  to open the isolation valves  216 ,  1216 . If the portable trailer stabilizer  200 ,  1200  includes a fifth wheel plate  224 ,  1224  and the tractor  108 ,  110  includes a fifth wheel  112 ,  114  disposed on a rear portion of the tractor  108 ,  110 , coupling the tractor  108 ,  110  to the portable trailer stabilizer  200 ,  1200  may include driving the tractor  108 ,  110  in a rearward direction. 
     If the trailer stabilizer positioning element includes an extended arm  120  and the positioning element engagement element includes a channel  324  configured to receive the arm  120 , coupling the tractor  110  to the portable trailer stabilizer  300  may include engaging the at least one channel  324  of the portable trailer stabilizer  300  with the at least one arm  120  of the tractor  110 . Coupling the tractor  110  to the portable trailer stabilizer  300  may include moving the valve operator element  320  to open the isolation valve  316 . If the portable trailer stabilizer  300  includes at least one channel  324  and the tractor  110  includes at least one extended arm  120  disposed at a front end portion of the tractor  110 , coupling the tractor  110  to the portable trailer stabilizer  300  may include driving the tractor  110  in a forward direction. 
     In some example embodiments, the support surface engagement element (e.g., ground pad  202 ,  1202 ,  302 ) may be raised above the support surface  102 , which may include pressing the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ) against the forward end portion  118  of the trailer  100  and/or compressing the hydraulic cylinders  210 ,  1210 ,  310 . Compressing the hydraulic cylinders  210 ,  1210 ,  310  may direct pressurized hydraulic fluid to the hydraulic accumulator  214 ,  1214 ,  314  via the open isolation valves  216 ,  1216 ,  316 . The pressurized hydraulic fluid may be stored in the accumulator  214 ,  1214 ,  314 . The portable trailer stabilizer  200 ,  1200 ,  300  may be moved away from the trailer  100  using the tractor  108 ,  110 . 
     In some example embodiments, as the portable trailer stabilizer  200 ,  1200 ,  300  moves away from the forward end portion  118  of the trailer  100 , the trailer engagement element (e.g., trailer engagement bar  204 ,  1204 ,  304 ) may move out from beneath the forward end portion  118  of the trailer  100 . When the trailer engagement element is no longer in contact with the trailer  100 , pressurized hydraulic fluid from the hydraulic accumulator  214 ,  1214 ,  314  may flow through the open isolation valves  216 ,  1216 ,  316  to the hydraulic cylinders  210 ,  310 , which may extend the hydraulic cylinders  210 ,  1210 ,  310 . Extending the hydraulic cylinders  210 ,  1210 ,  310  may extend the trailer engagement element relative to the support surface engagement element, such as to the fully extended configuration. 
     Tractors  1110 ,  2110  comprising upwardly facing hooks  1120  and hooks  2120 , and portable trailer stabilizers  1300 ,  2300  comprising corresponding downwardly facing channels  1324  and bars  2324 , respectively, may be operated in generally the same manner as described above with reference to tractors  110  having extended arms  120  and portable trailer stabilizers  300  have corresponding conduits  324 . Repeated description is omitted for brevity. 
     Generally, in some example portable trailer stabilizers comprising hydraulically operated components, the hydraulic fluid may comprise any fluid suitable for use as a medium for hydraulically transferring power. Some such fluids may be substantially incompressible under expected operating conditions. For example, the hydraulic fluid may include one or more of water, propylene glycol, a petroleum-based oil, and/or a synthetic oil. 
     Some example portable trailer stabilizers according to at least some aspects of the present disclosure may include location reporting devices. For example, a portable trailer stabilizer may be provided with a satellite navigation system (e.g., Global Positioning System (GPS)) unit configured to transmit its location via a wireless network, such as a local area network, a cellular network, and/or a satellite communications network. 
     The present disclosure contemplates that some known trailer stabilizers may require an operator, such as a terminal tractor driver, to manually operate various components of a trailer stabilizer. For example, the individual may operate jacks or other mechanisms associated with the trailer stabilizer while outside of the terminal tractor and on the ground adjacent to the trailer stabilizer. Some example embodiments according to at least some aspects of the present disclosure may allow a terminal tractor driver to position or remove a portable trailer stabilizer while remaining on the terminal tractor. Accordingly, in some circumstances, some portable trailer stabilizers according to at least some aspects of the present disclosure may improve safety and/or efficiency of freight terminal operations involving parked semi-trailers. 
     Some example embodiments according to at least some aspects of the present disclosure may include trailer restraint and/or retention features, which may be configured to prevent movement of a parked semi-trailer. For example, restraint and/or retention features may be configured to couple to the king pin of a semi-trailer and/or to couple to a ground cleat (e.g., anchor) secured on the support surface. Some example restraint and/or retention features which may be used in connection with various embodiments according to the present disclosure are disclosed in U.S. Pat. No. 9,656,637 and U.S. Patent Application Publication No. 2021/0048141, each of which is incorporated by reference in its entirety. 
     Example methods of manufacturing apparatus according to at least some aspects of the present disclosure and components thereof may include operations associated with acquiring, producing, and assembling various parts, elements, components, and systems described herein. 
     Unless specifically indicated, it will be understood that the description of any structure, function, and/or methodology with respect to any illustrative embodiment herein may apply to any other illustrative embodiments. More generally, it is within the scope of the present disclosure to utilize any one or more features of any one or more example embodiments described herein in connection with any other one or more features of any other one or more other example embodiments described herein. Accordingly, any combination of any of the features or embodiments described herein is within the scope of this disclosure. 
     Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute example embodiments according to the present disclosure, it is to be understood that the scope of the disclosure contained herein is not limited to the above precise embodiments and that changes may be made without departing from the scope of the disclosure. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects disclosed herein in order to fall within the scope of the disclosure, since inherent and/or unforeseen advantages may exist even though they may not have been explicitly discussed herein.