CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/812,755, filed Apr. 17, 2013, entitled “Suction Pool Cleaner,” the entire contents of which are incorporated herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to equipment and methods for cleaning water of vessels such as swimming pools and spas and more particularly, although not necessarily exclusively, to automatic cleaners whose bodies need not necessarily turn in use and are less subject to directional influence of attached hoses, thus allowing the cleaners to, among other things, move and collect debris omnidirectionally. 
     BACKGROUND OF THE INVENTION 
     Conventionally, an automatic pool cleaner (“APC”) may be considered either “hydraulic” or “electric” depending on the source of energy employed to effect its movement within a pool, spa, or other water-containing vessel. “Electric” cleaners, sometimes also called “robots,” typically use electricity to power motors used to drive wheels or treads to allow the cleaners to move throughout the vessel. Although on-board batteries are sometimes considered to supply electricity to the robots, more likely electricity from mains outside the vessels is conveyed via electrical cords to the robots within the vessels. 
     “Hydraulic” cleaners, by contrast, connect to external pumps and utilize water flow caused by operation of the pumps to effect their movement within a pool or spa. Some hydraulic cleaners connect to pump outlets; these devices are called “pressure-side” APCs, as pressurized water from pump outlets typically drives the cleaners. Alternatively, hydraulic cleaners may connect to inlets of pumps. These “suction-side” cleaners often include valves and supporting structure designed periodically to interrupt water flow through their bodies to the pumps. Periodic flow interruption creates a “water-hammer” effect, with the resulting energy used to move the APCs within pools. 
     U.S. Pat. No. 4,742,593 to Kallenbach discloses exemplary valves useful in water-interruption, suction-side hydraulic APCs. A flexible-walled, “diaphragm” valve of the Kallenbach &#39;593 patent may be placed within a chamber of a body of an APC, with the chamber filling with water upon immersion of the APC within a pool. As noted therein: 
     Expansion of the valve and release for it to reassume its relaxed condition is by the creation of a pressure differential across the valve member walls, i.e., a pressure difference between the chamber and the interior of the valve member. This is created by the suction [of the external pump]. The valve is autonomously opened and closed. Applied suction initially causes the valve to open; but with water flow established, the pressure within [the] valve drops below that of [the] chamber. The valve thus closes. The cycle autonomously repeats. 
     See Kallenbach &#39;593 at col. 2, 1. 64 to col. 3, 1. 6 (numerals omitted). 
     U.S. Pat. No. 5,014,382 to Kallenbach illustrates an exemplary suction-side APC in which, for example, a valve of the Kallenbach &#39;593 patent may be positioned. As shown in the Kallenbach &#39;382 patent, the APC includes a flexible disc designed periodically to contact the surface to be cleaned as well as a body and an extension pipe both having a water-flow passage therethrough. Well depicted in the sole FIGURE of the Kallenbach &#39;593 patent is that, when the flexible disc contacts a pool floor or other generally horizontal surface, water flows through the water-flow passage at an angle of approximately forty-five degrees thereto. A flexible hose connected to the end of the extension pipe remote from the disc continues to convey the water toward an inlet of a pump. 
     Combined with the acutely-angled flow path, the water-hammer effect provided by the interrupt valve tends to lead the APC in the direction of the horizontal vector component of the flow path. The result is that the APC effectively “follows” the hose, decreasing the randomness of movement of the APC along the pool floor and thus inhibiting cleaner of the entire floor. Similarly, by “following” the hose with its movement, the APC may be led into a corner of a pool or behind an obstacle with no automatic means of escape. 
     SUMMARY OF THE INVENTION 
     The present invention provides APCs with both flexible discs and water flow paths oriented perpendicularly (or approximately so) to pool floors or other surfaces contacted by the discs. As a consequence, the flow path through a body of such an APC is substantially vertical, so that no material horizontal vector of the water flow within the body exists. This change dramatically reduces influence of a connected hose upon movement of the body within a pool or spa, as no longer can the hose lead the APC in any substantial way. 
     Absent leadership by connected hoses, no mechanism exists to move conventional disc-containing, suction-side APCs within pools. The present invention hence also provides movement means for the APCs. Presently preferred is that such movement means comprise collapsible feet formed as part of, or directly or indirectly connected to, the APC bodies. The feet may be oriented at a small angle (e.g. twenty degrees) to the pool floor and collapse slightly about a hinge point at their bases so as to produce horizontal movement of the bodies. Operation of the diaphragm or other water-interrupt valve of an APC causes collapse and straightening of the feet at the valve frequency, with each cycle producing “forward” movement of the cleaner. 
     Moreover, the feet may be arrayed circularly (or substantially so) on an underside of the body of the APC and pivotable about a (vertical) axis generally perpendicular to the disc and pool floor. Some or all of the feet may be linked one to another so that they may be rotated or otherwise moved together and may point in the same direction for movement. This array of rotatable feet further lowers the energy needed to alter direction of the APC, as the entire APC need not be turned around the hose. Instead, any desirable direction of the APC may be achieved merely by changing the direction of the array of feet. 
     Preferred feet are largely rigid, with softer, rubber-like tips present where they contact floor of pools and spas. Each foot may be hinged at its base about an axis intended to be generally parallel to the pool floor when the APC is in use. Stops may be employed to limit the hinging movement. 
     As noted earlier, when extended to its most vertical position relative to the pool floor, contact angle of a foot with the floor relative to the hinge preferably is approximately ten degrees. Conversely, the contact angle when a foot is collapsed is preferably approximately twenty-five degrees. Of course, persons skilled in relevant fields will understand that neither contact angle is critical and thus may differ from the preferred values identified herein. A compression spring or other means may bias each foot toward its extended position. 
     One manner of interconnecting the arrayed feet is by mounting each hinge on a circular flange, mounting each flange on a circular gear, and engaging each circular gear by a master circular gear. Rotation axes of both the circular gears and the master circular gear are designed to be perpendicular to the pool floor when the APC is in use, and each foot may rotate about the rotation axis of its corresponding circular gear. By mechanically or electrically turning either a foot or the master circular gear, all of the arrayed feet are turned. Alternatively, feet of the array may communicate electrically with a controller able to command rotation or collapse (or both) of the feet via electrical signals. 
     Features of the invention thus include (but are not limited to) turning feet, rather than entire bodies, of APCs, collecting debris on a pool floor omnidirectionally, and providing water-flow paths through bodies of disc-based APCs that are essentially vertically oriented. APCs consistent with the present invention need not have any discernible “fronts,” “rears,” or “sides,” although they may have fronts, rears, and sides if desired. Their structures additionally may minimize, if not substantially avoid, movement as influenced by connected hoses. 
     It thus is an optional, non-exclusive object of the present invention to provide disc-based APCs that, when in use, have water flow paths oriented substantially perpendicularly to pool floors. 
     It is another optional, non-exclusive object of the present invention to provide such APCs that are not, or are only minimally, influenced in their movement by connected hoses. 
     It is a further optional, non-exclusive object of the present invention to provide APCs with movement means in the form of collapsible feet. 
     It is also an optional, non-exclusive object of the present invention to provide means for mechanically or electrically linking some or all of the feet so that they rotate simultaneously. 
     It is, moreover, an optional, non-exclusive object of the present invention to provide APCs that need not have any discernible fronts, rears, and sides and that may collect debris from a pool floor omnidirectionally. 
     Other objects, features, and advantages of the present invention will be apparent to persons skilled in the relevant art with reference to the remaining text and the drawings of this application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary APC of the present invention. 
         FIG. 2  is another perspective view of portions of the APC of  FIG. 1 . 
         FIG. 3  is a view of the underside of the APC of  FIG. 1 . 
         FIG. 4  is a partially-exploded, perspective view of exemplary feet and other components of the APC of  FIG. 1 . 
         FIGS. 5A-D  are various perspective, elevational, and cross-sectional views of a foot consistent with the feet of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Illustrated especially in  FIG. 1  is exemplary APC  10  of the present invention. APC  10  may include body  14  having inlet  18  (see  FIG. 3 ) and outlet  22 . Directly or indirectly connected to body  14  in conventional (or other) manner may be disc  26 . Although disc  26  is shown as having features including fins  30  and slits  34  and being generally annular, it may be sized, shaped, and featured in any suitable way. Preferably, though, underside  38  of disc  26  is, in predominant part, planar (or substantially so). 
     Body  14  preferably includes a ring or fitting  42 . Although not shown in the drawings, a hose typically may be attached to fitting  42  so as to convey—to a debris filter or elsewhere—water exiting outlet  22 . Fitting  42  desirably allows the hose to swivel (rotate) relative to body  14 , as is conventional. 
     Clear from  FIGS. 1-3  is that, if underside  38  is contacting a generally horizontal surface such as a pool floor, the water flow path between inlet  18  and outlet  22  will be generally vertical—i.e. generally perpendicular to the pool floor. This may be contrasted with the corresponding flow path of the APC of the Kallenbach &#39;382 patent, for example, which forms an angle of approximately forty-five degrees to the floor. Because of this angle, valve closure contracting a hose associated with the APC of the Kallenbach &#39;382 patent will move the cleaner to the right of the page in the sole FIGURE, whereas valve closure within body  14  causing contraction of an associated hose likely will not. 
     Because not materially subject to motive force and tendencies of a hose, APC  10  requires some other means for moving within a swimming pool or spa.  FIGS. 1-2  thus also depict master gear  46  and gears  50 , which together with feet  54  may form motive mechanism  58  ( FIG. 4 ). As presently preferred, master gear  46  is circular (annular) and engaged by plural gears  50  (also circular) spaced equidistant about the circumference of the master gear  46 . Five gears  50  are illustrated in  FIG. 4 , although more or fewer may be used instead. Likewise, gears  50  need not necessarily be spaced uniformly about master gear  46  if otherwise desired. 
     Each foot  54  may comprise tip  58 , base  62 , hinge  66 , flange  70 , and spring  74 . Tip  58  is configured to contact the to-be-cleaned surface for support and motive purposes. It advantageously may be made of softer material than some or all of the remainder of foot  54 , although use of such softer material is not mandatory. 
     Base  62  and hinge  66  mount to flange  70 , which may be circular (annular) or generally so. Flange  70  in turn fixedly mounts to a gear  50 . Thus, if master gear  46  turns, each gear  50  will turn and each flange  70  will turn, thereby turning foot  54 . Because tip  58  normally is angled (e.g. ten degrees) to the pool floor relative to flange  70 , turning foot  54  causes base  62  to pivot about the hinge  66 , overcoming the bias force of spring  74  and further increasing the angle (to, e.g., twenty-five degrees) tip  58  forms relative to the pool floor as foot  54  collapses. As multiple feet  54  act in the same manner simultaneously, body  14  moves linearly (“walks”) along the pool floor in a direction effectively opposite the collapse. Ceasing turning of master gear  46  stops the force causing the collapse, allowing spring  74  to return feet  54  to their extended (uncollapsed) positions. Repeating this process over time allows APC  10  to move well within a pool or spa. 
     Indeed, because feet  54  may turn throughout three-hundred sixty degrees of rotation, body  14  of APC  10  may move in any direction at any time—effectively “pulling,” rather than being “pulled by,” a connected hose. Consequently, APC  10  need not have any discernible “forward” or “rearward” movement, nor need it necessarily have any discernible “front,” “rear,” or “sides.” This omnidirectional movement capability of APC  10  likewise allows omnidirectional collection of debris from a pool floor, increasing its functionality over conventional APCs. 
     Turning of master gear  46  may occur mechanically as, for example, through connection to another gearing mechanism. Electrical signals alternatively or additionally may be used, together with solenoids or other switches, to cause master gear  46  to turn. Although hydraulic APCs conventionally lack any on-board source of electrical power, such power may be provided by the equipment described in U.S. patent application Ser. No. 14/205,408, now U.S. Pat. No. 9,488,154, of van der Meijden, for example. 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention. For example, although much of the foregoing description relates to a suction-side, disc-containing, hydraulic APC, in some cases aspects of the invention may be utilized in connection with other equipment including, but not limited to, electric APCs, pressure-side hydraulic APCs, and suction-side hydraulic APCs that might not contain discs. Similarly, although gears may be employed to turn feet  54 , crank arms or other devices may be used instead. Moreover, “pool,” “swimming pool,” and their plurals may include within their definitions spas and other water-containing vessels used for recreational or therapeutic bathing or swimming. The entire contents of the Kallenbach &#39;593 and Kallenbach &#39;382 patents and the van der Meijden application are incorporated herein by this reference.
Automatic pool cleaners (APCs) and components thereof are detailed. The APCs may turn feet, rather than entire bodies, to change direction and may provide water-flow paths through the bodies that are oriented vertically. Thus, unlike existing disc-based cleaners, the APCs may reduce influence of connected hoses on their movements within pools.