turning now to a preferred embodiment of applicant &# 39 ; s invention , fig4 depicts an overhead view of tank cleaning system showing an oil storage tank 1 , the tank cleaning robot 2 , solvent supply means 4 , hydraulic power means 5 , hydraulic control means 106 , waste removal means 107 , waste fractioning means 108 , and sludge return means 109 . solvent supply means 4 will generally comprise one or more mobile solvent holding tanks 101 , which hold large quantities , typically 500 barrels , of the solvent to be used for spraying the tank interior , as well as an intermediate tank 102 containing a supply pump 103 which pumps solvent through supply hose 7 to robot 2 . supply pump 103 is capable of generating a spraying pressure of about 300 pounds per square inch ( psi ) and a flowrate of about 300 gallons per minute ( gpm ). the solvent pressure is monitored by two in - line pressure gauges 96 , one of which is attached to supply hose 7 just outside storage tank i near operator 3 , and another of which is attached to supply hose 7 immediately after its connection to supply pump 103 . holding tanks 101 are fluidically connected to each other and to intermediate tank 102 by way of a main supply line 104 , and solvent is transferred from holding tanks 101 using gate valves 105 positioned thereon . transfer pump 67 is located along main supply line 104 to facilitate the transfer of solvent from holding tanks 101 to intermediate tank 102 . hydraulic power means 5 and intermediate tank 102 are preferably included as part of a mobile platform 6 which can be placed in a convenient location with respect to storage tank 1 . hydraulic power means 5 is comprised primarily of a hydraulic reservoir and pump ( not shown ) assembled in a manner familiar to those skilled in the art , and has at least five ( 5 ) external sets of supply / return fittings 29 for use with the various components to to operated , as will be explained below . hydraulic supply lines 10 - 13 and return lines 14 - 17 , shown in more detail in fig5 are connected on one end to hydraulic power means 5 and on the other end to hydraulic control means 106 which is comprised of hydraulic control valves 81 - 84 . both supply lines 10 - 13 and return lines 14 - 17 continue from hydraulic control means 106 to their appropriate connections on robot 2 , and will be explained in more detail below . in fig1 robot 2 is shown in detail and includes a frame 20 , robot articulation means 8 , trailing wheel 22 , and washing means 23 . hose support train 24 is also included and is shown in fig3 . robot articulation means 8 preferably comprises front tires 21 , each actuated by hydraulic tire motors 28 fixedly connected to tire axle 9 . frame 20 consists of essentially two parts , namely the cross support tube 25 between front tires 21 , and supply tube 26 to which trailing tire 22 is attached . cross support tube 25 is preferably constructed of aluminum or other light - weight metal and forms an angle , preferably 15 ° at its midpoint such that front tires 21 are positioned slightly forward of the center of gravity of washing means 23 for stability . attached in a vertical plane to each end of cross support tube 25 are axle plates 27 which serve as a support for tire axle 9 and hydraulic tire motor 28 for each front tire 21 . hydraulic tire motor 28 is attached to the inner side of each axle plate 27 and each is operated independently by hydraulic control means 106 . supply tube 26 is an elongated hollow tube which acts in part as support for washing means 23 as well as to supply solvent to washing means 23 . supply tube 26 is also pivotable with cross support tube 25 and includes trailing wheel 22 . on its rear end , supply tube 26 is open to accept supply hose 7 for attachment by threaded collar 30 . trailing wheel 22 may simply be a pivotable caster - type wheel 31 attached to a caster bracket 32 welded to supply tube 26 . hose support cart bracket 33 also is attached to supply tube 26 and extends toward the rear of robot 2 to pivotally join with a first of several serially connected hose support carts 34 , as shown in fig3 . referring additionally to a more detailed depiction of washing means 23 and frame 20 in fig2 the front end of supply tube 26 contains a pivot bracket 35 having two horizontally parallel plates 36 designed to mate with pivot plate 37 attached to the rear of the midpoint of cross support tube 25 . pivot pin 38 is inserted through aligned holes ( not shown ) in both parallel plates 36 and in pivot plate 37 to pivotally connect cross support tube 25 to supply tube 26 . in order to prevent frame 20 from &# 34 ; jack - knifing &# 34 ;, the degree to which supply tube 26 may pivot should be no more than about 20 ° from a center position as shown by pivot angle 119 . therefore , any manner of mechanically limiting the motion of supply tube 26 in this way would be suitable , such as by using a spring - loaded pin 39 attached to pivot bracket 35 into a curved slot 40 formed in pivot plate 37 . front end of supply tube 26 forms a 90 ° bend upward near pivot bracket 35 and is connected with washing means 23 by way of horizontal rotary joint 41 which allows nozzle 42 to be moved in a horizontal plane and which maintains fluidic communication between supply tube 26 and first tube section 43 . washing means 23 is generally comprised of horizontal control means 44 , vertical control means 59 , and a series of tube sections 43 , 52 , 54 - 56 . horizontal control means 44 creates the notion of nozzle 42 in a horizontal plane . hydraulic horizontal motion motor 45 is bolted to motor bracket 46 which is in turn attached to supply tube 26 behind pivot bracket 35 . motor 45 includes a motor shaft ( not shown ) to which driver sprocket 50 is fixedly attached in a horizontal plane . driver sprocket 50 meshes with chain 49 which in turn meshes with horizontal motion sprocket 51 which is fixed to vertical first tube section 43 , thus allowing for reciprocating motion of nozzle 42 in a horizontal plane . to protect the mechanical components of horizontal control means 44 , chain guard 118 is attached to motor bracket 46 . first tube section 43 forms a first 90 ° bend 91 toward the side of frame 20 to connect to second tube section 52 where vertical rotary joint 53 is attached which allows nozzle 42 to be moved in a vertical plane and which maintains fluidic communication between second tube section 52 and the flow path through the remaining tube sections 54 - 56 . third tube section 54 is formed after a second 90 ° bend 92 in second tube section 52 toward the front of frame 20 and continues until it forms a third 90 ° bend 93 toward the middle of frame 20 to form fourth tube section 55 . fourth tube section 55 forms a fourth 90 ° bend 94 toward the front of frame 20 in order to form fifth tube section 56 which directs solvent flow away from robot 2 . nozzle 42 is attached by way of threaded coupling 57 to the end of fifth tube section 56 , and contains a tapered exit portion 58 for increasing the liquid pressure leaving nozzle 42 . vertical control means 59 comprises a double - acting hydraulic cylinder and ram 60 connected on one end to a rear bracket 61 welded to the front side of first tube section 43 and on the other end to a front bracket 62 welded to the underside of fifth tube section 56 . movement of ram 60 , therefore , effectuates motion of nozzle 42 in a vertical plane . because of the lifting strength associated with hydraulic ram 60 , a hoisting capability of the present invention is readily obtainable . therefore , grappling - type hook 63 is also suspended from fifth tube section 56 near nozzle 42 in order to pick up and deposit a waste removal pump 64 to desired locations within tank 1 , as explained below . waste removal pump 64 , as shown in fig6 is a separate hydraulic centrifugal pump powered by hydraulic supply and return lines 18 , 19 connected to hydraulic power means 5 on mobile platform 6 . pump 64 is generally of a low - speed type capable of handling non - newtonian waste material such as the dissolved oil sludge mixed with the used cutter stock solvent , and is connected to a 3 - inch diameter discharge hose 65 for delivering the waste material out of tank i for later separation of the oil sludge from the expended solvent in the waste fractioning means 108 as described below . handle 66 is attached to pump 64 for either manually handling pump 64 or grasping it by way of hook 63 suspended from fifth tube section 56 . to facilitate the movement of waste material to waste removal pump 64 during the cleaning process , clearing blade 68 is attached to cross support tube 25 by either welding or bolting along the front of robot 2 . clearing blade 68 may simply be a rigid metal plate 69 which includes an attached rubberized strip 90 along the bottom edge of plate 69 , or any other similar attachment capable of moving the accumulated waste material and expended cutter stock solvent away from the sprayed areas . as shown in fig3 each hose support cart 34 generally includes a main support member 70 , a pair of wheels 71 , and a hose guide 72 . wheels 71 are preferably 360 ° pivoting caster - type wheels and are attached to a cross bar 73 transversely attached to main support member 70 . hose guide 72 may simply be a pair of vertical members 74 tall enough to retain the assembly of hydraulic supply and return lines 10 - 17 and the solvent supply hose 7 extending from the robot 2 during operation . flat mating portion 75 having a hole 76 is formed on the rear end of cart 34 for attachment with other trailing carts 34 . on the front end of each cart 34 , a pair of parallel plates 77 having aligned holes 78 is used to engage mating portion 75 of a preceding cart 34 or the hose cart bracket 33 on supply tube 26 by insertion of a connection pin 79 through holes 78 . waste fractioning means 108 comprises one or more fractioning tanks 110 similar to holding tanks 101 of solvent supply means 4 . in a preferred embodiment , each of two fractioning tanks 110 is connected to the ends of a t - section pipe ill which in turn is connected to receive waste material from discharge hose 65 . waste material gate valves 112 are located just above each fractioning tank 110 for regulating the flow of waste material thereinto . solvent recovery gate valves 113 are also located on each fractioning tank 110 at a height which allows recovery of expended solvent 48 without removing any of the heavier sludge 47 accumulated at the bottom of the fractioning tanks 110 . recovered solvent 48 can thus be delivered back into main supply line 104 it through recovery lines 114 connected thereto . sludge exit valves 115 are located at the very bottom of each fractioning tank 110 and are connected to sludge return line 116 which delivers accumulated oil sludge 47 back to a pipeline 85 leading to the refinery . movement of the sludge 47 through the sludge return line 116 is facilitated by operation of a sludge pump 117 operated by electrical power provided on - site by the refinery . in operation , and as shown in fig4 the mobile platform 6 containing intermediate tank 102 , supply pump 103 , and hydraulic power means 5 is parked close enough to storage tank 1 so that robot 2 may freely traverse the distance between circumferentially adjacent manhole entrances 80 once all line and hose connections are made . spring - loaded pin 39 in supply tube pivot bracket 35 is 11 disengaged to allow supply tube 26 to collapse toward cross support tube 25 , and the entire frame 20 is inserted into the manhole entrance 80 to storage tank 1 . once frame 20 is re - expanded to conform to its working configuration , spring - loaded pin 39 engages curved slot 40 so as to limit the pivoting between supply tube 26 and cross tube 25 to about 20 &# 39 ; to either side . supply hose 7 is connected to the threaded collar 30 of supply tube 26 , and the hydraulic supply lines 10 - 13 and return lines 14 - 17 are connected to the horizontal motion motor , vertical motion cylinder , and left and right tire motors , respectively , as shown in fig5 . the opposite end of supply hose 7 is connected to intermediate tank 102 , and the opposite ends of hydraulic supply and return lines 10 - 17 are connected to hydraulic control valves 81 - 84 . hydraulic control valves 81 - 84 are stationed outside of tank 1 and next to manhole entrance 80 , and consist of two 4 - way float position directional control valves 81 , 82 for operating front tires 21 , a 4 - way directional control valve 83 for horizontal motion control of washing means 23 and a 4 - way directional control valve 84 for vertical motion control of washing means 23 . hydraulic supply and return lines 10 - 13 , 14 - 17 continue from hydraulic control valves 81 - 84 to the hydraulic power means 5 to complete the hydraulic circuit . waste removal pump hydraulic supply line 18 and return line 19 are connected on one end to waste removal pump 64 and on their opposite end to hydraulic power means 5 as shown in fig5 and is operated separately from the robot 2 directly from controls on hydraulic power means 5 . discharge hose 65 is also connected on one end to pump 64 , extends outside of tank 1 , and connects on the other end to waste fractioning means 108 . pump 64 is hung from hook 63 suspended from front bracket 62 , and hydraulic power is sent to the tire hydraulic motors 28 and hydraulic ram 60 on robot 2 so that robot 2 may lift pump 64 and deliver it to the desired location . hydraulic ram 60 is operated to lower pump 64 to tank floor 95 until hook 63 disengages itself from handle 66 on pump 64 . air movers 120 capable of air pressures of about 125 psi and operated from electricity supplied by the refinery are also attached to the other manhole entrances 60 in order to circulate toxic fumes outside of storage tank 1 . solvent supply means 4 is then actuated to deliver the cutter stock to washing means 23 , and cleaning of tank 1 is commenced by controlling the position of nozzle 42 and robot 2 by way of hydraulic control valves 81 - 84 until sludge is gradually dislodged from the surfaces of tank 1 . operator 3 still retains control of the movement of robot 2 by applying power to tire motors 28 . waste removal pump 64 is then energized from the hydraulic power means 5 to begin suctioning out dislodged sludge and expended cutter stock for delivery to the waste fractioning tanks 110 . waste material collected in fractioning tanks 110 is allowed to settle to the extent that the sludge 47 becomes concentrated below the expended solvent 48 . expended solvent 48 inside fractioning tanks 110 is then transfered back into main supply line 104 by opening solvent recovery valves 113 so that solvent 48 may again be used to spray the interior of tank 1 . at some point during the cleaning process , the collected waste material will have such a high concentration of sludge 47 that the viscosity of the liquid being returned to main supply line 104 will result in decreased pressure readings on in - line pressure gauges 96 . when the pressure drops to about 250 psi , an operator 3 can switch to another fractioning tank 110 by opening another gate valve 112 on the empty fractioning tank 110 and closing the gate valve 112 on the fractioning tank 110 filled mostly with sludge 47 . sludge 47 existing at the bottom of fractioning tank 110 is removed through sludge exit valves 115 and delivered to sludge return line 116 where sludge pump 117 assists movement of sludge 47 to the refinery pipeline 85 . meanwhile , the cleaning procedure is continued using the other fractioning tank 110 until tank 1 is satisfactorily cleaned and all of the sludge 47 is returned to the refinery 86 . although the present invention has been described in terms of specific embodiments , it is anticipated that alterations and modifications thereof will no doubt become apparent to those skilled in the art . for example , it should be understood that the mechanical features described herein , such as pump , hoisting means , clearing blade and sweep control mechanism , are entirely suited for use in a water - based system such as seen in the prior art . it is therefore intended that the following claims be interpreted as covering all such alterations and modifications as fall within the true spirit and scope of the invention .