Abstract:
A floating skimmer is used for automatically removing oil and other floating matter from the surface of liquid surrounding the skimmer, preferably in a basin or sump. Floats around the periphery and above the general body of the skimmer provide flotation while the unit is at rest. Two liquid removal devices are provided, one to remove the most dense liquid (generally oil) accumulated in the skimmer sump. A gasketed, hinged, floating weir rests on the fluid level in the skimmer sump and when liquid is removed from the sump by either the first or second device or a combination of both, the weir falls back, creating a cascade action which attracts the surface of surrounding liquid into the skimmer sump. Instrumentation is included to provide information for automatic operation and status reporting of the skimmer.

Description:
BACKGROUND OF THE INVENTION 
     This application was filed Jul. 22, 1998 as a provisional application Ser. No. 60/093,663. 
    
    
     This invention relates to a method and apparatus for cleaning the surface of liquid in a reliable and automated manner. 
     Many industrial, military and municipal facilities have separation tanks, sumps, lift stations and the like which must have oil or other floating material removed from the surface of the water in these facilities. In general, these tanks and sumps are not hospitable to human observation and consequently, they are not easily cleaned by standard methods. This invention provides a means for accurate reporting of the skimmer related conditions in such tanks and sumps, the control of debris, and the removal of oil accumulations. 
     Skimmers described in the prior art either deliver an oil and water output which must be separated by an expensive process or require the movement of physical means into the liquid layer to adsorb the oil, a process which is difficult to maintain and often provides unreliable performance. This invention attracts and collects floating oil and debris, stores the debris, and pumps the collected oil to surface collection tanks without underlying water. 
     SUMMARY OF THE PRESENT INVENTION 
     It is an important objective of this present invention to combine the attraction characteristics of a weir skimmer and the selectivity of a mechanical skimmer with automatic controls and status signals which provide automatic pure oil recovery in environments where human intervention is not appropriate. One important example of the invention&#39;s use is in a basin or sump that collects water (such as rain or wash water) and oil (such as automotive oils or fuels) from a parking lot or a roadway. 
     In one embodiment of the present invention the skimmer comprises a relatively large sump with flotation tanks, with a lower liquid removal means, an upper liquid removal means, a floating articulated weir for liquid input, a debris screen to keep out larger floating debris and a debris basket to accumulate smaller debris, and related instrumentation and level sensors, with associated logic controls to direct skimmer operations and to report skimmer status. 
     The logic control will recognize a “start cycle” signal such as a manual switch closure, the passage or arrival of a time event, or the recognition of an event such as a water level in a sump rising. Upon receipt of this signal, the logic unit will turn on the lower liquid removal means (water pump) which will start a skim over the floating weir which controls liquid input into the skimmer body and creates a cascade action that attracts floating material into the skimmer. 
     The nature of the floating weir is to create a void space behind the weir which has a tendency to cause the body of the skimmer to rise out of the water. As the skimmer rises, the floats are elevated and displacement is lost; ultimately, an equilibrium is established between the rise of the skimmer and the loss of displacement. This change in elevation in relation to the external water level is measured by instrumentation (float switch or ultrasonic level indicator for instance) and logged into the logic controls, thus allowing an accurate reporting of the skim status of the skimmer. If the external water level fails to reach the prescribed level, the logic unit can take corrective steps. In this preferred embodiment, the logic unit will shut down any pumps which are on and allow the system to remain dormant for a period of time; it will then resume the pumping. This procedure may be repeated several times before the skimmer pumps are shut down and an error condition is reported. The assumption behind this type of action is that any correctable problem is due to debris somehow lodging into the moving parts of the skimmer and cessation and resumption of skimming can often clear these problems. It has been observed that particularly viscous oils can prevent liquid from entering the skimmer, but cessation and resumption can overcome this problem. 
     During the skimming operation, surface liquid is drawn into the skimmer; the external debris screen bars larger debris such as beverage cans from entering the skimmer. A secondary debris basket collects the smaller debris which enters. This secondary debris basket is removable for easy cleaning. Oil accumulates in the upper area of the skimmer sump and is monitored by a specific gravity sensitive switch or other appropriate measurement device to determine when the accumulation of lighter specific gravity liquid (generally oil) is sufficient to activate a pump which has an intake orifice generally in the mid-depth of the accumulation of the light liquid, and which removes the lighter specific gravity liquid. The pump operation is terminated when the specific gravity switch is turned off by the detection of the removal of the lighter specific gravity fluid (or removal to a certain degree). 
     A low liquid level switch (or other appropriate level sensor) monitors the fluid level inside the skimmer sump. Should this switch indicate that the level of liquid in the skimmer sump is too low, the situation is reported to the control module. Upon receipt of this signal, the control unit may take corrective action. In one embodiment of this invention, the control will shut off any of the pumps which are on. The control will keep the skimmer pumps dormant for a period of time and then resume the pumping; if the signal is cleared, operation can continue as normal. If not, the skimmer will be shut down and an error condition will be indicated. The dormant cycle can be repeated several times before the error condition is indicated and the skimmer is shut down. Generally such a low-liquid condition would be caused by insufficient liquid entering the skimmer, over the weir. This could be from a blockage, or possibly from a problem with the weir itself, where it fails to admit outside liquid. 
     Because the present invention allows for the accurate presentation of the status of the skimmer and the liquid inside it, the logic controls can direct the operation of the skimmer to suit the needs of the situation. In one embodiment, the logic controls monitor a fluid level switch which measures the level of the liquid in an oil recovery tank which accepts the oil output of the skimmer. The logic controls can therefore suspend oil recovery and signal a “recovery tank full” condition. The logic controls may also determine if oil recovery has occurred over a period of time (example, eight hours of skimming) and if no such oil recovery has occurred, the skimmer can be shut down until the next “start cycle” event occurs. 
     It is thus an object of the invention to provide automatic operation in separation of two different-density liquids, preferably petroleum derivative and water, with reliable operation, in a situation where human observation and operation are inconvenient or difficult. 
     These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view in side elevation showing a system according to the invention. 
     FIG. 2 is a schematic perspective view, partially broken away, showing a floating skimmer comprising a part of the system. 
     FIG. 3 is a bottom view showing an instrument well of the system. 
     FIG. 4 is a side view, schematic and in section, showing the instrument well. 
     FIG. 5 is a schematic view indicating the construction of a specific gravity switch. 
     FIG. 6 is a schematic plan view of the switch of FIG.  5 . 
     FIG. 7 is a conceptual view in side elevation indicating a principle evaporation of the skimmer. 
     FIG. 8 is a schematic elevation view indicating operation of a floating weir of the system. 
     FIGS. 9A,  9 B and  9 C are schematic elevation views conceptually illustrating dynamics of the floating weir as related to the surface of surrounding liquid and other factors. 
     FIG. 10 is a schematic view in perspective, partially broken away, illustrating a baffle in the skimmer of the system. 
     FIG. 11 is a view similar to FIG. 10, showing a screen used at the entrance to the skimmer. 
     FIG. 12 is a perspective view similar to FIGS. 10 and 11, showing the use of an internal debris basket in the skimmer. 
     FIG. 13 is a simple flow chart indicating automatic operation of the system of the invention. 
     FIG. 14 is a simple flow chart indicating a maintenance cycle for the system, within which the system is checked for proper operation. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     As best illustrated in FIG. 1, a floating skimmer  10  is constructed to skim the surface S of a liquid L, accumulating the skimmed material for removal. In one of several possible arrangements, a water pump  11  takes input via a conduit  12  which may have a screen  13  attached to prohibit debris from entering the conduit and thus interfering with the pump  11 . The output of pump  11  is directed via a conduit  14  to a venturi type pump (as described below) in the body of skimmer  10 . This establishes the skim of the surface S of the liquid L. Electrical signals or the equivalent such as light or air pressure are transferred from skimmer instrumentation (as described below) via a conduit  15  which runs through an oil hose  17  to control circuitry  18 . In consideration of explosive environments associated with volatile vapors from surface S, all signals in the conduit  15  should be intrinsically safe as defined by the National Electric Code. 
     The control circuitry  18  controls the water pump  11  via a conduit  19 , and controls the oil off-load pump  20  via a conduit  21  (references to oil herein are intended to refer to any petroleum derivative). The oil off-load pump  20  takes input from oil hose  17  which pumps collected oil from the skimmer  10  (as described below) and discharges the oil through an oil output hose  22  to a suitable oil collection tank (not shown). All functions of the skimmer are under control of the control circuitry  18  which receives and analyzes conditions in the skimmer as reported by the instrumentation described below, and also directs skimmer operations by including other information received via a multiple conduit  23  which may include a signal that the oil collection tank is full, the status of on or off switches, time or date, or other information which would be suitable for input to the control circuitry. The control circuitry may also report different skimmer statuses via conduit  23  including error conditions, performance statistics, or confirmation of proper functioning. The control circuitry  18  also gets power from the multiple conduit  23 . 
     As best illustrated in FIG. 2 the floating skimmer  10  comprises an outer body  24  which defines the sides, and a bottom  25  thus defining an inner generally centrally-disposed cavity  26 . The outer body has an opening  27  in one peripheral part for admitting liquid into the central cavity  26 . 
     A drain opening  28  is formed in the lower portion of the body  24  for draining liquid from the central cavity  24  under control of a venturi pump  30 . As noted above, liquid under pressure is supplied to the venturi nozzle  32  from a pump (FIG. 1) via hose conduit  14 . 
     A movable weir  40  extends across the opening  27  and controls the quantity and velocity of liquid which can flow through the opening into the central cavity  26 . The weir  40  is attached to the outer body  24  by a hinge mechanism  42  which allows the weir to articulate and swing up and down about the generally horizontally extending axis of the hinge  42 . A petroleum resistant fabric  44  extends from the sides of the weir  40  to the sides of the opening  27  and prevents liquid from spilling over the sides of the weir  40 , and also prevents liquid from draining out of the central cavity  26  into the surrounding liquid L. The fabric  44  must be flexible enough to allow the weir to move without interference. 
     A baffle  46  extends behind, below, and on the two sides of weir  40  so as to reduce the velocity of the liquid as it flows off the weir. This assists in “stilling” the liquid in the central cavity  26  so that the surface material (generally oil) accumulates at the upper part of the baffle  46  rather than being carried to the output  28 . A rigid screen material  48  formed into a basket is placed in the central cavity  26  to capture small debris which may enter the skimmer with the liquid being skimmed. The debris basket  48  is sized so as to leave room for other operating parts of the skimmer. 
     An encasement  50  extends from the top of the central cavity  26  to a point near, but not touching the bottom  25  of the central cavity. Holes in the bottom of encasement  50  allow water to enter the encasement, thus providing a relatively oil free environment for float switches to operate freely in order to reflect the level of liquids in the central cavity  26 . Thus encasement  50  forms an “instrument well” which provides a relatively calm and oil-free area wherein instrumentation may be placed to reflect the fluid levels inside of the central cavity. 
     An oil drain conduit  51  extends from slightly below the liquid level in the central cavity  26 , during the operation of both the water pump ( 30  or equivalent) and the oil withdraw pump (FIG.  1 ), through the floor  25  of the central cavity to communicate with the oil withdraw hose  17 . When activated, the oil pump will remove the accumulation of surface material via the conduit/drain  51 . 
     Material with a defined specific gravity (generally SG 0.95), hinged at one end, forms an interface float  52 . This float will sink in the lighter fluids collected in the central cavity  26  and will float on the water layer (specific gravity 1 for fresh water, 1.05 for salt water). Float  52  will signal the depth of the accumulated light material in the central cavity (generally oil). 
     The floating skimmer  10  is supported in the water by three floats  53 . The floats  53  contemplated by FIG. 2 are hollow stainless steel tanks, filled with air. Other suitable flotation devices such as foam, or lighter than water material such as wood, would be acceptable. Size and positioning of floats is such that the central cavity defining material  24  and  25 , and other components in the skimmer system  40 ,  27 ,  50 ,  51 ,  52 ,  48  and any other necessary components will float on water, at rest, with an appropriate freeboard. The configuration in FIG. 2 contemplates a 3-inch freeboard. 
     Dense material such as steel or lead may be used as ballast  54  in order to compensate for any over-buoyancy of floats  53 . 
     FIGS. 3 and 4 further illustrate the instrument well  50 . The instrument well is comprised of an outer casing  50   a  which is attached to a bottom plate  50   b . Small holes  55  in the bottom plate  50   b  provide a conduit for the liquid inside the instrument well to equalize with the liquid in the central cavity  26  while substantially barring the entry of any stray oil into the chamber because of their small size. In order for stray or random droplets of oil to enter the chamber, they must be positioned virtually at the hole during a time when the liquid level in the sump is rising in relation to the liquid in the instrument well. The instrument well is further comprised of a cap  57  which provides attachment means  58  for the instrumentation in the well and a conduit  59  for wires or fiber optic cables to transfer information from the instrumentation in the well to a control means (FIG.  1 ). 
     For illustration of one type of instrumentation which can be used, FIG. 4 illustrates a double magnetic float switch arrangement where in a stem  61  which has threads to match attachment means  58  contains two hermetically sealed reed switches  62  which change states from open to closed, closed to open, depending on the proximity of magnets  64 , attached to floats  63  which will move up and down within the limits of retaining clips  65  as the liquid level in the instrument well rises and falls. Generally, the instrument stem  61  is closed at the bottom and filled with a “potting compound” which renders it air and liquid tight. The instrument well cap  57  is either loosely attached and held in with a retainer means such as retainer screw  66 , or is otherwise suitably vented in order to allow air to escape or enter as it must displace fluid exiting through holes  55  or be displaced by said fluid. 
     Vertical positioning of the instrument well  50  and thus the instruments inside are relative, based on the surface S of the body of liquid L in FIG.  1 . Preferred placement is that the upper float  63  “closes” the upper reed switch  62  approximately ½ inch below the surface of the water S 1  in the instrument well  50  as the liquid level rises in the well. S 1  is defined as the surface of the liquid in the instrument well  50  at its highest point which will be substantially equal to the height of the surface S of the surrounding liquid L. S 1  will be achieved while the skimmer  10  is “at rest”, that is, no pumps are operational. Drain  28  will allow the liquid inside the central cavity  26  to equalize with the surface S of the surrounding liquid L, and the holes  55  in the bottom of the instrumentation well  50  will allow equalization of the surface inside the central cavity with the surface of the liquid in the instrumentation well S 1 . Equalization of the liquid surfaces is based on the relative weights of the liquid columns and may not be equal in elevation due to differing amounts of oil on any of the columns. This will not interfere with proper functioning. Lower float and reed switch  62  should be located a few inches below the lowest expected liquid level S 2  in the instrument tube defined by the simultaneous pumping action of both the oil and water pumps. 
     FIG. 4 illustrates magnetic reed switches  62  as instrumentation for level detection, but other methods such as, but not limited to, electrical conductivity, optics or sonic detectors are equally suitable. The instrumentation herein illustrated can supply information about the liquid level in the instrumentation well. 
     FIG. 5 illustrates the specific gravity switch  52  in elevation. The back face  72  of a mounting plate  71  provides a base for a hinge arrangement  74  which allow a mass of predetermined specific gravity material  75  to act as a float and swing up and down perpendicular to the axis of hinge  74 . The specific gravity of the float  75  is such that it will sink in oil, but float on water, so that it will float on an oil-water interface. One preferred material is UHMWPE (Ultra High Molecular Weight Poly-Ethylene) which has a specific gravity of 0.97. Mounting plate  71  provides a base for attaching a tube containing reed switches  77  with appropriate wires which exit from the top of the tube to the control function. A magnet  78  embedded in the float  75  is positioned so that it will change the state of the upper reed switch  77  as the float  75  approaches the high end of the swing, and also will change the state of the lower reed switch  97  as the float  75  approaches the low end of the swing. 
     FIG. 6 shows a plan view of the switch  52 . The back plate  71  is mounted on the rear wall of the central cavity  26  (rear being defined as opposite to the weir opening  27 ), which allows a relatively large mass of float material to generate enough negative or positive buoyancy to overcome sticky or thick oils. The structure of the mounting plate  71 , and the back face  72  of the mounting plate, provide the proper orientation for the embedded magnet  78  to influence reed switches  77  as it reaches either the upper or lower reaches the float  75 &#39;s swing. 
     FIGS. 5 and 6 illustrate the magnetic reed switches as instrumentation for level detection, but other methods such as, but not limited to, electrical conductivity, optics or sonic detectors are equally suitable. The instrumentation herein illustrated can supply information about the depth of floating material collected from the surface S (see FIG. 7) of the surrounding liquid L (see FIG.  1 ). 
     FIG. 7 illustrates in a conceptual manner the accumulation of light material  115  (usually oil) from the body of liquid L. As the venturi pump  30  is activated from fluid under pressure from conduit  14 , water  118  is drawn out of the central cavity  26  of the skimmer  10 . This causes liquid and surface liquid to flow into the central cavity over the floating weir  40 . Because of the comparatively large area of the central cavity, the oil and water flowing over weir  40  tend to maintain separation, therefore the lighter surface elements (generally oil) tend to accumulate at the upper portion of the central cavity, while the water migrates down to be discharged through the drain  28 , due to the effect of the venturi pump  30 . This action consolidates the lighter material gathered from the surrounding liquid L at the upper portion of central cavity  26 , and thus appropriate instrumentation as depicted in FIGS. 4,  5  and  6  can signal to the controls to start and stop the oil removal pump at the appropriate times. The oil pump can then remove the accumulation of lighter materials through the oil drain conduit and hose  51 ,  17 . As the oil is withdrawn, water comes up into the sump from the water outlet and venturi opening  28 , since the venturi pump has been shut off for the oil pumping operation. The oil layer is pushed up in the sump and the oil is drawn off, pushed up and over the oil intake  51 . 
     FIG. 8 illustrates the floating weir which transverses the opening  27  of the central cavity  26 . Other parts of the skimmer  10  are eliminated for clarity. Weir plate  40  is attached by a hinge mechanism  42  to the front wall of skimmer outer body  24  (“front” being defined as the wall with the opening  27 ), thus being able to articulate up and down in a generally perpendicular range to the hinge mechanism  42 . The weir plate  40  is also connected to the sides of the opening  27  by the flexible fabric gasket  44 . The weir plate  40  is supported by the weir float  45  which is connected to the debris basket  48  by a hinge mechanism  42   a  similar to the weir hinge  42 . The weir plate  40  and the weir float  45  could be integrated as one part with a single hinge  42 , but having separate hinge mechanisms makes it easier to remove the debris basket  48  as only weir plate  40  need be pushed forward to facilitate removal of the basket. 
     FIGS. 9A,  9 B and  9 C are representational models of the dynamics of the effects of the floating weir, the size of the weir float, and the effect of the pumps on the fluid levels in the central cavity  26  of the skimmer  10  as they relate to the surface S of the surrounding liquid L as depicted in FIG.  1 . 
     As shown in FIG. 9A, when there is no pumping action on the skimmer, the fluid level inside the central cavity  26  reflects the level of the surface liquid S outside the skimmer  10  due to the exterior communication of the drain  28  and presence of holes  55 , and this liquid level in the skimmer is referred to as S 1 . The floating weir  40  and the gasket  44  effectively seal the central cavity  26  from the outside liquid L. 
     As shown in FIG. 9B, when fluid is forced out of the skimmer via the venturi pump acting on drain means  28 , weir  40  falls back on the support of float  45 . The ensuing liquid flow may be described by the following formula: Q=KLH 2/3 , wherein Q is the quantity being removed from the skimmer via drain  28 , K is a constant representing the characteristics of the liquid coming into the skimmer via opening  27 , L is the length of the weir as determined by the width of opening  27 , and H is the pressure head defined as the differential between the surface of the surrounding liquid S, and the tip of weir  40  (tip being defined as the downstream side). The resultant effect of this flow is that the liquid level in the central cavity  26  will drop by the height of H plus residual positive buoyancy in the weir float  45  in relation to the surface of the outer liquid S thus achieving S 2 . A void space  120  will form which will cause the skimmer  10  to rise slightly out of the water; this has the effect of “deepening” the level of S 2  in relation to the skimmer and thus to the instruments used to measure this differential. 
     As shown in FIG. 9C when the pump demand of the oil pump via oil withdrawal hose  17  and via oil drain conduit  51  is added to the water pump demand depicted in FIG. 9B, H will increase and consequently the fluid level in the central cavity  26  will drop at a 2/3 exponential ratio, less the amount of reserve buoyancy of the weir float  45  which will be taken in supporting the additional weight of a greater H thus establishing level S 3  in the central cavity  26 . 
     The levels S 1 , S 2 , and S 3  may easily be established empirically and then the desired instrumentation can report either the achievement of these levels or the failure to achieve these levels. Note that the instrumentation depicted in FIG. 4 would have the upper float  63  indicating the level S 1  and S 2 , but not indicating a change between S 2  and S 3 , while the lower float would indicate a theoretical level S 4  which would be consistent with an out of control situation wherein the pump or pumps were emptying the central cavity  26 , faster than the weir could replace the liquid. This information can be used by the control function to signal an error, or to cause the skimmer to take corrective action. 
     FIG. 10 illustrates the baffle  46 , which assists in changing the super or hyper-critical flow coming off the weir  40  to a subcritical, or relatively still flow. This allows the lighter portions of the surrounding liquid L to remain at the surface of the central cavity  26  to accumulate and subsequently be removed. The baffle  46  does not completely block inflow of surface liquid, since it does not extend to the front of the skimmer, allowing liquid to flow around it and into the sump area. 
     FIG. 11 illustrates the placement of a screen  125  of suitable size and strength so as to prevent the entrance of larger debris (beverage cans, logs and the like) from entering the skimmer opening  27 . A horizontal “window”  126  cut into the screen material will allow for the easy passage of oil into the skimmer while still blocking larger debris matter. 
     FIG. 12 illustrates the placement of the internal debris basket  48  in relation to the central cavity  26 . The debris basket  48  retains smaller debris (cigarette butts, bits of wood, etc.) In the confines of the basket, yet allows passage of oil or other lighter materials to the oil offload conduit  51 . 
     FIG. 13 is a flow chart outlining operation of the skimmer system. With the system turned on, a first decision block  140  indicates that the system looks for a preset time to start a skim cycle, such as every 24 hours. The system could be started according to another parameter, such as a liquid level, if desired. 
     If the time is arrived to start the cycle, it is determined whether the surrounding liquid, in the body of liquid in which the skimmer resides, has at least a predetermined minimum depth. If not, the system is shut off and this query is made again after a predetermined shut-off period. If after several tries there is not sufficient liquid in the body of water, the system is shut off, preferably with an alarm or notice activated. 
     Assuming the surrounding liquid is at sufficient minimum depth, a skim cycle is started. This involves switching on the water pump to start the skim. In a preferred operating procedure the system then checks for a good skim after about one minute. This is done by determining whether the skimmer rises in the surrounding body of water within such a period; if not, the system goes into an error routine. If the skim is confirmed, it is set for a preset period such as four to eight hours. 
     As in the decision block  150 , the system then looks for an oil layer of a predetermined thickness, for example about four inches, on top of the water within the sump. When this occurs, the system turns off the water pump and turns on the oil pump, as indicated at  152 . When the oil layer reaches a preset lesser thickness, the system turns off the oil pump and resumes the skim by turning the water pump back on, as at  154 . When the cycle time is over, as at  156 , the system shuts off the skim as indicated at  158 . 
     After each skim cycle, the system preferably determines whether oil was in fact removed during that skim cycle, as indicated in the decision block  160 . If not, there was not sufficient oil present, and the system returns to the start position. If oil was removed, the system preferably proceeds to the decision block  162 , inquiring whether the oil pump was on long enough during the cycle to indicate an oil spill was being collected. If not, the system returns to start another cycle, as indicated. If an oil spill is indicated, the system activates a warning alarm or notice as indicated at  164 , and again, another cycle is started because oil was in fact removed and it is assumed there might be more oil to remove. 
     FIG. 14 indicates schematically a maintenance routine of the system. In the example routine indicated, the water pump is started as noted at  170 , and the system records the duration of time before the skim switch is turned on, i.e. before a sensor is activated showing that the skimmer body has risen in the surrounding liquid to the point that a skim is indicated as occurring. This is noted in the block  172 . If this time is faster than a system-stored “normal” time, as noted in decision block  174 , then a warning is activated that the pump is operating too fast. If the time is slower than a system-stored normal time, as at  176 , then again a warning is activated. 
     The system also consults stored information and detects whether, over a period of time during which such tests are conducted, the time required to reach skim is consistently becoming longer, as indicated at  178 . If so, a warning is activated, as at  180 , to the effect that the instrument well (FIG. 4) is becoming clogged. 
     When this procedure is completed, the system stops the pumps as indicated at  182 . The liquid is allowed to level out as at  184 , i.e. water flows back into the sump through the venturi, and equilibrium is reached. Then, the system runs both the oil and water pumps simultaneously, as noted at  186 . It is then determined whether the sump becomes evacuated to a certain degree faster with both pumps on, as compared to only the water pump being on, as noted at  188 . If so, this indicates proper operation, since the two pumps operating together should evacuate liquid faster than only one. If not, a warning  190  is activated, indicating that the oil pump is not running. 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to this preferred embodiment will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.