US3031105A - Automatic oil transfer system - Google Patents

Description

- April 24, 1962 w, =1 WALKER AUTOMATIC 01 TRANSFER-SYSTEM Filed Oct. 16. 1958 INVENTOR.

WILLIAM WALKER I ATTORNEY United States Patent Company, Philadelphia, Pa., a corporation of New Jersey Filed Oct. 16, 1958, Ser. No. 767,549 6 Claims. (Cl. 222-67) This invention relates to an automatic oil transfer system, and more particularly to a system operating automatically to transfer oil from one or more producing oil wells (known as a lease) to an oil pipe line system, for transportation to a desired point.

For the gathering of crude oil and for getting the same into an oil pipe line system, it is highly desirable to use an arrangement for automatically transferring the custody of oil from the producer (or lease holder) to the oil pipe line company. An arrangement of this type is termed a Lease Automatic Custody Transfer (LACT) system, and this term will be used herein. Production (generally comprising oil, water, gas, and basic or bottom sediment) from the wells of a lease is ordinarily delivered by flow lines to treaters, where substantially all of the water, gas, and basic sediment is removed from the oil by the application of chemicals and heat. Then, in a LACT system, the clean, treated oil is automatically transferred from the treaters to the pipe line system, this transferring involving a measuring or metering step wherein the volume of oil transferred is measured.

An object of this invention is to provide a novel LACT system.

Another object is to provide a LACT system which is substantially simpler and less expensive than prior systems.

A further object is to provide a novel LACT system which has fail-safe and automatic interlock features.

The objects of this invention are accomplished, briefly, in the following manner. Three tanks are provided, a surge (storage) tank, a run (sales or metering) tank, and a smaller pipe line surge tank. Floats which operate respective float switches are associated with each of the two latter tanks. Clean, treated oil is pumped from the output of the treaters to the storage tank. When the run tank is empty, the run tank float is down and this operates fill valves and a pump to pump oil from the storage tank into the run tank. During this fill interval, the oil is monitored by a basic or bottom sediment and water (B.S. & W.) monitor, and if bad (non-merchantable) oil is detected, a valve is operated to divert the oil away from the run tank and back to the treaters. Assuming good oil is flowing, in time the run tank becomes full. Then, the run tank float is actuated, which closes the valves previously referred to and stops the pump. At the same time, a bottom valve in the run tank is opened to cause the oil to flow from this latter tank into the pipe line surge tank. This oil actuates the pipe line surge tank float, turning on a pipe line pump (which pumps the oil from the pipe line surge tank into the pipe line), and turning off the monitor pump. The pipe line pump runs until the pipe line surge tank float drops back down, when the run tank and pipe line surge tank are empty. When the run tank float finally drops, the run tank bottom valve is closed, and the fill valves are opened and the fill pump is started, thus beginning a new cycle. The volume of the run tank is accurately known, and by electrically counting the number of times that the fill valve and the bottom valve have. opened in sequence, the volume of oil delivered to the pipe line is metered or measured.

A detailed description of the invention follows, taken in conjunction with the accompanying drawing, wherein the single FIGURE is a schematic diagram of a LACT system according to the invention.

Now referring to the drawing, clean, treated oil is transferred (for example, by means of a pump which runs continuously) to a surge (storage) tank 1 by way of a suitable inlet pipe 2 labeled From Treaters." To backtrack somewhat, production from the well or wells of the lease (which production may comprise oil, water, gas, and basic sediment) is delivered by flow lines to suitable treaters (not shown), where substantially all of the water, gas, and basic sediment is removed from the oil by the application of suitable chemicals and heat. The output of the treaters (comprising clean, treated oil) is fed to pipe 2, and thus into tank 1.

An outlet pipe 3 extends from tank 1 to one side of a controllable valve 4, and the other side of this valve is coupled to the intake side of a fill pump 5 driven by a motor 6. A pipe 7 extends from the output side of pump 5 to one connection of a controllable three-way (i.e., having three pipe connections) two-position valve 8, and a pipe or conduit 9 extends from another connection of valve 8 to the upper side of a controllable valve 10 mounted at the top of a run (sales) tank 11. The lower side of valve 10 is in communication with the interior of tank 11, at the upper end thereof.

Communicating with the upper side of valve 10, and located above this valve, is a (run tank) float chamber 12 in which is positioned a (run tank) float 13. Float 13 is arranged to operate a float switch 14 illustrated schematically as comprising a movable conducting arm 15 mechanically coupled to the float and adapted to engage either one of two fixed contacts 16 and 17. In the (normal) position illustrated, the float 13 is down and arm 15 is in engagement with contact 16, which latter may therefore be termed a normally-closed contact.

One terminal of a suitable power supply (denoted in the drawing by P.S.) is connected to arm 15. Contact 16 is connected through the winding 18 of a time delay relay 19 to the other terminal of the power supply, so that when the float 13 is down (causing arm 15 to engage contact 16), a circuit is completed to energize winding 18, causing relay 19 (after a time delay) to assume the position illustrated, closing its pair of contacts 20 and also its pair of contacts 21.

When contacts 20 are closed, a circuit is completed to energize a solenoid '22 from the alternating current mains, and another circuit is completed to energize a solenoid 23 from the alternating current mains. Solenoid 22 is arranged to control valve 10 in such a way that this valve is opened in response to the energization of solenoid 22, but closes when this solenoid is de-energized. In a similar fashion, solenoid 23 controls valve 4 in such a way that valve 4 is opened in response to the energization of solenoid 23, but closes when this latter solenoid is de energized.

When contacts 21 are closed, a circuit is completed to energize the motor starter control 24 from the alternating current mains. This starter 24 in turn causes energization of motor 6, to drive the fill or transfer pump 5.

When the run tank float 13 is down (normal), arm 15 is disengaged from contact 17, which latter may therefore be termed a normally-open contact. However, when the float 13 is actuated to its up position, arm 15 engages contact 17, and a circuit is completed from one terminal of the power supply through the (now closed) contacts '15, 17 and the winding 25 of a time delay relay 26, to the other terminal of the power supply, energizing winding 25. When winding 25 is energized, relay 26 will (after a time delay) close its normally-open pair of contacts 27. When contacts 27 are closed, a circuit is completed to energize a solenoid 28 from the alternating current mains. Solenoid 28 is arranged to control a valve 29 located at the bottom of run tank 11, in such a way that this valve is opened in response to the energization of solenoid 28, but closes when this solenoid is de-energized.

When the run tank float 13 is down as illustrated, arm 15 is on contact 16, energizing relay 19 as illustrated. This opens valves 4 and 10 as described and energizes motor 6, starting the fill or transfer pump 5. The run tank bottom valve 29 is then closed, since relay 26 is deenergized as illustrated and no power is applied to the bottom valve solenoid 28. The fill interval or filling operation then begins, and oil is pumped by pump through outlet pipe 3, (open) valve 4, the pump, pipe 7, valve 8 (assuming the latter is in the normal position illustrated, wherein a fluid connection is completed from pipe 7 to pipe 9), pipe 9, and (open) valve 10, into run tank 11, to fill this tank (the bottom valve 29 then being closed).

A branch pipe 30 leads from pipe 7 (between the output side of pump 5 and valve '8) to the intake side of a monitor pump 31 which is driven by a motor 32. The output side of pump 31 feeds into a basic sediment and water (B.S. & W.) monitor 33, so that when pump 31 is running, a sample of the stream of oil flowing in pipe 7 is supplied to the input side of the monitor 33.

The BS. & W. monitor 33 is a known test device which can measure the percentage of basic sediment and water in a stream of oil flowing therethrough. If the monitor pump 31 is running, a sample of the oil being pumped to the run tank 11 is fed into monitor 33 by way of pipe 30, etc., and is pumped from the output side of this monitor back into the surge tank 1 by way of a pipe or conduit 34. Speaking generally, the monitor 33 is an instrument which measures capacitance, the amount of capacitance being proportional to the dielectric constant of the fluid passing between two electrodes in the capacitance test cell. The monitor 33 has a built-in relay 35 which is actuated to close its contacts 36 when a preselected percentage of Water (or basic sediment) is detected by the monitor. The closing of the relay contacts 36 completes a circuit to energize a solenoid 37 from the alternating current mains. Solenoid 37 is arranged to control the valve 8 in such a way as to move this valve to the other of its two positions (in effect, 90 counterclockwise from the normal position illustrated) when solenoid 37 is energized, and to return the valve 8 to the position illustrated when solenoid 37 is deenergized. In its said other position (90 counterclockwise from that illustrated), valve 8 breaks the connection between pipes 7 and 9, and completes a fluid connection from pipe 7 to the third connection of valve 8, which latter is a pipe 38 leading back to the input side of the treaters. Thus, when valve 8 is in its other position from the one illustrated, the oil, instead of being pumped into run tank 11, is diverted back into the treaters for further treatment.

The operation of the monitor 33 may then be summarized in the following way. Assuming that monitor pump 31 is running during the fill interval being described (how this is brought about will be explained hereinafter), when the monitor 33 detects bad oil being transferred from the surge tank 1 to run tank 11, relay 35 is actuated to energize solenoid 37, operating valve 8 to recycle the oil through the treaters by way of pipe 38, instead of transferring the oil to the run tank. Bad oil is defined as oil containing too high a quantity of basic sediment and water to be acceptable for purchase by the pipe line company. When the monitor detects merchantable or acceptable oil, relay 35 is de-energized, thus de-energizing solenoid 37 and returning the valve 8 to its original, normal position illustrated, wherein the oil is pumped from surge tank 1 into run tank 11. Then, the operation of filling the run tank 11 is resumed.

It will now be explained how the monitor pump 31 is caused to run during the fill interval or filling operation (the filling referring to tank 11). A small pipe line surge tank 39 is located below or downstream of bottom valve 29, and the inlet to tank 39 is from bottom valve 29 by way of a pipe 40. A float 41 is installed in tank 39, this float operating a float switch 42 illustrated schematically as comprising a movable conducting arm 43 mechanically coupled to float 41 and adapted to engage either one of two fixed contacts 44 and 45. In the normal or original position illustrated, tank 39 is empty (and remains empty during the fill interval, valve 29 being closed and the tank 39 having previously been pumped dry), float 41 is down, and arm 43 is in engagement with the contact 44, which latter may therefore be termed a. normally-closed contact.

One terminal of the power supply is connected to arm 43. Contact 44 is connected through the winding 46 of a time delay relay 47 to the other terminal of the power supply, so that when the float 41 is down (causing arm 43 to engage contact 44), a circuit is completed to energize Winding 46, causing relay 47 (after a time delay) to assume the position illustrated, closing its pair of contacts 48. When contacts 48 are closed, a circuit is completed to energize the motor starter control 49 from the alternating current mains. This starter 49 in turn causes energr. tion of motor 32, to drive the monitor pump 31. Thus, it may be seen that the monitor pump 31 is caused to run during the fill interval, and monitoring of the oil is consequently effected, as previously described, during the fill interval.

If a power failure occurs during the fill interval, valves 4 and 10 will close, because of the removal of power from their respective solenoids 23 and 22 due to the deenergization of relay 19 when the power fails; also, the transfer and monitor pumps 5 and 31, respectively, will stop because of the removal of power from the respective motor starter controls 24 and 49 (relays 19 and 47 then both being de-energized). When power is restored, the valves 4 and 10 will open, the pumps 5 and 31 will start, and the filling of tank 11 will be resumed. Thus, the system is fail-safe when a power failure occurs during the fill interval.

The top of the float chamber 12 is higher in elevation than the top of surge tank 1, and from the top of this chamber 12 a pipe 50 communicates with the top of tank 1. The pipe 50 is used to equalize pressure in the run tank 11 and the surge tank 1. Without this pipe, vapor pressure would become trapped in the top of the run tank float chamber 12, and oil could not travel up this chamber far enough to actuate the float 13. Another pipe 51, having a diameter of 2" for example, extends from the top of run tank 11 to the top of surge tank 1. A valve 52 is provided in pipe 51, adjacent to the top of tank 11, this latter valve being controlled by a solenoid 60. Solenoid 60 is connected in parallel with solenoid 28, so solenoid 60 is energized when contacts 27 are closed. Valve 52 is opened in response to the energization of solenoid 60, but closes when this solenoid is de-energized. Like run tank bottom valve 29 previously described, valve 52 is closed during the fill interval. As will be described further hereinafter, the line 51 is a low volume line which serves to equalize the pressure, so that the run tank 11 will drain properly.

As previously explained, when the run tank float 13 is down as illustrated, valves 4 and 10 are opened and transfer pump 5 is turned on. Assuming valve 8 is in the normal position illustrated, oil is pumped from surge tank 1 into run tank 11. When the tank 11 is full, oil will travel up through the riser on the top of the tank, through valve 10, and into float chamber 12. When chamber 12 becomes full, the run tank float 13 is actuated or raised. During the fill operation described, valves 29 and 52 are both closed.

When the float 13 moves to its up position, arm 15 of the float switch 14 moves away from contact 16, thus opening the circuit connected thereto; this arm then moves around to engage the normally-open contact 17. The breaking of the circuit at contact 16 de-energizes relay 19, opening its contacts 20 and 21. The opening of contacts 20 de-energizes solenoids 22 and 23, causing valves and 4 to close. The opening of contacts 21 de-energizes the motor 6, stopping the pump 5. With valves 10 and 4 closed and pump 5 stopped, oil is no longer pumped from surge tank 1 to run tank 11.

The engagement of arm with contact 17 completes an energization circuit from the power supply to winding 25 of time delay relay 26. Then, after a time delay, relay 26 closes its normally-open pair of contacts 27, energizing solenoids 28 and 60, and opening valves 29 and 52. When valve 29 opens, oil from the run tank 11 travels by way of pipe 40 to the pipe line surge tank 39. Valve 52 being open at this time, pipe 51 serves to equalize the pressure, so that the run tank 11 will drain properly. When the small tank 39 fills, float 41 therein rises, causing arm 43 of the float switch 42 to move away from contact 44 and to engage contact 45.

A pipe line pump 53, when running, takes oil from tank 39 by means of a pipe 54, and pumps the same through a check valve 55 to the pipe 56 which is in direct communication with the pipe line system owned by the pipe line company. Pipe line pump 53 is driven by a motor 57. When arm 43 engages contact 45, a circuit is completed to energize the winding 62 of a relay 61 from the power supply. Relay 61 then closes its normally-open contacts 63, to energize the motor starter control 58 from the alternating current mains. Starter 58 in turn causes energization of motor 57, to drive the pipe line pump 53.

Therefore, when valve 29 opens and oil from the run tank 11 runs into tank 39 and causes float 41 to rise, pump 53 is started. This pump continues to run, transferring oil from the run tank 11 to the pipe line 56, as long as float 41 is in the up position. Float 41 will remain up" until all of the oil has been pumped out of the tank 39 (and also until all of the oil has been pumped out of the run tank 11, since the oil drains, by way of valve 29, from the run tank into the pipe line surge tank 39). When the fluid level in the tank 39 is pumped down (i.e., when the run tank 11 and pipe line tank 39 are empty), the float 41 drops, breaking the circuit at contact 45, deenergizing relay 61 and thus also control 58, and turning off the pump 53. The transfer of a measured quantity of oil to the pipe line company, from the lease, is then complete.

When the float 41 in the pipe line surge tank 39 moves up, the arm 43 moves away from contact 44. This de-energizes relay 47, opening contacts 48 and de-energizing motor 32, thereby stopping the monitor pump 31. Thus, the monitor pump 31 does not run while the run tank 11 is on the line, that is, while this tank is connected through valve 29, etc. to the pipe line 56.

When top valve 10 closes (due to the actuation of float 13, as previously described), the float chamber 12 is isolated from the run tank 11. Since valve 4 is also closed at this time, oil is trapped in float chamber 12, and also in the line between valve 4 and valve 10. The monitor pump 3:1 is still running at this time, float 41 not yet having been actuated to the up position. Since the intake pipe 30 to this pump is tied into the line between valves 4 and 10, monitor pump 31 is pulling off asmall quantity of the trapped oil. However, the monitor pump, being of low capacity, does not have time enough, before valve 29 opens, to pump off the trapped oil sutficiently to drop float13. When valve 29 opens, as previously described, oil actuates float 41 and kills pump 31. Therefore, at this time (when pump 31 is killed), oil is trapped between valves 4 and 10 and the monitor pump 31. The oil in the float chamber 12 is still above the level of float 13, and thus this float is locked by the oil in an up position.

A'pipe connection 59 extends from the upper end of tank 39 to the upper end of tank 1. This connection is used to equalize pressure, and to prevent vapor from being trapped in the top of tank 39. There is no transfer of oil through this pipe from the surge tank 1 to the pipe line surge tank 39, or vice versa. When valve 29 opens, oil drops from the run tank 11 into the pipe line surge tank 39, and when the tank 39 fills the oil will travel up the pipe 59; however, because of the elevation of the pipe 59, the oil cannot travel up this pipe far enough to spill back over into the surge tank 1. When the pipe line pump 53 starts, it will eventually pump the oil out of the pipe 59, as well as out of the tank 39.

The run tank 11 has a measured volume. After being filled, and before the run operation begins, the volume is that volume between the three (now closed) valves 10, 29, and 52. Any spill-over will have time to clear the line 50 to the surge tank 1 because of the time delay (due to time delay relay 26) before valve 29 opens.

The number of runs into (and out of) the run tank 11 could be counted by an electrical dump counter which would count each time valves 10 and 29 have opened in sequence. This would require a complete cycle of operation per count, and power failure would not register a false count, since the circuits to valve solenoids 22 and 28 are never closed at the same time (due to their operation from the two sets of contacts in the same float switch 14).

As another way of determining the total volume of oil transferred, a temperature recorder could be used, this running only during the time delay to valve 29; the number of runs would then be evident on the temperature charts. A pressure head recorder could also be used, this measuring the head of fluid in the run tank; the number of runs would then also be evident from the pressure head charts.

When the float 41 in the tank 39 drops back down at the end of the pump-out (of tanks 11 and 39), arm 43 of the float switch 42 leaves contact 45, breaking the circuit to motor 57 and stopping pump 53. Also, arm 43 re-engages the (normally-closed) contact 44, energizing relay 47 and restarting the monitor pump 31. A rather long time delay relay is used at 47, one providing five or ten minutes of delay. During this delay, valve 29 is still open and the run tank 11 has ample time to drain completely. If there is suflicient drainage to actuate the pipe line tank float 41 again, the pipe line pump.53 will restart, and power to the relay 47 will be broken. When the float 41 drops down again, the above stepswill repeat,

thus assuring a complete'run before the'monitor pump 31 is restarted. r

When the monitor pump 3.1 restarts, it operates to pump the oil trapped between valves 4 and 10, using as its suction or inlet lines the conduits 7,; 9, and 30. 7 It will be noted that conduit '9 communicates with the lower end of fioat chamber 12 .The .oil present-in the suction lines described is pumped by pump 31 back through the monitor 33 to the surge tank" 1'. When pump 31 has pumped sufficient oil to lowerlthe fluid level in the float chamber -12 below float 13, this float drops and actuates the valves and pump to start the next cycle.

More'particularly, when the run'tank' float 13 drops, the energization circuit forrelay 26 is brokenat 17, opening relay contacts 27, which in turn r'emovespower from solenoids 28 and 60 and closes valves 29 and 52. The energization circuit for relay 19- 'is made at16, closing contacts 20 and 21 (after a short timedelay); the closing of the contacts of relay 19 opens valves 4 and 10 by energizing their solenoids, and turns on the transfer or fill pump 5. p The filling operation is then resumed, and the cycle repeats.

If a power failure occurs during a run (i.e., during the.

time oil is flowing from run tank 11 out to the pipe line 56), relay 26 will be de-energized,dc-energizing valve solenoids28 and 60 and closing valves 29 and 52. It I will be remembered, in, this connection, that valv'es 4 and 1 0, are alreadys'hut at this time-. 'AlsO, the pipe line pump. I

53 will stop, due to the failure of power to motor 57. When power is restored, relay 26 will be energized, thereby energizing solenoids 28 and 60 and opening valves 29 and 52. Similarly, the pipe line pump 53 will start, and therefore the run will be completed. Thus, the system is also fail-safe when a power failure occurs during a run.

In connection with the design of a LACT system according to this invention, the following items are desired to be pointed out. First, the status of the pipe line system will govern the design. If the pipe line 56 can take large quantities of oil at a rapid rate, surge capacities are increased and run tank size can be decreased. Also, the system can be adapted to twin run tanks for a more continuous operation. Further, if the pipe line has to program the running of the oil, a SOD-barrel run tank would probably be used, in which case valve 10 would be 6" and the chamber 12 above it would be 6", while valves 4, 29 and 8 would be 4". In this case, the pipe line tank float 41 would signal the pipe line programmer, and the programmer would open a valve and start the pump 53.

To prevent tripping the top float 13 before the tank 11 is full, a 6" valve would be used at 10. This valve will allow a flow of approximately two barrels per minute at one lb./sq. in, difference. The size of pump and the height of the top float 13 would be determined to prevent a premature fill-up.

The LACT system of this invention has a number of advantages. In the first place, the cost of the system is well below that of any LACT system now on the market. Next, there is no programming required, and the system can be built from stock electrical and mechanical items; any electrician can install the system. Surplus tanks, pumps, etc. can be used to build the system, thus making the system very cheap; a present battery can be adapted to the automatic system. Moreover, power failure or pneumatic failure shuts all critical valves. In this connection, it is pointed out that the valves 4, 8, 10, 29, and 52 are all electrically-controlled, pneumatically-operated valves. With the return of power, the system continues on its cycle where interrupted. Again, the system assures an empty run tank before the fill cycle repeats. In addition, the system, by operating from two sets of contacts in the same float (see float switches 14 and 42), has a built-in interlock. Unless something gets lodged under a valve, it is impossible to fill into a tank on the line. Individual valve trouble, or float trouble, does not disturb the cycle; it only delays the cycle at that point until repair is made.

With a lease shut-in feature, the surge tank 1 can be practically any size or height desired, and the pumpers only job would be one of inspection. A common type of lease shut-in feature is a valve between all of the oil wells on the lease and the treaters, this valve being controlled by a float in the surge tank 1 in such a way that when the surge tank fills up it actuates the float and shuts the aforementioned valve. This in turn shuts in all of the wells and prevents the surge tank from running over, in the event of power failure.

Without a lease shut-in feature, the surge tank 1 would be sized large enough to hold all production overnight without running the surge tank over, in the event of failure such as power failure. More than one tank could be used for surge (storage), by tying the bottoms together. Without lease shut-in, the pumper would inspect and produce wells to allow for overnight power failure, in much the same manner as formerly. More particularly, the pumper would check for overnight storage on the ground level gauge, and check to see if the power is on, before going off duty in the evening.

The invention claimed is:

1. In a system for automatically transferring a fluid, a first tank adapted to be supplied in a substantially continuous manner with the fluid to be transferred, said tank having an outlet; a second tank having a predetermined volume and having inlet and outlet connections with a valve in each of said connections; a fluid connection between the outlet of said first tank and the upstream side of the second tank inlet valve, said fluid connection including therein a pump; a float in a float chamber located on the upstream side of said inlet valve and communicating with the interior of said second tank by way of said inlet valve, a switch mechanically actuated by said float from a first position to a second position when said second tank is filled and fluid enters into said chamber, means controlled by said switch to open said inlet valve and to energize said pump when said switch is in its first position and to open the second tank outlet valve when said switch is in its second position, and means operating automatically, following each opening of said outlet valve and the emptying of said second tank to a predetermined level, for drawing fluid out of said float chamber, thereby to return said switch from its second position to its first position.

2. A system as set forth in claim 1, wherein the lastmentioned means includes a pump having its inlet coupled to said first-mentioned fluid connection and its outlet coupled to said first tank.

3. In a system for automatically transferring a fluid, a first tank adapted to be supplied in a substantially continuous manner with the fluid to be transferred, said tank having an outlet; a second tank having a predetermined volume and having inlet and outlet connections with a valve in each of said connections; a fluid connection between the outlet of said first tank and the upstream side of the second tank inlet valve, said fluid connection including therein a pump; a float in a float chamber located on the upstream side of said inlet valve and communicating with the interior of said second tank by way of said inlet valve, a switch mechanically actuated by said float from a first position to a second position when said second tank is filled and fluid enters into said chamber, means controlled by said switch to open said inlet valve and to energize said pump when said switch is in its first position and to open the second tank outlet valve when said switch is in its second position, a third tank having an inlet coupled to the downstream side of said outlet valve; and means operating in response to the absence of fluid in said third tank for drawing fluid out of said float chamber, thereby to return said switch from its second position to its first position.

4. A system as set forth in claim 3, wherein the lastmentioned means includes a pump having its inlet coupled to said first-mentioned fluid connection and its outlet coupled to said first tank.

5. In a system for automatically transferring a fluid, a first tank adapted to be supplied in a substantially continuous manner with the fluid to be transferred, said tank having an outlet; a second tank having a predetermined volume and having inlet and outlet connections with a valve in each of said connections; a fluid connection between the outlet of said first tank and the upstream side of the second tank inlet valve, said fluid connection including therein a pump; a float in a float chamber located on the upstream side of said inlet valve and communicating with the interior of said second tank by way of said inlet valve, a switch mechanically actuated by said float from a first position to a second position when said second tank is filled and fluid enters into said chamber, means controlled by said switch to open said inlet valve and to energize said pump when said switch is in its first position and to open the second tank outlet valve when said switch is in its second position, a third tank having an inlet coupled to the downstream side of said outlet valve and also having an outlet; a pump coupled to said last-mentioned outlet, and means operating in response to the presence of fluid in said third tank for energizing said last-mentioned pump, and operating in response to the absence of fluid in said third tank for drawing fluid 9 out of said float chamber, thereby to return said switch from. its second position to its first position.

6. A system as set forth in claim 5, wherein the lastmentioned means includes a pump having its inlet coupled to said first-mentioned fluid connection and its outlet coupled to said first tank.

757,903 Ford Apr. 19, 1904 10 Kingsbury July 20, 1920 Simmons June 24, 1930 Le Fever Sept. 1, 1931 Gschwind June 15, 1943 Kangas May 21, 1957 Hebard July 7, 1959 Hill Apr. 4, 1961 FOREIGN PATENTS Great Britain Nov. 6, 1946

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