US2995139A

US2995139A - Automatic custody transfer system

Info

Publication number: US2995139A
Authority: US
Inventors: Marvin A Remke; Glen G Hebard
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1959-11-16
Filing date: 1959-11-16
Publication date: 1961-08-08
Anticipated expiration: 1978-08-08

Description

Aug..8, 1961 M. A. REMKE ETAL AUTOMATIC cus'rooy TRANSFER SYSTEM- 2 Sheets-Sheet 2 Filed Nov. 16, 1959 United States Patent 9 AUTOMATIC Q'USTGDY TRANSFER SYSTEM Marvin A. Remke and Glen G. Hebard, Bartlesville,

Okla, assignors to Phillips Petroleum Company, a corporation of Delaware Filed Nov. 16, 1959, Ser. him-853,075 13 Claims. (11.137-2 This invention relates to the automatic metering and transfer of metered liquids. In one aspect it relates to the automatic transfer of measured volumes of crude oil of predetermined quality as regards B.S. and W. (basic sediment and water) content. In another aspect it relates to the automatic custody transfer of crude oils in areas removed from conventional electric power.

The pumping, transporting, treating and storing of crude oil on the lease has been made automatic to various degrees in recent years. However, the measurement and handling required for the sale or custody transfer of crude oil have not changed to any great extent until quite recently. As far as we are aware, automatic custody transfer of crude oils has not been carried out in regions beyond which conventional electrical power is available.

The present invention is intended to provide an automatic custody transfer system operable in regions which do not have available sources of electrical power. The system and its method of operation involves largely pneumatic controls. However, in such instances where electrical energy is required, the apparatus involved can be modified to operate on battery power.

The terms lease automatic custody transfer, lease auto matic transfer, automatic transfer or automatic transfer system as used throughout this specification and claims are used synonymously and interchangeably, and are intended to mean any system, process carried out thereby, or apparatus particularly adapted for use therein and comprise automatic means to inspect a liquid for the presence of a predetermined undesirable amount of at least one selected undesirable constituent, and automatic means to reject the liquid when said constituent content is above said amount, to meter accurately said liquid when said constituent content is below said amount and pass the inspected and metered liquid to a dispensing line, and subcombinations thereof, such as metering means, inspection means, valving means and automatic control means particularly adapted for use therein, and processes carried out thereby. Furthermore, the automatic means to reject contaminated liquid, that is, liquid containing more than the predetermined undesirable amount of the undesirable component, are provided to operate continuously except as interrupted by automatic operation of the system.

The term custody as used in conjunction with lease automatic custody transfer is intended to convey the meaning of the transfer of a liquid, for example, from one owner to another owner. For example, it refers to the transfer of crude oil from the producer to a purchaser.

In this specification we will describe our apparatus and process as applied to the automatic transfer of measured Volumes of crude oil of predetermined quality as regards BS. and W. merely as an example of our process and apparatus. It is realized that measured volumes of other liquids of predetermined quality can be transferred by our apparatus according to the method disclosed herein, such as refined oils, natural gasoline, hydrocarbon products in process, finished hydrocarbon products, and such other hydrocarbon liquids as might be desired to be sub stantially continuously transferred.

An object of this invention is to provide an automatically operable system for custody transfer of a liquid,

particularly of crude oil. Another object is to provide such a system which is operable in regions beyond which conventional electrical power is available. Yet another object of this invention is to provide such a system and method of its operation involving largely use of pneumatic controls. Still another object of this invention is to provide a pneumatically operable system suitable for the inspection of crude oil for BS. and W. content, for measuring volumes of the inspected crude oil and for transferring the measured volumes of oil to a pipe line or other source of disposal. Yet other objects and advantages of this invention will be apparent to those skilled in the art upon reading the following description which, taken with the attached drawing, forms a part of this specification.

'In the drawing, FIGURE 1 illustrates, in diagrammatic form, an arrangement of apparatus parts suitable for the purpose of this invention. FIGURE 2 illustrates, diagrammatically, the principles upon which the control mechanism operates. FIGURE 3 illustrates, diagrammatically, one form of a pilot valve used in the controls of this invention. FIGURE 4 illustrates, diagrammatically, another form of a pilot valve used in the controls of this invention.

In FIGURE 1, reference numeral 71 identifies a metering vessel of predetermined volume. The outer walls of vessel 71 extend upward above this vessel to form the walls of a surge or degassing vessel 72. The bottom of the metering vessel is of an inverted conical shape while the top thereof is of conical shape, with the apex pointing upward. The conical-shaped metal top of the metering vessel also serves as the bottom for the degassing vessel 72. A tank 73, herein termed an overflow tank, is provided with a float control F A pipe '74 provides for passage of gas separated from oil n vessel 72, while a pipe 75 is a liquid oil overflow line. A pipe 79 provides for return of oil from tank 73 to a heater-treater system, not shown, for retreating the crude oil for reduction of its 13.8. and W. content to a predetermined value. A pipe 80 provides for passage of crude oil from the heatertreater to the degassing vessel 72. A conduit 85, provided with a capacitance cell 76 extending into the conduit, leads from the lower portion of degassing vessel 72 to the lower portion of the metering vessel 71, as shown. This conduit, provided with a diaphragm-operated, normally open motor valve V-1, is connected tangentially to the lower conical portion of the meter vessel so that oil entering the vessel therethrough flows tangentially around the inner walls thereof. Solid matter, such as wax, deposited from the oil tends not to settle on the lower conical wall when oil is added tangentially. A conduit 86, provided with a normally closed, pneumatically-operated motor valve V-3, leads from conduit upstream from valve V-1 as regards direction of oil flow to the overflow tank 173. Also, a conduit 87 leads from about the same portion of conduit 85 to pipe 79. Conduit 87 is provided with a manually operable valve V-4. Normally closed, pneumatically-operable motor valves V-Z and V-2a are provided in outlet pipe 89 andin pipe line 78, respectively. A sump tank 77 is provided, as shown, and may {be provided 'with a level control apparatus 84 in conjunction with 'a pipe line pump 82 in pipe 78a. Pipeline '73 communicates through valve 1-26! with the bottom of the meter vessel.

A small diameter pipe 88 extends upward from the apex of the meter tank to a level above the level of the outlet to pipe 75. A float FL'C is positioned in the degassing vessel at about the elevation indicated in FIG- 1, he, somewhere along pipe 88 but well below the outlet to pipe 75. Another fioat 'FLCZ is positioned at the bottom of the meter vessel.

Briefiy, the operation of this apparatus is as follows.

At the time of starting, valve V-2 and V-2a are closed, valve V-l is open, and oil enters the degassing vessel through pipe 80. With valve V-1 open, oil flows through conduit 85 and in contact with the capacitance cell 76 of the monitor 83 into the meter vessel 71. This oil flow continues until the meter vessel is full, that is, until the oil rises into pipe 88. The levels of the oil inside and outside pipe 88 are then the same. When the oil level outside pipe 88 reaches the float of FLC the valve V-l closes and valve V-2 or valve V-2a opens to allow the metered volume of oil to run to pipe line. When the meter tank goes empty the float of FLC goes down and valve V-2 or V-2a closes and valve V-1 opens and oil flows again through conduit 85 into the metering vessel 71. When the monitor assembly senses bad oil in conduit 85, regardless of the status of the apparatus, the monitor 83 operates to close valve V-l and to open valve V-3, thereby running oil from the degassing vessel to the overflow tank 73 until the monitor senses good oil, at which time valve V-3 closes and valve V-1 opens. If bad oil is sensed at a time at which valve V-l is closed, this valve stays closed and valve V-3 opens.

By the use of such a small diameter pipe as pipe 88, which can be from one-half inch to one inch in inside diameter, any error in oil level in pipe 88, as detected by float FLC (i.e., oil level in tank 72) is negligible, particularly when it is realized that meter tank 71 is of from to 25 barrels (of 42 gallons) capacity.

When the oil levels in the degassing tank and in pipe 88 reach a predetermined common level as sensed by the float of FLC valve V-1 closes and valve V-2 opens to drain the meter tank. Oil continues to flow into the degassing tank from the heater-treater through pipe 80. In case the level of oil in the degassing vessel reaches the level of pipe 75, oil merely overflows into the overflow tank. The float F in the overflow tank 73 is merely for the purpose of shutting in the wells which produce the oil being metered until suflicient oil in this tank is transferred to the heater-treater that the float F drops. At this time oil continues to go to the heater treater and the wells are opened up for production.

When starting the operation with meter vessel 71 and degassing surge vessel 72 empty, floats of FLC and FLC are down and with valve V-l open and valve V-2 (V-Za) closed. Valves V-3 and V4 also are closed. Under these conditions the controls illustrated in FIGURE 2 are as follows: Float FLC being down, the valve of the pilot valve 17 is up, since the float is hinged to the housing of the pilot as illustrated, and pressure is vented from a diaphragm motor of pilot valve 19 through tube 16 to vent 18 by way of conduit a in the pilot valve 17. The valve of pilot valve 19, being spring loaded by compression spring 21, is down thereby making connection from tube 35 through conduit 7 of pilot 19 to vent through 59. Tube 35 thus vents air pressure from the diaphragm of diaphragm motor 32 by way of

tubes

37 and 36. While pressure from diaphragm motor 32 of pilot 29 is vented and there is pressure in diaphragm motor 28 from tube 23, conduit d in pilot valve 19, and tubes and 26, the valve of pilot 29 is also down and no operation of importance occurs in pilot 29. Air pressure from tube 25 also enters diaphragm motor via tube 27 and forces the valve of pilot valve 31 downward thereby providing communication from tube 42 to tube by way of conduit l of the pilot valve 31. Valve 46 is open by air pressure through tube 56 as long as operating air pressure is available to the system, thus the diaphragm of motor 48 of valve V-1 is up and the valve is open, air pressure having been vented through tube 47, valve 46, tube 44, conduit k in a solenoid operated pilot valve 43 (the valve of pilot 43 being up), tube 42, conduit 1 in pilot valve 31, tube 40, conduit 0 in pilot valve 41 (the valve of this pilot valve being down), tube 36, tube 35, conduit 1 in pilot valve 19 and through vent 59.

The pipe line valve V-2 is closed with pressure being vented from the diaphragm motor 49 of valve V-2 through tube 10, open motor valve 11, tube 12, conduit s in pilot valve 13 since float FLC is down, and through vent 14. Linkage 65 connects motor 49 with pilot valve 41 and linkage 48a connects motor 48 with pilot valve 50.

Upon entry of oil through pipe from a heatertreater system, not shown, into the degassing and surge vessel 72, it flows through a capacitance cell 76 of a monitor 83 and through open valve V-1 into meter vessel 71. This first oil lifts float FLC thereby lowering the valve of pilot 13 to change the venting of air from tube 12, conduit s and vent 14 in pilot 13 to conduit r in pilot 13 and through tube .15, conduit i in pilot 29 to vent through 63. These conditions exist until the meter tank 71 and the degassing tank 72 fill and the float of FLC, rises and the transfer valve V-1 then begins to close. The valve V-1 closes as follows: When the float of FLC rises, the valve of the pilot 17 moves downward thereby closing conduit a therethrough and communicating tube 24 with tube 16 by way of conduit b in the pilot valve 17 thereby pressuring the diaphragm motor 20 and raising the valve of the pilot 19 against the compression of spring 21. This operation allows presure from

diaphragm motors

28 and 30 to vent through

tubes

26 and 27, respectively, and thence through tube 25, and conduit c in pilot 19 to vent 58. This operation also admits air pressure from tube 23 through conduit 2 in pilot 19 to tube 35,

tubes

36 and 37 to diaphragm motor 32 thereof spring 21. This operation allows pressure from diaphragm motor has been vented. When air pressure enters tube 35, it quickly enters the diaphragm motor 48 because tube 35 already is open thereto through tube 36, conduit 0 in pilot 41, tube 40, conduit 1 in pilot 31, tube 42, conduit k in pilot 43 and through tube 44, valve 46 and tube 47. Valve V-1 thus closes and its closing pushes the valve of pilot 50 downward thereby admitting air pressure from tube 60 to the diaphragm motor 49 of valve V-2 by way of conduit g in pilot 50, tube 16, conduit of pilot 29, tube 15, conduit r of pilot 13, tube 12, valve 11 and tube 10. Valve V-2 thus opens.

With the opening of valve V-2, the valve of pilot 41 moves upward thereby changing the fluid passage from tube 36 to tube 42 from that just mentioned to the following: From tube 36 pressure air passes through conduit p of pilot 41 into tube 39. From this tube pres.- sure air passes through tube 38 to pressure diaphragm motor 33 thereby raising the valve in pilot 31 to cause pressure air from tube 39 to pass through conduit m to tube 42, thus maintaining valve V-1 closed.

Valve V1 is a spring-loaded, normally open valve. Valve V-2 is a spring-loaded, normally closed valve.

The above described condition exists while oil is running to pipe line and as long as float FLC is up. When the meter tank becomes empty, float FLC drops thereby raising the valve of pilot 13 and allowing air pressure from the diaphragm motor 49 of valve V-2 to bleed off through tube 10, valve 11, tube 12, conduit s in pilot 13 and vent 14, under which condition valve V-2 closes since it is a normally closed valve. The float FLO, remains up and the valve V-l closed while the meter tank is running to pipe line.

When valve V-2 closes, the valve of pilot 41 moves downward thus allowing tube 39 to communicate through conduit q in pilot 41 with vent 61 thereby relieving air pressure from the diaphragm motor 48 of valve V1 through tube 47, valve 46, tube 44, conduit k in pilot valve 43, tube 42, conduit m in pilot 31 to tube 39 and out through conduit q and vent 61 as mentioned. Wher pressure is thus removed from diaphragm motor 48 valve V-l opens since it is a normally open valve. Tlu valve in pilot 50 then rises thereby opening tube b way of conduit h in pilot 50 to vent 34. When valve V-l opens, oil flows from the degassing tank 72 through thl capacitance cell 76 and valve V-i into the meter vessel Upon lifting of the float FLC the venting of the motor 49 of valve V-2 is changed from vent 14 to tube 15, as hereinbefore set forth.

When valve V-l is fully open, oil ordinarily passes into the meter vessel from the degassing vessel at a faster rate than it enters the degassing vessel through pipe 80 from the heater-treater. In this manner float FLC drops thereby placing the valves of

pilots

17, 19, 50, 2.9 and 40 in the same positions they occupied at the beginning of the operation.

The system operates as above-described as long as the oil is of a marketable BS. and W. content. A capacitance cell 76 is included in the conduit leading from the degassing vessel 72 to the meter vessel to keep a continuous check on the BS. and W. content of the oil in pipe 85. In case the oil ever becomes unmarketable as regards BS. and W. content, apparatus is provided to return the .oil to the heater-treater for retreatment. Since this present lease automatic custody transfer equipment is intended .for use in remote areas, that is, in areas in which electrical power is not available, the monitor 83, which includes a capacitance cell and certain electronic recording-equipment, is adapted to be operated with batteries as a source of current. A transistorized monitor, with .a minimum of changeover to make suitable for battery operation, is described in the Oil and Gas Journal, September 7, 1959, page 215, and can be obtained from United Engineers, Inc., 824 E. Sixth Street, Tulsa, Oklahoma. A similar monitor is also available from The Fisher Governor Company. The electronic and recording equipment of the, monitor is housed in a box 83a with proper conduit communication to the capacitance cell and to -the controller 81. If desired, the contents of box 83a can be positioned within the box of controller 81, or box 83a can be positioned adjacent the controller 81, as desired.

Also, conventional monitors can be operated with a suificient number of batteries in series to give the required voltage.

The two

solenoid valves

43 and 51 are also battery operated and are connected in the monitor system. On reference to FIGURE 1, the monitor is arranged with thesolenoid valves (FIGURE 2) positioned in controller 81 (FIGURE 1) to open or close the operating air supply to valves V-1, V-2 and V-3. Upon sensing bad oil with the monitor while starting up the metering operation, the solenoid 45 connected to valve 43 operates to disconnect tube 44 from tube 42 and to admit air pressure from tube 57 through conduit 1 in valve 43 to tube 44 thereby closing the valve V-l so that the bad oil cannot enter the meter vessel. Furthermore, solenoid valve 51 is provided to regulate air flow to the diaphragm motor of valve V-3 to open this normally closed valve for the bad oil sensed by the monitor to flow to the overflow tank 73 and thence return by way of pipe 79 to the heater-treater for retreatment. Valve 11 is a normally closed valve and during operation in which the oil contains a suitable low BS. and W content, the solenoid circuit is open and-the valve of pilot 51 is down and air pressure from tube 22 flows through conduit 1 .in the valve of pilot 51 and through tube 54 to the motor of valve 11 thereby maintaining this valve open. When bad oil is sensed, the solenoid 53 circuit is closed thereby raising the valve in pilot '51 to admit air pressure from tube 22 through conduit 'w in pilot 51 and tube 55 to the underside of the motor of valve V-3 thereby opening this valveior gravity drainage of oil firom the degassing vessel to the overflow tank. This valve V-3 remains open as long as the monitor indicates bad oil. Upon passage of good oil through the monitor cell, the solenoid 53 circuit opens and the valve of pilot 51 drops to bleed pressure air from the motor of valve V-3 through tube 55, conduit 11 and out vent 64. At the same time air flow from tube 22 is re-established to motor valve 11 to open same for passage-of meter tank .oil to pipe line in normal opera- 6 tion. A time delay feature-could, if desired, be installed to cooperate with the monitor assembly so that bad oil would .need to flow through the capacitor for 15 to 30 seconds before the monitor controls would operate to close valve V-l and open valve V-3.

If bad oil is indicated at the time the valve V-l is closing (full meter vessel), the metered oil will run to pipe line through valve V-Z but valve V-l will close and remain closed and valve V-3 will open in the manner just described until the oil is cleaned up.

In case had oil is indicated by the monitor system while valve V-l is closed, the solenoid valve 43 will admit air pressure to the diaphragm motor 48 and valve V-l cannot open, but valve V-3 will open. These valves will remain in these latter positions until the oil is cleaned up. At the time the meter vessel has just emptied and valve V-2 is closing, bad oil in the monitor will not permit valve V-1 to open or, if opened, will close the valve. Also pivot valve 51 will hold valve V-Z flosed so that bad oil cannot possibly enter the pipe Referring to FIGURE 1, a branch pipe is provided by-passlng valve V-2 to pipe line 78. Also, a sump tank 77 is illustrated as positioned between valve V-2 and pump 82' or pipe line 78. When pump 82 is used on the pipe line, the tank provides some storage capacity for oil so that in case a pump is used, oil will be available to the pump so that it will not go on air. Also, by providing tank 77 of suitably large capacity, continuous oil pumping by pump 82 to pipe line 78a can be obtained. In case it is desired to pass oil directly from the meter vessel to pipe line by gravity flow, valve V-Za is provided, as illustrated. This valve is exactly like valve V-Z, and it can be operated in the system as herein explained by merely disconnecting the operational conduit from valve V-2 and connecting it with valve V-Za so that controller 81 'fimctions to operate this valve. The sump tank 77 can also be used when a pipe line pump is not employed. In this case, the meter tank rapidly dumps into the sump tank, which is much less rapidly discharging to pipe line. In this manner, by the time the meter tank is empty, the sump tank is full, the meter tank quickly fills and starts discharglng into the sump tank before the sump tank is empty of its previously metered oil. In this manner, gravity flow to 'pipe line is continuous as long as good oil is available from the heater-treater.

The controller assembly 81, in FIGURE 1, contains most of the apparatus illustrated in FIGURE 2. Parts not included in 81 are such elements as valves V-l, V 2, V-Za and V-B, and of course the floats of FLC and FLC Controller box 83a may contain such equipment as the batteries for operation of the monitor and solenoids 45 and 53.

While it is possible to provide automatic starting and stopping equipment for a gas engine used to power a pipe line pump, the present lease automatic custody transfer system is intended to be used in areas which do not have electrical power available. In such a case a pipe line pump is not used and the metered oil runs through valve V-2a to the pipe line merely by gravity flow, or by way of the sump tank 77. When the sump tank 77 is used Without a pipe line pump, floats and controller 84 obviously are not employed.

In FIGURE 1 is illustrated the construction of the degassing tank-meter tank combination. As mentioned above, the inside diameter of pipe 8t (one-half inch to one inch) is so small when considered relative to, for example, a 10 to 25 barrel capacity meter tank 71, that an error of even several inches in the level sensed by float FLC for closing valve V-l and opening valve V-2, or V-2'a, is negligible' FIGURES 3 and 4 illustrate forms of pilot valves which can be used for

pilot valves

17, 19, 50, 29, 43, 39, 41, 13 and 51.

In FIGURE 3 is illustrated a spring loaded valve, like pilot valve 19. This valve, as illustrated also in FIGURE 2, is provided with a diaphragm motor 20 and at the other end a compression spring 21.

Tubes

23, 25 and 35 and vents 58 and 59 are illustrated as used with pilot valve 19 of FIGURE 1. Pilot valve 41 is not provided with a spring but a linkage 65 attaches the valve of the pilot to the diaphragm motor. Linkage or rod 65 is, in this case, attached to the top of valve 92 (FIGURE 3) in such a manner that rod 94 is attached to the valve.

The valve body 91 and spring 21 are provided with a cap 93, as shown.

The valve of pilot 51 is attached to the solenoid 53.

Pilot valves

17, 50, 29, 43, 31 and 13 are, in general, similar to the valve illustrated in FIGURE 4. Specifically, FIGURE 4 shows pilot 17 having a slidable valve 95 in case 96 and operatively pivoted to a float 96a. It is shown having inlets and outlets 24, 1'6 and 18.

While this system is described as being pneumatically operated and thus adapted for operation in isolated areas, It can be provided with electrical controls for use in areas in which electric power is available. In this respect the utility of the system is thus extended.

While this system is herein described as having the meter vesssel 71 directly under the receiving vessel 72, this particular arrangement of vessels is not critical because, if desired, the meter vessel can be positioned at one side of the receiving vessel or even at some distance therefrom. However, the meter vessel must be placed at an elevation below the receiving vessel in such a manner that liquid can flow by gravity from the receiving vessel into the meter vessel.

In the operation of the degassing tank-meter tank combination of this invention, it is intended that the outlet pipe from the meter tank to the pipe line or to other disposal be quite large in diameter. The conduit 85 leading from the degassing tank to the meter vessel also should be quite large in diameter. The oil inlet pipe 80 should be small in diameter in comparison to conduit 85 and the outlet from the meter vessel so that the meter vessel can be filled and emptied before the oil level in the degassing vessel reaches the level of the overflow pipe 75, in which case oil will overflow to the tank 78. Such overflow oil then is unnecessarily handled.

Pipe line companies frequently refuse to purchase crude oils having BS. and W. contents greater than /a%. In such case the monitor is set to actuate apparatus to close valve V-1 and to open valve V-3 when oil having a higher B.S.'and W. than /2%. However, such monitors can be adjusted to actuate the control mechanisms at other BS. and W. contents, when necessary.

While certain embodiments of the invention have been described for illustrative purposes, the invention obviously is not limited thereto.

That which is claimed is:

l. A method for transferring a known volume of a liquid having less than a predetermined concentration of an impurity to a point of delivery comprising continuously passing liquid containing said impurity into a receiving zone, flowing liquid from said receiving zone by gravity flow into an impurity sensing zone and therein sensing the concentration of said impurity, flowing by gravity flow only liquid having leSs than said predetermined concentration of said impurity from said impurity sensing zone into a metering zone of known volume until the level of liquid in said metering zone and the level of liquid in said receiving zone reach a predetermined common level, terminating the gravity flow of liquid into said metering zone and passing the liquid from the metering zone to said point of delivery.

2. A method for transferring a known volume of a liquid having less than a predetermined concentration of an impurity to a point of delivery comprising continuously passing liquid containing said impurity into a receiving zone, flowing liquid from said receiving zone by gravity flow into an impurity sensing zone and therein sensing the concentration of said impurity, flowing by gravity flow only liquid having less than said predetermined concentration of said impurity from said irripurity sensing zone into a metering zone of known volume until the level of liquid in said metering zone and the level of liquid in said receiving zone reach a predetermined common level, terminating the gravity flow of liquid into said metering zone and passing the liquid from the metering zone to said point of delivery, the minimum possible rate of liquid flow from said receiving zone being greater than the rate of passing of said liquid into said receiving zone.

3. A method for transferring a known volume of a liquid having less than a predetermined concentration of an impurity to a point of delivery comprising continuously passing liquid containing said impurity into a receiving zone, flowing liquid from said receiving zone by gravity flow into an impurity sensing zone and therein sensing the concentration of said impurity, flowing by gravity flow liquid having said predetermined concentration and more than said predetermined concentration of said impurity from said impurity sensing zone into an intermediate zone, flowing by gravity flow only liquid having less than said predetermined concentration of said impurity from said impurity sensing zone into a metering zone of known volume until the level of liquid in said metering zone and the level of liquid in said receiving zone reach a predetermined common level, terminating the gravity flow of liquid into said metering zone and passing the liquid from the metering zone to said point of delivery.

4. A method for transferring a known volume of a liquid having less than a predetermined concentration of an impurity to a point of delivery comprising continuously passing liquid containing said impurity into a receiving zone, flowing liquid from said receiving zone by gravity flow into an impurity sensing zone and therein sensing the concentration of said impurity, flowing by gravity flow liquid having said predetermined concentration and more than said predetermined concentration of said impurity from said impurity sensing zone into an intermediate zone, flowing by gravity flow only liquid having less than said predetermined concentration oi: said impurity from said impurity sensing zone into a metering zone of known volume until the level of liquid in said metering zone and the level of liquid in said receiving zone reach a predetermined common level, terminating the gravity flow of liquid into said metering zone and passing the liquid from the metering zone to said point of delivery, the minimum possible rate of liquid flow from said receiving zone being greater than the rate of passing of said liquid into said receiving zone.

5. A method for transferring a known volume of a liquid having less than a predetermined concentration oi an impurity to a point of delivery comprising continuously and slowly passing liquid containing said impurity into a receiving zone, flowing liquid from said receiving zone by gravity flow into an impurity sensing zone and therein sensing the concentration of said impurity, rapid ly flowing by gravity flow only liquid having less that said predetermined concentration of said impurity frorr said impurity sensing zone into a metering zone 01 known volume until the level of liquid in said metering zone and the level of liquid in said receiving zone reacl a predetermined common level, terminating the gravit: flow of liquid into said metering zone and rapidly pass ing the liquid from the metering zone to said point 0 delivery.

6. A method for transferring a known volume of liquid having less than a predetermined concentration 0 an impurity to a point of delivery comprising continuously and slowly passing liquid containing said impurity into a receiving zone, flowing liquid from said receiving zone by gravity flow into an impurity sensing zone and therein sensing the concentration of said impurity, rapidly flowing by gravity flow liquid having said predetermined concentration and more than said predetermined concentration of said impurity from said impurity sensing zone into an intermediate zone, flowing by gravity flow only liquid having less than said predetermined concentration of said impurity from said impurity sensing zone into a metering zone of known volume until the level of liquid in said metering zone and the level of liquid in said receiving zone reach a predetermined common level, terminating the gravity flow of liquid into said metering zone and rapidly passing the liquid from the metering zone to said point of delivery.

7. A metering system for liquids comprising a first vessel having a first liquid outlet near its bottom, a second outlet near its top and a liquid inlet intermediate these outlets, a second vessel having a bottom outlet line provided with a first valve, a conduit extending from said first liquid outlet to said second vessel, a second valve in said conduit, said second vessel being disposed at such an elevation below the elevation of said first vessel that liquid flows by gravity through said conduit filling said second vessel, an opening in the top of said second vessel, a tubular member extending from said opening to said first vessel at a level above the level of said second outlet, means for sensing liquid level in said first vessel at a level intermediate the levels of said inlet and said second outlet and closing said second valve.

8. The system of claim 7 incuding second means for sensing liquid level in said bottom outlet line intermediate said first valve and the bottom of said second vessel and adjacent said second vessel and closing said first valve.

9. In the system of claim 8, said second means also opening said first valve.

10. In the system of claim 9, a third vessel having its top at an elevation below the elevation of said second liquid outlet, a second conduit communicating said second liquid outlet with said third vessel, a third conduit communicating said first conduit intermediate the valve therein and said first outlet with said third vessel, a third valve in said third conduit, and means for sensing an 10 impurity in a liquid in said first conduit intermediate said first liquid outlet and the point of communication of said third conduit with said first conduit and for closing said second valve, for opening said third valve, for closing said third valve and opening said second valve.

11. A metering system for liquids comprising an upright tank having a frusto-conical partition therein dividing said tanks into an upper first vessel and a lower second vessel, said frusto-conical partition having its smaller diameter end above its larger diameter end, a first liquid outlet in the upper vessel near said partition, a second outlet in said upper vessel near its top, a liquid inlet in said upper vessel intermediate the outlets, a tubular member sealed fluid-tight to the periphery of the smaller diameter end of said partition and extending upward to an elevation above said second outlet, a liquid outlet provided with a first valve in the bottom of said lower vessel, a liquid inlet in said lower vessel, a first conduit leading from said first liquid outlet to the liquid inlet of said lower vessel, a second valve in said conduit, means for sensing liquid level in said upper vessel at an elevation intermediate the elevations of said liquid inlet and said second outlet and for closing said second valve.

12. In the system of claim 11, a means for sensing liquid level in the liquid outlet of said lower vessel and intermediate said first valve and said lower vessel and for closing said first valve and opening said second valve.

13. In the system of claim 12, 'a third vessel having its top at an elevation below the elevation of said second liquid outlet, a second conduit communicating said second liquid outlet with said third vessel, a third conduit communicating said first conduit intermediate the valve therein and said first outlet with said third vessel, a third valve in said third conduit, and means for sensing an impurity in a liquid in said first conduit intermediate said first liquid outlet and the point of communication of said third conduit with said first conduit and for closing said second valve, for opening said third valve, for closing said third valve and opening said second valve.

Raymond May 16, 1939 Meyers Dec. 11, 1956