US3120979A - Pneumatic materials conveying system - Google Patents

Description

Feb. 11, 1964 1.. D. MCDONALD PNEUMATIC MATERIALS CONVEYING SYSTEM 2 Sheets-Sheet 1 Filed Nov. 6, 1961 INVENTOR. law/72044 fl Mia/74b .4 TTORNEYS.

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Feb. 11, 1964 D. MCDONALD PNEUMATIC MATERIALS CONVEYING SYSTEM 2 Sheets-Sheet 2 Filed NOV. 6, 1961 Law/ante Q/WeWa/m/d BY Z Mu?! United States Patent 3,329,979 PNEUMATIC MATERHALS NVEYHNG SYSTEM Lawrence D. McDonald, 455d Main St., Kansas City, Mo. Filed Nov. 6, 19M, Ser. No. l',63 9 Claims. (Q1. 3ll235) This invention relates generally to pneumatic materials conveying systems, and refers more particularly to improvements therein for better and more eilicient operaion of same.

Pneumatic conveying of finely divided materials, for example flour, cement and the like, has become widely accepted. In particular, it is being used quite successfully in flour mills, large bakeries and the like. However, there are many problems, both as to first cost and as to operation, which still remain to be overcome.

In most plants where such systems are used, it is conventional to have a plurality of what may best be termed sub-systems, each of which has its own air pump and control. There is no interrelation between sub sub-systems, other than perhaps they may be connected with a master control panel. in other words, the air from any given pump is confined to the specific sub-system for which it is designed.

Each of the sub-systems may include various bins which can be cut into or out of the sub-system as needed, as well as various outlets for the material. However, in designing the system, the air pump therefor must be selected on the basis of one which will supply sufficient air to effectively power the sub-system at its fully loaded condition. Since most sub-systems are ope-rated at many times at less than full load, that is, with certain component parts cut out, this means that there is often considerable wastage of power. Moreover, with separate sub-systems, each sub-system requires its own pump and if there are a number of sub-systems, the first costs are quite hi r.

One of the principal objectives of the present invention is to provide a pneumatic conveying system which is so constructed and controlled that each sub-system derives its air supply from a single air source, namely, a header or air main which has connected with it in common the necessary number of pumps to meet the maXimum load conditions for the system as a whole. Each sub-system is supplied by a branch line from the common header; however, through special control means the air supplied to each branch line is held to a velocity which is selected as optimum for the conveying conditions to be met, and this is true despite increase or decrease in the resistance to air flow through the sub-system. Stated otherwise, each branch line is so controlled that it will receive air from the header as required by the conveying conditions, and no more.

Since it is seldom, if ever, that all branch lines will be in simultaneous operation, I am thus able to limit the number of air pumps to less than that which would be required for separate sub-systems, thus saving greatly on the cost of the over-all system. Moreover, by providing for control in the individual branch lines of the air flow therethrough in response to demand, the air supplied by the pumping system is efficiently utilized where actually needed. It is a feature of the invention in this respect that the control means operates to prevent air robbing through empty lines at the expense f loaded lines.

A further important object of the invention is to provide a multiple line pneumatic conveying system in which the air is supplied from a central source, yet in which the back pressure on the air pumping equipment is automatically controlled to a minimum value required to meet the air flow requirements of the system as a whole.

Since back pressure determines the load on the pumping equipment, through this arrangement I have been able to eifcct a great saving in operating power.

till another object of the invention is to provide a system of the character described in which multiple pumps are connected with the header, but in which the pumps individually are automatically cut into and out of operation in accordance with the air demand in the system. A feature of the invention in this respect resides in the manner of controlling the pumps and the means for cutting in or taking out pumps under changing conditions.

Yet another object of the invention is to provide a pneumatic conveying system which, because of the use of a common air source for all conveying lines, lends itself to highly flexible operation and makes possible expansion of the system to include additional lines at low cost.

A further object of the invention is to provide unique means for controlling the air velocity through the conveying lines to maintain it substantially constant despite changes in static pressure, which means is capable of instant operation in response to changing flow characteristics in the conveying line.

Other and further objects of the invention together with the features of novelty will appear in the course of the following description.

in the accompanying drawings, which form apart of the instant specification and are to be read in conjunction therewith, and in which like reference numerals indicate like parts in the various views:

FIG. 1 is a schematic diagram showing a system constructed in accordance with a preferred embodiment of the invention; and

FIG. 2 is an enlarged detail illustration, still principally schematic, showing the differential pressure comparator, the air relay and air control valve for one of the branch lines of the preferred embodiment.

The principles of the invention will be described as applied in an illustrative pneumatic flour conveying system involving two positive displacement air pumps 10 and ii. The pumps 1% and ill have their discharge outlets connected with a common header 12 by lines 19a and 11a, respecitvely. in the example being given the header l2 feeds air to the branch lines 14, 14 and 14'. To facilitate the description, and since the components associated with each branch line are in substance identical, detailed amplification will be confined to the lefthand branch line 114- with the understanding that the same reference numerals followed by a prime identify like components on the branch line 14, and that branch '14" has the same components (although not shown).

As shown, the branch line 14 has interposed therein a variable throttling valve 15 which is operated by a pressure responsive actuating mechanism to later to be described. The air passed by the valve 15 is directed to the input side of a conventional air lock rotary material feeder 17. The feeder i7 is located at the bottom of a storage bin or hopper 18. The feeder includes the drive motor 19, which, as is known by those skilled in this. art, drives the rotor of the feeder to deliver material to an air pickup position from whence it is carried into the discharge conveying line 20.

Returning now to the pumps ill and 11 and considering first pump Ill, it will be seen that this is powered by an electric motor 21 which is adapted to be connected with the power lines L L and L through the magnetic starter 22,. Conductors 23, 24 and 25 are connected respectively with the lines and have the normally open contacts 26, 2'7 and 23 interposed therein. The starter solenoid 29 operates the latter in the usual fashion. The starter solenoid is included in a circuit between lines L and L which includes conductor 31, main throw switch 32, and conductors 33, 34 35, 36 and 24. Obviously, upon closing of switch 32 solenoid 29 will be energized, thus closing the starter contacts and completing the circuit to motor 21 to start the pump The second pump 11 has its drive motor 37 which is adapted to be connected to lines L L and L through conductors 38, 39 and iii, and the magnetic starter 41. The starter solenoid 4-2 of this pump is in a circuit between lines L and L which includes conductor 35:, switch 32, conductors 33, 43, no mally open contact 44 of relay i5, conductor 46, the normally open contact 47 having the pressure actuating mechanism :8, conductors 49, and 51 having interposed therein the normally closed contact 52 with a pressure actuating mechanism 53, and conductor 39. It Willbe observed that the closing of switch 32 serves to arm the circuit to the second starter solenoid 42 by energizing the relay 45. The latter is connected in parallel with the first starter solenoid 2% by conductors 54- and 55. However, the circuit to starter solenoid 42 is not completed until the contact 47 is thereafter closed. 'I hus, pump 11 will not be started at the same time as pump 10, the reason for which will subsequently be brought out.

Turning again to the air valve and its associated component, the operation of this valve is preferably controlled by a difierential pressure regulator 56 having an relay 57. The output line 58 from the relay leads to the pressure sensitive valve actuating mechanism 16. The input line to the air relay is indicated at 59, this being a branch from a main air line as having a constant pressure outlet valve 61 and a control valve 62. The line 6i? leads from any suitable source of compressed air (not shown), such as a compressor, and is designed to maintain a supply of air to the operating system at from 15 psi. to p.s.1.

Referring now to FIG. 2 and describing in more detail the nature and manner of operation of air valve 15 and its control components, provided inside conduit 14, preferably downstream of the valve 35, is a iitot tube 63 having the nose port 64 land the static ports 65. The pressure at port 64 is communicated by line 66 to a chamber 67 formed in a housing 68. The static pressure measured at ports 65 is passed by line 69 to another chamber 7 ii in the housing. The chambers 67 and 70 are separated by a diaphragm 71 which carries a post '72 extending outwardly through the wall of the housing, a suitable seal being provided to prevent pressure leakage from chamber 7% while still permitting up and down movement of the post in response to flexing of the diaphnagm under pressure diiierentials in the chambers 67 and 7d. The post 7 2 bears at its outer end against a lever 73 pivoted as at 74L to a stationary support. The free end of lever 7 3 controls a leak port 7 5 forming a part of the air relay 57.

It will be understood that for the purpose of simplifying the description I have shown only the principal elements of a typical differential pressure regulator 56. Such devices are well known and commercially available. An eminently suitable commercial device operating on these principles is the model R=2 sold by Johnson Service Company of Milwaukee, Wisconsin.

The air relay 57 is of the direct acting gradual type and is also commercially available from the same company under model number Rl. In FIG. 2 such a device is shown in simplified form. Air pressure from the pressure line 6 3 is fed by branch line 59 into a first chamber 76 having the outlet 77 controlled by the normally closed valve 7 8. Outlet 77 leads to a second chamber '79 which is in communication with the output line 58 to the valve regulator 16. 'The chamber 79 communicates with an adjacent chamber 3t) through the center hole in an exhaust seat 81 and the ports 32 of a spacer 83.

As will be noted, chamber is open to the atmosphere through the aperture 34. Therefore, under normal conditions (before start-up of the system), atmospheric pressure exists in the line 53.

The air pressure from line 59 is also supplied to a chamber 85 through passageway 86 and restrictor 87. As will be evident, the pressure in this 35 is determined by the position of the lever 7 3 relative to the leak port 75. Under dead air conditions in conduit 14, i.e., no air motion, the pressures in chambers 67 and 7% of the differential pressure regulator will be equal. At this time the lever 73 is in its closest position to the leak port, which is the position illustrated in solid lines in FIG. 2.

It may be helpful to go briefly into the operation oi the pressure diiierential regulator and relay at this point. When the entire systemin operation, air is available to the relay through line 59 at a preselected pressure, say 15-28 psi. Immediately the pressure is applied, it builds up in chamber 85 of the relay and :forces diaphnagm 85a to the right. The movement of the latter is transmitted through spacer 83 to diaphragm title and the exhaust valve seat 851. The latter is seated against the valve 7%, thus closing chamber '79 to the atmosphere. A continued increase in pressure in chamber causes further move- .cnt of exhaust seat 81 to the right, forcing the valve 78 open and allowing pressurized air from line 59 to enter chamber 79 and the line 5%. The pressure in chamber 79 rises until this pressure, acting against the diaphragm 85a, forces exhaust seat 81 to the left and allows the valve '73 to close.

The relay is now in a balanced position with the force exerted by the pressure in chamber 353 acting on diaphragm 85a exactly equal to the force exerted by the pressure in line 53 acting on diaphragm 89a, and since the leak port is at its most closed position, this means a maximum pressure is being transmitted through line 58 to valve actuating mechanism 16.

Obviously, upward movement of lever 73 will result in a reduction in pressure in chamber 85. The force then exerted by the pressure in line 58, plus the force of spiral spring 88, are greater than the force of the pressure against diaphragm 8'7, and exhaust seat n1 is therefore moved away from the valve '78. Air from line 58 thus escapes to atmosphere through the center hole in the exhaust seat and exhaust hole 84. When the pressure in line 58 is reduced to the point Where the forces are again balanced, exhaust seat 31 closes against valve 7 8.

From the foregoing description it is seen that for every value of pressure existing in chamber 85, there is required a definite value of pressure in line 5% in order for the forces operating the valve mechanism to be in balance. Any other pressure in line E8 would result in an opening either at exhaust seat 31 or outlet 77 which would cause the pressure in line 58 to change in the directions required to bring about the necessary balance.

Obviously, it is the difierential between the total pressure measured at port d4 of the Pitot tube and the static pressure measured at port d5 which determines the pressure in line 58 at any given time. This differential is actually a measurement of the air velocity through the conduit 1 14. With no air motion, lever 73 is in the position shown in solid lines in FIG. 2, which, as earlier noted, corresponds to the maximum pressure in line 58. As the velocity past the Pitot tube increases, the total pressure will increase and lever 73 will be lifted, thus proportionately reducing the pressure in line 58. This in turn operates to change the condition in the valve 15.

The valve 15 and its pressure actuating mechanism 16 are conventional in construction. The valve member is biased toward the closed position by the spring @1. Line 58 is connected with the diaphragm chamber 5 2. The diaphragm 93 serves to shift the stem 94 of the valve thus to vary the amount of air that will be passed by the valve downstream toward and past the Pitot tube 63. It will be evident from the description that has pre ceded that when the control air pressure is present in line 5h to the relay 5'7, the first tendency of the pressure actuating mechanism is to shift the valve body 99 to the full open position. The position of the body 9%) thereafter will be dependent on the velocity head in conduit 14- downstream of the valve.

In designing a complete system I prefer to so relate the pressure regulator 56, relay 57 and valve actuating mechanism 16 so that at no time during operation will the valve body 9% completely close against its seat. In other words, I desire to maintain a substantially constant velocity of air through conduit 14 downstream of the valve under all conditions, including the condition in which bin 18 is empty and conduit 20 has no resistance in it. For purposes of illustration, a rate of 4,000 feet per minute will be used. Obviously the Pitot tube 63 gives a means of determining velocity despite variations in static pressure and this measurement of velocity is in turn utilized to control the valve 15 so that the design velocity will be maintained despite changing static pressures.

Going back again to FIG. 1, it will be seen that I have provided a third differential pressure regulator and relay ltlil which has the air input line 101 from the pressure line 60. The unit 100 is in all respects like that of the unit 56. The output line from the relay is indicated at 192 and this line leads to the pressure actuating mechanism 53 for contact 52, the pressure actuating mechanism 43 for contact 47, and a pressure actuating mechanism 104 for a variable pressure relief valve 105. The latter components are similar in construction and operation to the main air valve 15 and its operating mechanism 16. The pressure relief valve N5 is mounted in an exhaust line 106 connected with the header 12.

The pressure in line 102 is controlled by the unit 100 in response to differentials in static pressure between the header l2 and the highest of the static pressures in line 14, 14 and 14". The static pressure in the header is transmitted to one side of the regulator 1% through line 107. The static pressure from each of branch lines 14-, 14' and 14/ is taken from a point downstream of the valve by lines 108, 1% and 163" respectively, to a pressure selector it of conventional construction. The pressure selector selects the highest of the pressures in lines 108, 103 and i553" and passes it to the other side of regulator 10% through line 110.

It will be apparent that the pressure in line 102 from the pressure regulator 100 is thus a direct function of the static pressure differential between the header 12 and the highest pressure in line 14, 14', 14 on the downstream side of valve l5, l5, 15'. The pressure actuating echanism 104 of the variable relief valve 105 is preset so that the valve will maintain a preselected positive differential between the header and highest branch pressure between certain maximum and minimum limits. In other words, valve 195 will be at its full closed position when the differential drops below the preselected minimum and will be full open when the maximum differential is reached. In the variable range the valve should operate to maintain a low positive differential, say 1 psi. The actuating mechanism 53 for contact 52 is set to cause opening of contact 52 at the preselected maximum differential. On the other hand the actuating mechanism 48 for contact 47 is so set that contact 47 will close when at the preselected minimum differential.

Operation In starting up the system switch 32 is closed, thus starting pump 10 which supplies air to the header 12 and the branch lines 14, i4 and 14-". Air valve 62 is also opened to arm the control system with control air pressure through line 60. It will be assumed that at the outset none of the feeders is being operated so that in effect there is little resistance to flow through the branches i4, 14- and 14" and their conveying conduits. I11 this condition valves l5, 15' will be in the most restricted condition as will also be true with the similar valve (not shown) in line 14-", with the static pressure on the downstream side of the valves very low and the valves open only enough to supply the preselected velocity head through the conveying conduits.

Because of the restriction at the valves 15, 15' the static pressure in the header will be relatively high and the pressure differential measured at regulator will also be high. Pressure relief valve 1% will be full open, contact 47 still open, and contact 52 closed since pump 10 cannot inherently supply enough air to result in opening of this contact.

Assume now that feeder 17 is energized and material starts feeding into line 20, thus increasing the resistance to air flow and increasing the static pressure in line 14 downstream of the valve 15. The increase in static pressure results in an initial reduction in the air velocity, which is reflected at Pitot 63. The change at Pitot 63 immeditely actuates the regulator and relay 56 to change the setting of valve 15 to open it further. Through the regulator, valve 15 will be instantaneously adjusted to produce the design velocity despite the increase in static pressure. As will be evident as the pressure and velocity at the Pitot tube change, valve 15 will be operated to further restrict or increase the valve opening as the situation may require.

Air robbing through the as yet empty lines 14 and 14" is prevented by their valves, which remain in the most restricted condition because of the low static pressure below the valves. Therefore, the header will be able to supply enough air to line 20 to effect satisfactory conveying despite the fact that the other branches are not loaded. Moreover, relief valve 1% will begin to relieve the header if the static pressure in the header rises enough above the static below valve 15.

It is assumed that the over-all system is so designed that the capacity of pump 10 is such that it could adequately supply enough air to effect normal material conveying through two of the branch lines such as branches is and 14. However, it is not able by itself to also supply enough air for this purpose in the third branch 14". Accordingly, so long as the third branch remains inactive and so long as normal conveying pressures are present in lines 20 and 20', pump 10 alone will be enough for the system.

If, however, the air demand from the over-all conveying system becomes great enough that the differential pressure measured by regulator 100 drops to the preselected minimum, the contact 47 in the starting circuit to pump 11 will be closed by the pressure actuating mechanism 48. Since this circuit has already been armed by closing of contact 44 at the time of starting the pump 10, starter 41 will now be closed, bringing pump 11 into operation.

Since pump ll supplies additional air, the diiferential at regulator ltltl again increases. While contact 47 will immediately reopen due to the diiferential rising above the selected minimum, the starter remains energized through the locking circuit from conductor 39 through contact 52 and conductors 50 and 51.

The second pump 11 will remain operating so long as pressure in line 1M does not exceed the predetermined value which will cause pressure mechanism 53 to open contact 52;. However, if the load on the system decreases to the point where the pressure in control line 192 rises above said value then contact 52 will be opened, thus breaking the locking circuit across starter 41 and stopping pump 11. Thereafter pump 10 will operate alone to supply air to the system until such time as the conveying air demand rises above what that pump can effectively supply, again bringing pump 11 into play, as previously described.

It is important to note that the pressure differential at regulator Tilt) is always measured between the highest conveying line static pressure and the static in the header. The selector 10$ passes only the highest of the conveying line pressures, so the demand of the system is always based on the most loaded conveyor conduit. Moreover, through the pneumatic control system for the valves I am able to achieve almost instantaneous response to any change in conditions in the lines, thus maintaining continuous flow at all points and avoiding any intervals of air robbing through unloaded lines.

By virtue of the arrangement employed the load on the pump meters 21 and 37 is maintained substantially at that which is required for effective operation of the system, thus effecting a great saving in power as compared with systems of which I am presently aware. The relief valve 1% serves to relieve the back pressure whenever substantially more than sufficient air for conveying is available. The ability of the system to automatically cut pump 11 into and out of use likewise serves to hold the costs of operation to a minimum since this pump is used only when needed. 7 It will be evident that the system can be expanded to include more pumps and more lines by simply connecting each additional pump motor into the preceding one in the same relationship as between pumps 10 and 11. The pressure regulators and pressure switches associated with the additional pumps would be set at the values necessary to cut in each additional pump as the system demands.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the ructure. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim:

1. In a pneumatic conveying system, a header, a plurality of air pumps connected with said header and operable, when energized, to supply air to said header, a plurality of branch discharge lines each connected with said header, each said line having interposed therein a variable throttling valve, velocity sensing means located in each line, control means for each valve operably connected with the sensing means in the line containing such valve, each said control means operable to vary the valve in a direction to tend to maintain the velocity through said line constant despite changes in static pressure in the line, and means operable to vary the static pressure in said header at a predetermined differential relationship with the highest of the static pressures in the respective lines.

2. In a pneumatic conveying system, a header, a plurality of air pumps connected lWlth said header and operable, when energized, to supply air to said header, a plurality of branch discharge lines each connected with said header, each said line having intenposed therein a variable throttling valve, velocity sensing means located in each line, control means for each valve operably connected with the sensing means in the line containing such valve, each said control means operable to vary the valve in a direction to tend to maintain the velocity through said line constant despite changes in static pressure in the line, and means operable to viary the number of pumps in simultaneous operation responsive to the static pressure differential between said header and the highest of the static pressures in said lines.

3. In a pneumatic conveying system, a header, first and econd air pumps each connected to discharge into said header, first and second motors respectively drivingly connected with said pumps, a plurality of branch lineseach connected with and leading from said header, each line having feeder means for selectively introducing material to be conveyed therein, a variable throttling valve in each line ahead of said feeder means, velocity sensing means in each line operable to measure the air velocity therethrough, valve control mechanism connected with and operated responsive to said velocity sensing means to vary said valve in response to changes in velocity in the line from a predetermined constant velocity, and pump control means operable to energize and deenergize said second pump motor in response to selected minimum and maximum static pressure diiierentials between said header and the highest static pressure in said respective lines.

4. In a (pneumatic conveying system as in claim 3, static pressure relief means connected with said header and operable to tend to maintain the static pressure in said header at a selected limited differential with respect to the highest of the static pressures in said branch lines.

5. in a pneumatic conveying system as in claim 4, said relief means including an outlet from said header, a variable throttling valve said outlet, static pressure sensing means connected respectively with said lines and said header, and regulator means for said valve in said outlet connected with said (sensing means and actuated responsive thereto.

6. in a pneumatic conveying system, a header, first and second air pumps each connected to discharge into said header, first and second motors drivin-gly connected with said pump, starter circuits for said motors and operable to selectively energize same, means operable upon closing of the starter circuit to said first motor to arm, but not close, the starter circuit to the second motor, a plurality of branch lines each connected with and leading from said header, each line having feeder means for selectively introducing material to be conveyed therein, a

variable throttling valve in each line ahead of said feeder means, air velocity sensing means in each line operable to measure the air velocity therethrough, valve control mechanism connected with and operated responsive to said velocity sensing means to vary said valve in response to changes in velocity in the line from a predetermined constant velocity, and pump motor control means operable to close and open the starter circuit to said second motor in response to selected minimum and maximum static pressure diiierentials between said header and the highest static pressure in said respective lines.

7. In a system as in claim 6, said pump motor control means including pressure sensitive switches interposed in said starter circuit to said second motor and respectively sensitive to said minimum and maximum differentials.

8. In a system as in claim 7, said switch responsive to said minimum differential being normally open and said switch responsive to said maximum differential normally closed.

9. In a system as in claim 8, said normally closed switch operable to maintain said starter circuit to said second motor closed following closing of said normally open switch until said maximum pressure difierential is attained.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,937 Anderson July 30, 1946 2,665,707 Stover Ian. 12, 1954 2,726,122 Hagerbanmer Dec. 6, 1955 2,770,584 Ray Nov. 13, 1956 2,884,940 Garrie May 5, 1959 3,002,521 Greenlees Oct. 3, 1961 3,005,462 Hillman Oct. 24, 1961

Claims (1)

1. IN A PNEUMATIC CONVEYING SYSTEM, A HEADER, A PLURALITY OF AIR PUMPS CONNECTED WITH SAID HEADER AND OPERABLE, WHEN ENERGIZED, TO SUPPLY AIR TO SAID HEADER, A PLURALITY OF BRANCH DISCHARGE LINES EACH CONNECTED WITH SAID HEADER, EACH SAID LINE HAVING INTERPOSED THEREIN A VARIABLE THROTTLING VALVE, VELOCITY SENSING MEANS LOCATED IN EACH LINE, CONTROL MEANS FOR EACH VALVE OPERABLY CONNECTED WITH THE SENSING MEANS IN THE LINE CONTAINING SUCH VALVE, EACH SAID CONTROL MEANS OPERABLE TO VARY THE VALVE IN A DIRECTION TO TEND TO MAINTAIN THE VELOCITY THROUGH SAID LINE CONSTANT DESPITE CHANGES IN STATIC PRESSURE IN THE LINE, AND MEANS OPERABLE TO VARY THE STATIC PRESSURE IN SAID HEADER AT A PREDETERMINED DIFFERENTIAL RELATIONSHIP WITH THE HIGHEST OF THE STATIC PRESSURES IN THE RESPECTIVE LINES.

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