US1913195A - Method of and apparatus for controlling feed-water delivery and blow-down for boilers - Google Patents

Description

R. R. DONALDSON. JR, ET AL METHOD OF AND APPARATUS FOR CONTROLLING FEED June 6, 1933.

WATER DELIVERY AND BLOW-DOWN FOR BOILERS Filed July 7, 1951 2 Sheets-Sheet l June 6, 1933. R. R. DONALDSON. JR., ET AL 5 METHOD OF AND APPARATUS FOR CONTROLLING FEED WATER DELIVERY AND BLOW-DOWN FOR BOILERS Filed July 7, 1931 2 Sheets-Sheet 2 5'4 4 I j F l l i 146 4- 4 145 E I '1 i 1.

I a I v 12 11a 115 I ,(165 r I 165 16? fgfiu A K B INVENTOR3 at 3%; Conceni'rai o/bQi/er wafer v W Patented June 6 1933 UNITED STATES PATENT oF icE ROBERT LR. DONALDSON, JR, OE PITTSBURGH, AND EDWARD W. BUTZLER, OF BELLEVUE, PENNSYLVANIA, ASSIGNOBS TO JOHN M. HOIWOOD, OF DORMON'I', PENNSYLVANIA METHOD OF D APPARATUS FOR CONTROLLING FEED-WATER DELIVERY AND BLOW-DOWN IOR BOILERS Application and m 7, 1931. Serial No. 549,188.

This invention relates to a' method and apparatus for controllingthe concentration of precipitate forming materials contained in a body of liquid, to and from which quancities of liquids are added and withdrawn either intermittently or continuously. For example, such a body of liquid may be the water confined in theboiler of a boiler furnace.

It is well known in the art, pertaining to the operation of boilers that water must be added or supplied to replace thatwhich has been evaporated by the boiler and utilized in the form of steam.

It is also well known, that, in the operation of boilers, various precipitate-forming materials enter the boiler with the feed water,

while others are formed therein by the chemi cal reactions taking place within the boiler. In either case, such materials concentrate in the boiler. I

The precipitate-forming materials, of limited solubility, soon reach their saturation point and thereafter precipitate either as sludge or as scale, while others, (for the.

most part sodium salts) having a greater 7 solubility, concentrate to a much higher degree before their saturation point is reached.

If theconcentration ,of the salts, having greater solubility, is not regulated, deleterious effects are occasioned; for example, the water in the boiler foams, causing wet steam to be delivered to the steam lines.

In order to maintain the concentration of the more objectionable precipitate-forming materials, within such limits that no deleterious effects shall be produced, water must be discharged. from the boiler as blow-down,

either continuously or intermittently, and

feed water added to replace the water diS-.'

charged as blow-down and thatwhich has been evaporated, in order that the quantity of water confined in the boiler shall be diluted to a point at which the concentration of the soluble salts, or the precipitate-forming materials, is reduced to within the permissible operating limits.

If too much water is withdrawn from the boiler, feed water and heat energy is wasted, thereby impairing the boiler efliciency;

whereas, if too little boiler water is discharged the water may become so concentrated with precipitate-forming materials that the aforementioned objectionable deleterious efi'ects are produced.

To obtain the proper boiler water concentration, without wasting heat and water, the amount of Water discharged from the boiler should, therefore, be governed jointly in acdegree of concentration of the precipitate forming materials contained in the boiler water.

For convenience, we depend upon the amount of sulphates contained in the boiler water in order to determine the exact amount of water to be discharged from the boiler.

To determine the concentration of the sul phates, a sample of the boiler water is withdrawn, preferably continuously, and to this sample is added a precipitate-forming reagent such as barium chloride. The .sulphates in solution react with the barium chloride, to form barium sulphate which, being insoluble and in suspension, renders the solution turbid.

To this turbid suspension so formed is added continuously a predetermined quantity of clear, miscible liquid that is free from precipitate-forming materials. Since the amount of reagent, miscible liquid, and boiler Water, brought together in this manner, re-. mains fixed, one with respect to another, it follows that the degree of turbidity will vary as the concentration of the soluble salts, or

the precipitate forming materials, in the boiler water varies.

In order to utilize the variations in the turbldity of the suspension, we pass a beam of light through the suspension. The light dispersed by the suspension is focused upon one or more light-sensitive control devices, .so arranged that adjustments in the blowdown, that is, the amount of water discharged from the boiler, are affected in accordance with the amount of sulphates or precipitateforming materials contained in the boiler water.

By controlling the supply of feed water in accordance with variations in the boiler water level, and by regulating the amount of blowdown by and in accordance With the amount of Water delivered to the boiler, and the degree of concentration of the precipitate-forming materials therein, the boiler water may be maintained at any predetermined degree of diluteness.

For a fuller understanding of the invention, reference maybe had to the following description taken in conjunction with the accompanying drawings in which:

Figure 1 is a diagrammatic view of a boiler feed water and blow-down control system arranged and constructed in accordance with the invention;

Fig. 2 is a view in side elevation, partly in section, of a compensating relay embodied in the system of Fig. 1;

Fig. 3 is a top plan view of a cam device embodied in the system;

Fig. 4 is a side view, in elevation, partly in section, of a boiler water analyzer;

Fig. 5 is a view in section of the analyzer taken on line VVofFig. 4, and a diagrammatic illustration of a light sensitive control system arranged to operate in accordance with the analysis of the boiler water as determined by the analyzer; and

Fig. 6 is a graphic illustration showing the relation between turbidity of suspension in the analyzer to concentration of boiler water and intensity of light dispersed by the analyzer.

In the drawings, a boiler 1 is shown to which the apparatus and the method embodyingghe invention may be applied and practice Feed water from any suitable source is delivered through a feed line 2 to a drum 3 of the boiler. Valves 4 and 5 located in the feed line are provided to regulate the flow of feed water. A regulator 6 is provided to open and close valve 4 in'accordance with changes or variations in the water level of the boiler, hence in proportion to and in accordance with the demand for steam, and the amount of water discharged as blow-down.

Valve 5 is operated by regulator 7. Regulator 7 responds to the pressure differential, or pressure drop, across Valve 4 and to the position of or the amount that valve 4'is open. As illustrated, valve 5 is so located that, as it opens, the pressure to the inlet side i of valve 4 is increased or, as it is closed, the

pressure to the inlet side of the valve 4 is decreased.

As will be made apparent hereinafter, regulator 7 operates in such a manner that as valve 4 is opened, valve 5 is opened to increase the pressure on the inlet side of valve 4 and, as valve 4 is closed, valve 5 is closed to decrease the inlet pressure. By utilizing this form of control, it will be apparent that the inlet pressure on the valve 4 is caused to vary substantially, directly in proportion to its position, or the amount that it is open. It will also be apparent that by manipulating or operating valve 5 in this manner, the pressure drop through valve 4 will vary in accordance with its position.

Regulator 6 comprises a return bend pipe, or tube 8 having U-bends a and b in the legs thereof. Tube 8 has communication with boiler drum 3 through its bottom and with the interior of the drum at its top. The horizontal leg of the return bend pipe and the lower portion of the upwardly inclined leg or branch thereof will, therefore, be filled with water to a level that corresponds to and varies with water level in the boiler drum, while the upper portion of the upwardly inclined leg or branch thereof will be filled with steam. Therefore, as the water level in the boiler drum rises and falls, respectively, the temperature of the return bend pipe will fall and rise, respectively, causing said tube to contract or expand, respectively.

In order to utilize the contraction and expansion of the return bend tube or pipe, as a means for operating valve 4, a bell crank 9 pivotally supported at 10 is provided. One arm of the bell crank is pivotally connected at 11 to an extension 12 carried by the outermost end of the return bend tube or pipe 8, while the other arm of the crank is pivotally connected at 13 to the valve stem 14 of valve 4.

It will be apparent by inspection of the drawings, that if the water level in drum 3 falls, the return bend tube or pipe will expand (its temperature being increased) and turn bell crank counteryclockwise, as viewed from the drawings, thereby opening valve 4 to increase the supply of feed water to the boiler. As the water level rises in the drum, the temperature of the return bend pipeor tube will fall, hence it will contract and turn bell crank 9 clockwise to actuate valve 4 towards its closed position and reduce the amount of feed water supplied to the boiler.

Regulator 7, as illustrated, may be of .the type constructed in accordance with the dis closure of United States Letters Patent No. 1,371,243 granted to John M. Hopwood on March 19, 1921. It will be appreciated that other forms or types of regulator may be employed, although we prefer the type illustrated in said patent as it has demonstrated its practicability for our purpose.

Briefly, regulator 7 includes a pressure metering device 15, such as shown in Patent No. 1,371,243, having a diaphragm or pressure responsive element arranged to turn or rock a weighted lever arm 16 on its fulcrum as the pressure drop across valve 4 varies. If the pressure differential or drop increases, lever arm 16 will turn clockwise on its fulcrum, or counter-clockwise if the pressure differential decreases.

Regulator 7 includes also an actuating device, or motor 17 arranged to open and close valve in response to movements of the weighted lever arm 16 caused by variations in the pressure drop or differential across valve 4. Actuating device or motor 17 is also illustra ted and fully described in detail in Patent No. 1,371,243, and in a pending application, Serial No. 520,949, filed March 7, 1931, by George V. Smith, and assigned to John M. Hopwood.

Motor 17 comprises a cylinder '18 in which a reciprocating piston (not shown) -is disposed. A piston rod 19 attached to the piston extends through the upper end of the cylinder and carries a vertically movable frame 20. The lower end of frame 20 is connected by a link 21 to one end of a lever 21'. Lever 21 is pivotally mounted medially of its ends on a link L which is pivotally supported on the valve body of valve 5. The other end of lever 21' is pivotally connected to the stem of valve 5. Thus if frame 20 moves upwardly valve 5 is actuated towards its closed position, or if the frame moves downwardly the valve is actuated towards its open position.

A control valve 22 mounted on cylinder 18 is arranged to admit pressure to the cylinder either at the top. or the bottom sides of the piston according to the position to which the valve is actuated by weight lever 16. If

pressure is admitted at the top of the piston,

frame 20 moves downwardly to open valve 5, and moves upwardly to close valve 5 when pressure is admitted to the cylinder at the underside of the piston.

Control valve 22 is operated by weight arm 16 through a system of levers such as illustrated in the patent and application referred to above. By means of these levers regulator frame 20 is caused to move in incremental steps, to thereby operate valve 5 step-by-step,

If weighted lever arm 16 turns counterclockwise, in response to a reduction in the pressure drop across valve 4, valve 22 will be shifted to that position in which fluid under pressure is admitted to cylinder 18 at the top side of the piston thereby causing frame 20 to move downwardly and open valve 5 until the pressure differential across valve 4 is restored to normal. On the other hand if the weighted lever arm 16 turns clockwise, in response to an increase in pressure differential across valve 4, valve 22 will be shifted to that position in which pressure is admitted to the cylinder at the bottom of the piston thereby causing frame 22 to actuate valve 5 towards its closed position until the pressure differential across valve 4 is again restored to normal.

Such operation of regulator 7, as described above, results in a substantially constant pressure differential, or drop, being maintai'ned across valve 4, instead of a varying pressure differential.

In order, therefore, to cause regulator 7 to so adjust valve 5 that the pressure on the inlet side of valve 4 will vary in accordance.

with the position thereof, so as to vary the mits a relatively low pressure to bellows 25' causing it to contract. The contraction of the bellows imposes a clockwise acting force on lever arm 16 that decreases the effect of weight 28; hence the lever arm will move upwardly whereby operation of motor 17 is effected to close valve 5 a predetermined amount to reduce the pressure on the inlet side of valve 4.

If valve 4 is actuated towardsits open position, sending device 24 effects an increase in the pressure sent to bellows 25, whereby lever 26 imposes a counter-clockwise acting force on arm 16, thus increasing the effect of weight 28 on arm 16 with respect to the differential pressure acting on the pressure responsive element or diaphragm of regulator 7. Therefore, lever arm 16, being out of balance with the differential pressure acting on the diaphragm will lower, causing the regulator frame 22 to move downwardly and open valve 5 until the pressure drop across valve 4, as reflected upon the diaphra m of regulator 7, is in balance with the forces acting on weighted lever arm 16. -When valve 5 is opened, as aforesaid, the inlet pressure on valve 4 is increased.

said manner, a variable differential is produced across valve 4. By varying this differential, the inlet pressure on valve 4 will be relatively low when the boiler is receiving little or no feed water, hence leakage of feed water to the boiler when banked or operating at low rating, is prevented. The reverse takes place, when valve 4 is relatively wide open,.-and large amounts of feed water are delivered to the boiler. In the latter case the inlet pressure on valve 4 is increased suffi- By operating valves 4 and 5 in the aforeciently to insure that the demand for feed water will be met.

While regulator 7 produces a variable differential across valve 4, it will be apparent that it also maintains the differential constant for each and every position to which the valve is actuated.

The pressure sending device 24 comprises a bellows 30, that operates against a compression spring 31, and a multi-way valve 32, the position of which is controlled jointly by the bellows and water-level regulator 6. The bellows carries a push rod 33, the upper end of which is pivotally connected to a floating'lever 34 betweenthe ends thereof. One end of floating lever 34 is connected by a link 35 to the horizontal arm of bell crank 9 and its other end is connected by a link 36 to stem 37 of multi-way valve 32.

If the boiler water level rises, the return bend tube or pipe of regulator 6 will contract, as aforesaid, causing bell crank 9 to turn clockwise and move valve 4 towards its closed position. Clockwise turning of the bell crank causes floating lever 34 to turn counter-clockwise, about its pivotal connection with push rod 33, and move multi-way valve 32 upwardly to a position at which the pressure acting on bellows 30 and 25 is reduced. Bellows 30 will, therefore, contract in response to such reduction in pressure, and turn floating lever 34 clockwise, about its pivotal connection with link 35, and move multi-way valve 32 downwardly to its neutral position. When the valve is in neutral position, further reduction in the pressure acting on bellows 30 and 25 is prevented.

The reduced pressure acting on bellows 25 causes it to contract, and turn lever 26 c'ounter-clockwise, whereby an upward force is imposed on the'weight arm. Such upward force, acting on weight arm 16, reduces the resultant downward force acting thereon; hence an unbalanced condition between the forces exerted by the pressure diaphragm of regulator 7, the weight 28 and bellows 25 on the weight arm 16. cause it to move upwardly. Upward movement of arm 16, as stated hereinbefore, results in an upward movement of regulator frame 22 and a corresponding closing of valve 5 with consequent reduction in the inlet pressure to valve 4.

If the boiler water-level is lowered, the reverse operation takes place because the return-bend tube of regulator 6 will expand, a

greater part thereof being in contact with steam than with boiler water. In response to such expansion of this tube, bell crank 9 will turn counter-clockwise, move valve 4 upwardly towards its open position and at the same time effect movement of multi-way valve 32 to that position in whichthe pressure transmitted to bellows 30 and 25-is increased.

Bellows 30 responds to such increase in pressure and moves floating lever 34 upwardly whereby the multi-way valve 32 is returned to its neutral position to prevent any further increase in pressure to the bellows. In like manner, bellows 25 expands imposing a downward force on weighted lever arm 16, which added to that of weight 28, causes the lever arm to turn downwardly with the result that valve 5 is moved towards its open position to increase the inlet pressure to valve 4. The above described system for feed water control is disclosed and claimed in a co-pending application, Serial No. 291,090, filed July 7, 1928 by Thomas A. Peebles.

Fromthe foregoing description it has been shown how the supply of feed water to the boiler is regulated by and in accordance with the demand for steam which, of course, is reflected in the boiler water level. In accomplishing this result valves 4 and 5 are so manipulated that the pressure differential across valve 4 is caused to vary substantially in direct proportion to the position of valve 4.

As stated hereinbefore, water must be drawn off or discharged from the boiler, as blow-down, either intermittently or continuously in order that the water in the boiler may be maintained at the propcr diluteness with respect to the concentration of the precipitate-forming materials contained there in. If the chemical composition of the water remains constant with respect to the content of the precipitate-forming materials therein, the proper diluteness may be maintained by drawing off or discharging water. as blow-down, in substantially direct proportion to the amount of feed water supplied to the boiler.

However, in practice, the chemical composition of the boiler feed water does not remain constant, because the amount of precipitate-forming materials varies from time to time. Therefore, the amount of blowdown (the amount of water discharged from the boiler) must vary both in proportion to the amount of feed water supplied and to the concentration of the precipitate-forming materials. For our purpose the amount of blowdown may be proportioned in accordance with the amount of sulphates contained in the boiler water.

In order that the blow-down may be regulated by and in accordance with the amount of feed water delivered to the boiler, a blowdown valve 38 and a regulator 39, for operating the valve, are provided. Regulator 39 includes a pressure responsive actuating device 40 for controlling the operation'of fluid motor 41 arranged to operate the blow-down valve. The valve operating device or motor 41 may be identical in construction to valve actuating motor 17 and it is so'illustrated;

' hence similar and corresponding parts bear the same reference characters.

Pressure responsive actuating device 40 is utilized to operate valve 22 of blow-down valve motor 41, and comprises pressure actuated bellows 42 and 43 mounted on a base B. Belows 42 and 43 are provided with push rods 42' and 43, respectively, towhich the nds of a beam 44 are pivotally connected. Beam 44 is connected by a link 47 to the operating lever of valve 22 controllingthe movements of fluid motor 41. Beam 44 and link 47 are raised or lowered in accordance with the resultant forces exerted by bellows 42 and 43 on the beam.

The interior of bellows42 is subjected to apressure that varies in accordance with the extent of opening of valve 4, and the interior of the bellows 43 is subjected to a pressure that varies in accordance with a response of apparatus which will be hereinafter described, to the concentration of precipitateforming materials in the boiler Water.

If the general movement of beam 44 and link 47 is upwards, caused by an increase in pressure in one or the other of bellows 42 or 43, or both, regulator frame 20 of fluid motor 41 will move upwardly toopen blowdown valve 38. If the. general movement of beam 44 and link 47 is downward caused either by a reduction of pressure within either bellows 42 or 43, or both, valve 22 will be operated to such a position that frame 20 of fi uid inotor 41 will move downwardly to close blow-down valve 38.

In order that pressure responsive actuating device 40 may be caused to operate the blowamount of feed water delivered to the boiler, the interior of bellows 42 is subjected to a variable pressure communicated thereto, by

a pipe line 48, from a compensating relay 49.

The compensating relay is under the control of the pressure sending device 24, hence the pressure delivered to the interior, of bellows 42 will be caused to vary in accordance with movements of the pressure sending device ,as affected by changes in position of valve 4 and, therefore, in accordance with the amount of feed water delivered to the boiler. In some cases relay 49 may be omitted by connecting bellows 42 with a pipe line directly to pressure sending device 24. y

As illustrated in the drawings, compensating relay 49 is interposed. between the pressure sending device 24 and the pressure responsive actuating device 40. The compensating relay, as will be set forth more fully hereinafter, is so arranged that the operating pressure delivered to bellows 42 may be greater than, equal to, or less than the pres-.

i t fere with 't movem t clown valve motor 41 1n accordance with the n er 1 S justed independently of the operating characteristics of the feed water control apparatus.

The compensating relay (see Fig. 2) comprises a frame 51 upon whichjs mounted a bellows 52. Operating pressure is communlcated, through a pipe line 53 from the pressure sending device 24, to the interior of bel Connecting rod 55 carries a pin 56 that operatively engages lever 57. One end of lever 57 is pivoted to the frame of the relay as at 58 and its other end ispivotally connected to a stem of a multiway valve 60. Multiway valve as an inlet port 61 which is connected to a-pipe line 62 carrying fluid under pressure.

Multiway valve 60 is provided also with a port 63 that communicates with the interior of the valve, the interior of lower bellows 54 and pipe line 48. Pipe line 48 conveys pressure to the interior of bellows 42. The valve is provided also with an exhaust port -"64, whereby, when the inlet port of'the valve is closed, the pressure in lower bellows 54 land the interior of bellows 42 may be reduced, in varyingamounts, from the pressure at the ,source to atmospheric.

Compensating relay 49 is provided also with a bell crank 65 pivotally mounted at 66 on frame 51. The horizontally extending arm of this crank has a bifurcated end that embraces the connecting rod 55,but does not The connecting rod, also carries an adjustable stop 67.

Between stop 67 and the upper side of the horizontal arm of the bell crank is interposed.

a compression spring 68. A compression ofthe lower bellows 54 and the horizontal arm of the bell crank. By adjusting the position of the bell crank, the tension in the springs may be varied to thereby impose a greater initial spring pressure on oneof the bellows than on the other, or the initial spring pressure may be adjusted to equal values on both.

The adjustment of the bell crank is accomplished by a screw 70 operated-by a hand wheel 71. The screw has a traveling nut 71 that carries a pin 72 which is received in the bifurcated end of the vertical arm of the bell crank. By turning the hand wheel, the traveling nut will move, hence the position of the bell crank may be changed. For example, if the bell crank is turned clockwise, spring 68 will be compressed against stop 67 whereby lows 52 will be increased whereas the pressure of spring 69 on the lower bellows will be relieved or decreased. It will, therefore, be

spring 69 is also interposed between the top v the initial pressure imposed on the upper belapparent, that a greater pressure must be applied to the interior of the upper bellows 52 in order to cause the same downward movement of connecting rod 55 as would be occasioned by a lower pressure had not spring 68 been compressed. Likewise, if the bell crank is turned counter-clockwise, spring 69 will impose a greater pressure on the lower bellows 54. Therefore, a greater pressure must be applied to the interior of the lower bellows to effect the same upward movement of the push rod that would have taken place, in response to a lower pressure, had not the spring pressure on this bellows been increased by the change in position of the bell crank.

The operation of the compensating relay is as follows :If the sending device 24 operates to transmit a pressure through line 53 to the interior of the upper bellows 52, this pressure causes the bellows to expand and move connecting rod 55 downwardly. Downward movement of the connecting rod causes lever 57 to turn counter-clockwise. Valve stem 59 is, therefore, moved downwardly until the valve establishes communication between the pressure supply line 62 and the interior of the lower bellows 54 and the pipe line 48 that communicates with the interior of bellows 42. The pressure delivered to the interior of bellows 54 causes it to expand and move the connecting rod upwardly. Upward movement of the connecting rod causes lever 57 to turn clockwise whereby the valve stem is moved upwardly to that position in which the passage leading from valve 60 to the interior of the lower bellows 54 is closed. 7

If sending device 24 operates to reduce the pressure transmitted to the upper bellows 52, an unbalanced condition obtains between upper bellows 52 and lower bellows 54. Therefore, the lower bellows will expand, and move push rod 55 upwardly whereby lever 57 is moved still further clockwise until valve plug 61 is in that position in which passage 63 is uncovered. When in this position, the fluid under pressure in the lower bellows and in pipe line 48 will escape to the atmosphere until the pressure in the lower bellows is equal to that in the upper bellows, at which time, the lower bellows will contract, turn lever 57. counter-clockwise and return the valve to its neutral position. The compensating relay will operate, as aforesaid, in response to variations in pressure in the upper and lower bellows 52 and 54, valve plug 61 being always returned to neutral position when the upper and lower bellows are in balance or equilibrium.

From the above it will be apparent that the compensating relay will transmit pressure variations to bellows 42 of the pressure responsive actuating device 40 in accordance with variations in pressure sent out by pressure sending device 24 as affected by adjustments in valve 4. Pressure responsive actuating device 40 being responsive to these variations will therefore effect such adjustments in the blow-down valve 38, that the amount of water discharged from the boiler, as blowdown, will be substantially in direct proportion to the amount of feed water delivered to the boiler.

Since, as stated hereinbefore, the concen tration of the precipitate-forming materials in the boiler water is not constant at all times, it therefore becomes apparent that the ad ustments of the blow-down valve must be modified to compensate for such variations in the concentration of the boiler water.

In order to determine the concentration of the precipitate-forming materials in the boiler water, we determine, continuously, the concentration of a suspension formed by the reaction between a sample of the boiler water and a reagent, and dilute the suspension so formed with a clear, miscible liquid. Without the addition of the clear miscible liquid, the suspension will be decidely turbid, but by adding the miscible liquid thereto, the turbidity will be lessened and for certain concentrations the suspension may be substantially clear. The amount of miscible liq uid required to clarify or reduce the turbidit of the suspension to a predetermined stan ard is, therefore, a measure of the boiler water concentration.-

Through a predetermined thickness of this diluted suspension, we pass a beam of light, and the amount of light dispersed by this suspension will vary with variations in the turbidity thereof.

Having determined beforehand the permissible concentration of the boiler water, we so proportion the diluent (clear miscible liquid) boiler water sample, and reagent, that the turbidity of the suspension will be of a predetermined value when the concentration of the boiler water is at-or near the permissible degree of concentration.

If the concentration of the boiler water varies, the turbidity of the suspension will vary or depart from that degree of turbidity that would obtain when the boiler water is of the proper concentration. As the turbidity of the suspension varies in accordance with variations in the concentration of the boiler water, the amount or the intensity of the light dispersed by the suspension will vary. Such variations in light intensity are utilized to effect operation of apparatus 7 5 that causes a variable pressure to be set up within bellows 43 of the pressure responsive actuating device 40. This pressure will vary in accordance with changes in the concentration of the suspension and hence will so modify the operation of the blow-down valve re ulator 39 that more or less boiler water wi 1 be discharged from the boiler, as blowdown, until the concentration of the boiler cipitate forming materials in the boiler water comprises a container or cell 76 into which boiler water, reagent and clear mis cible liquid flows.

Boiler water flows from the boiler through a pipe line 77 into a filter 7 8' wherein scale and other impurities, not entering into the determination of the concentration of the boiler water are removed. From the filter, the water flows through a cooling coil 79 disposed in a tank 80, throughwhich suitable cooling medium, such as .cold water, is

circulated, and thence to a constant head tank 81. Tank 81 has an outlet pipe 82 through which the boiler water sample flows to the container or cell 76, and an overflow spout 83 located near to the top of the tank. A restriction or orifice 84 is provided in outlet pipe 82, so that, when the level of the boiler water sample in tank 81 is maintained constant at the level of outlet spout 83, a

constant flow of boiler water sample will be delivered to the cell or container 76. A valve 85 is placed in the pipe leading from the filter 78 to the cooling coil 79 and this valveis so adjusted that the head of boiler water sample in tank 81 will remain constant at the level of the overflow spout.

Suitable reagent, such as barium chloride, stored in a tank 86, flows through a pipe 87 to a constant head container 88. To the reagent in tank 86 is added a suflicient amount of hydrochloric acid to neutralize the alkalinity of the boiler water and render the suspension slightly acid.

Constant head container 88 has an outlet \pipe 89, having an orifice or restriction 90 therein, that conveys the reagent to the cell or container 76. The reagent, barium chloride, reacts with the boiler water sample in the cell or container 76 toform barium sulphate.

Constant head tank 88 has an overflow spout 91 near to its top. The level of the reagent in this tankis maintained constant at the'outlet spout level by means of a valve 92 located in the line 87 leading from the reagent tank to the constant head tank.

' Suitable diluent in the form of clear, miscible liquid, such as distilledwater, is stored in a container or tank 93 and delivered therefrom, through-a pipe line 94, to an adjustable head tank 95. Adjustable-head tank 95 delivers diluent liquid through a pipe 96, having an orifice or restriction 97 therein,

to thecell or container 76. The amount of diluent delivered to the variable head tank may be regulated by means of a valve 98.

Variable head tank 95 has an outlet 99 near its bottom, that is connected to a flexible hose or conduit 100 having an outlet spout 101 attached to the end thereof. The outlet spout is suspended from a flexible cable 102 operating over pulleys 103, and counterbalanced with a weight 104. By moving the weight up or down' the outlet spout may be lowered or raised. It will be apparent that the position of the outlet spout will determine the level or head of liquid in variable head tank 95.

In order to insure thorough mixing of the boiler water sample, reagent and diluent delivered to the cell or container 7 6, and a stirring of the suspension, the discharge ends of pipes 82, 89 and 96 are disposed near to the ottom of the cell or container 76, whereby upwardly moving.turbulent currents of the several constituents entering into the suspension are set up. The amount of suspen- I sion in the cell or container may be maintained constant by employing an overflow spout 106 positioned near to the top of the cell or at any suitable distance from the bottom of the cell depending upon its construction.

The form of construction of the cell or container 76 suitable for our purpose is illus trated in detail in Figs. 4 and 5. As illustrated, the cell or container comprises a transparent receptacle 107, preferably of glass disposed in an opaque housing 108, preferably of metal. The glass receptacle, as shown, is rectangular in cross section and the thickness of the glass walls is substantially uniform from top to bottom. Both the glass receptacle and its housing are open at the top and closed at the bottom.-

Side 109 of the housing is provided with a window 110 and adjacent this window is mounted a source of light 111 preferably an electric incandescent light. The opposite wall of the housing is provided with windows 112 and 113 equally spaced with respect to the axes of window 110 in the housing wall 109. Beams of light from source 111 pass through window 110 and the adjacent wall of the glass receptacle into the suspension.

Some of the light passing into the suspension is dispersed therefrom through windows 112 and 113. The intensity ofthe light dispersed will depend upon or vary in accordance with the turbidity of the suspension.

Since the distance between window 110 and windows 112' and 113 is fixed, beams of light from light source 111 always pass through a predetermined thickness of the suspension formed in cell 76. Hence the light sensitive devices 115 and 116 viewthe light source through a predetermined thickness of the sus ension.

.n order that the apparatus illustrated at 75 may be caused to function in response to and in accordance with variations in the turbidity of the suspension in cell 76, to thereby modify the operation of blow-downvalve regulator 39, and effect a corrective change in the concentration of the boiler water, light sensitive devices 115 and 116 are provided and mounted adjacentto windows 112 and 113.

Light sensitive devices 115 and 116 com- 5 prise photocells 117 and 117, respectively,

andgrid glow tubes 118 and 118' respectively.

Photocell 117 includes a plate or anode 119 and a cathode 120 and photocell 117' includes a similar plate or anode 119 and a cathode 120'. Plates or anodes 119 and 119 have a thin coating of light sensitive material deposited thereon, such as caesium, sodium, potassium or lithium. Any of these metals when exposed to light become electro-active and if subjected to a difierence of potential, pass electric current.

Grid-glow tube 118 comprises a plate or anode 121, a cathode'122 and a grid 123. Glow tube 118' includes similar elements designated by characters 121, 122' and 123'. Photocell 117 is so connected to the elements of grid glow tube 118 that current flows in the plate circuit of the latter when the intensity of the light impinging on the photocell 117 is below a predetermined value.

Grid 123 under such conditions is rendered sufliciently positive by photocell 117 to permit the flow of current in the plate circuit of glow tube 118. The plate current flows continuously until the intensity of the light increases above the aforementioned value in which case the potential on grid 123 is rendered negative by photocell 117 to preverit the flow of current.

As shown, anode 119 of photocell 117 is connected by a conductor to anode 121 of glow tube 1.18, and cathode 120 and grid 123 are interconnected by a conductor 124. A condenser 125 and a resistor 126, connected in series with each other, .are connected to cathodes 120 and 122 and to grid 123 in the manner illustrated.

The elements of photocell 117 and glow tube 118 are reversely connected with respect to the connections of the elements of photocell 117 and glow tube 118. By reversely connecting these elements, the potential on grid 123 will be negative so long as the intensity of the light impinging on photocell 117 is above a predetermined value. but positive'when the intensity of the light falls below this value. Therefore when the intensity of the light impinging on photocells 117 and 117 is above a predetermined value, current flows in the plate circuit of glow tube 118, but no current flows in the plate circuit of glow tube 118. If the intensity of the light is below this value, current flows in the plate circuit of glow tube 118, but does not flow in the plate circuit of glow tube 118.

The plate circuit currents of glow tubes 118 and 118 are utilized to energize relays 128 and 128. These relays control the op eration of the apparatus illustrated at 75.

Relays 128 and 128 comprise coils 129, 129, respectively, movable armatures 130, 130, respectively, stationary contact members 131-432 and 131'132, respectively, and bridging contact members 133 and 133', respectively, the bridging members being carried by said armatures.

Coils 129 and 129 of the above-mentioned relays may be connected in series to cathodes 120' and 122 of photocell 117 and glow tube 118, and to the common point of connection of cathode 122 to resistor 126 of glow tube 118. The junction point between condenser 125' and plate 121' of glow tube 118' is con- ,nected by a conductor 13A to plates or anodes 119 and 121 of photocell 117 and glow tube 118, respectively.

As a means for energizing light sensitive devices 115 and 116, and thereby to cause currents of electricity to flow in the abovementioned plate circuits of glow tubes 11S and 118', an alternating current step-up transformer 136 is provided. Transformer 136 comprises a primary winding 137 connected to a source of alternating voltage, and a secondary winding 138. One side of secondary winding 138 is connected by a conductor 139 to the point of common connection of relay coils 129 and 129' and the other side thereof is connected to conductor 134. Thus, light sensitive devices 115 and 116 are connected across the secondary winding of the transformer, the coils of relays 128 and 128' being connected in series with the output Cll'r cuits of glow tubes 118 and 118', respectively.

Light sensitive devices 115 and 116, being connected as described above to transformer 136, device 115 acts as a half-wave rectifier, when the intensity of the light impinging on photocell 117 is below a predetermined value, and supplies current to coil 129 of relay 128; and device 116 acts as a half-wave rectifier when the light intensity is above said predetermined value to deliver current to coil 129 of relay 128'. It will, therefore, be apparent that as the light intensity impinging .on photocells 117 and 117 varies below and are utilized to initiate and control blow-down valve modifying apparatus indicated at 75 as will be set forth more fully hereinafter.

Apparatus 75 comprises a pressure sending device 140 similar to sending device 24, hence similar elements or parts are designated by the same reference characters. Multi-way valve 32 of sending device 140 is actuated by floating lever 34 whereby pressure variations are set up within bellows 30. These pressure variations are communicated to the interior of bellows 43 of actuating device 39, through a pipe line 141.

The necessary movements of floating lever 34 required to effect these pressure variations in bellows 43 are obtained by means of a cam 142 upon which a pin 143, secured to the right-hand end of lever 34, rests. A spring 143 urges lever 34 and its pin towards the cam, whereby, as the cam turns, the pin follows the contour of the cam surface. As the pin follows the cam surface, lever 34 is rocked to thereby actuate the valve 32 in the manner required to obtain the necessary pressure variations in bellows 43.

As illustrated, the form of cam 142 is that of a circular disc mounted eccentrically on a shaft 144 to which it is secured by a key or other suitable means. Shaft 144 carries a friction wheel or disc 145 which is secured thereto by a key or other suitable means. By turning the disc, the cam may be turned either clockwise or counter-clockwise as the case may be.

Clockwise turning of the wheel and cam pivotally supported between its inner and outer ends on a lever 147, the inner end of the latter being loosely mounted on shaft 144. The outer end of pawl 146 is connected by a link 148 to an armature 149. Armature 149 is arranged for upward movement by a solenoid 150 which is under the control of relay 128 and hence under the control of light sensitive device 115.

When solenoid 150 is energized, link 148 is pulled upwardly by the armature. During the initial upward movement of link 148,

the inner end of pawl 146 grips the friction wheel 145 so that, when the armature has completed its stroke, the cam will have advanced clockwise a predetermined distance. When solenoid 150 is deenergized, lever 147 and pawl 146 drop by gravity, and the pawl is released from the friction wheel. Upon reenergization of solenoid 150, the pawl again grips the friction wheel and advances it in a clockwise direction a predetermined distance, and will advance such amount,'in a clockwise direction, each time solenoid 150 is energized.

As the cam turns clockwise, lever 34, of sending device 140 is turned clockwise thereby about the upper end of push rod 33 whereby valve 32 is shifted to that position in which the pressure of the fluid in bellows 30 and bellows 43 is reduced. After each such operation of valve 32, it is returned to neutral position by the bellows; therefore, if cam 142 is advanced clockwise stepby-step, the pressure in bellows 30 and bellows 43 will be reduced step-by-step.

If the pressure in bellows 30 and 43 is i being reduced Step-by-step, regulator motor 41 responds and opens blow-down valve 38 step-by-step until the amount of water discharged from the boiler, as blow-down, has

been increased to that value at which the concentration of the boiler water is at the permissible operating degree of concentration.

Counter-clockwise turning of cam 142 has the opposite effect on sending device 140 and pressure responsive actuating device 40. When the cam is turning or advancing in a counter-clockwise direction, valve 32 of device 140 is being opened to admit air or motive fluid under pressure from the source of supply to the interior of bellows 30 and bellows 43. Thepressure increase in bellows 43 causes regulator motor 41 to close valve 38 to=decrease the amount of water discharged frolnthe boiler as blow-down. Cam 142 ceases to turn counter-clockwise when the concentration of the boiler water has been increased to the permissible operatin g value. I

Cam 142 is turned counter-clockwise stepby-step by means of a solenoid 152 and armature 149, link 148, pawl 146' and lever 147; these elements being identical to those described for turning the cam clockwise, and operating in the same manner, except that pawl 146 operates on the opposite side of friction wheel from that on which pawl 146 operates.

Solenoid 152 is under the control of light sensitive device 116 and is energized intermittently when relay128' is closed thereby advancing cam 142 step-by-step in a counterclockwise direction.

The amount that cam 140 is advanced each time one or the other of solenoids 150, 152 are energized may be controlled by adjustable stops 153 upon which the pawls and levers rest when the solenoids are deenergized.

Since each of relays 128 and 128 is energized and remains closed so long as the particular light sensitive device to 'whichit belongs passes current, an interrupter 155 is empfoyed to make and break the circuits to solenoids 150 and 152 at definite recurring intervals The interrupter, therefore, causes these solenoids to effect the step-by-step movements of cam 142 and the friction wheel 145.

As illustrated one side or terminal of solenoid 150 is connected. to contact member 131 of relay 128, and one terminal of solenoid 152 is connected to re ay contact member its 132', the other terminals ofthe solenoids being connected together by a conductor 156 to one side of interrupter 155. The other side of the interrupter is connected to one side of the power supply line to which the transformer is connected. Relay contact'members 132 and 131 are connected by a common conductor 156 to the otherside of the power supply line. Thus, the energizing circuits for solenoids 150 and 152 have been identified. Interrupter 155 may be of any form suitable for the purpose. As illustrated, it comprises a metal disc 157 having diametrically opposed inserts 158 of insulating material in its periphery. Brushes 159 contact with the periphery of the disc. The disc may be driven by a motor 160 operating through reduction gears 161.

If interrupter disc 157 is driven at a definite speed and relay 128 is closed, solenoid 150 will be alternately energized and deenergized. Similarly solenoid 152 will be alternately energized and deenergized if relay 128 is closed.

From the above description it will be apparent that the concentration of the boiler water sample is continuously determined or analyzed in cell or container 76. The result of the analysis of the boiler water sample, as determined in cell 76, is indicated by the amount of light dispersed by the suspension therein. The intensity of the light dispersed is utilized to energize light sensitive devices 115 and 116, which, in turn, control the operation of pressure sending device 140. The pressure sending device sets up pressure variations in bellows 43 of regulator 39. In response to these pressure variations, the regulator causes blow-down valve 38 to open, if the concentration of the boiler water is too high, or to close, if the concentration is too low.

However, if the concentration of the boiler Water does not vary from that which is permissible in boiler operations, the blow-down valve is controlled directly by the feed-water regulating means; but if the concentration of the boiler water varies, then the blow-down valve is adjusted in accordance with the analysis of the boiler water as determined by cell 76, to either increase or decrease the amount of water discharged as blow-down in the manner set forth above.

The operation of cell 76 and the light sensitive devices associated therewith and the flexibility which is afforded thereby in controlling the blow-down of a boiler is graphically illustrated in Fig. 6.

In Fig. 6, the relation between the turbidity of the suspension in cell 76 to the concentration of the boiler water, and the intensity of the light dispersed therefrom, is illustrated graphically.

In this figure curve 162 represents the relation between the turbidity of the suspension and the concentration of the boiler water, for a given amount of clear miscible liquid flowing into cell 76 from adjustable head tank 95. Curve 163 illustrates the relation between the turbidity of the suspension and the intensity of the light dispersed therefrom. The point of intersection, as A, of curves 162 and 163 may, for purposes of illustration, be taken as the normal operating point; that is, when the suspension is of that degree of turbidity corresponding to point A, the intensity of the light dispersed by the suspension will be of that value at which neither of the light sensitive devices passes current. The concentration of the boiler water is, therefore, at the permissible operating value.

If the concentration of the boiler water increases, the turbidity of the suspension increases, hence the intensity of the light dispersed by the suspension decreases. When the intensity of the light is decreasing from point A, light sensitive device 115 functions to effect, through solenoid 150, clockwise turning of cam142. As set forth previously herein, clockwise turning of the cam results in an increase in the amount of water discharged from the boiler as blowdown. It is, therefore, obvious that if the amount of concentrated boiler-Water discharged from the boiler is increased and the amount so discharged is replaced by relatively dilute feed water, the boiler Water will be diluted and its concentration reduced. As the concentration of the boiler water decreases, the turbidity of the suspension decreases, wherefore the intensity of the light dispersed thereby increases. When the intensity of the light increases to that value indicated by point A on the curve, light sensitive device 116 ceases to pass current, thereby preventing further energization of solenoid 150.

If the concentration of the boiler water and the turbidity of the suspension continue to decrease, the intensity of the light dispersed by the suspension increases. As long as the intensity of the light increases above that value represented by point A on the curve 163, light sensitive device 116 passes current and effects operation of cam operat ing solenoid 152 whereby counter-clockwise turning of the cam is effected. Counterclockwise turning of the cam results in a closing of blow-down Valve 38 and a reduction in the amount of water discharged from the boiler, as blow-down.

It will be apparent by inspection of Fig. 6 that when the turbidity of the suspension and the concentration of the boiler water remains constant, at the value A for example, the amount of water discharged from the boiler, as blow-down, will be governed entirely by the feed water regulator 6 and the prelslsure sending device 24 associated therewit As stated hereinbefore, variable head tank 95 may, by moving outlet spout 101 up or down, be utilized to vary the amount of clear, miscible liquid delivered to the suspension cell 76. Hence by varying the amount of such liquid delivered to the suspension cell, the turbidity of the suspension, fora fixed degree of concentration of boiler Water, may

be varied. For example, if it is desired to operate the boiler on Water having a higher percentage of concentration than that corresponding to point A on curve 162, outlet spout 101 is raised until the relation between the turbidity of the suspension and the concentration of the boiler Water is that represented by'curve 164. \Vhen such a relation obtains between the turbidity of suspension and concentration of boiler water, light sensitive device 116 will operate or function in the manner hereinbefore described to effect a reduction in the amount of water discharged from the boiler until the boiler Water concentration has been increased to that value represented by point B. The moment the concentration of the boiler water-increases beyond this value, light sensitive device 115 functions to effect an increase in the amount of water discharged from the boiler as blowdown. I

If it is desired to operate the boiler at a relatively low degree of concentration, ad-

' justable spout 101 may be lowered, thereby decreasing the amount of clear, miscible liquid delivered to the suspension cell 76, until the relation between the turbidity of the suspension and the concentration of the boiler water is that represented by curve 165. When operating on curve 165, a larger amount of water will be admitted to the boiler and a correspondingly larger amount of Water will be discharged, as blow-down, in order to maintain the concentration of the boiler water below that which obtains when operating on curves 162 and 164.

From the foregoing description, it will be apparent that the system herein disclosed operates to regulate the amount of feed water admitted to a boiler by and in accordance with the-demand therefor; to regulate the amount of water discharged from the boiler, as blow-down, by and in accordance with the amount of water delivered to the boiler; and to control the amount of water discharged, as blow-down, by and in accord- I ance with the concentration of the boiler water as affected by precipitate forming materials, such as soluble sulphates. Y

The system disclosed is flexible in that the concentration'of the boiler water is directly under the control of the operator and may be varied to suit operating requirements and conditions.

While but one embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that various changes placed on the invention as are imposed byv the prior art and the appended claims.

What We claim as new and desire to secure by Letters Patent is:

1. The method of continuously determining the concentration of suspension that con- 'sists in varying the turbidity thereof by continuously diluting a constant volume flow of the suspension with a clear, miscible liquid, viewing a luminous object through a predetermined thickness of the difuted suspension, and continuously measuring the visibility of said object whereby the concentration of said suspension may be continuously determined.

2. The method of controlling the concentration of precipitate forming materials in a moving body of liquid that comprises continuously forming a suspension of a sample of said moving liquid, continuously diluting the suspension with a clear, miscible liquid, viewing a luminous object through a predetermined thickness of said suspension, .measur ing the visibility of said ObJGCt, and then in discharging liquid from said body of moving liquid in accordance with said measurements of visibility.

3. The method of controlling the concentration of precipitate forming materials in tity of body liquid to form asuspension, di-

luting said suspension with a clear, miscible liquid, viewing a luminous object through a predetermined thickness of said suspension, and then in varying the amount of body liquid discharged in accordance with variations in the visibility of said luminous object.

4. The method of regulating the amount of water discharged from a boiler as blowdown that consists in running a continuous sample of boiler water into a container, continuously adding a reagent to precipitate the sulphates as a suspension, continuously diluting the suspension so formed with a constant flow of clear, miscible liquid, viewing a luminous object through a predetermined thickness of said suspension, measuring variations in the intensity of the luminosity of said object as observed through said thickness of the suspension, and then in regulating the amount of Water discharged as blow-down in accordance with variations in the luminosity of said object.

5. In combination, a boiler, means for supplying feed water to the boiler by and in accordance with variations in the boiler water level, means for discharging Water from the boiler as blow-down, means for continuously forming a suspension from a portion of the boiler water, means for measuring the concentration of said suspension, and means responsive conjointly to the amount of feed water delivered to the boiler and to the concentration measuring means for regulating the amount of water discharged as blowdown.

6. Apparatus for determining the concentration of a liquid having precipitate fenning materials therein comprising a container having transparent portions so arranged that beams of light may be passed therethrough, means for delivering a flowing measured quantity of said liquid to the container, means for delivering a flowing measured quantity of reagent to the container thereby to form a suspension therein, means for delivering a flowing measured quantity of clear, miscible liquid to said suspension, light sensitive electro-active means disposed V in the path of light beams dispersed by the suspension, and means for measuring the response of said electro-active means to variations in the intensity of the light beams so dispersed.

7. In combination, a cell having alined transparent portions in opposite walls thereof, means for delivering flowing measured quantities of liquid having precipitate forming materials therein and reagent to said cell to thereby form a turbid suspension therein, means for delivering a flowing measured quantity of clear, miscible liquid to the suspension thereby to vary the turbidity of the suspension as the concentration of said liquid varies, a light source adjacent one of said transparent portions, a light sensitive electro-active device adjacent the other of said transparent portions, whereby said electro-active device is affected bynvariations in the light dispersed by the suspension and means responsive to variations in the activity of said electro-active device arranged to measure the concentration of said liquid in terms of the variations produced in said electro-active device.

48. In combination, a boiler, means for delivering feed water to the boiler, means responsive to the water level of the boiler for controlling the amount of feed water delivered, means for discharging water from the boiler as blow-down in accordance with the amount of feed water delivered thereto, means for forming a turbid suspension from a continuous sample of the boiler water, and

means responsive to variations in the tur-- bidity of the suspension for modifying the amount of water discharged from the boiler as blow-down.

9. The combination with a boiler having a supply of feed water therefor, and means for discharging water from the boiler as blow-down, of means for forming a suspension of varying turbidity from a portion of the boiler water, means for passing a beam of light through said turbid suspension, a light sensitive electro-active device, a source of electromotive force applied thereto, said device being disposed to pass electric current when the intensity of the light is above a predetermined value, means controlledby said device arranged to operate said boiler water discharge means to thereby reduce the amount of water discharged, a second light sensitive electro-active device having connections to said source of electromotive force, said second device being disposed to pass electric current when the intensity of the light dispersed is below said predetermined value and means controlled by the current so passed arranged to operate said boiler water discharge means to increase the amount of water discharged as blow-down.

10. The combination with a boiler having means for discharging water therefrom as blow-down, means for forming a suspension of'said boiler water, the turbidity of which varies with the concentration of the boiler water, and means for passing beams of light through said suspension, of two electron-discharge devices each having an anode, cathode and grid therein, electrical devices in the output circuits of said devices, and light sensitive electro-active means for varying the grid potential of said electron-discharge devices in accordance with variations in the turbidity of said suspension, to thereby effect operation of said electrical devices, and means controlled by said, electrical devices for operating said water discharge means.

11. In combination, a suspension forming device adapted to receivea constant fiow of boiler water having precipitate forming materials therein, means for passing a beam of light through a predetermined thickness of the suspension formed in said device, an electron discharge device having an anode, a cathode and a grid therein, a light sensitive electro-active device disposed in the path of light dispersed from said suspension forming device, said electro-active device having an anode and a cathode in circuit with the grid of said discharge device, said electroactive device being disposed to render said grid positive When the intensity of said dispersed light is above apredetermined value, a source of alternating current for said electro-active and electron-discharge devices, another electron-discharge device having an anode, a cathodeand a grid therein, another light sensitive electro-active device having an anode and cathode in circuit with the to the light dispersed from said suspension formin device and arranged to render the grid 0 said last mentioned electron-discharge device negative when the intensity of the light dispersed is above a predetermined value and positive when the intensity of said light is below a predetermined value, and electric control devices disposed in the output circuits of said electron-discharge devices, said control devices being adapted to control apparatus associated with said boiler arranged to discharge water therefrom as blow-down, one of said control devices being operative to efiect an increase in the amount of water discharged as blow-down and the other of said devices being disposed to, effect a decrease in the amount of water discharged as blow-down.

12. The method oicontrolling the con- 4 centration of precipitate forming materials in a body of liquid that comprises adding liquid to. said body, substantially continuously sampling the-liquid of said body and forming a suspension thereof, continuously diluting the suspenslon with a clear, miscible liquid, measuring the' visibility of a luminous object through a predetermined

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