Patent Publication Number: US-3880964-A

Title: Hot water supply and distribution structure for cooling towers

Description:
United States Patent 1 1 Fordyce et al.  
 [ Apr. 29, 1975 1 1 HOT WATER SUPPLY AND DISTRIBUTION STRUCTURE FOR COOLING TOWERS [73] Assignee: The Marley Company. Mission.  
 Kans.  
 [22] Filed: Sept. 5. 1972 [21] Appl. No.: 286.341  
  US. Cl ..26l/ll1:261/D1G. ll Int. Cl BOlf 3/04 [58] Field of Search 26l/D1G. 11. 110. 111. 261/66. 67. 71. 113. 91  
 156] References Cited UNITED STATES PATENTS 1.987.097 1/1935 Coubrough 261/113 2.512.271 6/1950 Green 261/111 2.517.639 8/1950 De Flon 261/110 X 2.558.222 6/1951 Parkinson 261/113 3.115.534 12/1963 Bottner 261/1 10 X 3.243.166 3/1966 Osenga et al. 261/D1G. 11 3.265.122 8/1966 Ostrander 26l/D1G. l1  
 3.322.409 5/1967 Rccd 261/111 X 3.498.590 3/1970 Furlong 261/111 3.606.984 9/1971 Robertson 261/91 Prinmr Examiner-Tim R. Miles Assislunl E.\&#39;aminerRichard L. Chiesa Attorney. Agent, or FirmSchmidt. Johnson. Hovey &amp; Williams 57] ABSTRACT A crossflow cooling tower having fireproof liquid supply means including a riser opening directly into an overhead flume located inwardly of and adjacent to a hot water distributor for supplying hot liquid to be cooled to the latter. A liquid stilling chamber is provided between the riser and flume to prevent nonuniform, turbulent liquid delivery to the distributor. A horizontal conduit which is norinally submerged in the hot liquid delivers liquid from the inlet flume to an outer section of the distributor to permit variation of the water delivery pattern to the fill assembly for temperature control purposes to deice the fill assembly during below freezing operation. Valve means actuated by a pneumatically expansible baffle variably restricts flow through the conduit, and the resilient nature of the baffle facilitates breakup of any ice which may tend to form thereon. A shiftable gate-controlled opening in the stilling chamber allows the operator to bypass the hot liquid around the fill assembly without cavitating the liquid power supply means.  
 6 Claims, 10 Drawing Figures EATENTEHPRZSEB 0,954  
 saw m 3 I HOT WATER SUPPLY AND DISTRIBUTION STRUCTURE FOR COOLING TOWERS This invention relates to liquid cooling towers and relates more specifically to improved hot liquid supply means therefor.  
  Liquid cooling towers generally include a hot liquid distributor in the form of a distribution basin that overlies a fill assembly through which the liquid graviates in intimate, evaporative heat exchange relationship with a cooling airflow passing through the fill assembly. The cooled liquid is collected in an underlying basin and returned to be utilized in, for instance, a power plant from where the liquid is pumped back to be recycled through the cooling tower. Cooling towers of the class described may employ natural draft techniques for creating a crossflow movement of cooling air through the fill assembly such as by utilization of a hyperbolic stack wherein the fill assembly is placed circumferentially around the lower portion of the stack. Also an induced draft of cooling air may be created by incorporating fans for drawing airflow through the fill assembly.  
  Heretofore. cooling towers have necessarily required substantial lengths of large diameter piping for supplying the liquid to the distribution basin in flow patterns assuring liquid delivery to all portions of the basin for efficient cooling tower operation. Particularly in larger sized cooling towers such as those capable of handling flow rates upwards of hundreds of thousands of gallons per minute or more, such supply piping is extremely expensive in initial construction and is difficult and expensive to assemble in place in the tower in the normal liquid delivery disposition thereof. Most efficient cooling operation occurs when liquid is delivered uniformly to the overhead distribution basin throughout the entire length thereof, thereby necessarily requiring equivalent lengths of horizontal feeder piping extending generally parallel to the distributor. Furthermore, conventional piping has also been utilized for riser structure carrying liquid to the elevated, horizontal feeder pipes. In many instances where high volume flow rates are encountered, a plurality of risers must be incorporated to deliver liquid to separate sections of the horizontal feeder piping.  
  Preferably, the supply piping is formed of noncombustible, noncorrosive material. While it has been known to construct such piping of suitable wood material such as redwood, it has been found that wooden components are undesirable, particularly where very large cooling towers are involved; because the use of wood presents a fire hazard as well as expensive construction and continual maintenance problems. Furthermore, the relatively massive nature of such piping presents serious problems of installation.  
  It has been conventional practice, especially in crossflow type cooling towers, to locate the riser exteriorly of the fill assembly, thereby requiring more piping to deliver liquid horizontally into the feeder piping. Attempts to utilize open-top inlet flume&#39;s in place of the feeder piping have heretofore been unacceptable in practice as the large flow volumes have created excessive boiling of the liquid in the flume and consequent nonuniform liquid delivery into the distribution basin. The need is apparent, therefore, to provide an alternate, economically acceptable. flreproff arrangement for supplying liquid to the overhead distribution basin which utilizes a minimum amount of liquid supply pip- It is desirable in many instances that the water loading on different portions of the fill assembly be selectively varied in relation to different ambient temperatures and other climatic factors to assure optimum tower performance. For instance, it is desirable to increase the water loading at the outer section of the fill assembly adjacent the air inlet thereto during below freezing operation to preclude icing of the air inlet louvers which would otherwise greatly restrict airflow through the fill assembly. One successful answer to this problem is taught in U.S. Pat. No. 3,322,409, owned by the assignee hereof, wherein the overhead distribution basin includes a pair of separate sections overlying inner and outer portions of the fill assembly. Piping delivers liquid along separate paths to these two sections of the distribution basin, and control valve means interposed in the supply pipes allow selective variation of flow to respective sections of the basin. However, this arrangement still necessarily includes a considerable amount of expensive supply piping. The piping which carries liquid to the outer section of the distribution basin usually carries a less than full water load except on occasions when substantially the entire liquid flow is diverted therethrough to the outer section to deice the air inlet louvers of the fill assembly. Also, such piping can freeze-up during low water loading under extremely low temperature. An associated problem is the tendency of the actuating mechanism of the valve which controls flow to the outer section of the distribution basin, to collect ice and freeze solid. Necessarily this actuating mechanism is disposed above the distribution basin in a location exposed to an atmosphere of cold, fine water spray tending to ice the mechanism. When frozen solid of course, malfunction occurs with consequent loss of control of the liquid flow to the outer distribution basin which may ultimately require shutdown of at least certain portions of the .cooling tower during cold weather for deicing.  
  In many instances of operation of a power plant utilizing the liquid being cooled by such a cooling tower, it is desirable to cool the liquid only to a certain level before return thereof to the power plant. For example, when starting up large turbines of a power plant wherein the turbines must be brought to a certain temperature before efficient operation occurs, it is necessary to continually recirculate hot liquid through the turbines. Underground piping carries liquid back and forth from the tower to the plant, and it has been con-. ventional practice to include additional bypass piping, also usually located underground, extending between the supply piping and return piping. Remotely operated control valves selectively control flow of hot water through this bypass piping so that the liquid may be returned to the plant in its fully heated condition without passing through the cooling tower. A problem associated with such bypass arrangement is the tendency to form cavitation conditions at the inlet liquid circulating pump when the cooling tower is being bypassed. Loss of back pressure usually occurs when the liquid is by passing the cooling tower, causing liquid starvation and erosion of the pump by cavitation. Furthermore, the additional bypass piping and remotely operated control valves add to the cost of the cooling tower installation.  
  It is, therefore, the primary object of the present invention to provide a cooling tower which utilizes a minimum amount of expensive piping for supplying liquid thereto, while at the same time allowing variable hot liquid delivery to the tower in flow patterns assuring most efficient cooling operation thereof.  
  An important object of the invention is to provide a cooling tower wherein the utilization of expensive, overhead, horizontal feeder piping for delivering liquid to the distribution basin is substantially avoided without sacrifice of uniform supply of the liquid to the basin along substantially the entire length thereof for efficient tower operation.  
  A corollary aim of the invention is to provide an open top inlet flume in place of conventional feeder piping, wherein the flume is comprised of a plurality of prefabricated components that may be precast at ground level in any desired configuration and which are of a size permitting handling thereof by conventional construction lifting equipment, thereby providing an inlet flume which may be efficiently and economically assembled at far less expence in construction than heretofore using other forms of liquid supply apparatus.  
  Another object of the invention is to provide a prefabricated liquid supply riser of inexpensive design and construction which delivers liquid to the flume, wherein both the riser and the flume components are precast out of noncombustible material so that the entire liquid supply means of the cooling tower is fireresistant.  
  Another important object is to provide a supply riser that is located directly underneath the flume for delivering liquid generally vertically thereinto to eliminate overhead horizontal supply piping, as well as to permit the riser to be configured as desired since it simply opens into the bottom of the trough&#39;like flume instead of being connected in sealed relationship with circular feeder pipes, thereby allowing use oflarger risers which are less expensive, yet capable of handling greater flow rates than conventional pipe-type risers and attendantly reducing the number of risers required.  
  Another object is to provide such an arrangement wherein the inlet flume and supply riser are sufficiently massive to remain in place on the tower without being rigidly attached or fastened thereto.  
  A further object is to provide a cooling tower wherein liquid is delivered from the riser vertically into an inlet port in the flume without causing boiling of liquid in the flume which would otherwise create excess liquid flow into portions of the distributor proximal to the inlet port, thus assuring substantially uniform liquid flow into all portions of the distributor. A more particular object is to provide simple, inexpensive means for preventing such boiling of the liquid in the form of a liquid-stilling chamber located between the riser and the flume which substantially reduces the vertical velocity of the liquid prior to its introduction into the flume.  
  A further object is to provide a cover overlying portions of the flume proximal to the inlet port for assisting in reducing the vertical velocity of the liquid at conditions of maximum or near maximum inlet flow rates, so that the stilling chamber may be of smaller dimensions effective to adequately reduce the liquid vertical velocity at normal flow rates, without creating excessive boiling at maximum flow rate conditions.  
  Another important object of the invention is to provide a cooling tower which utilizes an inlet flume and supply riser as characterized in the foregoing objects which are arranged to supply liquid in various proportions to separate inner and outer sections of the distribution basin to permit optimum, efficient operation of the cooling tower under markedly varied climatic enviroments and under different operational conditions.  
  Another very important object of the invention is to provide a cooling tower having supply means for directing liquid in various proportions along separate paths to two independent sections of a distribution basin overlying inner and outer portions of the fill assembly respectively so that liquid loading on the outer portion of the fill assembly may be selectively varied to permit operation of the tower at optimum efficiency throughout a variety of climatic and operational conditions. Hot liquid flows from the supply means to the outer section of the basin through a conduit which is submerged in liquid collected in the inner section of the basin.  
  Another important object of the invention is to provide a liquid cooling tower wherein liquid flow may bypass the fill assembly without cavitating the pump which is delivering liquid to the cooling tower.  
  Another object of the invention is to provide a cooling tower wherein liquid may be bypassed around the fill assembly without the use of heretofore required expensive underground bypass piping and remotely operated valve means configured to control flow through the bypass piping.  
  A more particular object is to provide a riser for sup plying liquid to a distribution basin overlying the fill assembly, wherein the riser has an opening through which liquid may gravitate directly back to the underlying collecting basin in bypassing relationship to the fill assembly without flowing through additional bypass piping.  
  Another object is to provide such a bypass opening which is disposed at a height to maintain positive back pressure in the riser to prevent liquid starvation and consequent formation of cavitation conditions at the supply pump while the fill assembly is being wholly or partially bypassed.  
  Yet another object is to provide a riser, flume and stilling chamber arrangement as set forth above wherein the bypass opening is located in the stilling chamber to assure complete liquid bypass of the distribution basin and fill assembly even at high inlet flow rate conditions.  
  Another particular object of the invention is to provide economical, dependable valving for controlling flow through the bypass opening in the form of a gate that is vertically shiftable to variably close the opening so that the drive means for operating the gate may be disposed at an easily accessible location above the distribution basin.  
  Another important object of the invention is to provide improved valve means for controlling flow through a conduit supplying liquid to a cooling tower, wherein the valve means has a reliable actuating mechanism that is not subject to malfunction by freezing even though exposed to an atmosphere of cold liquid spray tending to ice the mechanism. Another object is to provide an actuating mechanism including a resilient actuator which flexes during operation to readily breakup films of ice thereon each time it is operated to preclude malfunction due to freezing. A more particular object is to provide such an actuating mechanism in the form ofa pneumatically expansible bladder of resilient material which expands and contacts to actuate the flow control valve, wherein the resilient nature of the bladder facilitates easy breakup of icing thereon every time the bladder expands and contracts.  
  These and other objects and advantages of the present invention are specifically set forth or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings, wherein:  
  FIG. 1 is an elevational view ofa natural draft cooling tower embodying the present invention with the left half of the tower being in cross section to reveal internal construction;  
  FIG. 2 is a top plan view of the tower illustrated in FIG. 1&#39;.  
  FIG. 3 is an elevational, cross-sectional view of the fill assembly portion of the tower and showing the liquid supply means;  
  FIG. 4 is a cross section as viewed along lines 4-4 of FIG. 3;  
  FIG. 5 is a partial elevational, cross section similar to FIG. 3 and showing operation of the liquid supply means during deicing of the air inlet louvers of the tower;  
  FIG. 6 is an enlarged. fragmentary. perspective view of the common sidewall between the inlet flume and the distribution basin;  
  FIG. 7 is a partial top plan view of the arrangement shown in FIG. 3 with portions broken away to reveal details of construction;  
  FIG. 8 is a front elevational view of the valve controlling flow to the outer distribution basin;  
  FIG. 9 is a side elevational view of the valve shown in FIG. 8 with portions broken away for clarity; and  
  FIG. 10 is a top elevational view of the valve shown in FIG. 8.  
  Referring now more particularly to FIGS. l7, a crossflow type natural draft water cooling tower is broadly designated by the numeral and includes a circular shell foundation 22 located below ground level 24. A series of inclined support columns 26 carry an upright, hyperbolic reinforced concrete shell 28 in supporting relationship upon the foundation. The shell has an air outlet 30 at its upper end and a lower circular margin 32 is spaced from ground level to define an air inlet around the entire circumference of the shell. The configuration of shell 28 creates a natural draft of airflow horizontally through this air inlet, and defines an exhaust path for exhausting this airflow generally vertically out of air oulet 30.  
  An annular, concrete, cold water collection basin 34 surrounds shell 28 and serves to support framework, broadly referred to as 36. which carries a series of crossflow fill assemblies 38 in overlying relationship to collection basin 34. The fill assembly may comprise, for instance. a plurality of noncombustible, horizontal splash bars 40 of corrugated configuration carried by vertical, noncombustible support grids 42. At the outer peripheral margin 41 of the fill assembly which is sloped inwardly because of the tendency of water gravitating through the fill assembly to draw back in the direction of airflow, there is provided a series of relatively wide, horizontal air inlet louvers 44 through which air is drawn generally horizontally through the fill assembly in crossflow relationship to water gravitating vertically downwardly through the latter. The louvers 44 are inclined in the direction of airflow through the fill assembly and are positioned in vertically staggered relationship with the lowermost margin of each louver located above an area of the louver there next below intermediate the longitudinal margins of the latter. A suitable ring of drift eliminators 48 is located at the inner side of the fill assembly 38 to promote removal of carrry-over or drift of liquid in the airflow prior to being discharged vertically out of shell 28. A curb wall 46 at the outer peripheral margin of collection basin 34 facilitates collection of liquid therein for subsequent exhaust through return piping (not shown).  
  Overlying fill assembly 38 is a hot liquid distributor generally designated by the numeral that comprises a plurality of precast, radical segments which are of a size facilitating lifting thereof by construction equiqment for emplacement above the fill assembly in an annular ring around the circumference thereof. Each of these distributor components includes a plurality of floor panels 62 having orifices 64 therein adapted to receive metering nozzles which distribute liquid uniformly across the till assembly. The distributor has an inner wall 66 of greater height than its outer wall 68, and a third wall 70 of a height than its outer wall 68, and a third wall 70 of a height intermediate that of the inner and outer walls. Wall 70 divides the distributor into inner and outer liquid collecting and distribution basings 72 and 74 which respectively overlie inner and outer portions of fill assembly 38, the outer portion being located closer to the outer peripheral margin 41 than the inner portion. The lowermost outer wall 68 is located adjacent outer peripheral margin 41 of the assembly so that liquid overflowing wall 68 will cascade down air inlet louvers 44. Each of the basins 72 and 74 extend circumferentially around the fill assembly, and a vertical partition 76 is included at a location diametrically opposite riser 56, as best illustrated in FIG. 2.  
  The liquid supply means generally includes a horizontal, buried inlet pipe 50 having a right-angle elbow section 52 at one end thereof which opens upwardly at a location inside the outer peripheral margins of the collection basin 34 and fill assembly 38. A concrete block 54 cast around elbow 52 absorbs inclined thrust exerted upon the elbow by liquid flowing therethrough. A large diameter, precase concrete riser 56 (shown as being octagonal although it may be of any crosssectional shape) rests atop elbow 52 and extends vertically upwardly toward the upper proximity of the fill assembly. An open top, liquid collection box 58 is positioned in stacked relationship upon riser 56 to communicate with the upper discharge end thereof. Box 58 is also preferably precast out of concrete material and is of a size having substantially greater transverse, crosssectional area than the transverse. cross-sectional area of the circular interior of riser 56.  
  Disposed directly above collection box 58 is a trough-like, open top inlet flume 78 which has an inlet port 79 in a bottom panel thereof providing liquid communication between the collection box and the flume. Flume 78 is located inboard of distributor 60 in relation to the flow of air therethrough, and is comprised of a plurality of precast concrete components disposed adjacent respective segments of the distributor to extend circumferentially around the fill assembly. The distributor inner wall 66 presents a common sidewall between flume 78 and the distributor 60. Preferably, wall 66 is provided with a plurality of depressions 80, at least one for each respective component of the distributor, so that liquid is delivered to the distributor along the entire length thereof simply by collecting in the flume to a level overflowing depressions 80. Uniform flow into all segments of the distributor is readily accomplished by locating depressions 80 at a uniform height. Inboard flume wall 82 is. of course, higher than depressions 80 to facilitate the collection of liquid in the flume to the overflow level to assure delivery therefrom throughout the length of the flume and distributor. If desired, vertically adjustable panels 84 at each depression 80 may be included so as to vary the effective height thereof.  
  A cover 86, as best seen in FIG. 7. may be included above the portions of flume 78 proximal to collection box 58 and riser 56. The cover may be coplanar with, and define a portion of a horizontal access walkway 88 that has a side handrail 90. A canopy 92 in the form of a series of precast concrete panels extends between the lower marginal edge of shell 28 and flume inner wall 82 to close the space therebetween and assure passage of air in crossflow relationship horizontally through the fill assembly into the lower portion of the shell.  
  Collection box 58 has a relatively wide. rectangular bypass opening 96 in the inboard vertical wall thereof facing away from the fill assembly. A rectangular platelike gate 98 blocks opening 96 in its closed position illustrated to prevent bypass flow through opening 96. Gate 98 has rollers at its opposite marginal edges which are shiftably received within vertical channels 100 secured to the inside of collection box 58, channels 100 acting as guides for gate 98 as it shifts vertically to allow flow through opening 96. A vertical screw shaft 102 is rotatably secured to gate 98 and extends upwardly therefrom to above walkway 88 wherein drive means 104 is secured to the upper end of the screw shaft 102. In the form illustrated, gate 98 is manually operated by rotation of a control handle 106 to actuate the drive means in raising and lowering the screw shaft and gate.  
  A series of conduits 94 extend across respective segments of the inner distribution basin 72 and through walls 66 and 70 to deliver hot liquid from flume 78 to the outer distribution basin 74. The conduits 94 are disposed at an elevation below depressions 80 and submerged within liquid collected in the inner distribution basin 72.  
  Valve means generally designated by the numeral 108 variably restricts the flow through conduit 94 to outer basin 74. As best seen in FIGS. 8-10, the valve means includes a plate 110 substantially traversing the interior of conduit 94 in a position allowing minimum flow therethrough. Plate 110 is secured for rotation with a transversely extending shaft 112 that is rotatably carried upon conduit 94 offset to one side of the center thereof. An actuator in the form ofa pneumatically expansible, annular bladder 114 formed of resilient material is mounted atop conduit 94 by a support which includes horizontally and vertically arranged plates I16 and 118. Bladder 114 is secured through a metal ring 120 to vertical plate 118 with a pressurized inlet port and conduit I22 in plate 118 communicating with the interior of bladder 114. The opposite side of bladder 114 is connected to linkage in the form of a longitudinal bar 124 and pivotal link 126 to an upper end of shaft 112 lying outside conduit 94. Link 126 is rigidly attached to shaft 112 and pivotally secured to bar 124 at point 128 so that longitudinal expansion and contracting of bladder 114 effects rotation of shaft I12 and plate 110 between the minimum flow position illustrated, and a position affording maximum flow through the conduit 94 wherein plate extends generally parallel to the longitudinal axis of the conduit as shown by phantom lines in FIG. 10. A crossbar 130 secured to bar I24 is guided upon a pair of spaced, vertical plates I32. Adjustable stop nuts I34 carried by the vertical plates 132 and crossbar 130 are respectively engageable with the crossbar and stop lugs 136 on the vertical plates for limiting the linear, longitudinal stroke of bladder 114. Nuts 134 are adjustable to vary the length of stroke of the bladder.  
  In operation, hot liquid is forced by high volume pumping means through the underground inlet pipe 50 and elbow 52 to flow vertically upwardly in riser 56 into collection box 58. The larger transverse, crosssectional area of box 58 in relation to the riser causes liquid to disperse in the box prior to flow into the flume so that the collection box 58 acts as a stilling chamber, causing substantial reduction in the vertical velocity of liquid delivered from riser 56. The height of box 58 assures that the vertical velocity of the liquid is reduced to an extent such that the liquid, upon consequently flowing into flume 78, spreads horizontally throughout inlet flume 78 without creating a boil of liquid in the flume at inlet 79 of greater height than the normal level of liquid collected in the flume. Without inclusion of collection box 58 to reduce the vertical velocity of the liquid, such liquid would boil upwardly to a higher than normal level in the portion of the flume proximal to its inlet port 79, to create an attendent excess flow into the adjacent portions of the distributor at the expense of reduced flow into the remote portions of the distributor. This nonuniform flow would accordingly reduce the efficiency of the tower in cooling the liquid.  
  The hot liquid distributes and collects along the entire length of flume 78 to the level overflowing the several depressions 80 in wall 66 to distribute uniformly throughout the entire peripheral length of inner distribution basin 72. As necessary, the panels 84 may be variably adjusted in height to assure uniform liquid distribution into basin 72. The hot liquid flows through oriflces 64 in the floor panels of the inner basin 72 to be distributed uniformly for gravitation through the underlying fill assembly 38. Normally, valve means 108 is in its minimal flow position allowing a certain preselected volume of flow into outer basin 74. Liquid subsequently gravitates uniformly through all portions of the fill assembly in intimate, evaporative heat exchange relationship with the path of cooler air passing in horizontal crossflow relationship to the liquid flow. The cooled liquid is collected in underlying basin 34 and returned to be recycled through the power plant being serviced by the cooling tower.  
  Accordingly, the supply means of the present invention delivers hot liquid to the overhead liquid distributor 60 in flow patterns assuring uniform flow through the entire fill assembly for most efficient cooling tower operation, and accomplishes this without inclusion of any overhead, horizontal feeder piping, and with the riser 56 located inwardly of the fill assembly in disposition to deliver liquid vertically into the inlet flume without creating boiling of liquid therein. The riser 56, collection box 58, flume 78 and distributor 60 are all precast concrete elements which are sufficiently massive in weight so as to remain in place upon the fill assembly framework 36 without being rigidly fastened thereto. Accordingly. assembly of the cooling tower is drastically simplified, requiring only that the several elements be lifted into place by construction equipment.  
  Preferably, collection box 58 is sized to cause the necessary reduction in liquid vertical velocity at normal liquid inlet flow rates. Upon occasions when larger than normal flow rates are being handled by the cooling tower, cover 86 is effective in assisting in reducing the vertical velocity of the liquid. In particular. the liquid entering the flume through inlet port 79 will impinge upon the lower face of cover 86 so that the latter acts as a baffle assisting in tending to spread the liquid uniformly horizontally throughout the flume. Preferably, therefore, cover 86 overlies the entire collection box 58 and portions of flume 78 proximal thereto, and is disposed with its lower surface located slightly above depression 80.  
  When it is desired that the liquid be returned to the power plant still in a heated condition, gate 98 may be shifted vertically upwardly to allow bypass hot liquid flow through opening 96 for gravitation directly back to the underlying collection basin 34 in bypassing relationship to the fill assembly 38. The elevated disposition of opening 96 assures maintenance of a positive back pressure upon riser 56 and inlet pipe 50 to preclude formation of cavitation conditions at the pumping means (not shown) which force the liquid to the cooling tower. Positioning of opening 96 in the wall of collection box 58 wherein the liquid collects and comes to a relatively calm condition prior to passage into inlet flume 78, assures substantially complete liquid bypass on the fill assembly. Without collection box 58, it will be apparent that portions of the liquid, even with gate 98 in its open position, would boil upwardly past opening 96 and ultimately into distributor 60. The arrangement of vertical gate 98 presents an economical bypass flow control valve with drive means 104 therefor disposed at an easily accessible location above the inlet flume at walkway 88.  
  During cold weather operation the external atmosphere around air inlet louvers 44 and above distributor 60 and flume 78 may be saturated with a fine spray of liquid that is capable of icing over air inlet louvers 44 to restrict the flow of air into the fill assembly. To deice louvers 44 when necessary, it is therefore desirable to fill outer basin 74 so that the hot liquid may overflow outer wall 68 and cascade along the louvers as depicted in FIG. 5. To accomplish this, the bladders 114 of the several valve means 108 may be pneumatically inflated to allow full liquid flow to the several conduits 94. If necessary, substantially the entire inlet liquid flow may pass through the several conduits 94 to fill basin 74 and cascade along louvers 44 to deice the same. By varying the pressure of air supplied to bladders 114, the latter can be inflated to the extent desired to locate plate H in positions intermediate its minimum and maximum flow position, thereby variably restricting flow through conduit 94 as desired. To reduce flow through a conduit 94, pressure in the associated bladder 114 is reduced, and the natural resiliency thereof causes contraction of the bladder and shifting of plate 110 to a more closed position.  
  The bladder actuator 114 is also exposed to a fine spray of cold liquid which tends to form a film ofice on the bladder. The resilient nature of bladder 114 allows it to be readily expanded when pneumatic pressure is applied thereto to break any ice film formed thereon. Upon relieving pneumatic pressure from the interior of bladder 114, the natural resiliency thereof causes the bladder to shift plate to a closed position, again readily breaking any films of ice formed on the bladder. Accordingly, films of ice collected upon the external surface of bladder 114 are broken up each time the bladder expands or contracts, thereby preventing the actuating mechanism from freezing solid. It is to be noted that plate 110 is disposed within conduit 94 so that the normal flow of liquid therethrough to outer basin 74, tends to move the plate to its minimum position so that the liquid flow through the conduit assists the natural resiliency of the bladder in closing the valve means.  
 I claim:  
  1. For use with a cross-flow cooling tower provided with a fill assembly having an air inlet face and an air outlet with inner and outer portions therebetween for serial passage of air therethrough:  
 horizontally adjacent, inner and outer hot liquid distribution basins defined by spaced inner and outer sidewalls and respectively overlying said inner and outer portions of the fill assembly for receiving and distributing hot liquid to be cooled to respective portions;  
 liquid supply means including an open-top, liquid collecting flume located inwardly of said inner distribution basin and having a common sidewall therewith for supplying liquid to said inner distribution basin when liquid collects in said flume to a level overflowing said common sidewall prior to subsequent gravitation of the liquid to said inner portion of the fill assembly; and  
 a conduit interconnecting said flume and outer distribution basin for delivery of fluid to the latter, said conduit being in communication with said flume at a level therein below the level at which liquid overflows said common sidewall, whereby liquid is uniformly delivered to said outer distribution basin during all liquid cooling operations of said tower.  
  2. A cooling tower as set forth in claim 1, wherein is provided valve means in said conduit for variably restricting flow therethrough to said outer distribution basin.  
  3. A cooling tower as set forth in claim 1, wherein said outer distribution basin has an outer sidewall of less height than said common sidewall, said conduit being of a size capable of delivering liquid to said outer distribution basin at a rate causing sufficient overflow thereof over said outer sidewall to impede collection of ice in blocking relationship to the air inlet opening.  
  4. A cooling tower as set forth in claim 3, wherein is provided a series of horizontal air inlet louvers located across said air inlet face of the fill assembly and positioned in vertically staggered relationship with the lowermost margin of each louver located above an area of the louver therebelow intermediate the longitudinal margins thereof, said series of louvers being inclined in the direction of airflow and the uppermost louver being located below said outer sidewall of the outer distribution basin whereby liquid overflowing said outer sidewall cascades down the series of louvers.  
  5. A cooling tower as set forth in claim 1, wherein said liquid supply means further includes a liquid collection box and a generally upright riser disposed in stacked relationship directly beneath said flume and registering therewith whereby liquid is delivered gener= ally upwardly from said riser through said collection box to said flume. said collection box being of a size 1 l 12 and configuration to reduce the vertical velocity of the ing an opening therein allowing escape of liquid from liquid prior to entry thereof into said flume to an extent i li id supply means f gravitation to id ll to allow su bstantially uniform distribution and collection basin in bypassing relationship to Said inner and non ofhquld throughout the length of smd flume&#39; outer distribution basins and the fill assembly, and  
  6. A cooling tower as set forth in claim 5, wherein is 5 provided a liquid collection basin underlying said collection box and the fill assembly for collecting liquid through Said p gravitating through the latter, said collection box huvwherein is provided means for controlling liquid flow