CA2046834A1 - Underdrain for liquid purification systems - Google Patents

Abstract

ABSTRACT

An underdrain lateral for a liquid purification system is described. The lateral has three chambers, a primary chamber, a compensating chamber, and gas chamber. Turbulence is minimized during cleansing of the purification media by isolating the gas from the liquid and the backwash liquid. This is accomplished by feeding gas into the gas chamber so that the chamber is occupied by gas only during cleansing. Orifices in the wall between the primary and compensating chambers and in the baffle between the compensating and gas chambers provide compensation for even distribution of liquid in the lateral.
The design also enables the use of cut outs in the gas chambers to equalize gas pressures and flow among the laterals and throughout the system bed and cut outs in the primary chambers to equalize liquid pressure and flow among the laterals and throughout the system bed. Nozzles with threaded stems having gas inlet orifices may be used and the levels of the entrances to the nozzles adjusted by rotating the stems to equalize backwash liquid flow among the nozzles. To minimize liquid pressure for greater gas flow during cleansing, an insert in the stem, adjacent the gas inlet orifices, may be added.

Description

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UNDERDRAIN FOR LIQUIO PURIFICATION SYSTEM

This invention relates generally to collecting and distributing apparatus or underdrains which are part of liquid purification systems.

One method of purifying liquid uses filtration systems with filter beds having one or more layers of material.
The top layer consists of a granular media which is made up of fine particulate matter such as anthracite, and, carbon, or garnet. The next level below the granular filtration media comprises support or packing gravel. Underdrain laterals are placed below the layer of gravel. These are long narrow channels which are laid laterally across the width or length of the filter bed. A plurality of such underdrain laterals are placed side by side, so that the entire lower portion of the filter bed beneath the gravel layer as composed of the laterals.
The liquid to be filtered is applied across the top of the granular layer. As it seeps through the granular layer, waste material removed from the liquid accumulates and adheres to the particles of the granular layer. The liquid then flows through the qranular layer through openings in the top of the underdrain laterals and then through a flume be~eath the underdrain, through which the filtered liquid is discharged.
To maintain the efficiency o~ the filtering system, it is necessary to periodically clean the waste material from the granular and gravel layers. This is accomplished by the use of backwash water, which flows in the reverse direction through the filtration system. The backwash water is introduced at the flume beneath the underdrain. It flows upward through the underdrain into and through the gravel layer and the granular layer, from whence it is discharged.
In order to make the backwash process more efficient, ~ gas such as air is often used. The purpose of the gas is to sufficiently agitate the gravel and granular material to loosen and fr,ee waste material which has adhered during the filtering process. During the gas cycle, a water level slightly above the top of the granular level is maintained.

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After and or during the gas cleansing cycle, the backwash water is introduced ~o remove the waste material which has been loosened and freed by the gas.
Two approaches are used with regard to the cleansing of the fil~er media. In one approach, the gas cycle is usPd first and immediately followed by a cycle during which backwash water alone is used. Another approach is to use the gas cycle fir~t and immediately follow with a cycle during which both gas and backwash water are introduced and flow through the filtration system simultaneously.
The use of the combined cycle of gas and backwash water is more efficient since the ~mount of water required is drastically reduced as compared to the backwash water required with a second cycle of backwash water only. Fur~hermore, the combination of gas and water for the second cycle provides a ~ore efficient cleaning operation during the use of water alone. However, when the granular material is very fine, the combined ~ycle cannot be used because some granular material is carried away by the gas bubbles in the backwash water and lost.
A typical operation might be the use of gas only in the order of 3-5 standard cubic feet per minutQ per square foot of the filter bed 2-5 minutes. ~hen the gas at 2-5 standard cubic feet per square foot per minute is mixed with water at 5-7~ gallons per minute per square foot ~or 2-5 minutes. If the second cycle is backwash water only, up to 30 gallons per minute per square foot 3-5 minutes might be required depending on the filtration media.
The filter bottom of M. L. Stuppy, United States Letters Patent 3,110,667 specifies a block with two lower chambers alongside each other and two upper cha~bers, each one above a lower chamber. Ports be~ween the lower chamber and the upper chamber provide compensation which assist in evening out the pressure distribution of the backwash water and lowering the amount of head pressure required. Stuppy however, does not provide for insertion o~ gas such as air to assist in the backwash process. The only way that gas can be applied in the backwash process in Stuppy is to add a network of pipes to supply gas above the granular material level, which would be ;: .: : ..

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prohibitively expensive, or to add a network of pipes above the underdrain which would disturb the granular material and cause it to mix with the gravel. The ~iner granules could then clog the ports at the underdrain and seep into the underdrain.
Maldistribution of granular material across the filter bed could also result.
Farrabough, United States Letters Patent No.
4,065,391, discloses an underdrain which provides for the use of the gas for cleansing. Chambers are formed by diagonal walls. ~his results in alternate chambers that mix gas and water and chambers that carry water only, with compensating orifices in the diagonal walls.
Sassano et al., United States Letters Patent 4,214,992 specifies a block with an air and water chamber in the center and water dispensing chambers on both sides. The chambers are formed with diagonal and straight walls and are rhombic in shape.
A major problem with the underdrains of Farrabough and sassano is that when the gas and water mix in the chamber during the gas cycle, turbulence is often set up which creates standing waves which can become destructive. The turbulence often result in the mixing of the granular particles with the gravel, (six layers of gravel are required with Farrabaugh and Sassano underdrains), and the seepage of yranular particles into the chambers which clog the orifices on the top of the underdrain and in the diagonal walls of the underdrain.
If the turbulence becomes severe enough, catastrophic damage can occur and has occurred, causing poor distribution of water and gas, damage to and breaking up of the underdrain, and lifting of the underdrain blocks or laterals off the filter bed floor.
Furthermore, it is not possible to connect the gas chambers from one underdrain lateral to another with cutouts to equalize the gas distribution. It is also not po~sible with the underdrains of Farrabough and Sassano to interconnect with cutouts the water chambers from one underdrain lateral to another to equali.ze water distribution.

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Accordingly, it is the general ob~ect of the instant invention to provide an underdrain for liquid purification systems which overcomes the shortcomings of present structures.
It is ~ further object of the instant invention to provide an underdrain for liquid purification systems which provides for a minimal amount of turbulence in the water during the gas cleansing cycle and the combined gas and backwash water cycle.
10It is still a further object of the instant invention to provide an underdrain for liquid purification systems which allows for cutout means for equalizing gas and water pressures and distribution between the parallal units of ' the underdrain laterals.
! It is still yet a further object of the instant ! invention to provide an underdrain for liquid purification systems which comprises a primary chamber, a compensatinq chamber, and a separate gas chamber.
It is another object of the instant invention to provide underdrain for liquid purification systems which allows for easy manual adjustment of th2 level of the ports for the entry of ~ackwash water tD flow out of the underdrain, in order to equalize the water pressure at each port and to equalize the distribution of the backwash water.
It is still another object of the instant invention to provide an underdrain for liquid purification systems which minimizes the required depth of the gravel layer.
It is still yet another object of the instant invention to provide an underdrain for liquid purification systems which prevents the clogging of the input ports to the underdrain and the compensating orifices between the chambers of the underdrain with granular material.
It is still an additional object of the instant invention to provide an underdrain for liquid purification systems which i6 inexpensive to manufacture and is easy to install and maintain.

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These and other objects of the instant invention are achieved by providing an underdrain comprised of laterals which have three chambers; a lower chamber or primary chamber, a middle chamber or compensating chamber, and a top gas chamber. Compensating orifices are placed in the separator wall between the compensating and primary chamber and in a horizontal baffle which defines the top of the compensating chamber and the bottom of the gas chamber. These compensating orifices and the horizontal baffle ~end to equalize gas and water pressures during cleansing operations and to prevent turbulence or th~ creation of destructive standing waves during bac~wash.
A series of nozzle assemblies are placed in the top I wall of the underdrain lateral along its length. Filtered ¦ water flows through distribution orifices in the top of the ¦ nozzle assembly through a threaded stem into the compensating chamber, to the primary chamber and through a flume from which it is discharged.
Parallel runs of the laterals comprising the chambers and nozzles assemblies are installed under the gravel layer. There are various types of gas and water distribution systems known to those familiar with the art. The instant invention may be used with front flume designs, wall sleeve designs and center flume designs, depending upon the size of the filter bed and other factors in the design and installation. Furthermore, the underdrain design of the instant invention allows for cutouts in each lateral between the parallel underdrain blocks which connect the primary chambers together to e~ualize water pressure, distribution and flow and which connect the gas chambers together to equalize gas pressures and flow.

Other objects of many of intended advantages of this invention will be readily appreciated when the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

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Fig. 1 is a cross-sectional view of an underdrain lateral installed at the bottom of the filtering system.
Fig. 2 is a plan view of the underdrain showing the top of the underdrain laterals and the nozzle assemblies of the underdrain.
Fig. 3 is a vertical cross-sectional view of the filtering system which shows the granular media and gravel packing levels and the underdrain laterals taken along the line 3-3 of Fig 2.
Fig. 4 is a partial, cross-sectional view taken along the line 4-4 of Fig 3 which shows the gas inlet pipes for a front flume distribution system.
Fig. 5 is a cross-sectional view of a filter bed using a wall sleeve distribution system.
Fig. 6 is a cross-sectional view of a filter bed using a center flume distribution system.
¦ Fig. 7 is a cross-sectional view of the underdrain lateral of the alternative embodiment.
Fig. 8 is a cross-sectional view of a filter bed using a wall sleeve distribution system with the alternative embodiment.

Referring now in greater detail to the various figures of the drawing, wherein like reference characters refer to like parts, there is shown in Fig. 1 a vertical cross ; sectional view of an underdrain lateral 2 of the present invention. As shown in Fig. 1, the underdrain lateral 2 comprises a lower, primary chamber 4, a middle, compensating chamber 6 and an upper, gas chamber 8. Nozzle assembly 10 has a threaded stem 12 with orifices 14 and 16 for gas input into the filter bed during cleansing.
The nozzle assembly 10 is located on a spacer 18 which is positioned on top wall 20 of the underdrain lateral 2.
The inner surfaces of the ~pacer 18 and the top wall 20 ~ormed by a hole for placement of the cylindrical stem 12, are threaded to accept the threads at the top of the threaded stem 12. Distribution orifices 24 are placed in upper member 22 of the nozzle assembly 10. ~he distribution orifices 24 are made - . ~ -.~ , ~ . , .

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small to prevent passage of any granular material which has settled into the gravel packing level during filtering and during cleansing.
Pormed in the separator wall 26, which defines the top of ths primary chamber 4 and the bottom of the compensating chamber 6 are compensating orifices 28 which equalize water distribution and pre~sures during the filtering and the gas and backwash cycles. A horizontal baffle 30 separates the compensating chamber 6 from the gas chamber 8. The horizontal baffle 30 contains orifices 32 which equalize gas and water pressure during the filtering and t:he gas and backwash cycles.
As will be describad in detail la er, during filtering of waste water, the water flows through the granular media level and then through the gravel pac~ing level a~ shown in figure 3, through distribution orifices 24 and into the threaded stem 12. The waste water then flows through orifices 28 and then out through a liquid flume from which it is discharged.
During backwash water is forced back into the system first through the primary chamber 4 then into the compensating chamber 6 and out through the threaded stem 12.
It then ~lows through the distribution orifices 24 into the gravel layer and upward into and thro~gh granular layer from whence it is conducted out of the filtering system and discharged.
For greater cleansing efficiency a gas is introduced into the gas chamber 8. The gas flows through orifices 14 and 16 into threaded stem 12 and out of the distribution orifices 24 through the gravel layer and then through the granular layer. ~he gas bubbles ~ormed agitate the granular material so as to loosen accumulated waste material which was formed during the filtering cycle.
After the qas cycle, a backwash cycle is initiated so that backwash water flows through the gravel and media layers removing and carrying away the waste material which was loosened during the gas cycle. As described previously, it i5 more efficient to follow the gas cycle with a combined gas and backwash water cycle then to follow the gas cycle with a .

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backwash cycle only. However, a combined cycle cannot be used when the granular media is vary fine since the granular material would be carried away in the gas bubbles by the bacXwash water.
During the gas cycle, a water level above the qranular level is maintained. The gas entering the qa~ chamber 8 forces the water in the underdrain downward until the level of the water is slightly below the top of the compensating chamber 6. Water enters at the opening at the bottom of the cylindrical threaded stem 12 and yas enters the threaded stem 12 through the orifices 14 and 16. The gas and water then go through the distribution orifices 24 and then rise through the gravel and granular levels from whence they are discharged.
This process loosens and removes the waste material which has accumulated on the granular particles.
After the gas cycle which was described above, a cycle of backwash water or a combined cycle of backwash water and gas may be used to clear away the waste material which has been loosened during the gas cycle.
The underdrain prevents turbulence during the gas and backwash water cycles as compared to underdrains in present use. With the water level in the compensating chamber 6 just below the hori20ntal baffle 3Q, the amplitude of ~tanding waves ! is reduced and water turbulence d~es not occur as in existing devices. Furthermore, the threaded portion of the stem 12 enables, during installation and maintenance, the setting of the entrances 33 of the various stems 12 to exact levels above the underdrain floor to assure that the water pressure and flow entering the various stems 12 are equalized throughout the entire filtering system. Also by placing all stems at the same level, the orifices 14 and 16 are positioned for even gas pressure and flow in the filtering system.
The inside diameter of threaded stem 12 may be reduced by inserts 35 placed near the orifice 14 to reduce pressure during backwash allowing greater gas flow through the orifice 14.
Fig. 2 shows a plan view of the underdrain laterals 2. Each underclrain lateral 2 sxtends laterally across the , ~;, 2~1~6~3~

width or length of filter bed 34. The array of the nozzle assemblies 10 are shown in the view. At the le~t are the gas inlet pipes 54 which feed gas into each of the underdrain units 2. The fil~er bed 34 comprises side walls 36, 38, 40 and 42.
Shown dotted on the right hand ide of Fig. 2 are cutouts 56 which connect the primary chambers 4 of the underdrain laterals 2 together to equalize water flow and pressure in the underdrain.
Fig. 3 shows a vertical cross section of the `10 $iltering system along the line 3-3 of Fig. 2. As can be seen in Fig. 3 a layer of granular material 46 is placed above a layer of gravel 48. The underdrain laterals 2 cover the bsttom 44 of the filtering bed 34 beneath the gravel layer 48. Gas inlet pipes 54 are placed in gas distribution chamber 49 for feeding gas into each of the gas chambers 8 of the underdrain laterals 2. Cutouts 51 at the end of each of the underdrain laterals 2 connect the gas chambers 8 to equalize gas pressure and allow an equal flow of gas throughout all the gas chambers 8.
Below the underdrain laterals 2 is a liquid flume 50 through which the filtered water exits and into which bacXwash water flows during the backwash cycle.
The gas inlet pipes 54 are placed at the front of ths filter bed ~4 are shown in Fig. 4, which is a partial cross sectional view taXen along the line 4-4 of Fig 3. As can be seen in Fig. 4 cut outs 56 in the bottom of the primary chambers ~ at each end of each underdrain blocks 2 provide for equalization of water pressure and water flow throughout the underdrain.
As is well know to those skilled in the art, various arrangements with regard to water and gas distribution are in common use. The arrangement shown in Figs. 2, 3, and 4 is a front flume design. In addition to the front flume design, water and gas distribution can be achieved through a wall sleeve design as shown in Fig. 5 or through a center flume design as 6hown in Fig. 6. The choice of distribution design depends upon the size of the filtering system, the amount of water to be filtered, and various other considerations with :`

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regard to any specific installation. However, the instant invention is applicable to all such arrangements.
A wall sleeve water and gas clistribution system with the present invention is 6hown in Fig. 5. Both gas inlet pipes 58 and liquid flume 60 are in placed in side wall 42.
Cutout 62, at both ends of underdrain lateral 2 connect the primary chambers 4 of each lateral 2 together to assure equal distribu~ion of water pre6sure and flow throughout the underdrain. Similarly, the gas chambers 8 of the underdrain laterals 2 are connected together at one end of the laterals 2 by cutouts 64 which equalizes gas pressure and flow throughout the underdrain.
Fig. 6 shows a center flume gas and water i distribution system. Liquid flume 66 is shown centered in bottom wall 44. Gas distribution also takes place centrally.
The gas enters into the gas chambers 8 via J tube 68. Cutouts i (not shown) may also be used to equalize water and gas pressures and flow.
An alternative embodiment of the invention is shown in Figs. 7 and 8. In this embodiment, the distribution orifices 24 in the upper member 22 of the nozzle assembly 10 are made larger. The dimensions of the distribution orifices 24 of the alternative embodiment are 1/4 inch wide by 1 inch long as compared to 1/32 inch wide by 1 inch long in the first embodiment. Also as can be seen in Figs. 7 and 8, the threaded stem 12 is made longer so that entrance 33 is in the lower chamber 4. In addition, the middle chamber 6 is made longer and the lower chamber 4 is shortened.
Also in ~his alternative embodiment, the functions of the chambers 4 and 6 are reversed. Chamber 6 is the primary chamber into which the backwash water is inserted. The lower chamber 4 is now the compensating chamber.
Fig. 8 is a cross-sectional view of a filter bed with a wall sleeve distribution system using the alternative emoodiment. As can be seen in Fig. 8, backwash water enters through liquid ~lume 60 into the middle primary chamber. The upper chamber 8 remains ths gas chamber as in the first embodiment and gas enters through gas inlet pipes 58.

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The alternative embodiment is intended to guard against the p~ssibility that after about five years of service, waste material might clog the openings of the distribution orifices 24. The orifices 24 are therefore made wider. This necessitates three to four layers of the gravel 48 beneath the granular material 46. The larger s.L~e gravel is placed in the lower layer with each higher layer being successively of smaller size with the smallest ~iZI' gravel in the top layer, beneath ths granular layer. In the first embodiment, on the other hand, only one gravel layer iis required because smaller size gravel can be used abutting the noz~le assembly 10, because the openings of the distribution orifices 24 are much narrower.
With this system it is possible that large gulps of air entering with the backwash water could lift the finer I gravel which could be washed out when the backwash water is ¦ discharged. Therefore, the threaded stem 12 made longer so that the entrance 33 was considerably below the backwash intake into the middle chamber 6 to prevent air from entering into the threaded stem 12 and thence through the distribution orifices 1 24 rising up through the gravel layers.
An underdrain system which provides for several clear and i~portant advantages over the previous and current art has been described. These include the use of a gas cleansing cycle and a backwash liquid cycle or a combined gas and backwash liquid cycle wherein turbulence in the liquid is minimized. Existing systems often create sufficient turbulence to result in the mixing o~ the granular media with the gravel, causing clogging of orifices which jams the system.
Furthermore, the disturbances are sometimes severe enough to cause catastrophic results such as the lifting or breaking up of the laterals of the underdrain.
The reduction in turbulence during the cleansing cycles allows for the reduction of the amount of granular media required as less mixing between tbe granular and gravel layers occurs as well as less shifting of granular materials causing unequal amounts of material at various locations in the filter bed. While the systems in common use today require six layers .
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of gravel, the first embodimen~ of this invention requires only one layer of gravel, whilç the 6econd embodiment requires only three or four layers of gravel.
The underdrain laterals 2 may be composed of ceramic, fiber glass, plast$c, metal or any other suitable material.
The instant invention also provides an easy means for leveling the back~ash liguid intakes to provide for even liquid distribution by rotating the threaded stems of the nozzles. Also, through the use of cut outs in the underdrain laterals 2, gas and liquid pressures and flow are equalized within each of the underdrain laterals and throughout the filter bed 34.
Although the embodiments described herein use filtration to purify waste water it should be noted that the instant invention is equally applicable to other methods of purification and to purify liquids other than waste water.
Without further elaboration, the foregoing will so fully illustrate my invention that others may, by applying current or future knowledge, readily adapt the same for use under the various conditions of service.

Claims (21)

1. A liquid purification system comprising a bed into which the liquid to be purified flows; a liquid purification media located in said bed; an underdrain placed in said bed beneath said liquid purification media, said underdrain comprising a plurality of underdrain laterals laid laterally in said bed, each of said plurality of laterals being parallel; and a means to cleanse said purification media during cleansing periods, using gas and backwash liquid introduced into said underdrain, said system being characterized by each of said laterals comprising a gas chamber, defined by surrounding walls; and a means to isolate said gas from said backwash liquid by providing that only said gas occupies each of said gas chambers during said cleansing periods, said isolating means comprising each of said gas chambers and a means for injecting gas into each of said gas chambers.

2. The system of Claim 1 wherein each of said laterals comprises a primary chamber, a compensating chamber above said primary chamber and said gas chamber above said compensating chamber.

3. The system of Claim 2 wherein said means to cleanse said purification media comprises said means for injecting gas into each of said gas chambers to loosen impure matter adhering to said purification media as a result of said purification and a means to introduce said backwash liquid into each of said primary chambers to remove said impure matter from said bed.

4. The system of Claim 3 wherein said means to introduce gas into said gas chambers comprises at least one gas inlet pipe and said means to introduce said backwash liquid into said primary chambers comprises a liquid flume.

5. The system of Claim 2 wherein each of said plurality of underdrain laterals comprises a separator wall between each of said primary chambers and a respective one of said compensating chambers and a means to compensate for differences in liquid pressures and flow during purification and cleansing, said compensating means comprising orifices in each of said separator walls.

6. The system of Claim 2 wherein said system comprises a means to minimize liquid turbulence during said cleansing periods of said purification media.

7. The system of Claim 6 wherein each of said plurality of underdrain laterals comprises a horizontal baffle between each of said compensating chambers and a respective one of said gas chambers, and said means to minimize liquid turbulence comprises each of said baffles, each of said baffles being positioned a predetermined distance from the interface between said gas and liquid during cleansing of said purification media to minimize liquid standing waves and turbulence during said cleansing periods.

8. The system of Claim 7 wherein said each of said baffles has orifices therein to compensate for differences in liquid pressures and flows during purification and during cleansing.

9. The system of Claim 2 wherein said system comprises a means to equalize liquid distribution and backwash liquid distribution in said underdrain.

10. The system of Claim 9 wherein said means to equalize liquid distribution and backwash liquid distribution comprises at least one cutout in each of said primary chambers allowing said liquids to flow between said primary chambers.

11. The system of Claim 10 wherein said system comprises a means to equalize gas distribution in said underdrain.

12. The system of Claim 11 wherein said means to equalize gas distribution in said underdrain comprises cutouts in each of said gas chambers allowing said gas to flow between said gas chambers.

13. The system of Claim 2 wherein each of said plurality of underdrain laterals comprises a top wall with a plurality of openings through which said liquid flows during purification and through which said gas and backwash liquid flow during cleansing.

14. The system of Claim 13 wherein each of said plurality of underdrains comprises a plurality of nozzle assemblies, each of said plurality of nozzle assemblies being positioned in a respective one of said plurality of openings and comprising an upper member with distribution orifices, and a threaded stem attached to said upper member.

15. The system of Claim 14 wherein each of said threaded stems extends through a respective one of said gas chambers and into the respective compensating chamber of each of said laterals, each of said threaded stems comprising at least one orifice for entry of gas during said cleansing periods and an entrance for entry of backwash liquid during said cleansing periods, whereupon the position of said entrance is adjustable by rotating said threaded stem.

16. The system of Claim 15 wherein each of said threaded stems comprises at least one insert positioned within each of said threaded stems adjacent said at least one orifice to reduce backwash liquid pressure at said at least one orifice for greater gas flow.

17. An underdrain lateral for a system which purifies liquid utilizing a purification media, said underdrain lateral comprising a means to introduce a gas into said underdrain lateral to cleanse said liquid purification media during cleansing periods; and a means to introduce backwash liquid into said underdrain lateral to cleanse said purification media during said cleansing periods, said underdrain lateral being characterized by a gas chamber defined by surrounding walls; and an isolating means to provide that only said gas occupies said gas chamber during said cleansing periods.

18. The underdrain lateral of Claim 17 wherein said lateral further comprises a means to compensate for differences in said liquid and backwash liquid pressures and flow between said lateral and at least one other lateral.

19. The underdrain lateral of Claim 17 wherein said lateral comprises a lower primary chamber, a middle compensating chamber above said lower primary chamber and said gas chamber is above said compensating chamber.

20. The system of Claim 1 wherein each of said laterals comprises a lower compensating chamber a middle primary chamber above said lower compensating chamber and said gas chamber is above said primary chamber.

21. The underdrain lateral of Claim 17 wherein said underdrain lateral comprises a lower compensating chamber, a middle primary chamber above said lower compensating chamber and said gas chamber is above said primary chamber.