Abstract:
An apparatus and method for distributing a fluid. A fluid distribution device includes a flow chamber comprising an inlet and an outlet, an equalization chamber; and a diaphragm separating the flow chamber and the equalization chamber, wherein a valve positioned in a flow path between the flow chamber inlet and the flow chamber outlet comprises a valve body coupled to the diaphragm.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for the distribution of a fluid and, more specifically, to an apparatus for providing distribution of a fluid from two or more sources. 
     2. Description of the Related Art 
     A number of different methods and techniques are available for the disinfection of water. These methods include, for example, filtration, heating, treatment with UV radiation, and treatment with a variety of chemicals, often oxidizers such as chlorine, chloramine and ozone. One of the most widely used treatments for both potable and waste water is to dissolve chlorine in the water. Chlorine may be in a variety of forms, such as, for example, a gas (Cl 2 ), a liquid (sodium hypochlorite solution) or a solid (calcium hypochlorite). Because it is effective, inexpensive and readily available, chlorine gas, which may be compressed to a liquid, is a widely used oxidant in the water treatment industry. 
     Chlorine gas is typically manufactured off site and is delivered to a water treatment facility in pressurized containers, such as gas cylinders. At the site, for example, a municipal water treatment facility, the chlorine is introduced into the water in a concentration adequate to provide an acceptable level of disinfection. Often, the gas is introduced into the water via a vacuum injector system or a vacuum induction system that draws the chlorine into the water at a pressure that is below atmospheric pressure. When such a technique is used, chlorine is less apt to escape from the disinfection system because, if a leak forms in the system, the constant draw of the vacuum source will prevent the escape of gas to the atmosphere. However, for efficient storage and transportation, chlorine is generally shipped and stored in pressurized containers, and the pressure of the gas must first be reduced to feed a vacuum injector. Such a system is disclosed, for example, in U.S. Pat. No. 6,105,598, which is hereby incorporated by reference in its entirety herein. 
     Often, a series of pressurized gas cylinders are drawn from in parallel to provide an adequate supply of gas. Multiple cylinders may be plumbed to a single vacuum regulator, so that the gas is at greater than atmospheric pressure upstream of the regulator and below atmospheric pressure downstream. A vacuum regulator, such as the S10K™ vacuum regulator, available from United States Filter Corporation, Vineland, N.J., may be used to provide a low pressure source of chlorine, or other gases, to a vacuum injector system from a number of gas sources, such as chlorine cylinders or tanks. When a pressurized gas, for example, chlorine gas, is fed to a regulator from multiple tanks, the tanks may be emptied without significant drops in temperature as there is minimal gas expansion upstream of the regulator. 
     Many users of vacuum injection systems, particularly those disinfecting a water supply, may prefer to use a bank of cylinders where each gas cylinder is independently regulated. In this case, each cylinder may be fitted with a vacuum regulator that is then used to feed a common, low-pressure gas manifold. Such a configuration may reduce the total amount of high pressure gas piping that is required at a facility. However, this configuration may also mean that high pressure gas is being reduced to low pressure gas at numerous locations, such as at the point of exit of each of the gas cylinders. If there are slight differences in regulator design or construction, or if each cylinder is not identically situated, gas may be drawn preferentially from one cylinder rather than equally from all, resulting in unequal gas distribution from containers within a bank or between banks. In this instance, significant gas expansion and/or boiling may occur in a tank being drawn down at an excessive rate, which may result in a variety of problems, including frosting, that may interfere with the function and output from one or more cylinders. This unequal and unpredictable cylinder depletion may result in a failure to maintain a consistent supply of gas to the low pressure system. 
     SUMMARY OF THE INVENTION 
     In one aspect, a fluid distribution device is provided, the fluid distribution device comprising a flow chamber comprising an inlet and an outlet, an equalization chamber; and a diaphragm separating the flow chamber and the equalization chamber, wherein a valve positioned in a flow path between the flow chamber inlet and the flow chamber outlet comprises a valve body coupled to the diaphragm. 
     In another aspect, an equal drawdown device is provided, the equal drawdown device comprising a vacuum gas regulator comprising a valve in fluid communication with a gas source and with a vacuum source, the vacuum source providing a first force in a direction to open the valve, and a second force acting on the valve, wherein the second force is variable and opposed to the vacuum force. 
     In another aspect, an equal drawdown device is provided, the equal drawdown device comprising a compartment having at least a first and a second outlet and at least a first and second inlet, a first valve comprising a valve body and a valve seat positioned in a fluid pathway between the first inlet and the first outlet, a second valve comprising a valve body and a valve seat, positioned in a fluid pathway between the second inlet and the second outlet, and wherein the valve body of the first valve is coupled to the valve body of the second valve. 
     In another aspect, an equal drawdown device is provided, the equal drawdown device comprising a vacuum gas regulator comprising a valve in fluid communication with a sub-atmospheric disinfectant source and with a vacuum injection system, the vacuum injection system providing a force tending to open the valve, and means for controllably opposing the force provided by the vacuum injection system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic cross-sectional illustration of an equal drawdown device having two inlets and two outlets; 
     FIG. 2 is a schematic cross-sectional illustration of an equal drawdown device having a single inlet and a single outlet; 
     FIG. 3 is a schematic illustration of a system using three of the devices shown in FIG. 2; 
     FIG. 4 is a schematic cross-sectional illustration of a vacuum regulating device; 
     FIG. 5 is a schematic cross-sectional illustration of an electromagnetic biased vacuum regulator, which is part of an electromechanical equal drawdown system; 
     FIG. 6 is a schematic illustration of a electromechanical equal drawdown system, each including an electromagnetic biased vacuum regulator device as shown in FIG.  5 . 
     FIG. 7 is a schematic cross-sectional illustration of an equal drawdown device; and 
     FIG. 8 is a schematic cross-sectional illustration of a modular system using three of the devices illustrated in FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     The invention provides for an apparatus to equalize the drawdown (mass flow) between two or more fluid sources feeding one or more outlets. The apparatus provides a system that detects differences in rates of drawdown among fluid sources, for example, gas cylinders, and adjusts the output of one or more sources accordingly. The apparatus may provide, for example, mechanical or electrical feedback mechanisms that constantly or intermittently adjust the rates of flow from each of a plurality of sources. The apparatus may be used with existing fluid distribution systems and may be particularly useful with gas disinfection systems, such as those that use chlorine gas to disinfect municipal water supplies. Furthermore, the apparatus may be used to equalize flow within a bank of cylinders and also between banks of cylinders. Thus, a set of cylinders in a particular bank may be emptied, and thus replaced at approximately the same time. 
     In one aspect, an equal drawdown device is provided that has two inputs, one for each of two different low pressure gas sources such as, for example, chlorine, ammonia or sulfur dioxide. For example, two chlorine gas cylinders, each equipped with a vacuum regulator may feed the device simultaneously. The device may have two separate outlets, feeding one or more low pressure systems, such as a vacuum injection system or a chemical induction system such as the WATER CHAMP® chemical induction system (U.S. Filter Stranco Products, Bradley, Ill.). 
     An embodiment of an equal drawdown device is shown in FIG.  1 . FIG. 1 provides a schematic cross-sectional view of an equal drawdown device  100  having a first inlet  110 , a second inlet  120 , and a compartment divided into a first low pressure chamber  130  and a second low pressure chamber  140  by flexible diaphragm  150 . The flow of gas between inlet  110  and low pressure chamber  130  is controlled by the positioning of valve body  162  in relation to valve seat  164 . Likewise, the flow of gas from inlet  120  into low pressure chamber  140  may be controlled by the positioning of valve body  172  in relation to valve seat  174 . Outlets  180  and  190  each lead to the same low pressure source, such as a vacuum injector or vacuum inductor (not shown) and provide for the flow of gas from chambers  130  and  140 , respectively. Thus, gas may flow through inlet  110 , through orifice  166  into chamber  130  and out of the equal drawdown device through outlet  180 . Likewise, gas may flow through inlet  120  through orifice  176  into chamber  140  and out of the equal drawdown device through outlet  190 . 
     Valve spool  182  provides a common connection between valve bodies  162  and  172  via valve pins  168  and  178 . Valve spool  182  is clamped onto diaphragm  150  by nut  184  such that when diaphragm  150  is deflected, valve bodies  162  and  172  are both shifted in the direction of the deflection. Thus, if the pressure in chamber  140  increases in relation to the pressure in chamber  130 , diaphragm  150  will deflect from right to left, moving the valve pins and valve bodies in the same direction. Therefore, if the diaphragm is deflected from right to left, valve  160  is opened and valve  170  is closed, thus increasing the flow through inlet  110  and decreasing the flow through inlet  120 . Because the valve bodies are connected, the distance between each valve body and its corresponding valve seat changes inversely to a change in distance between the opposing valve body and its corresponding valve seat. This configuration may result in a self regulating system as outlets  180  and  190  are subjected to substantially the same vacuum pressure when they are plumbed to a common vacuum source. Thus if equal gas flows enter chambers  130  and  140 , diaphragm  150  will remain stable and the flow through each of the respective inlets will remain approximately the same. Should the flow from one side, however, vary, for instance if the flow through inlet  110  increases, the relative pressure in chamber  130  will be greater than that in chamber  140  and the diaphragm will deflect to the right. This deflection will, in turn, move both valve bodies  162  and  172  to the right, throttling the flow through orifice  166  and increasing the flow through orifice  176 . Diaphragm  150  will stabilize in a new position once the gas flow through each of the inlets, and therefore the pressure in each of chambers  130  and  140 , is substantially equal. 
     By using common geometries for valves  160  and  170 , and by mutually opposing the two valve assemblies, any drag force effects on each of the valves may be cancelled due to the common connection. Therefore, while compensating for drag force might play an important role in adjusting and maintaining a specific flow through a single valve, the common connection between the two valve bodies illustrated in FIG. 1 provides for accurate flows without regard to the actual drag force on the mutually opposed valve bodies. This can provide for a simpler design and a simplification, or even elimination, of a control system. It is preferred that the valve bodies be conically shaped, and that the valve bodies be spaced apart, so that regardless of the positioning of diaphragm  150 , the total gas flow through inlets  110  and  120  is adequate to supply the amount of fluid called for by the vacuum source. The distance between the valve bodies may be adjustable to allow for different flow rates through the system. 
     Materials of construction are preferably chosen to be compatible with the fluid that is being distributed and with the environment in which the device is used. For example, the parts of the equal drawdown device that come into contact with the gas being distributed may be of corrosion resistant material such as alloyed steel or polymeric material. Preferably, fluid wettable parts, such as the inlet, the valving, the compartment and the outlets are of corrosion resistant alloys such as HASTELLOY® (Haynes International, Indiana). 
     It is preferred that diaphragm  150  be constructed of material that is flexible enough to allow deflection of the valve&#39;s spool and resistant enough to withstand exposure to harsh environments such as those provided by chlorine, ammonia or sulfur dioxide gas. For example, if the device is to be used to distribute chlorine or sulfur dioxide, it may be preferred that the diaphragm material be of synthetic rubber, such as VITON® elastomer, available from E. I. Du Pont (Delaware). If a gas such as ammonia is to be distributed, it may be preferred that the diaphragm be of a corrosion resistant elastomeric material such as a chlorinated polyethylene, for example, HYPALON® elastomer available from E. I. Du Pont (Delaware). 
     In another aspect, the invention provides for a fluid distribution device in which the flow of fluid through a single inlet to a vacuum source is independently controlled. Multiple devices can be joined together so that the flow of fluid through any one of the devices can be equalized in relation to the flow through the joined devices. One embodiment of such a device is depicted schematically in FIGS. 2 and 3. Fluid distribution device  200  includes a housing  280  which may include an inlet  250 , an outlet  242  and an equalization orifice  290 . Device  200  also includes rolling diaphragm  270  that is held between two diaphragm plates  272  and  274 . Rolling diaphragm  270  is connected to valve body  212  by valve pin  218  which helps to support the valve body in combination with bearing  278 . Bearing  278  may also slidably align and center valve body  212  in reference to orifice  216 . When valve body  212  is moved to the right (as shown in FIGS.  2  and  3 ), orifice  216  is opened as the distance between valve body  212  and valve seat  214  increases. Thus, if a source of low pressure, for example, a vacuum source, is connected to outlet  242  and a higher pressure gas source is connected to valve  250 , the gas will flow from inlet  250  through orifice  216  into chamber  230  and through outlet  242  to the low pressure source. Equalization orifice  290  may provide fluid communication between chamber  230  and another equalization chamber, such as an additional equalization chamber in a similar device. Equalization chamber  260  may be connected, for example, with the flow chamber of a similar or identical device, through orifice  262  (in the other device). Alternatively, connection  262  may communicate with the surrounding atmosphere to assure that equalization chamber  260  is at ambient pressure, or  262  may be sealed to provide a substantially constant absolute pressure in equalization chamber  260 . 
     When vacuum is applied to outlet  242 , the pressure in chamber  230  may be below atmospheric and may be a function of the amount of gas flow through valve  250  into the chamber. Thus, if fluid flow into chamber  230  increases for any reason, for example, a change in upstream pressure, the pressure in chamber  230  will increase in relation to the pressure in chamber  260  and rolling diaphragm  270  will move from right to left (as oriented in FIG.  2 ). This movement will also move pin  218  from right to left, drawing valve body  212  from right to left as well. This will serve to decrease the size of orifice  216 , thus reducing the flow of fluid from the fluid source through valve  250 . Thus, the flow through flow chamber  230  may be self-regulating due to the dynamic movement of rolling diaphragm  270 . This may provide for a substantially consistent flow rate without the need for external control, thus providing an inexpensive and easily serviceable fluid distribution device. If preferred, the pressure in equalization chamber  260  may be varied as a method of adjusting the flow through chamber  230 . 
     In a further embodiment, such as that shown in FIG. 3, one or more of the fluid distribution devices shown in FIG. 2 may be joined together to provide interactive regulation of fluid flow from two or more fluid sources. FIG. 3 illustrates a series of three of the devices shown in FIG. 2, devices  200 ,  300  and  400 . Each of these devices may be identical. Device  200  regulates a flow of gas from inlet  202  to outlet  242  that is connected to vacuum manifold  310 , which may in turn lead to a vacuum source such as a vacuum injection system (not shown). Likewise, device  300  distributes a gas from source  302  to outlet  342  which in turn feeds common manifold  310 . Device  400  may be configured similarly. A series of three devices as shown, may represent, for example, the feed from three individual sources such as cylinders forming a bank of cylinders or, alternatively, the distribution of fluid from three groups, such as different banks of cylinders. The flow chamber of each of the devices may be in communication with one or more of the equalization chambers of another device. For example, flow chamber  230  may be plumbed to fluidly communicate with equalization chamber  460 , and thus these chambers,  230  and  460 , may be maintained at substantially equal pressures. Likewise, flow chamber  430  and equalization chamber  360  may be at substantially equal pressures, and flow chamber  330  and equalization chamber  260  may also be at substantially equal pressures. 
     As the flow through each of valves  250 ,  350  and  450  may be influenced by changes in the flow rate and/or pressure in any one or more of the devices, each of the devices may adjust the flow from its fluid source in response to a change in the flow of any one or more of the other fluid sources. As the vacuum pressure at manifold  310  is in communication with each of the flow chambers, an approximately equal vacuum force may be applied to each of the flow chambers. One example of how the flow through each of the devices may be regulated is as follows. 
     If a flow through valve  250  increases due to external factors such as, for example, an adjustment in an upstream vacuum regulator, the pressure in chamber  230  will increase, resulting in a concurrent increase in pressure in equalization chamber  460  of device  400 . When the pressure in chamber  460  increases in relation to the pressure in adjacent flow chamber  430 , rolling diaphragm  470  may slide from left to right (oriented as shown in FIG. 3) resulting in an opening of valve  450  and an increase in flow of fluid from source  402  to outlet  442 . This increase in flow through chamber  430  will result in an increase in pressure in the chamber and this increase in pressure will also be realized in equalization chamber  360  of device  300  which is in fluid communication with chamber  430  via connector  362 . This increase in pressure in equalization chamber  360  may result in a shift of rolling diaphragm  370  from left to right resulting in an opening of valve  350  and an increase in the flow of fluid from source  302  to outlet  342 . Conversely, an opposite series of shifts may occur if there is a decrease in the pressure (decrease in flow) in one of the flow chambers. 
     Therefore, because of the communication between the three devices shown in FIG. 3, a change in the flow through one of them, for example device  200 , may lead to a similar change in flow in each of the other devices,  300  and  400 . This change in flow may be triggered by an increase in demand at manifold  310 , for example, or by a change in supply at one of the three gas sources  202 ,  302  or  402 . It is preferable that whatever change occurs in the flow through one of the devices also occurs in the connected devices as well. This may help to draw down gas supplies equally from each of multiple sources, helping to eliminate preferential depletion of one source over another. In turn, this may help in reducing frosting and its related deleterious effects, and may also allow for the changing out of empty cylinders within a bank at substantially the same time. Any number of devices may be included in a system and any number of systems may be used in parallel or in series to combine the flows of multiple groups of fluid sources. 
     The materials with which each of the devices may be constructed include any material that is suitable for the environment in which the fluid distribution device is to be used. For example, the valves, housings and piping may be made out of alloys such as stainless steel or, alternatively, a polymeric material, such as polyamide. Preferably, the material can withstand any corrosive effects of the fluid being distributed and is resistant to temperatures that may be encountered when the device is used on site. Most preferably the housing is constructed of PVC polymer and the valve components are of PTFE. 
     Rolling diaphragm  270  may be substituted by any component capable of adjusting the position of the valve in response to a change in pressure differential between the flow chamber and the equalization chamber. For example, a rolling diaphragm, a bellows-type diaphragm or a stationary flexible flat diaphragm may be used. Alternatively, a pressure transducer in one or in each of the two chambers may be employed, and the difference detected between the two pressures may be used to adjust the positioning of valve body  212 . Thus, the interactive adjustment between devices may be, for example, mechanical, electrical, hydraulic or pneumatic. Preferably, a diaphragm, and most preferably a rolling diaphragm is used, because it provides low resistance to a change in pressure differential as well as providing a relatively extensive length of travel. 
     By allowing for an extensive length of travel, the positioning of valve body  212  in relation to valve seat  214  may be adjusted in response to small pressure changes without causing excessive increases or decreases in the rate of flow through the valve. This may help avoid upsets or cascade effects that can result from under or over adjustment. Preferably, the length of travel is more than one inch, and more preferably, is greater than or equal to three inches. For example, if a three inch length of travel is required between a completely closed and completely open position of valve  250 , a change in pressure that results in movement of a fraction of an inch will result in only a slight change in the flow through valve  250 , possibly reducing the chance of an upset that might occur should the flow of fluid through the valve be over-adjusted in response to a pressure change. 
     The rolling diaphragm may be made out of any material that is impervious and compatible with fluids that may be distributed with the device. For example, if chlorine or sulfur dioxide gas is being distributed, a diaphragm of chemically resistant elastomer, such as VITON® polymer (E. I. du Pont, Wilmington, Del.) may be preferred. Alternatively, if ammonia gas is being distributed, a chlorosulfonated polyethylene elastomer, such as HYPALON® elastomeric material (E. I. du Pont, Wilmington, Del.) may be preferred. 
     The geometry of the valve body and the valve seat is preferably designed so that an amount of travel in the valve body results in an approximately equal percentage change in gas flow, regardless of the positioning of the valve body in relation to the valve seat. For example, a 10% deflection in the position of the rolling diaphragm, and therefore in the position of the valve body, preferably results in an approximately a 10% difference in the amount of fluid passing through the valve. More preferably, this ratio stays substantially constant regardless of whether the valve body is positioned to the left, to the right, or in the center of the position of travel. It is preferred that the valve body surface (and valve seat) be hemispherical, as such a configuration results in a more linear response between amount of travel and change in the rate of flow. More preferable, however, is a conically shaped valve body surface, as such a geometry provides flow characteristics comparable to those obtained with a hemispherical shape, yet may be more easily manufactured. 
     These devices may be used in any system that is feeding a low pressure point from one or more sources of fluid. Preferably, the device is used to feed a subatmospheric gas to a low pressure source such as a vacuum injector. Most preferably, each device is down-stream of a vacuum regulator so that all of the componentry and plumbing downstream of the pressurized gas source is below atmospheric pressure, reducing the probability of gas leaking from the system into the ambient environment. 
     FIG. 4 provides a cross-sectional illustration of a known multi-position vacuum regulator that may be used to feed a compressed gas such as chlorine or sulfur dioxide from a pressurized source to a vacuum system. A vacuum source is connected to outlet  540  and may apply a vacuum force to valve body  510  which may form a seal against valve seat  520 . As the vacuum force is increased, any resistant force that may be applied by valve pin  530  is overcome and valve body  510  may be drawn to the left, opening the valve and providing for flow of fluid from cavity  550  past valve seat  520  and through outlet  540 . The vacuum force may also be counteracted by an opposing force, provided by, for example, a valve spring  512 . Thus, once this vacuum regulator is attached to a source of fluid, the flow of the fluid to the regulator may be determined, in part, by the vacuum force that is apparent at outlet  540 . Therefore, if the amount of vacuum present at outlet  540  increases, the flow of fluid through the vacuum regulator should also increase. 
     FIG. 5 provides an illustration of an aspect of the invention in which the flow of fluid through a vacuum regulator may be actively controlled by a counterforce that in turn may be regulated in response to the rate of flow, or a change in the rate of flow, from one or more fluid sources. For example, while a vacuum force applied at outlet  640  may provide a force to move valve body  610  from right to left, thus opening the valve and increasing the flow of fluid through the regulator, an opposite force applied in the direction of force  670 , will pull valve body  610  closer to valve seat  620 , thus reducing the flow of fluid. Such an opposing force may be applied, for example, by a spring, a piston, or a magnet. As shown in FIG. 5, the opposing force is adjustable and may be supplied by an electromagnet, or solenoid coil  662 . As the current supplied through leads  664  is increased, the force applied to pin  660  in the direction of force  670 , as shown in FIG. 5, is increased. Thus, as the current to the solenoid increases, the valve will be closed to a greater degree, as this electromagnetic force opposes the opening force applied by vacuum source  640 . 
     Although force  670  may be applied in more than one direction so that it can serve to either open or close the valve, it is preferred that the force only be applied in a direction opposite to that supplied by vacuum source  640 . In this case, any failure of the system would result in the regulator reverting to operation as a standard vacuum regulator and should not result in any excessive flow of gas through the device. Thus, it is preferable that the device be configured so that the counterforce can only throttle the fluid flow, not increase it. Pin  660  is preferably composed of magnetically responsive material, more preferably is steel, and most preferably is plated steel, to avoid corrosion. The magnetically responsive material may be internal or external to the regulator and may depend on the size of the pin or the size of the coil that is required to provide a necessary counterforce. An example of an appropriate solenoid system is the Series 8225, available from Automatic Switch Co., Florham Park, N.J. 
     The amount of force applied at point  670  may be controlled by a number of controllers or feedback mechanisms. For example, a solenoid coil may be controlled in response to a flow meter, or flow meters, measuring the fluid flow from a single fluid source, or from several fluid sources. For instance, a flow meter, such as a rotameter, may be placed in line in each of a set of gas cylinders, for example, between the vacuum regulator on each cylinder and a vacuum manifold. Once an increase in flow from a particular source is detected, a signal may be processed and the current may be increased to the solenoid coil controlling the vacuum regulator for that gas source. The increased current may increase force  670 , causing the valve to throttle and to reduce the flow of fluid through the vacuum regulator. The system may be configured so that a sensed decrease in flow rate may have the opposite effect. Alternatively, the same sensed increase in the rate of flow may be responded to by decreasing the current to the solenoids on sister vacuum regulators (those for which there has not been a perceived increase in flow), the resulting decrease in current reducing the resultant force  670  for each of these regulators. Thus, the increase in flow from one source may be equalized through an increase in the flow from each of these adjusted sister fluid sources. 
     Preferably, the rate of drawdown from each fluid source, for example, a gas cylinder, may be measured by detecting a change in the rate of mass decrease for each of the gas cylinders feeding a system. For example, each gas cylinder may be positioned on an electronic balance and the weight of each cylinder may be fed to a processor, such as a computer. The computer may monitor the rate of decrease in the weight of the cylinder which may provide a direct reading of the amount of gas being drawn from the cylinder. The weight may be constantly reported, or may be read at specific intervals. If the mass of one of the cylinders starts to decrease at a rate greater than desired, for example, a pre-determined rate or the measured rate of decrease for its sister cylinders, the system may react to prevent frosting and to avoid other problems that may develop as a result of excessive drawdown. Once an increased rate of drawdown is perceived, a signal may be sent to the appropriate solenoid coil or coils, increasing the current to the coil and thus increasing force  670 . This should result in a throttling of the valve, bringing the regulator flow back in line with the flow through its sister regulators. 
     An illustration showing a system embodiment of the invention is provided in FIG. 6. A bank of five identical chlorine gas cylinders is each attached in parallel to a vacuum manifold  770  that leads to a vacuum injector. Each of the gas cylinders may be monitored by an electronic balance such as balance  720  which measures and reports the weight of cylinder  710 . A signal from balance  720  is sent to processor  730  via electronic connection  722  and processor  730  calculates a rate of flow from cylinder  710  as well as from its four sister cylinders. Alternatively, any other device capable of detecting the rate of drawdown may be used. For instance, flow meters, preferably mass flow meters, may be placed in line for one or more of the cylinders, for example, in line  760 , in order to directly measure the fluid flow from the gas cylinder. In this case, such a flow detector may be connected to processor  730  to monitor the rate of flow in a method similar to that employing weight monitoring. Once processor  730  has measured and evaluated the flow from each of the five cylinders, a signal may be sent to controller  740  to increase or decrease the current being provided to any one or more of the five regulators, e.g., regulator  600 . The processor may be programmed to react instantaneously to any changes, or preferably is programmed to react when flow variation from one or more fluid sources exceeds a particular threshold for a particular length of time. 
     Thus, if an upset in the system causes an increase in the flow from cylinder  710 , processor  730  may direct controller  740  to adjust regulator  600  by sending a signal through lines  750  and  752 , increasing current to solenoid  662  (FIG.  5 ). This may result in a throttling of flow from cylinder  710  and an equalization in flow among each of the five cylinders. Alternatively, the flow to each of the other four cylinders may be increased. Multiple banks of cylinders may be placed in series or in parallel and may be controlled either independently or by a common processor. 
     FIGS. 7 and 8 provide illustrations of an embodiment where two or more fluid distribution devices may be stacked together to form a modular system. A single device that can be used with the system is shown in FIG. 7 The components of each device may be made from the same materials as the devices described above. System  800  may be composed of any number of individual devices such as  810 ,  812  and  814 . In the embodiment shown, each of these devices is identical. The total number of devices used may be either an odd or an even number. The system operates similarly to that shown in FIG. 3, however, connection and disconnection of the separate devices is facilitated by a common modular design. 
     Each of the individual devices includes a flow chamber such as  820 ,  822  or  824  and an equalization chamber such as  830 ,  832  or  834 . Using the centrally located device,  812 , as an example, fluid may be fed from a fluid source such as vacuum regulator, to inlet  840 . The vacuum regulator, may draw fluid from a source such as a cylinder of chlorine, ammonia or sulfur dioxide. Fluid, such as chlorine gas, flows through inlet  840  and into flow chamber  822  after passing through annular orifice  842  which is formed when valve body  860  is moved from right to left. Rolling diaphragm  866  isolates equalization chamber  832  from flow chamber  822  and rolls left or right in response to a variation in pressure between the two chambers. Thus, if the pressure in chamber  832  exceeds that in chamber  822 , the valve body  860  will be moved from right to left, thus increasing the size of orifice  842  which will result in an increase in flow. If the pressure in chamber  832  is less than the pressure in chamber  822 , the rolling diaphragm will move from left to right, thus moving valve body  860  from left to right and decreasing the size of orifice  842  with a resulting decrease in flow through the orifice. Vacuum is provided by vacuum injection or induction system  856  which is in fluid communication with outlet  850  that receives fluid flow from flow chamber  822 . Vacuum source  856  is also in fluid communication with the flow chambers of each of the associated individual devices. Between device  812  and its two adjoining devices are a pair of connectors  870  and  872  that may be identical. Connectors  870  and  872  provide conduits,  886  and  888  respectively, that serve to provide a fluid connection between flow chamber  822  and equalization chamber  834  as well as between equalization chamber  832  and flow chamber  820 . Pressure in flow chamber  822  is equalized with that of equalization chamber  834  by a fluid connection provided by conduit  882 , connector  898  and conduit  888  which is in fluid communication with equalization chamber  834 . Likewise, flow chamber  820  of device  810  communicates with conduit  880  which in turn communicates with connector  896  and conduit  886  that is in communication with equalization chamber  832 . Thus, multiple units may be joined together by placing a middle connector, such as  870 , between the two modular units along with union  896 . Middle connector  870  is designed to mate with receiver  878  (FIG. 7) that provides for a fluid-tight connection between adjacent devices. A middle connector is configured to join two similar or identical devices in series. An end connector, however, is designed to terminate either end of the series and to provide fluid communication between an equalization chamber on one end of the series and a flow chamber on the opposite end. 
     Either or both ends of the modular system may be terminated by the use of an end connector such as  874 . End connector  874  may include conduit  876  that communicates with tube  890  via threaded connector  892 . Thus, while pressure-fit union  896  may join a connector and device using an unthreaded O-ring seal, end connector  874  may be designed to threadably receive connector  892 . Likewise, connector  894  may be connected to conduit  884  in device  814  by a pressure fit design. Tubing  890  provides communication between flow chamber  824  and equalization chamber  830  via connector  894 , tubing  890 , connector  892 , and conduit  876 . Tubing  890  may be flexible polymeric material, such as PTFE, that is resistant to the fluid being used and may be of variable length to accommodate modular systems of different sizes without requiring change out of the tubing. Each of the connectors and/or devices includes clamps for securing the modules and connectors together and may also include integral hangers for wall mounting of the system. Thus, using the modular system illustrated in FIG. 8, the number of fluid sources may be increased or decreased within minutes, by simply adding or subtracting a modular unit, connector and union. When properly configured, the interdevice communication of the modular system will provide for equal drawdown from each of the fluid sources independently connected to each device. 
     Further modifications and equivalents of the invention herein disclosed will occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the invention as defined by the following claims.