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Constant Pressure Concept Stops Line Breaks Constant pressure is not so much a thing as it is a different idea or a concept in pumping systems. An idea, which consist of always keeping the water flowing. Changing the amount of flow produced to match the flow being used, yet never stopping the flow entirely. Constant pressure can eliminate many problems in water supply systems, increase dependability, and reduce energy cost. For the system pressure to remain at a constant, supply and booster pumps must be able to vary their output to instantly and exactly match the demand. Any water supply system that is large enough to have more than 5 GPM going to distribution at all times is considered to have a continuous demand. Any system with the equivalent of 50 homes or more should qualify, with 350 GPD per home that is an average of 12 gallons per minute. Smaller systems can utilize a small pressure relief that returns 5 GPM to the supply tank when there is zero flow to the system. Peak demands could be as high as each system requires while the minimum system requirement is set at 5 GPM. Even the smallest systems (such as one house) can utilize constant pressure but, must deal with zero flow conditions. In these smaller systems constant pressure can only exist when some flow is being used. If flow is at zero, pressure should be allowed to increase slightly as a pressure tank fills. When pressure has increased to a preset amount above the required constant pressure, a pressure switch will turn off the pump. Now the volume of water stored in the pressure tank must be expressed into the system before the pressure lowers to a point that restarts the pump. Any continuous demand is held at a constant pressure while zero flow conditions can utilize a pressure band width. In the past pressure tanks and elevated tanks were allowed to fill completely at full pump capacity, then valves are closed and or pumps are stopped. When the level in these tanks is lowered, pumps are started and or valves are opened. This process is repeated over and over causing pumps to cycle frequently, pressure to vary widely, and creating devastating water hammer and pressure surges each time the flow starts or stops. Never completely stopping or having to restart the flow in supply lines eliminates these problems. Constant Pressure systems require a different thought process. Ground storage and elevated tanks can use a non-closing pressure reducing valve to maintain a constant level or pressure. 40 PSI constant will maintain a level in an elevated tank of 92'. 10 PSI constant will maintain a level in a ground storage tank of 23'. Maintaining a constant level in these tanks requires that the supply pump or pumps be able to produce the exact same flow as is being used from the tank. If 7 GPM is all that is being drawn from the tank, then 7 GPM is the rate that must be filling the tank. If 19,622 GPM is being drawn from the tank, then 19,622 GPM is the rate that must be filling the tank. This requires that the pump or pumps be able to match the demand instantly, exactly, and efficiently. Maintaining a constant downstream pressure the Cycle Stop Valve attached to the discharge of the pump knows that if pressure tries to increase, less flow is needed. If pressure tries to decrease, more flow from the pump is needed. The valve will vary the size of its opening to allow the pump to produce exactly the amount of flow being used. Multiple pumps working together is the best way to efficiently produce a wide range of flow rates. Minimum flow can be efficiently produced by a small pump while average flow may require a larger pump. Then when peak demands or fire flow is required, even larger pumps come on line until the demand is satisfied. These pumps can be in the same pump house or scattered in different locations. The Cycle Stop Valves hold a different constant pressure with each pump on the system. The pressure held constant by the small pump is the same pressure that shuts off the medium size pump. The pressure held constant by the medium size pump is the same pressure that shuts off a larger pump and so on. A system with four pumps and a minimum required pressure of 60 PSI would have the valve on the largest pump supply exactly 60 PSI. The next largest pump would supply 65 PSI. The valve on the medium size pump would supply 70 PSI, and the valve on the smallest pump would be set at 75 PSI. This ensures that only the right size pump or pumps are running to handle the particular job. When the system is running at full capacity a minimum of 60 PSI is maintained while all four pumps are running. As the system flow decreases, pressure increases, and pumps begin to turn off as they are no longer needed. Turning on or off pumps #2 through #4 as needed does not cause water hammer. The Cycle Stop Valve on each pump chokes its pump to 5 GPM before the pump is started or stopped. The system will be held at 75 PSI constant when only the small pump #1 is needed. The small pump will run all the time keeping some flow moving. As long as even a small amount of water is moving down the pipe, the flow never stops or has to be restarted eliminating water hammer completely. This system can be supplying water to a storage tank 10 miles away and can be tapped for distribution anywhere along the 10 miles of pipeline. At the storage tank which is 10 miles away, more booster pumps can be drawing from this storage tank. The process can be repeated to boost to distribution and or storage tanks another 10 miles or so away and so on. The same water can be pumped from one booster system to another fourteen times if there are 140 miles of pipeline to supply. Water lines can branch off anywhere along the line and go in any direction. These branches can have boosters along the way if needed as well. As the branches get smaller, so does the size of the booster systems. If elevated tanks are not included in the system, fire protection can be achieved with increased ground storage. Booster pumps can be fitted with emergency generators. Diesel or gas driven auxiliary pumps that exercise themselves regularly, can also start up on low pressure or power off conditions and provide unlimited flow for emergency conditions. These gas or diesel engines fitted with a governor can also be controlled with Cycle Stop Valves. These emergency pumps can be huge in comparison to the regular supply pumps. Controlled by a Cycle Stop Valve they can produce enormous flows when required or continue to supply demand at any flow rate for an indefinite time period. Utilizing ground storage and backup pumps for emergencies can increase the amount of water available tremendously. Eliminating elevated storage can cut cost considerably, reduce control problems, and help with many other related difficulties. It should also be understood that these booster systems can also pick up water directly from the line at whatever pressure is left and boost again. Storage tanks along the pipeline are only needed where storage for fire protection and the like would be helpful. One booster feeds another at exactly the flow rate needed. That booster feeds another booster the exact flow it needs and so on. This saves energy by using smaller horse power pumps. These pumps use less horse power to boost from 40 PSI to 80 PSI than they do when drawing water from a storage tank at atmospheric pressure and boosting to 80 PSI. The incoming pressure to a booster system is not wasted into a storage tank, then having to be re-pressurized from basically zero pressure back up to the required constant pressure. The same principle applies with high rise buildings, mines, or other systems that continually rise. Starting at the bottom with a booster pump picking up city water at about 40 PSI and boosting it to 80 PSI. Seven floors up another booster picks up the 40 PSI left from the first booster system below and boost it to 80 PSI. At the fourteenth floor a third booster picks up the 40 PSI left from the second booster and boost it to 80 PSI again. This process is repeated every seven floors or so until the top floor has 40 PSI. As the demands decrease going up the building, the booster pumps get smaller. This keeps from having to pump from bottom to top at 300 PSI and having to deal with these high pressures at each floor as well as needing a high pressure piping systems. Water supply systems can vary greatly in flow requirements, elevation, friction loss, fire protection requirements, and so on. There can be many ways to adapt these systems to constant pressure. The concept of constant pressure must first be changed in the mind. Our thought process must make a major switch from trying to supply varying demands by constantly starting and stopping flow to, simply matching the demand continuously. Once our brain has adapted to the concept of “constant pressure”, we can increase dependability, reduce energy cost, and eliminate many of the problems associated with water supply systems of the past. |
| Cycle Stop Valves® is a registered trademark. All right reserved unless prior authorization is obtained. Cycle Stop Valves are patented: Patent number 5,988,984 and other patents pending. |
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