Handling Low Flow Conditions in Large Pumping Applications
Low flow conditions can be the biggest problem for your pumping system. Large water distribution systems with miles of pipe lines and numerous connections will inevitably develop leaks that are undetectable. A seep here and a leak there, a few dripping faucets, leaking toilets, or a weeping zone valve and you have a low flow problem. Systems such as golf courses, nurseries, feed lots, and municipalities, are all susceptible.
When using a Cycle Stop Valve there are many different ways of handling these low flow conditions, which we call a "continuous demand" system.
One of the best and most efficient ways is to use a "Jockey Pump" or, when used in conjunction with a Cycle Stop Valve it is better described as a "pressure maintenance pump" or PM Pump. These small pumps can be sized to produce three to five times the amount of the minimum flow or "leak". The PM pump in conjunction with a Cycle Stop Valve will run 24/7. Using a system with a minimum flow or leak of 10 GPM as an example, a 50 GPM PM pump would continue to run producing a constant pressure and be fairly efficient with leaks as low as 5 GPM. As small usage is required the Cycle Stop Valve would match the usage up to 50 GPM, which is the limit of the PM pump. Usage above 50 GPM would cause the system pressure to decrease. When the system pressure is a few PSI lower than the pressure controlled by the Cycle Stop Valve on the PM pump, a larger or base load pump would be called to start. Multiple large pumps can be brought on line as needed and when each is controlled by it's own Cycle Stop Valve, will continue to match the increasing system flow requirements. When the system flow requirement again falls below 50 GPM, the PM pump with it's Cycle Stop Valve will be able to bring the system pressure up to the point where the large pump or pumps will be shut off. The PM pump type system is not only the most efficient but, can considerably reduce wear on the larger more expensive pumps.
These large systems will always have a continuous, and yet sometimes very small demand. When using the PM pump and Cycle Stop Valve system there is really no need for a pressure tank. Only a small one-gallon sized bladder tank is required connected to, and for the cushioning of, the pressure switches. This basically tankless system should use a small pressure relief valve set at higher pressure than the Cycle Stop Valve on the PM pump. The PM pump is designed to run all the time and therefore does not need a pressure switch. The pressure relief valve will discharge 5 GPM if the system for some unknown reason was ever shut down to a zero flow condition.