There are other ways of handling continuous low flow in systems where there is no place to install a small Pressure Maintenance pump. An example would be a system with a water source being a single water well with a 100 HP pump. When used with a Cycle Stop Valve the 100 HP would be able to supply a demand as small as 5 GPM without causing damage to the pump or the system. However, the 100 HP pump when restricted would only drop to about a 60 HP load. While the 5 GPM flow will not hurt the pump or motor in any way, it is not very efficient to use 60 HP to pump 5 GPM. Therefore, another option is recommended. For this example we are going to start the 100 HP at 50 PSI and turn it off at 60 PSI. The Cycle Stop valve will also be set at 50 PSI. The 100 HP and it's Cycle Stop Valve will feed from 5 GPM to 2,000 GPM into the system while maintaining 50 PSI. The only way the 100 HP will be shut off is if the flow rate being used is less than 5 GPM. Then 5 GPM will enter a small pressure tank until the pressure reaches 60 PSI and the 100 HP will be shut off. This is never going to happen because the system is large enough that there is about 10 GPM minimum flow at all times.
We can still install a PM pump. Somewhere in the distribution system, it can be past the controls at the 100 HP well or anywhere along the pipe line, a ground storage tank is needed. For this example we are going to use a 3,000 gallon atmospheric tank tied into the main line 100 yards from the supply well. A 3" solenoid valve is used to fill the 3,000 gallon tank. The solenoid valve is opened by a low probe and closed by a high probe in the tank. Drawing water out of the 3,000 gallon tank is a 3 HP 50 GPM PM pump. The PM pump is controlled by a Cycle Stop Valve and a pressure switch with a small pressure tank. The PM pump starts at 60 PSI and is turned off at 70 PSI. The Cycle Stop Valve on the PM pump maintains 60 PSI when usage is between 5 GPM and 50 GPM. The PM pump simply discharges into the main line. When the 3,000 gallon storage tank is full and usage is less than 50 GPM the 3 HP pump is the only pump running. When the 3,000 gallon tank is empty the low probe would shut off the PM pump and open the solenoid valve at the same time. The pressure would drop to 50 PSI and the 100 HP would be started. The Cycle Stop Valve on the 100 HP would hold the system at 50 PSI matching the usage in the system while refilling the 3,000 gallon tank. When the storage tank is full and the top probe is reached the solenoid valve would shut and the PM pump would be restarted. If the usage is less than 50 GPM the PM pump will be able to bring the system pressure up to 60 PSI which would shut off the 100 HP pump. If usage is above 50 GPM the PM pump will not be able to bring the system pressure up to 60 PSI. The Cycle Stop Valve on the 100 HP will maintain 50 PSI and add only what extra water is needed above what the 3 HP cannot produce. As long as the usage remains below 50 GPM the 100 HP pump only comes on to refill the 3,000 gallon tank as needed.