The number of starts per day directly influences the life of all pumping systems. Excessive cycling affects the life of control components such as pressure switches, starters, relays, and capacitors. Cycling can also cause motor spline or key damage, bearing damage, and motor overheating. All of these conditions reduce the effective life of any pumping system.
The valve size, tank size, and other controls should be selected to keep the starts per day as low as practical for longest pump system life. The maximum number of starts per day vary according to pump type, pump size, and other considerations. Consult your motor manufacturer for maximum number of starts per day for your particular application.
Most small motors need to run a minimum of 1 minute, and remain off for a minimum of 1 minute to properly dissipate heat. Larger motors will need to run longer and stay off longer between starts. The lower the number of starts per day, the longer the pump system will last.
Worst Case Number of Starts Per Day with Large Pump Systems
The Cycle Stop Valve or CSV makes a variable flow pump from any standard submersible, turbine, or centrifugal pump. Water comes directly from a full speed pump, through the CSV, past the inlet to the captive air pressure tank, then straight on to the open tap or taps. A slight increase in system pressure causes the CSV to restrict the flow. A tiny decrease in system pressure causes the CSV to open and increase the flow. Controlled by the CSV, the pump will match flows from as little as 5 GPM to as much as the pump will put out. No excess water remains to fill a pressure tank. The CSV can never completely close. In its most closed position the CSV still allows 5 GPM to "leak" through the valve. If all the taps in the system are closed reducing flow to 0 GPM, this 5 GPM "leaking" through the CSV has no place left to go except into the pressure tank. The system pressure begins to increase as the pressure tank fills at 5 GPM. When pressure increases to the pressure switch cut out point, the pump is stopped.
The amount of draw down available in the tank can be used slowly or dumped quickly. A tank with 25 gallons of draw down will supply a tap of 1 GPM for 25 minutes. This 25 gallons of draw down could also be dumped in seconds if a large tap is opened. Either way the system pressure is lowered to the pressure switch cut in point and the pump is started.
As long as a tap is open and using at least 5 GPM, the pump continues to run, and the CSV maintains a constant pressure on the entire system. Worst case is a small tap or system leak of less than 5 GPM. When the pump is running the CSV will always allow 5 GPM into the system. An open tap using 2.5 GPM will cause the other 2.5 GPM to slowly fill a tank. A tank with 25 gallons of draw down will be filled in 10 minutes and the pump will be shut off. With the 2.5 GPM still being released at the open tap the 25 gallons in the tank will be expressed in 10 minutes and the pump will be restarted.
Using a tank with 50 gallons of draw down will double the time to 20 minutes on and 20 minutes off, changing the maximum number of starts per hour from 3 to 1.5. Minimum run time and maximum starts per hour can only occur at flows of less than 5 GPM. Any system with demands or leaks of less than 5 GPM should use this worst case scenario to size the tank or install a small maintenance pump in the system. Larger systems which never have a flow less than 5 GPM can use a smaller tank. As long as more than 5 GPM is being used in the system the CSV will never allow a tank of any size to fill.
The CSV controls the pump or pumps to always exactly match the flow used in the system. There needs to be enough pump or pumps to supply the maximum flow required. The pump or pumps should draw water from a source large enough to supply maximum demand on a continuous basis. (ie. huge ground storage tanks, underground aquifers, lakes, rivers, etc.) Large hydro tanks and even water towers are minuscule in size when compared to the supply sources. Water stored in large hydro tanks and water towers can only be used for short time periods of emergency use. Emergency water usage can be extended indefinitely if generators or emergency pumps are used. Emergency power or pumps can draw water directly from the source. This provides an unlimited supply for emergency use and cost a fraction of the amount spent on water towers and large hydro pneumatic tanks.