The average number of starts per day greatly influences the life of a submersible pumping system. For example, let’s say an elderly couple has a 3/4 HP 10 GPM pump, a 34 gallon pressure tank, and averages 10 pump cycles per day. In this scenario, I would expect their pump to last 15, 20, 30+ years due to such a small demand. Now let’s say the elderly couple sells their house and a family of 9 moves in. Kyle homeowner, father of 7, decides to install a massive 5-zone 9 GPM sprinkler system but he does not make any renovations to the existing well pump equipment. Due to the undersized pressure tank his pump is now cycling over 300 times per day. I’d be surprised if the well pump lasted 2 years under these conditions.
Excessive cycling affects the life of everything in the system - pressure switches, starters, relays, and capacitors. Rapid cycling of the motor can cause spline damage, bearing damage, and excessive heat. Motors are either liquid or air-cooled, so while the pump is running the heat is kept at an appropriate temperature. But on startup, huge amounts of current (and heat) surge into the motor windings to get it spinning. If the motor has several starts in a short time period, then the motor windings will not have a chance to cool and they will begin to break down. This quote from one of our motor suppliers sums it up well: “You only get so many starts out of a motor - whether you use them over 15 years or 15 minutes.”
Run time is another piece of the puzzle: 4” motors up to ¾ horsepower should run for at least one minute and motors over ¾ horsepower should run a minimum of two minutes to dissipate the heat build up from starting current. A properly sized pressure tank will ensure that the motor runs for the minimum recommended time (Bigger is always better!). The caveat to this rule is for large irrigation systems (10+ GPM): Instead of installing several large pressure tanks it usually makes more sense to just keep the pump running continuously via a Constant Pressure Controller or Cycle Stop Valve.
Choosing the right combination of pump size, tank size and pump controls can keep the starts per day as low as practical for the longest life. Our experts are ready to help you with your well water system needs! Call 855.329.4519 or email Customer.firstname.lastname@example.org
Click the links below to see related R.C. Worst blogs and YouTube videos:
Troubleshoot: Water Well Pump Starts too Often (Rapid Cycling)
How Long Should My Submersible Well Pump Last?
Sizing a Pressure Tank Correctly - More Protection for your Pump
* Keeping starts per day within the recommended numbers provides the best system life. However, when used with a properly configured Reduced Voltage Starter (RVS) or Variable Frequency Drive (VFD), 7.5 thru 30 hp three-phase motors can be started up to 200 times per 24 hour period.