How many sources should run at once?

As many as the level band calls for, limited by what the electrical system and the treatment can take; the design states the maximum and the sequence enforces it. Running one source longer beats running three sources in short cycles.

Should wells alternate or should the best well lead?

Both can be true: rotate for exercise and drawdown recovery, and weight the rotation toward the well with the best quality or lowest cost. A well never run is a well with a surprise in it.

The tank never reaches the off level in summer.

The sources cannot keep up with demand at the pumping hours allowed. Extend the schedule window, add a source to the stage, check that every source is actually producing its rated flow, and look at the demand for leaks or unusual users.

Where does the sequence live, in the tank site controller or the source controllers?

Usually in one controller with the level, the tank site or the plant, which sends run commands to the sources; each source keeps local protection and a fallback. A sequence split across several controllers with no master is hard to reason about.

Pump Sequencing for Storage | CurryControls.com

The short answer

Sequencing decides which pumps run, in what order, and when, to keep a tank within its band using the sources a system has. The basic form is staging on level: the first source starts at the lead-on level, the second at a lower band, and so on, with all stopping at the off level; the refinements are rotation so that each well or pump shares the duty and each is exercised, scheduling so that pumping happens in cheap power hours and the tank is full before the morning demand, minimum run and rest times so that no source short-cycles, staggered starts so the electrical system sees one motor at a time, and a failure logic that promotes the next source when one is unavailable. Where the sources differ, in capacity, in water quality, or in cost, the sequence also decides which to prefer, and the operators need to see the reasoning on the screen. The proof that it works is in the trends: level within band, hours balanced, starts within rating, and energy in the off-peak hours.

Key points

Stage on level bands sized from the tank volume, the source capacities, and the starts-per-hour limits.
Rotate sources for even wear and exercise; prefer sources by cost or quality when the design says so.
Schedule pumping into off-peak hours with the level bands as the limits and a full tank before peak demand.
Minimum run, minimum rest, and staggered starts keep motors and the electrical system within limits.
A failed or unavailable source is skipped automatically and alarmed; the sequence never waits for an operator.

Staging on level

Level band	Action	Sizing
Off	All fill sources stop	Below the overflow with margin; above the level that keeps water moving
Lead on	First source starts	Volume between off and lead-on sets the cycle frequency for one source
Lag on	Second source starts	Below lead-on by a volume that gives the first source time to show it is winning or losing
Third and more	Further sources start	Successively lower; each band gives the previous stage time
Low alarm	Operator alerted	Enough volume above the pump cutoff for a response
Low cutoff	Draw pumps stopped	Pump protection

The bands can be fixed levels or a level PID output that stages pumps at output thresholds; the fixed bands are easier to understand at a lift station or a tank site and are what most systems use. Hysteresis between the on and off levels for each stage, and a minimum run time, stop a source from cycling on a level that hovers at its band.

Rotation and preference

Rotate the lead source each cycle or by run hours so that wells share the drawdown and pumps share the wear.
Exercise a source that has not run for a set period, so that a standby well does not sit idle for a season.
Prefer the cheaper or better-quality source by making it lead more often, with the reasoning on the screen.
Hold a source out for water quality, a sanding well or one with a rising nitrate, by a selection that the sequence respects and alarms on after a set time.
Blend sources by running them in proportion where the quality requires it, with the blend ratio as a setpoint.

Scheduling

Power costs differ by hour, and demand differs by hour, and the tank is the buffer between them. A schedule lets the sequence pump the tank full during off-peak hours and hold the fill sources off during peak hours as long as the level stays above a reserve band; the level bands remain as the limits so that a hot day overrides the schedule. The schedule is a setpoint table on the screen, the reserve level is a limit the operators cannot set below the fire reserve, and the energy report shows how much pumping happened in each period.

Required fill rate = (L_target − L_now) × A_tank ÷ t_window

L_target = the level wanted at the end of the window
L_now = the current level
A_tank = the tank area, so that level times area is volume
t_window = the hours left in the off-peak window
Compared with source capacities to decide how many to run

Protecting the equipment

Minimum run time: Once started, a source runs for a set minimum unless a fault or the high level stops it; well pumps in particular need minutes, not seconds.
Minimum rest time: Once stopped, a source waits before restarting; the motor rating for starts per hour sets it.
Staggered start: Sources called at the same time start seconds apart, and on generator power the stagger is longer.
Ramped start: Drives and soft starters ramp; across-the-line starts are staggered and the check valves and surge protection sized for them.
Drawdown limits: A well is not run below its safe drawdown; a level or a pressure in the well casing stops it and the sequence promotes the next source.

Failure handling

A source that fails to start, trips, is in off, or is locked out is skipped: the sequence promotes the next source at once, alarms, and holds the failed source out until it is reset. A level transmitter that fails is detected by its diagnostics and by rate-of-change checks, and the sequence falls back to a local level signal, a timed fill, or a safe state, according to the narrative. A communication loss between the tank and the sources is handled the same way. Every one of these is tested at commissioning by simulating the failure, and the response is in the control narrative.

Frequently asked questions

How many sources should run at once?: As many as the level band calls for, limited by what the electrical system and the treatment can take; the design states the maximum and the sequence enforces it. Running one source longer beats running three sources in short cycles.
Should wells alternate or should the best well lead?: Both can be true: rotate for exercise and drawdown recovery, and weight the rotation toward the well with the best quality or lowest cost. A well never run is a well with a surprise in it.
The tank never reaches the off level in summer.: The sources cannot keep up with demand at the pumping hours allowed. Extend the schedule window, add a source to the stage, check that every source is actually producing its rated flow, and look at the demand for leaks or unusual users.
Where does the sequence live, in the tank site controller or the source controllers?: Usually in one controller with the level, the tank site or the plant, which sends run commands to the sources; each source keeps local protection and a fallback. A sequence split across several controllers with no master is hard to reason about.

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