Submersible Pump Stages: What They Are and How Many You Need
The number of stages sets a submersible pump’s head, motor power and cost. What a stage is, how to calculate the stage count and the maximum stages in each FANPO series.
What is a stage?
One impeller and one diffuser: one stage
Submersible pumps are multistage pumps. Each stage consists of an impeller that adds energy to the water and a diffuser that converts that energy into pressure. The water passes through the stages in turn, gaining head at each one. Within a series, the number of stages therefore sets the head, while the hydraulic design of the stage sets the flow.
Stage count sets the head
Within a series, the head a pump can produce rises roughly in proportion to the number of stages.
Flow does not rise with stages
For more flow you need a higher-flow series, not more stages.
Power demand rises with stages
Every additional stage needs additional power, so more stages require a larger motor.
Axial thrust rises with stages
At high stage counts, check that the axial thrust generated by the pump stays within the thrust bearing rating of the motor.
How to calculate the number of stages
Worked example
Consider an installation with a total dynamic head of 159 m. If the performance table on the product page of the chosen series shows roughly 8 m of head per stage at the design flow, then 159 ÷ 8 = 19.9, and the 20-stage configuration is selected. Finally, check that this stage count is within the maximum for the series.
The head per stage in this example only illustrates the method. The real value depends on the series and the flow; always use the stage-by-stage performance table on the relevant product page. For total dynamic head, see the total dynamic head calculation guide.
Maximum stages in FANPO series
| Series | Material | Size | Max stages | Max head |
|---|---|---|---|---|
| 6017 | Stainless steel | 6″ | 40 | 460 m |
| 6024 | Stainless steel | 6″ | 33 | 442 m |
| 6030 | Stainless steel | 6″ | 40 | 633 m |
| 6046 | Stainless steel | 6″ | 25 | 372 m |
| 6060 | Stainless steel | 6″ | 25 | 370 m |
| 8075 | Stainless steel | 8″ | 22 | 423 m |
| 8095 | Stainless steel | 8″ | 22 | 551 m |
| 8096 | Stainless steel | 8″ | 22 | 467 m |
| 10110 | Stainless steel | 10″ | 20 | 549 m |
| 5004 | Cast iron | 5″ | 6 | 85 m |
| 6012 | Cast iron | 6″ | 10 | 295 m |
| 6013 | Cast iron | 6″ | 25 | 420 m |
| 6019 | Cast iron | 6″ | 18 | 270 m |
| 7021 | Cast iron | 7″ | 25 | 435 m |
| 8420 | Cast iron | 8″ | 18 | 436 m |
| 8530 | Cast iron | 8″ | 14 | 414 m |
| 8535 | Cast iron | 8″ | 14 | 405 m |
Maximum head is the series limit reached at the highest stage count and low flow; it does not occur at the same operating point as maximum flow.
When the stage count is wrong
Too few stages
The pump cannot reach the required head; water arrives at the delivery point with insufficient flow, or not at all.
Too many stages
The pump produces more pressure than needed, is throttled with a valve and wastes energy. The larger motor it requires also raises the initial cost.
Selected from well depth
Well depth is not head. The stage count must be based on the sum of dynamic water level, discharge height, friction loss and outlet pressure.
Frequently asked questions
Does more stages mean more flow?
No. Within a series, more stages increase the head; the flow range depends on the hydraulic design of the series. For more flow, choose a higher-flow series.
How does the number of stages affect motor power?
Each stage needs additional power. Once the stage count is set, read the absorbed power at the duty point from the product table and select the next motor rating above it.
Can stages be added later?
It depends on the pump design and on the power and thrust capacity of the motor. Before adding stages, always check the new duty point and whether the motor is still suitable.
Can FANPO calculate the stage count for me?
Yes. Send the dynamic water level, required flow, discharge height, pipe details and casing diameter through the contact page, and our technical team will propose a suitable series and stage count.
Prepared by the FANPO engineering team · Last updated: 8 November 2026