When a customer asks us for a horizontal multistage pump, one question comes up quite often: how many stages do I need?
There is no fixed answer such as "three stages for water supply" or "five stages for boosting." The required number of stages depends mainly on two things: the flow the system needs and the total head the pump has to produce.
In practical pump selection, we do not normally start from the number of stages. We start from the duty point.
For example, a customer may need 4 m³/h at 20 m head, while another system may require the same 4 m³/h at 40 m head. The flow is the same, but the second pump has to generate much more pressure. Depending on the hydraulic design, it will normally need more stages.
That is why "I need a 4-stage pump" is not enough information for us to select a model.
Start With the Required Head, Not the Stage Number
The first step is to determine how much head the system actually needs.
For a typical water transfer or pressure-boosting system, total head may include the vertical lifting height, pressure required at the outlet, pipe friction and pressure loss through valves, filters, heat exchangers or other equipment.
A pump therefore does not need enough head just to lift the water from one level to another. It also has to overcome all the resistance between the suction point and the final point of use.
This is where buyers sometimes underestimate the requirement.
A system may have only 12 m of vertical height, but after pipe losses, valves and required outlet pressure are included, the pump may actually need 25 or 30 m of total head.
The opposite problem also happens. Some buyers add a large safety margin and select a pump with much more head than the system needs. The pump then has to operate with a throttled valve, which is usually not a good way to solve an oversized selection.
So before deciding whether the pump needs three, four or six stages, calculate or estimate the total dynamic head first.
Then Check How Much Head Each Stage Can Produce
Once the required flow and total head are known, the next step is to look at the hydraulic performance of the pump series.
In a horizontal multistage centrifugal pump, the impellers work in series. Each stage adds energy to the water, so adding stages mainly increases the available head.
But there is an important point: the head produced by one stage is not a fixed number for every pump.
A stage in a small-flow pump and a stage in a larger-flow pump may use different impeller diameters and hydraulic designs. Even within the same series, the actual head per stage changes with flow.
This means a rule such as:
- one stage = 10 m head
should not be used as a universal selection method.
For a preliminary estimate, an engineer may compare the required total head with the approximate head produced by one stage at the required flow. But the final stage count should always be confirmed against the manufacturer's pump curve.
A simple way to understand the relationship is:
Estimated stages ≈ Required head ÷ Head produced per stage at the required flow
This is only an initial estimate. It is not the final model selection.
MISLIER's current horizontal pump range includes CMF and CMI configurations with different hydraulic sizes and head ranges, which is why the same required head may lead to a different number of stages depending on the selected flow range.
Why Flow Must Be Checked at the Same Time
Stage count mainly affects head, but that does not mean flow can be ignored.
Suppose a system requires 8 m³/h at 35 m head. The first step is not to find any five-stage pump that can produce around 35 m. We first need a hydraulic size that is designed to operate around 8 m³/h.
After the correct flow range is identified, we then select the stage configuration that can provide the required head around that operating point.
If the hydraulic size is too small, simply adding more stages will not solve the flow problem.
This is one of the reasons buyers sometimes receive very different quotations for what appears to be the same request. One supplier may select a smaller hydraulic size with more stages, while another may select a larger hydraulic size with fewer stages.
The model numbers look different, but what really needs to be compared is the operating point on the pump curve.
For purchasing, we therefore recommend comparing at least:
Flow + Head + Motor Power + Materials + Voltage/Frequency + Pump Curve
rather than comparing the number of stages alone.
More Stages Are Not Always Better
A higher-stage pump is not automatically a safer choice.
If the pump produces considerably more head than the system needs, the operating point can move away from the preferred range of the pump. The system may then require throttling to control flow or pressure.
This can increase unnecessary energy use and may also affect long-term operation.
Motor power must also be checked.
As the required head increases, the power required to move the same flow normally increases as well. This is why a higher-stage model may use a larger motor even though the rated flow remains similar.
There is also a physical difference. More stages usually make the pump section longer. For equipment manufacturers or compact skid systems, available installation space may therefore become part of the selection.
So the objective is not to choose the pump with the most stages. It is to choose the lowest practical stage configuration that still meets the required duty point within a suitable operating range.
A Practical Example of Stage Selection
Take a simple industrial water system as an example.
The customer first confirms that the system requires:
Flow: 6 m³/h
Total head: 32 m
Liquid: clean water
Temperature: 25°C
Power supply: 380 V / 50 Hz / 3 phase
At this point, we would first select a horizontal multistage pump hydraulic range that can comfortably handle around 6 m³/h.
Then we check the performance curves of the available stage configurations.
If a lower-stage model cannot reach 32 m at 6 m³/h, it is excluded. If the next configuration reaches the required point within a suitable part of the curve, there is normally no reason to continue adding stages just to obtain extra pressure.
After that, motor power, materials, connection size and installation conditions are checked before the final model is confirmed.
This process is more reliable than starting with a statement such as "six stages should be enough."
It is also why, when we receive a pump inquiry, flow and head are normally the first two parameters we ask for.
The values above are only an example of the selection process. The actual model should always be confirmed from the performance data of the selected pump series.
What Should You Send Us for Stage Selection?
If you are buying a horizontal multistage pump and are not sure about the number of stages, you do not need to calculate the stage count yourself.
The most useful information to send is:
- Required flow
- Required head or discharge pressure
- Liquid
- Liquid temperature
- Voltage, frequency and phase
- Pump inlet and outlet size, if specified
- Material requirement
- Installation or application
- Quantity
If the pump is replacing an existing unit, send the nameplate photo and model number as well. A pump curve or installation photo is even more useful.
From these parameters, the hydraulic size and stage configuration can be checked together instead of selecting the pump only from the stage number.
You can also review the current MISLIER horizontal pump range. The range includes horizontal pump configurations for industrial liquid transfer, circulation, pressure boosting, cooling and water-treatment applications. MISLIER's CMI series, for example, is currently listed for industrial liquid transfer, chilled-water circulation, water treatment and process boosting.
Need Help Choosing the Right Number of Stages?
Shanghai Mislier Pump Industry Co., Ltd. is a water pump manufacturer established in Shanghai in 2010. Our current product portfolio includes horizontal centrifugal pumps, vertical multistage pumps, booster systems, sewage pumps and other water-handling products, and we provide pump selection and technical support for distributors, contractors, system integrators and OEM customers. Shanghai Mislier Pump Industry Co., Ltd
For a horizontal multistage pump, there is no need to guess the stage count before requesting a quotation.
Start with the required flow and head. From there, we can check the hydraulic size, pump curve, stage configuration, motor power and materials.
You can view our horizontal pump products first if you want to compare available configurations.
If you already have a project requirement or an existing pump to replace, send us your operating parameters for pump selection and quotation. A nameplate photo, pump curve or basic system information can also help us confirm the selection more quickly.