There's more than one way to satisfy high head requirements in a pumping system. But which will work best for your process? Utilizing a multistage centrifugal pump, or setting up multiple centrifugal pumps in series are two design strategies available. We'll compare these in this post.

When considering whether to go with pumps in series, or a multistage centrifugal pump for a project, the most critical items to solve for are pump performance, system operation, and the cost. Let's compare how each method measures up in these areas.

Efficiency

Typically the multistage pump will win this battle. These pumps have smaller impeller diameters and tighter clearances for higher performance and efficiency. Additionally, expect less motor horsepower to be required. With only one motor, your energy usage should be less with this configuration.

Space

Multi-stage pumps can save on floor space with their vertical configuration. Single stage can also be installed vertically, but multiple, single stage pumps will take up a lot of space in series, regardless of installing vertically or horizontally.

Pressure Flexibility

Assuming a constant flow, a VFD is needed to control the multistage pump and adjust any pressure build.

When piping multiple centrifugal pumps in series, with isolation/bypass options, the flow could potentially be diverted from one or more pumps, thus reducing the pressure generated in a “manual” way.

Solids

Multistage centrifugal pumps do not handle solids. If the process fluid contains debris or significant solids, a multistage pump will not be the right selection.

Maintenance

Depending on pump size and quality, single stage pumps will be easier to fix as they have fewer parts and stages. Additionally, with multiple pumps in the system, spares are technically available, or hopefully enough running to keep your process going. But keep in mind that more pumps mean more preventative maintenance as well.

Cost

It certainly depends on the pumps chosen and application type, but by evaluating the factors of equipment, piping, labor, energy usage, and maintenance, this category could go either way. In a clean fluid, simple application, generally, the multistage would be recommended.

Making the Choice

Multistage centrifugal pumps offer the benefit of better efficiency due to tighter impeller clearances and smaller impeller diameters. Higher pressure can be achieved with a smaller motor size and less energy. They also have a smaller footprint. Multistage centrifugal pumps can cost more than a little end suction, but running costs will be less. They also do not handle solids and would require a VFD for any sort of pressure variation. But perhaps the biggest watch out is, if the pump goes down, you run the risk of being dead in the water.

Single stage centrifugal pumps in series, with isolation/bypass valves, allow for system flexibility and manual pressure control. Piping can divert flow from a pump if less pressure build is desired, for example. This allows for spare pumps in the system, or at least a few running if failures occur. However, these pumps may not be as efficient, depending upon the impeller type. Motors may be larger than the multi-stage, not to mention the greater quantity of motors required.

The choice between generating more head with multiple pumps or multiple stages is one that is highly dependent upon each application. Be sure to involve an engineer well versed in pumping systems to make this decision.

Multi-Stage Centrifugal

AMT - Calpeda

1 1/4" - 6" Discharge

2600 GPM

2600' TDH

Constant Pressure Booster Pak Systems Available

Multi-Stage Centrifugal Pumps from AMT & Calpeda

Pump Solutions distributes multi-stage centrifugal pumps from a number of manufacturers, including AMT and Calpeda. If you have questions or would like to order a multi-stage centrifugal pump, contact our pump provider. 

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Applications Ideal for Multi-Stage Centrifugal Pumps

For applications that require a high output or just high pressure in general, a multi-stage centrifugal pump might be the right pump for your needs.

To design a centrifugal pump with a single impeller developing a differential pressure of more than 150 PSID between the suction and the discharge is difficult and costly. A more economical approach to gaining the same results is to go with a multi-stage centrifugal pump.

A multi-stage centrifugal pump is a centrifugal pump that contains two or more impellers: either mounted on the same shaft or different shafts.

To achieve higher pressures at outlet, the impellers may be connected in series. 

For high output, the impellers may be connected parallel.

 Here’s a visual example of series and parallel impeller set-up:

Diagram of Impellers in Series

Diagram of Impellers in Parallel

Note: when connected in series, the impellers don’t have to be in a square shape, they just have to be connected.

Pros and Cons of Multi-Stage Centrifugal Pumps

Pros Cons Higher efficiency Many parts inside the casing to maintain and service Higher output power (PSID) Parts inside the casing are difficult to get to Various and customizable build Expensive initially and to maintain

Centrifugal Pump Basics

Centrifugal pumps consist of one or more rotating impellers inside a stationary volute – the casing 

The liquid enters the pump through the suction inlet into the eye of the impeller

The speed of the rotating impeller(s) forces the substance out through the discharge nozzle

The liquid enters the inlet of the centrifugal pump under atmospheric pressure, and flows into the eye of the impeller

Using centrifugal force, the substance moves away from the impeller eye and out along the impeller vanes where the substance is forced against the inside walls of the volute and out through the discharge of the pump

Due to the reduction of pressure occurring at pump inlet and impeller eye, substance is drawn into the pump in continuous flow through suction

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