Types and Working Principle of Vertical Centrifugal Pump

A vertical centrifugal pump can circulate chilled water through a building, boost water pressure in a treatment plant, or lift water from a deep sump. These duties may use very different pump designs, even though all three are described as "vertical."

The term refers to the orientation of the pump shaft. It does not, by itself, tell you how many impellers the pump has, where the motor sits, or whether the pump can handle solids.

Understanding those differences makes it easier to choose a pump that fits the installation-and to avoid problems that a larger motor will not solve.

A vertical centrifugal pump uses one or more rotating impellers on a vertical shaft to transfer energy to a liquid. The motor drives the shaft, and the hydraulic components guide the liquid from the inlet to the discharge.

The vertical arrangement can reduce the floor space required for installation. In some designs, it also allows the pumping element to sit below the liquid level while the motor remains accessible above it.

However, a small footprint does not necessarily mean a small maintenance space. Motor removal, shaft withdrawal, and access to internal components may require considerable clearance above the pump.

When comparing vertical centrifugal pump types, remember that the names describe different features. "Inline" describes the nozzle arrangement, "multistage" describes the number of hydraulic stages, and "sump" describes an installation arrangement. A single pump can fit more than one description.

1. Vertical Inline Pumps

A vertical inline pump has suction and discharge connections arranged along the same pipe centerline, with the motor usually mounted above the casing. This layout is commonly used in heating, air conditioning, and water circulation systems. Reference: KSB, In-line Pump

Many vertical inline pumps use a single impeller. Their practical appeal is straightforward: they fit neatly into a pipe run and occupy relatively little floor space.

Typical applications include:

• Chilled-water and heating-water circulation
• Cooling-water loops
• Building water services
• General clean-water transfer

For installation, check the manufacturer's support requirements. An inline arrangement does not automatically mean that the pipework can carry the full pump and motor weight. Pipe strain can also distort the casing or affect alignment.

2. Vertical Multistage Pumps

A vertical multistage pump has several impellers connected in series on one shaft. Liquid passes through each stage in turn, gaining additional head as it moves toward the discharge.

The important distinction is that stages add head. Adding stages does not multiply the flow rate in the same way. Reference: KSB, Multistage Pump

These pumps are commonly considered for pressure boosting, reverse osmosis feed, and industrial water systems requiring relatively high discharge pressure.

For example, if one stage develops approximately 20 metres of head at a particular flow, five comparable stages may provide roughly 100 metres at that flow. This is an illustration; the actual duty must be checked against the pump curve.

Many compact vertical multistage pumps have narrow internal passages intended for clean liquids. They should not be assumed suitable for sand, fibres, or other solids.

3. Vertical Turbine Pumps

A conventional lineshaft vertical turbine pump places the bowl assembly below the liquid level. A motor above the installation drives the impellers through a vertical shaft, and water travels upward through the column to the discharge head.

The bowl assembly may contain one or several stages, depending on the required duty. Reference: Goulds, Vertical Turbine Pumps

Typical applications include raw-water intake, irrigation, cooling-water supply, and water withdrawal from wells or wet wells.

The lowest operating water level matters as much as the normal level. Insufficient submergence or poor intake conditions can allow air entrainment and unstable operation. Bowl setting, intake geometry, and shaft-bearing arrangements therefore need attention during selection.

4. Vertical Sump Pumps

A vertical sump pump suspends its pumping element in a tank or pit while keeping the drive motor above the liquid.

Depending on the hydraulic design and materials, this arrangement can serve clean liquids, contaminated process liquids, or liquids containing solids. Solids-handling capability must be confirmed for the specific model. Reference: Sulzer, Vertical Sump Pumps

These pumps are used for industrial drainage, collection pits, and process sumps.

A key selection point is the shaft-support arrangement. Some designs use submerged guide bearings; others use a cantilever shaft without submerged bearings. That difference affects allowable installation depth, maintenance requirements, and suitability for abrasive liquids.

The vertical centrifugal pump working principle follows the same energy-transfer process as other centrifugal pumps. Mounting the shaft vertically changes the mechanical arrangement, but the impeller still supplies the energy that moves the liquid.

Step 1: Liquid Reaches the Impeller Inlet

Liquid enters the suction connection or submerged intake and moves toward the impeller eye.

The inlet must receive a continuous supply of liquid. For a conventional surface-mounted pump, the casing and suction arrangement must be filled and vented as required before starting. A vertical shaft does not make a pump self-priming.

For a submerged pumping element, sufficient liquid level is still necessary to maintain suitable intake conditions.

Step 2: The Impeller Transfers Energy to the Liquid

The motor rotates the shaft and impeller. As liquid passes through the impeller passages, the rotating blades increase its energy.

In a typical radial-flow impeller, liquid enters near the centre and moves outward toward the impeller periphery. Pressure rises within the impeller as well; it is not produced only after the liquid leaves the blades.

Step 3: The Casing or Diffuser Recovers Pressure

Liquid leaving the impeller enters a volute casing or diffuser. These stationary passages collect and guide the flow, converting part of its velocity energy into pressure energy. Reference: ASHRAE, Centrifugal Pumps

In a vertical multistage pump, return passages guide the liquid toward the next impeller, where it receives more energy.

Step 4: Liquid Flows into the System

The liquid leaves through the discharge connection and moves through the connected pipework.

The actual flow depends on the interaction between the pump curve and system resistance. Changing a valve position, pipe resistance, or pump speed can shift the operating point. A centrifugal pump therefore does not deliver one fixed flow under every operating condition.

Start with the duty conditions, then choose the arrangement.

Required Flow and Total Head

Specify the required flow rate and total dynamic head at that flow. Include elevation differences, pipe friction, equipment losses, and any required pressure difference between the system boundaries.

For a fully filled closed circulation loop, building height is not simply added to the circulating head. The pump mainly overcomes circuit resistance, while system fill pressure is addressed separately.

Liquid Properties

Confirm the liquid temperature, density, viscosity, chemical composition, and solids content.

These properties influence hydraulic performance, motor power, materials, seals, and bearing selection. A pump that performs well on clean water may be unsuitable for the same flow and head with an abrasive or viscous liquid.

Suction Conditions

Check inlet pressure or minimum liquid level, suction-line losses, and liquid temperature. Available net positive suction head must exceed the pump's requirement with an appropriate margin.

A larger motor cannot correct inadequate suction conditions.

Maintenance Access

Allow space for the work the pump will eventually need. Check whether the motor, seal, rotating assembly, or complete column must be lifted during service.

This is particularly important where a vertical centrifugal unit is selected to fit into a narrow plant room.

An inline pump may suit a circulation loop, while a vertical multistage pump may better fit a higher-pressure water supply. Water drawn from a deep wet well may call for a vertical turbine arrangement. A process collection pit may require a purpose-designed sump pump.

Before requesting a quotation, prepare the required flow, total head, liquid details, minimum inlet pressure or liquid level, power supply, and installation dimensions. With that information, a supplier can evaluate the pump curve and construction against the actual job.