When Should You Choose a Vertical Inline Pump?

A vertical inline pump can make a water system more compact because its suction and discharge connections sit on the same pipeline centreline. Instead of creating a large floor-mounted arrangement around a horizontal pump, the installer can place the pump directly into the pipe run.

That advantage is valuable in plant rooms, commercial buildings, cooling systems and industrial water networks where floor space is limited. However, a vertical inline pump is not automatically the best choice for every project. Suction conditions, maintenance access, liquid properties and pipe support are just as important as the available space.

A vertical inline pump is a surface-mounted centrifugal pump with the motor positioned vertically above the pump casing. The suction and discharge flanges are usually the same nominal size and arranged on one horizontal centreline.

The SLAPK ISG series is a vertical single-stage, single-suction centrifugal pump. Its inline layout allows it to be installed in a straight section of pipe in a similar way to a valve. The range is intended mainly for clean water and liquids with similar physical and chemical properties, while related versions are available for hot water, corrosive liquids and petroleum products.

It should not be confused with a vertical long-shaft pump or a submersible pump. A long-shaft pump has its hydraulic components below the mounting level and transfers power through a long shaft. A submersible pump places both the pump and motor in the liquid. An inline pump normally operates dry on the surface.

The main reason to choose an inline pump is efficient use of installation space. Because the pipe connections share the same centreline, the piping arrangement can be simpler and the floor area smaller than many conventional horizontal pump installations.

Typical applications include:

• Building water-pressure boosting

• Heating and chilled-water circulation

• Cooling-water systems

• Industrial clean-water transfer

• Garden irrigation

• District heating

• Washing and process-water systems

• Water supply for high-rise buildings

The design is useful when equipment must fit into a narrow mechanical room or an existing pipeline.

Space saving should not be considered in isolation. The installation must still provide enough room above and around the pump for motor removal, seal inspection and routine maintenance.

A horizontal end-suction pump can be easier to access when a project has enough floor space. Technicians may find it more convenient to remove the motor, coupling or rotating assembly without working directly above the pump.

A horizontal arrangement can also provide more flexibility for large pumps, heavy motors and baseplate-mounted systems. Where the piping creates significant external loads, a properly designed baseplate and foundation may offer better mechanical support.

If the liquid level is below the pump and the system requires suction lift, neither a standard vertical inline pump nor a normal horizontal centrifugal pump should be assumed to self-prime. The suction arrangement, available net positive suction head and priming method must be checked. A self-priming, vertical turbine or submersible pump may be more appropriate.

A vertical inline pump must be selected at the real operating point.

Required flow should be based on the demand of the building, process or circulation loop. Total dynamic head should include elevation difference, required outlet pressure and friction losses through pipe, valves, elbows, heat exchangers and other equipment.

In a closed heating or cooling loop, the pump does not normally overcome the building height as a continuous static lift after the system is filled. It must overcome the resistance of the circulating circuit. In an open transfer or booster system, elevation and required delivery pressure may form a major part of the head.

Do not select the motor first and assume the pump will produce the required result. Ask for the performance curve of the exact model and check that the duty point falls inside its recommended operating range, preferably near the best-efficiency region.

For more information, see How to Select a Suitable Pump Type for Pipe Head Loss.

Poor suction design can cause more problems than an incorrectly sized discharge pipe.

The pump inlet should receive a stable, air-free flow. Check the liquid level, suction pressure, water temperature, pipe diameter, pipe length and pressure losses before the pump. The available net positive suction head must remain above the pump's required value with a suitable project margin.

Hot water requires particular attention because increasing liquid temperature reduces the pressure margin before vaporisation. A pump that operates normally with cold water may experience cavitation in a hot-water circuit without adequate inlet pressure.

Avoid high points where air can collect in the suction pipe. Reducers, valves and strainers should follow the manufacturer's instructions. The casing must be filled and vented before starting unless the design is specifically self-priming.

Noise, vibration and fluctuating pressure can indicate air entry, cavitation or an unstable operating point. Increasing motor power does not correct a poor suction layout.

The standard ISG configuration is intended for clean water or a similar non-corrosive liquid. It should not automatically be used for sewage, abrasive slurry or water containing large solids.

The liquid review should include:

• Temperature

• pH and chemical composition

• Chloride concentration

• Viscosity and density

• Particle size and solids concentration

• Flammability

• Required hygiene standard

The catalogue identifies related variants for hot water, chemical liquids and petroleum products. These model designations represent different intended duties; they are not interchangeable labels. Material, mechanical seal, motor protection and certification must match the actual liquid.

If the project handles seawater, strong chemicals, solids or flammable products, provide a complete liquid analysis. A standard cast-iron clean-water pump may have a short service life or create a safety risk in an unsuitable application.

An inline casing may look as though it can carry the connected pipework, but the pump should not be used as structural support for an uncontrolled piping load.

Support and align the suction and discharge pipes independently. The flanges should meet without being forced into position. Excessive pipe strain can distort the casing, affect the seal and create vibration.

Also consider thermal expansion in heating systems. Pipe movement should be managed by the system design rather than transferred directly into the pump nozzles.

Larger units may require a mounting base or additional structural support. Follow the dimensional drawing and instructions for the exact model instead of relying on a generic diagram.

A compact installation is only useful if the pump can still be serviced.

Before finalising the layout, confirm how the motor, impeller and mechanical seal will be removed. Provide lifting clearance for heavier motors and working room around electrical connections, valves and instruments.

Isolation valves on both sides can allow maintenance without draining the complete system. A check valve may be required depending on the arrangement. Pressure gauges before and after the pump help operators check the differential pressure.

Where continuous service is essential, two pumps can be arranged as duty and standby units. Parallel operation may also serve changing demand, but the combined operating points must be checked against the system curve. Two identical pumps do not automatically provide twice the flow.

For an accurate selection, provide:

• Required flow rate

• Total dynamic head or system resistance

• Liquid type and composition

• Minimum and maximum temperature

• Suction pressure and liquid level

• Pipe diameter and layout

• Available installation space

• Voltage, frequency and phase

• Indoor or outdoor installation

• Continuous or intermittent duty

• Required materials and seal arrangement

• Control method and variable-speed range

• Applicable standard and inspection requirements

A simple piping drawing is often more useful than a long written description. It allows the supplier to identify suction problems, space restrictions and valve requirements before manufacturing.

Choose a vertical inline pump when the liquid is suitable, the suction conditions are stable and a compact pipeline installation provides a genuine project advantage. It can be an effective solution for building water supply, HVAC circulation and clean industrial water systems.

Do not select it only because it occupies less floor space. The pump must still match the required flow and head, liquid properties, inlet conditions, pipe loads and maintenance plan.

Send SLAPK your duty point, liquid information, suction conditions, pipe drawing, power supply and space limits. Our engineers can compare an ISG vertical inline pump with horizontal, multistage or submersible alternatives and recommend a practical configuration.

Contact SLAPK for a pump selection