What are Overhung Pumps? Design, Types & Applications

Overhung pumps are a staple in fluid-handling systems, thanks to their straightforward design and solid performance. If you work in water treatment, chemical processing, or HVAC, you’ve likely seen them in action.

What is an Overhung Pump?

An overhung pump is a type of centrifugal pump where the impeller is mounted on the end of a shaft that is supported by bearings on only one side. This configuration allows the impeller to “overhang” from the bearing support, making the design compact and accessible.

This simplicity results in:

• Fewer parts to maintain
• Lower installation and equipment costs
• Easier seal and impeller access
• Only one mechanical seal required

Overhung pumps typically conform to standards such as ANSI B73.1 (for chemical process pumps) or API 610 (for petroleum and petrochemical industries).

Design Characteristics of Overhung Pumps

The defining feature of overhung pumps is their cantilevered shaft design. This means the shaft extends out from the bearing housing with the impeller at the free end. Design attributes include:

• Compact footprint: Suitable for space-constrained installations.
• Single-sided support: Reduces the number of components and simplifies alignment.
• Ease of maintenance: Fewer parts and open design allow for quicker servicing.
• Hydraulic performance: Designed for medium head and flow conditions.
• Limitations: Susceptible to shaft deflection and increased radial loads, which can reduce bearing and seal life in high-flow/high-head applications.

Common materials used include:

• Cast iron for general service,
• Stainless steel for corrosive fluids,
• Duplex or super duplex alloys in highly corrosive or erosive environments.

Sealing options:

• Single/double mechanical seals (cartridge or component type),
• Packing glands for less demanding services,
• Use of seal flush plans (API Plan 11, 32, etc.) depending on fluid and operating conditions.

Pro tip: If your pump is running too far left or right of its best efficiency point (BEP), you’re wasting energy and  wearing it out faster than necessary.

3 Types of Overhung Pumps

1. Close-Coupled Overhung Pumps

• Extended motor shaft is attached to the impeller.
• No coupling needed, so setup is easier.
• Used in systems under 30 HP and lower pressure.

2. Frame-Mounted Overhung Pumps

• Motor and pump are separate and connected via a coupling. Motor and pump shaft alignment is required.
• Can handle stronger shafts and bigger bearings.
• Common in jobs over 30 HP and/or continuous duty service.

3. Horizontal vs. Vertical Overhung Pumps

• Horizontal: Easy to work on and often mounted on a baseplate.
• Vertical: Good for applications where space savings is needed such as skids and offshore rigs. Installs similar to a valve.

API 610 Overhung Pump Types (OH1-OH6)

In API 610 standards, overhung pumps are grouped into six main types, OH1 through OH6. Each one is defined by how the pump is mounted, how the shaft is supported, and how it connects to the driver:

• OH1 – Foot-mounted pump with a separate motor and flexible coupling. Simple and common.
• OH2 – Centerline-mounted with a single-stage impeller and flexible coupling. Mounted on a baseplate.
• OH3 – Vertical arrangement with the pump and motor. Great for saving floor space.
• OH4 – Vertical inline pump with a rigid coupling.
• OH5 – Vertical inline close-coupled pump. Compact, often used in HVAC.
• OH6 –High speed with integral gearbox driven, vertical in-line pump.

These categories help engineers and maintenance teams choose the right pump based on space, service conditions, and reliability needs.

Applications of Overhung Pumps

Overhung pumps are used in many industries:

• Water and Wastewater Treatment: Sludge, clear water, and chemical dosing. Material choices depend on the likelihood of scaling and corrosion.
• Chemical Processing: Suitable for fluids with a wide pH range. Often built to ANSI B73. standards for safety and reliability.
• Food and Beverage: Made of sanitary-grade stainless steel with clean-in-place (CIP) compatibility. Used for handling dairy, syrups, and other consumables.
• HVAC Systems: Found in chilled water loops, hot water circulation, and condenser water loops.
• Power Generation and Pulp & Paper: Utility water, white water, condensate transfer, and chemical dosing.

Sometimes it’s the smallest pump that keeps the whole system running.

Overhung vs. Other Pump Configurations

It’s helpful to compare overhung pumps with other styles:

Between Bearings (BB) Pumps

These pumps support the impeller on both sides using bearings. This helps with higher flow and pressure jobs. BB pumps usually go in big systems like crude oil transfer or boiler feed setups. Between bearing pumps require two seal chambers and sealing devices, either packing or mechanical seals.

Vertical Inline Pumps

This configuration aligns the suction and discharge connections vertically, which saves floor space and simplifies piping. Vertical inline pumps are commonly installed in HVAC and fire protection systems. However, they can be more challenging to access for maintenance compared to overhung pumps.

Multistage Pumps

These pumps use more than one impeller to get higher pressure. Overhung versions usually stay single-stage. Multistage designs are used in things like feedwater systems or reverse osmosis. They often need a BB or vertical can design.

Choose overhung pumps when space, simple access, and moderate service demands are top priorities.

Case for Retrofit and Upgrades

Many facilities with older between bearings or inline pumps find that switching to an overhung pump design simplifies maintenance and reduces floor space requirements. In retrofit scenarios, PumpWorks has helped customers convert legacy setups into more compact, serviceable systems by specifying the right overhung model. This has resulted in improved seal life, fewer alignment issues, and easier spare parts management.

Engineer’s Perspective

In one client’s facility, we replaced older split-case pumps with overhung models from PumpWorks. It’s made a noticeable difference in both uptime and labor hours.

Why Choose PumpWorks?

Overhung pumps don’t fit every situation; but when properly applied, they get the job done without extra complication. Think about flow, pressure, fluid properties, and NPSH before making a selection. Matching the pump design to the task upfront can lead to fewer problems later.

PumpWorks specializes in high-performance overhung pump solutions built for demanding industrial environments. If you’re looking for help specifying or sourcing the right configuration, our team is here to assist.

Reach out to PumpWorks today to find the right pump for your system!