Split Case Pumps/Between Bearings Pumps: Efficient Solutions for High-Flow Applications

Split case pumps, also known as between bearings pumps, are essential tools in many industries. These pumps are designed to handle large volumes of fluid efficiently and reliably. They come in two main types: horizontal and vertical split case pumps.

Split case pumps are prized for their easy maintenance and high efficiency, making them a popular choice for various applications. The unique design allows for quick access to internal components without disturbing the piping or motor connections. This feature saves time and money during routine maintenance or repairs.

These pumps are commonly used in water treatment plants, irrigation systems, and industrial processes. Their ability to handle high flow rates and operate under varying conditions makes them versatile and dependable. Whether it’s a horizontal or vertical configuration, split case pumps continue to be a go-to solution for many pumping needs. Within the wider family of pumps for wastewater and water supply, split case machines occupy the high-flow, clean-water end of the range, where their efficiency at design point is among the best available from any pump type.

Key Takeaways

• Split case pumps offer easy maintenance and high efficiency
• They come in horizontal and vertical configurations for different applications
• These pumps are widely used in water treatment, irrigation, and industrial processes

Basics of Split Case Pumps

Split case pumps are powerful and versatile pumping devices. They offer high efficiency and reliability for various industrial applications. These pumps have a unique design that allows easy access for maintenance.

Design and Operation

Split case pumps have a casing that splits horizontally or vertically. This design lets users open the pump without disturbing connected piping. The impeller sits between two bearings, giving it stability at high speeds and pressures.

Double suction split case pumps have inlets on both sides of the impeller. This balances hydraulic forces and reduces wear on bearings. The impeller spins to create centrifugal force, moving fluid from the center to the outer edges.

Split case pumps can handle large volumes of liquid. They work well with both clean and slightly dirty fluids. These pumps come in different sizes and materials to suit various needs.

Two terms are worth separating because they are often used interchangeably and mean different things. “Split case” describes how the casing comes apart — axially, along the shaft centerline, which is what allows the upper half to be lifted off without disturbing piping. “Between bearings” describes where the impeller sits — supported on both sides rather than cantilevered from one end, which is what eliminates the shaft deflection that limits centrifugal pumps in overhung configurations. Most split case pumps are both, but the two features contribute different advantages and a specification should state which one it is relying on.

Applications and Uses

Split case pumps are common in many industries. They excel in water supply systems, irrigation, and fire protection. These pumps also serve in heating, ventilation, and air conditioning (HVAC) systems.

In manufacturing, split case pumps move chemicals and process fluids. They help in power generation, moving water through boilers and cooling towers. The oil and gas industry uses them for pipeline transport.

Split case centrifugal pumps work well in high-pressure applications. They can pump large volumes efficiently, making them ideal for municipal water systems. Their reliability and easy maintenance make them popular in critical operations.

Split Case Pump Topics: Subcategory Overview

The split case category divides into four areas: the double suction impeller design that gives these pumps their defining hydraulic characteristics, the applications they serve, the manufacturers that build them, and the maintenance program that determines whether their efficiency advantage survives into year ten.

Double Suction Pump Design

The double suction impeller is what makes a split case pump distinctive, and its two benefits are separate. First, feeding the impeller from both sides balances the axial hydraulic thrust that would otherwise load the thrust bearing continuously, which is a major contributor to the long bearing life these pumps are known for. Second, and more consequentially for selection, each side of the impeller passes only half the total flow, so eye velocity is substantially lower than in a single suction impeller of the same capacity — and that lower velocity translates directly into a lower net positive suction head requirement. Coverage of the double suction pump addresses this design in detail. It is worth being precise about the source of the NPSH advantage, because it comes from the double suction impeller rather than from the split casing or the mounting orientation.

Split Case Pump Applications

These pumps dominate a specific band of duty: high flow at moderate head, on clean or lightly loaded liquid. Coverage of split case pump applications addresses municipal water supply and distribution, booster stations, raw water intakes, HVAC chilled and condenser water service, cooling water circulation, fire protection, and flood control pumping. What unites them is the combination of large volume and clean liquid. Split case pumps are not solids handling machines — a double suction impeller with its narrow passages and central splitter is among the worst possible geometries for rags and stringy debris, which is why raw wastewater service belongs to non-clog and chopper designs instead.

Split Case Pump Manufacturers

The supplier decision matters here mainly through parts availability, because these are long-lived machines and a pump installed today will need wear rings, seals, and bearings from someone twenty years from now. A survey of the top split case pump manufacturers covers the major suppliers in water and wastewater service. When comparing offerings, the questions that matter are efficiency at the actual duty point rather than at BEP, the published NPSH required and how it was tested, wear ring material and renewability, and whether the local service organization can actually perform a rotating element change.

Split Case Pump Maintenance

Maintenance is where the efficiency advantage is either preserved or quietly lost. Guidance on a split case pump maintenance plan covers inspection intervals, spare parts stocking, and work order structure. The single most important item in that program is wear ring clearance. As the rings wear, internal recirculation increases, and the pump delivers less flow for the same power — a loss that appears gradually, produces no alarm, and can reach several percent of capacity and efficiency before anyone notices. On a large pump running continuously, that percentage is worth more annually than the entire maintenance budget.

Horizontal Split Case Pumps

Horizontal split case pumps are widely used in industrial and municipal applications. These pumps offer high efficiency and easy maintenance due to their unique design.

Advantages of Horizontal Configuration

Horizontal split case pumps have several benefits. They are easy to install and maintain. The casing splits horizontally, allowing access to internal parts without disturbing piping. This design reduces downtime during repairs.

These pumps handle large flow rates at moderate to high heads. They work well in water supply, irrigation, and fire protection systems. The horizontal layout provides stability and reduces vibration.

Horizontal split case pumps can be single or double suction. Double suction designs balance axial thrust, extending bearing life. They also offer higher efficiency than single suction pumps.

Specific Types

Centrifugal horizontal split case pumps are common in industrial settings. They move fluids using centrifugal force created by a rotating impeller. These pumps handle a wide range of liquids and flow rates.

Fire protection systems often use horizontal split case fire pumps. These pumps deliver high pressure water for sprinkler systems and fire hydrants. They meet strict safety standards and provide reliable performance during emergencies.

Double suction horizontal split case pumps are ideal for high-capacity applications. They allow fluid to enter the impeller from both sides. This design reduces net positive suction head requirements and improves efficiency.

Vertical Split Case Pumps

Vertical split case pumps offer unique advantages in certain applications. These pumps combine the benefits of split case design with a vertical orientation, making them suitable for specific industrial and municipal needs.

Advantages of Vertical Configuration

Vertical split case pumps save floor space. This makes them ideal for facilities with limited footprints. They have a smaller base area compared to horizontal pumps.

These pumps have better suction performance. The vertical design helps prevent air entrapment, reducing the risk of cavitation. This leads to smoother operation and extended pump life.

Vertical split case pumps are easier to maintain. Their design allows for quick access to internal parts without disturbing connected piping. This cuts down on maintenance time and costs.

They handle solids more effectively. The vertical orientation helps prevent settled solids from accumulating in the casing. This is useful in applications dealing with liquids containing suspended particles.

Vertical vs Horizontal Split Case Pumps

Vertical split case pumps differ from horizontal ones in several ways. They have a smaller footprint, making them suitable for tight spaces. Horizontal pumps often require more floor area.

Vertical pumps have better NPSH (Net Positive Suction Head) characteristics. This allows them to handle liquids at higher temperatures or with lower vapor pressures more effectively.

Installation costs can be lower for vertical pumps. They often need less complex foundations compared to their horizontal counterparts. This can lead to savings in construction and setup.

Vertical pumps are preferred in deep well applications. They can be partially submerged, making them ideal for accessing water from great depths. Horizontal pumps are limited in this aspect.

Clarifying What the Vertical Configuration Actually Does

Three points above need correction, because the vertical split case configuration is frequently confused with an entirely different machine.

A vertical split case pump is not submerged and is not a deep well pump. It is the same hydraulic end as its horizontal counterpart, mounted with the shaft vertical to save floor space, sitting dry in a pump room like any other surface pump. The machine that is partially submerged and used to lift water from great depths is a vertical turbine pump, which uses stacked bowl assemblies on a line shaft extending down into a wet pit or well — a completely different design, covered under vertical turbine pumps. Specifying one and installing the other is not a possible substitution.

The NPSH advantage attributed to the vertical orientation is real but comes from a different source than orientation itself. Vertical units are often installed lower in a pump room, or in a below-grade station, which raises NPSH available by increasing suction submergence. The pump’s own NPSH required is essentially unchanged by turning it on its side; the double suction impeller is what lowers NPSHR, and that feature is present in horizontal units too.

Solids handling is the third point, and it is simply not a split case strength in either orientation. Double suction impellers have narrow passages divided by a central splitter, which is close to the worst geometry available for rags, stringy material, or fibrous solids. These are clean-water and lightly-loaded-liquid machines, and any application with meaningful solids content calls for a different pump family entirely.

Comparison with End Suction Pumps

Split case pumps and end suction pumps have distinct design features and performance characteristics. These differences impact their suitability for various applications.

Design Differences

Split case pumps have a horizontally split casing, allowing easy access to internal parts. The impeller sits between two bearings, providing better shaft support. This design helps reduce vibration and shaft deflection.

End suction pumps have a simpler design with the impeller at one end of the shaft. They are more compact and often less expensive. The suction inlet is on the end of the pump, while the discharge is on top.

Split case pumps can handle higher flows and pressures. They’re often used in large-scale industrial and municipal applications. End suction pumps are common in smaller systems and residential use.

Performance Considerations

Split case pumps generally offer higher efficiency, especially at higher flow rates. They maintain good performance over a wider range of operating conditions. These pumps can handle larger pressure heads compared to end suction pumps.

End suction pumps are more versatile for lower flow applications. They’re easier to install and maintain due to their simpler design. However, they may be less efficient at high flow rates.

Split case pumps have better suction lift capabilities. This makes them suitable for applications where the water source is below the pump. End suction pumps may require priming in similar situations.

One clarification on that last point: neither type self-primes. A double suction impeller gives a split case pump a lower NPSH requirement than a comparable single suction machine, which widens the range of suction conditions it will tolerate, but both configurations must be filled with liquid before starting and both require a positive suction condition or a priming system. The advantage is in NPSH margin, not in an ability to lift dry.

Comparing High-Flow Pump Configurations

The table below compares split case pumps against the configurations they compete with for high-flow water duty. Values are typical or approximate and vary widely by size and manufacturer.

Selection and Specification Framework

Split case selection is straightforward hydraulically and unforgiving in two specific areas: suction piping geometry and the discipline to select accurately rather than generously.

Step One: Confirm the Duty Belongs to This Family

Split case pumps earn their premium at high flow on clean liquid. Below a few hundred gallons per minute, an end suction pump does the same job at lower capital cost and smaller footprint. Where solids are present in any meaningful quantity, the family is wrong regardless of flow. Where head requirements are very high at moderate flow, a multistage between bearings machine rather than a single stage split case is the answer. Confirm the duty sits in the band before proceeding, because the most expensive split case mistake is buying one for a duty another configuration handles better.

Step Two: Design the Suction Piping Before Selecting the Pump

This step is skipped constantly and causes more split case problems than any other factor. A double suction impeller depends on flow arriving evenly at both sides. An elbow immediately upstream of the suction flange, or worse an elbow in the plane of the shaft, delivers more flow to one side than the other, which unbalances the axial thrust the double suction design exists to eliminate, loads the thrust bearing, and produces vibration that will be blamed on the pump for years. Provide a straight run of suction pipe ahead of the flange — commonly five to ten pipe diameters depending on the fitting upstream — and where a reducer is needed use an eccentric reducer with the flat side up so air cannot collect at the high point. This costs almost nothing at design and cannot be fixed cheaply afterward.

Worked Example: Power and the Cost of Wear Ring Clearance

Take a municipal duty of 4,000 gpm at 180 feet total dynamic head with a pump efficiency of 87 percent at that point — realistic for a well-selected split case machine. Brake horsepower is 4,000 multiplied by 180, divided by the product of 3,960 and 0.87, giving approximately 209 horsepower, pointing to a 250 hp motor. At a motor efficiency near 95 percent, the electrical draw is roughly 164 kilowatts, and at 8,000 operating hours per year that is about 1.3 million kilowatt-hours annually.

Now consider what wear ring clearance does to that number. As the rings wear open, liquid recirculates internally from discharge back to the impeller eye, so the pump delivers less useful flow for the same shaft power. A modest loss of five percent on a machine consuming 1.3 million kilowatt-hours costs roughly 65,000 kilowatt-hours every year — recurring, invisible, and larger than the cost of the ring replacement that would restore it. This is why wear ring clearance measurement belongs in the maintenance plan rather than in the overhaul-when-it-fails category, and why a performance test comparing current output against the commissioning baseline pays for itself.

Step Three: Select Against BEP and Specify the Test

Choose a pump whose best efficiency point sits at the most frequent operating condition, and confirm the full operating range stays within the preferred region — generally around 70 to 120 percent of BEP flow. Between bearings construction tolerates off-design operation better than an overhung pump because the shaft is supported on both sides, but the hydraulic penalties of low-flow recirculation and high-flow cavitation apply equally. Require a hydraulic performance test to a recognized standard at the specified duty, and for fire protection service confirm the pump is listed and tested to the applicable fire pump requirements, which impose their own curve shape criteria at churn, rated, and 150 percent flow.

Maintenance and Troubleshooting

Split case pumps need regular care and quick problem-solving to work well. Good upkeep and fast fixes keep these pumps running smoothly and avoid costly breakdowns.

Routine Maintenance

Regular checks are key for split case pumps. Look at the pump daily for leaks or odd noises. Check the bearings weekly and add grease if needed. Clean the pump’s outside monthly to spot any issues.

Every three months, check the shaft alignment. This helps stop wear and tear. Test the pump’s performance too. Look at flow rate and pressure to catch problems early.

Once a year, do a full check. Take the pump apart and clean all parts. Replace worn seals and gaskets. Check the impeller for damage or buildup. Look at the bearings closely and change them if worn.

Keep good records of all maintenance. This helps track the pump’s health over time.

Problem Diagnosis

When a split case pump acts up, check these common issues:

1. Low flow or pressure:
   • Clogged impeller
   • Worn wear rings
   • Air in the system
2. Loud noises:
   • Cavitation
   • Bearing failure
   • Loose parts
3. Overheating:
   • Low oil level
   • Blocked cooling system
   • Wrong pump speed

Use a vibration analyzer to find hidden problems. High vibration often means bearing issues or misalignment.

Check the power use. A sudden increase might mean the impeller is damaged or there’s extra friction somewhere.

For seal leaks, look at the faces for wear. Make sure the seal is fitted right and the shaft isn’t bent.

Field Notes on Split Case Pump Practice

These are long-lived machines, which means their problems tend to be installation problems that took years to surface rather than component failures.

Commissioning and Baseline Measurement

Record a full baseline: flow, suction and discharge pressure, motor amperage, vibration at each bearing, and bearing temperature at a documented operating point. Measure and record wear ring clearances at assembly, because that number is the reference for every future capacity question. Verify alignment cold and again after the machine reaches operating temperature, since thermal growth moves both pump and driver. Confirm the baseplate is fully grouted with no voids, as a hollow baseplate is a persistent vibration source that no amount of realignment resolves. And verify the suction piping arrangement against the drawings before startup, since a field-routed elbow at the suction flange is far easier to correct before the concrete is poured.

Common Specification Mistakes

Several errors recur. Placing an elbow directly on the suction flange, particularly in the plane of the shaft, unbalances flow between the two impeller sides and produces thrust and vibration problems that persist for the life of the installation. Oversizing to add margin puts the pump left of BEP permanently, where recirculation and radial loading shorten seal and bearing life. Specifying a split case pump for a duty with solids content produces a machine that clogs and cannot be cleared without opening the casing. Omitting wear ring clearance from the maintenance specification allows years of gradual efficiency loss with no trigger to act on. And selecting on capital price without comparing efficiency at the actual duty point, rather than at BEP, misses where nearly all the lifetime cost sits.

Operations and Maintenance

Trend flow at a fixed discharge pressure, or amperage at a fixed duty, and compare against the commissioning baseline. Declining capacity at unchanged power is the wear ring signature and appears long before anything sounds wrong. Check alignment on a schedule rather than after a failure. Monitor bearing temperature and vibration together, since either alone can miss a developing problem the other catches. Keep a rotating element or at minimum a full set of wear rings, bearings, and seals in stock, because these pumps are typically in critical service and lead times on large components are long.

Case Studies and Real-World Examples

Split case pumps have proven their worth in diverse industrial and municipal settings. Their reliability and efficiency shine through in challenging applications across various sectors.

Industrial Implementations

A large oil refinery in Texas installed split case pumps to handle high-temperature crude oil transfer. The pumps operated continuously for 5 years without major maintenance, saving millions in downtime costs.

A chemical plant in Germany used split case pumps for corrosive fluid circulation. The pumps’ robust design withstood harsh chemicals, reducing replacement frequency by 50% compared to previous models.

In a paper mill, split case pumps moved high-consistency pulp. Their ability to handle solids improved production rates by 15% and cut energy use by 10%.

Municipal Applications

The city of Chicago upgraded its water treatment plant with split case pumps. The new system increased daily capacity by 20% while reducing energy consumption by 25%.

A flood control project in the Netherlands employed large split case pumps. During a major storm, these pumps moved over 500,000 gallons per minute, preventing widespread flooding.

In Australia, a drought-stricken town installed split case pumps for a new desalination plant. The pumps’ efficiency helped produce 50 million liters of fresh water daily, meeting the needs of 300,000 residents.

Design Details and Standards

Split case specification rests on the hydraulic testing and operating region standards common to all rotodynamic pumps, plus the specific listing requirements that apply in fire protection service.

Sizing Methodology Overview

Establish flow across the full operating range and build the system curve with static and friction components separated, evaluated at both new and aged pipe roughness. Select the pump whose best efficiency point sits at the most frequent condition and confirm the operating range stays within the preferred region. Calculate NPSH available at the worst credible combination of temperature, suction level, and fouled piping, and confirm genuine margin over NPSH required — remembering that the published value is measured at a three percent head drop, meaning cavitation is present, not absent, at that figure. Calculate brake horsepower at both duty and run-out so the motor is not undersized. Then design the suction piping, and confirm the pump room has the overhead clearance and lifting capacity to remove the rotating element.

Key Parameters That Differ by Configuration

Horizontal split case machines are governed by suction approach conditions, baseplate grouting, and coupling alignment across a long bearing span. Vertical split case units are governed by the same hydraulics plus overhead removal clearance and vertical shaft alignment. Multistage between bearings pumps add axial thrust balance and interstage clearance. Vertical turbine machines are governed by submergence and line shaft straightness — a different set entirely, which is the practical reason the two vertical types should never be confused. Across all split case designs, wear ring clearance is the parameter that most directly determines delivered efficiency over time.

Applicable Standards and References

Key references include the Hydraulic Institute standards for rotodynamic pumps, covering hydraulic performance acceptance testing, NPSH margin guidance, allowable and preferred operating regions, vibration measurement and acceptance, and pump intake design; API 610 for between bearings pump types in petroleum and petrochemical service, including the axially split single and two stage and multistage classifications; NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection, which governs listing, curve shape, and acceptance testing for fire pump service; NEMA MG-1 for motor construction; the Hydraulic Institute guidance on pump life cycle costs; and the Recommended Standards for Water Works and Recommended Standards for Wastewater Facilities (Ten States Standards) for pumping station capacity and redundancy.

Specification Checklist

1. Duty confirmed to sit in the high-flow, clean-liquid band this family serves.
2. Solids content verified as negligible, since double suction impellers are among the worst geometries for rags and fibrous material.
3. System curve built with static and friction head separated, at new and aged roughness.
4. Best efficiency point located at the most frequent operating condition, not the peak condition.
5. Operating range confirmed within the preferred region across all expected conditions.
6. NPSH available calculated at the worst credible condition, with explicit margin over NPSH required.
7. Suction piping designed with adequate straight run and an eccentric reducer flat side up.
8. Efficiency compared between bids at the actual duty point rather than at BEP.
9. Wear ring material and renewability specified, with as-built clearances required to be recorded.
10. Baseplate grouting specified and verified void-free at installation.
11. Alignment required cold and hot, with results documented.
12. Overhead clearance and lifting capacity confirmed for rotating element removal.
13. Hydraulic performance test to a recognized standard written into the specification before bid.
14. For fire service, listing and acceptance testing to the applicable fire pump standard required.

Conclusion

Split case pumps occupy a well-defined niche and perform superbly inside it: high flow, moderate head, clean liquid, long service life, and maintenance access that no other configuration matches. Nearly every problem attributed to them traces back to a duty they should not have been asked to perform, or to suction piping installed without regard to how a double suction impeller actually works.

The specification discipline is short. Confirm the duty belongs to the family and that solids are absent. Design the suction approach before choosing the pump. Select accurately for the frequent condition rather than generously for a rare one. Require a performance test to a recognized standard. And record wear ring clearances at assembly, because that number quietly governs the operating cost for the next twenty years.

For a facility with split case pumps already installed, the highest-return action is a performance comparison against the original commissioning data. Lost capacity from open wear rings is common, invisible, and among the cheapest efficiency losses in a plant to recover.

Frequently Asked Questions

Split case pumps and between bearing pumps have distinct features that affect their applications and performance. These pumps offer unique advantages and considerations in various industrial settings.

What distinguishes horizontal split case pumps from vertical split case pumps?

Horizontal split case pumps are mounted parallel to the ground. They allow easy access to internal components for maintenance. Vertical split case pumps are installed upright. They take up less floor space and are often used where the pump room footprint is constrained.

Can you outline the main disadvantages of using split case pumps in industrial applications?

Split case pumps can be more expensive initially than other pump types. They may require more frequent maintenance due to their complex design. These pumps also tend to be larger and heavier, which can limit installation options in tight spaces.

What are the different types of between bearing pumps available in the market?

Between bearing pumps come in several varieties. These include axially split case pumps, radially split case pumps, and multi-stage between bearing pumps. Each type is suited for specific applications based on flow rates and pressure requirements.

Why might split case pumps be preferred over other types in certain scenarios?

Split case pumps offer high efficiency and reliability for large-scale operations. They handle high flow rates and moderate pressures effectively. These pumps are ideal for applications requiring easy maintenance access, such as water treatment plants and industrial cooling systems.

How does the operational mechanism of between bearing pumps differ from overhung pump designs?

Between bearing pumps have impellers positioned between two bearings. This design provides better shaft support and reduces deflection. Overhung pumps have the impeller cantilevered on one end of the shaft, which can lead to increased vibration and wear in high-load applications.

What considerations should be taken into account when selecting parts for between bearing pumps?

When choosing parts for between bearing pumps, material compatibility is crucial. The pump’s operating conditions, such as temperature and fluid properties, must be considered. Proper sizing of bearings, seals, and impellers is essential for optimal performance and longevity.