A split case pump impeller is the heart of a split case (or double-suction) centrifugal pump. Because split case pumps are designed to handle high-flow, medium-pressure applications (like municipal water supply, firefighting, and HVAC systems), their impellers have a very distinct design and function.
Here is a breakdown of how they work, their unique design features, and why they are used.
1.The Double-Suction Design
Unlike standard end-suction pumps where water enters from just one side, a split case pump typically utilizes a double-suction impeller.
How it looks: It looks like two traditional impellers placed back-to-back into a single casting.
How it works: Liquid enters the pump casing and is split equally, entering the impeller eyes from both sides simultaneously.
2. Key Advantages
Hydraulic Axial Balance: Because fluid enters from both sides with equal force, the axial thrust forces cancel each other out. This drastically reduces the load on the pump's bearings, leading to a much longer lifespan and less maintenance.
Lower NPSH Required: Splitting the inlet flow into two streams reduces the velocity at the impeller eye. This lowers the Net Positive Suction Head required ($NPSHr$), making the pump much less prone to cavitation.
High Efficiency: They are highly efficient at moving massive volumes of liquid compared to single-suction designs of a similar size.
3. Types of Split Case Impellers
Depending on the specific application, these impellers generally come in three configurations:
| Impeller Type | Design | Best Used For... |
| Enclosed (Closed) | Vanes are sandwiched between two solid shrouds. | Clean liquids, water works, high efficiency. (Most common for split case). |
| Semi-Open | Back shroud only; vanes are exposed on the front. | Liquids with light suspended solids or debris. |
| Open | Vanes are attached only to the central hub. | Rare in split case pumps; used for thick slurries or stringy materials. |
4. Materials of Construction
Because these pumps are often critical infrastructure, the impellers are built to last and are selected based on the fluid being pumped:
Bronze / Gunmetal: Standard for clean water; offers great corrosion resistance.
Cast Iron: Cost-effective for basic, non-corrosive utilities.
Stainless Steel (304/316 or Duplex): Used for aggressive fluids, chemical processing, or seawater to prevent erosion and corrosion.
5. Maintenance & Wear Components
When servicing a split case pump, the impeller itself rarely works alone. You will always want to inspect:
Wear Rings: These are sacrificial rings fitted onto the impeller hub and pump casing. They maintain a tight clearance to prevent high-pressure fluid from leaking back into the low-pressure suction side.
Shaft Sleeves: Protect the pump shaft from wear under the packing or mechanical seals.