A pump casing is the outer shell or housing of a pump. It is a critical component that serves two primary purposes: containment (holding the fluid and withstanding the pressure) and energy conversion (collecting the fluid and directing it toward the discharge point).
Think of it as the protective armor and the internal highway system of the pump.
Key Functions of a Pump Casing
Pressure Containment: It seals the internal components from the outside world, preventing hazardous or high-pressure fluids from leaking.
Energy Conversion (Volute/Diffuser): In centrifugal pumps, the casing is specifically shaped to slow down the high-velocity fluid thrown off by the impeller, converting that kinetic energy into pressure energy.
Structural Support: It provides the mounting points and structural integrity to hold internal parts like the impeller, shaft, bearings, and seals in perfect alignment.
Main Types of Pump Casings
Pump casings are generally categorized by their geometry and how they split for maintenance.
1. By Flow Design (Internal Geometry)
| Casing Type | Description | Best Used For |
| Volute Casing | A spiral-shaped casing that progressively widens toward the discharge point. This gradual expansion naturally slows the fluid and increases pressure. | General purpose, clear liquids, standard centrifugal pumps. |
| Circular (Vortex) Casing | Has a constant cross-section around the impeller. It is less efficient than a volute but is great for minimizing clogging. | Slurries, solids handling, and waste management. |
| Diffuser Casing | Features stationary, guide vanes surrounding the impeller. These vanes gradually open up to convert velocity into pressure very efficiently. | High-pressure applications and multi-stage pumps. |
2. By Mechanical Construction (How it Opens)
Radially Split Casing: The casing is split perpendicular to the pump shaft (like slicing a loaf of bread). It is typically used for high-pressure or high-temperature applications because it is easier to seal.
Axially Split Casing (Split-Case): The casing is split parallel to the pump shaft (like a clamshell). This design allows the top half of the casing to be removed for easy maintenance and inspection without disconnecting the piping.
Common Materials Used
The material chosen depends entirely on what is being pumped (corrosiveness, abrasiveness, temperature, and pressure):
Cast Iron: Economical, standard for water and non-corrosive liquids at moderate pressures.
Ductile Iron: Offers higher strength and shock resistance than standard cast iron.
Stainless Steel: Used for corrosive fluids, chemical processing, and hygienic applications (food/pharma).
Special Alloys (e.g., Hastelloy, Titanium): For extremely aggressive acids or chemical environments.