Which of the following is a type of impeller casing that channels flow through a diffuser?

• A. Single volute
• B. Double volute
• C. Diffuser
• D. Cascaded volute

Answer: (C)

After the impeller pushes fluid outward, its velocity is high and the pressure is relatively low. A diffuser is a stationary set of vanes or a shaped passage that surrounds the outlet and expands the flow cross-section. This slows the fluid and converts its dynamic energy into higher static pressure, effectively guiding the flow through the diffuser and increasing overall efficiency. That’s why the casing described as channeling flow through a diffuser is the diffuser-type casing.

Single volute and double volute casings are about collecting and directing flow to the discharge by wrapping the outlet around the impeller; they don’t create the diffusion of energy. Cascaded volute adds multiple passages to balance thrust and manage flow, but it isn’t specifically defined by diffusing the flow.