Question

(a) Sketch a simple cross section through a single stage centrifugal pump with a fully shrouded single entry impeller, name the components of the pump and indicate the direction of fluid flow

(b) Describe

(i) The function of the impeller and how suction is created by it

(ii) The funciton of the volute casing

(iii) State the material of each component of the pump

(c) State the materials of each component of the pump

(d) State why some centrifugal pumps have

(i) A double volute casing

(ii) A diffuser ring

Answer 1

(a) Cross-section of a Single stage centrifugal pump:

(b) (i) The impeller is a rotating component that imparts kinetic energy to the fluid. As it rotates, the vanes throw the liquid outward, increasing its velocity (kinetic energy). This high-speed movement creates a low-pressure area or vacuum at the impeller's eye, drawing fluid into the suction inlet. This vacuum effect is what allows liquid to be "sucked" into the pump, facilitating continuous flow.

(ii) The volute casing is a curved, spiral casing around the impeller. The volute casing gradually increases in area, converting the high-velocity fluid leaving the impeller into higher pressure energy. This gradual expansion minimises turbulence and maximises pressure conversion efficiency.

(c) Material of each component of the pump:

Part (d)

(i) Double Volute Casing: A double volute casing improves the pump's radial balance. The pressure distribution is split across two volutes, cancelling out radial thrust forces that could lead to shaft vibrations and premature wear.

(ii) Diffuser Ring: A diffuser ring increases pump efficiency. By gradually expanding the flow area after the impeller, it converts more of the fluid's kinetic energy into pressure energy, reducing velocity and turbulence losses. This results in higher pressure output and improved efficiency.

✓ Verified Model Answer (Text Solution)

(i) Double Volute Casing: A double volute casing improves the pump's radial balance. The pressure distribution is split across two volutes, cancelling out radial thrust forces that could lead to shaft vibrations and premature wear.