A centrifugal pump is tested in the laboratory The pump has

A centrifugal pump is tested in the laboratory. The pump has a 6-in. impeller and is operating at 3500 rpm. With water as the fluid, test results indicate that the pump delivers 280 gpm at 110 ft of head. Using the affinity laws, predict what the pump capacity and head would be if the rotational speed was reduced to 1750 rpm.

Solution

solution

from pump affinity laws

q₁ / q₂ = (n₁ / n₂) (d₁ / d₂)

here diameters of wheel are same

so,

q₁ / q₂ = (n₁ / n₂)

q₂ = q₁ / (n₁ / n₂)

= 280 / (3500 / 1750 )

   = 140 gpm

dp₁ / dp₂ = (n₁ / n₂)² (d₁ / d₂)²

where, dp = head or pressure

dp₁ / dp₂ = (n₁ / n₂)²

dp₂ = dp₁ / (n₁ / n₂)²

= 110 / (3500 / 1750)²

= 27.5 ft