Pumps

Vane

A curved blade used in a pump.

Impeller

A disc or a cylinder on which a set of vanes are attached. Main rotating element in a pump. Mounted on a shaft. The shaft is driven by an electric motor or IC engine.

Direction of the fluid flow

Axial flow

Fluid enters and exits the impeller axially.

Radial flow

Fluid enters the impeller axially. Leaves radially.

Mixed flow

Fluid enters the impeller axially. Leaves in both axial and radial directions.

Note

For s1, only centrifugal pumps are studied.

Parameters

Head provided

The head provided by a pump depends on the flow rate.

$$H=f(Q)$$

Here:

• $H$ - provided head
• $Q$ - flow rate

For a given pump running at a given speed, there is a unique variation of $H$ and $Q$.

Power input

Denoted by $P_i$. Varies with $Q$.

Efficiency

Denoted by $\mu$. Varies with $Q$.

$$\mu = \frac{P_o}{P_i}$$

Note

$$\text{Energy per unit volume} = \frac{P_{i_A}}{Q}$$

Performance characteristic

All these parameters, plotted vs $Q$, is known as performance characteristic of the pump. Will be given by the manufacturer. Can be found by laboratory testing. $$

In a pipeline system

$$H=H_0 + KQ^2$$

$H$ is the head required (or received) to create the flow rate $Q$ in the pipeline system. The above equation is known as system characteristic or system load curve.

Here $K$ is the loss coefficient and is given by: $$

$$K = \frac{8}{\pi^2gD^4}\bigg(K_L+\frac{\lambda L}{D}\bigg)$$

Note

Working state of a pipeline system is given by the intersection of system characteristic and performance characteristic (of the pump) curves.

Resultant pumps

In serial

When 2 pumps are operating in a series:

• $Q$ is same for both
• $H = H_1 + H_2$

In parallel

When 2 pumps are operating in a parallel:

• $Q = Q_1 + Q_2$
• $H$ is same for both