Performance Characteristic Curves of centrifugal pumps

The characteristic curves of a centrifugal pump are defined as those curves which are plotted from the results of a number of tests on the centrifugal pump. These curves are necessary to predict the behavior and performance of the pump, when the pump is working under different flow rate, head and speed. The following are the important characteristic curves for the pumps:

1. Main characteristic curves.

2. Operating characteristic curves and

3. Constant efficiency or Muschel curves.

1. Main Characteristic Curves:

the main characteristic curves of a centrifugal pump consists of a head (Manometric head 𝐻 ) power and discharge with respect to speed. For plotting curves of Manometric head versus speed, discharge is kept constant.

For plotting curves of discharge versus speed, Manometric head (𝐻 ) is kept constant. For plotting curves power versus speed, Manometric head and discharge are kept constant.

2. Operating Characteristic Curves:

If the speed is kept constant, the variation of Manometric head, power and efficiency with respect to discharge gives the operating characteristics of the pump.

The input power curve for pumps shall not pass through the origin. It will be slightly away from the origin on the y-axis, as even at zero discharge some power is needed to overcome mechanical losses.

The head curve will have maximum value of head when the discharge is zero.

3. Constant Efficiency Curves:

For obtaining constant efficiency curves for a pump, the head versus discharge curves and efficiency v/s discharge curves for different speeds are used. By combining these curves ∼ 𝑄 𝑐𝑢𝑟𝑣𝑒𝑠 𝜂 ∼ 𝑄𝑐𝑢𝑟𝑣𝑒𝑠 constant efficiency curves are obtained.

For plotting the constant efficiency curves (Iso– efficiency curves), horizontal lines representing constant efficiencies are drawn on the 𝜂 ∼ 𝑄 curves. The points, at which these lines cut the efficiency curves at various speeds, are transferred to the corresponding 𝐻 ∼ 𝑄 curves. The points having the same efficiency are then joined by smooth curves. These smooth curves represent the iso – efficiency curves.