Pump problems

 Noise is a significant factor used to determine the performance of the pumps.

PUMP PROBLEMS

1. Pump Noise

• Noise is a significant factor used to determine the performance of the pumps. 

• Any increase in noise level normally indicates wear and danger of failure of pump. 

• Normally noise is measured in units of decibels (dB).

• Generated noise levels depend on many factors such as the pump type, pump component materials, pump mountings, rigidity, manufacturing and fitting accuracies of the pump elements, size and flow capacity, pressure, speed of rotation, pressure pulsations, and the other components in the circuit.

• Table 4.10 presents the approximate noise levels for various pump designs. Generally speaking, external gear and the piston pumps are the noisiest while screw pumps are very quiet; vane and internal gear pumps have noise levels somewhere in between a piston and screw pumps.

Table 4.10. Noise levels for various pump designs

2. Slip

• Slip is the leakage occurs between the discharge and suction sides of a pump through the pump clearances.

• The extent of this leakage depends on the width, length and shape of the clearances, the viscosity of the pumped liquid, and the pressure difference between the discharge and suction sides of the pump.

• Pump speed does not influence slip. But slip increases with increasing liquid viscosity.

3. Cavitation

• Definition: The formation, growth and collapse of vapour filled cavities or bubbles in a flowing liquid due to local fall in fluid pressure is called cavitation.

• Phenomenon: For smooth operation, pumps should be completely filled with liquid. When liquid does not completely fill the pump chamber, a loss of capacity results. This may occur through the vapourization of some of the process liquid in the suction line or the pump chamber. The vapour bubbles are carried into higher-pressure regions of the pump where they collapse, resulting in noise and vibration. This phenomenon is called pump cavitation.

• Effects: The pump cavitation may cause severe erosion of the pump components (also called pitting) and reduce the pump life.

• Cavitation can be avoided by ensuring that the suction pressure is always greater than that required by the pump.

4. Pump Ripple

Small variations of fluid flow that takes place during pumping (due to some design problems) are called ripple.