Frequently Asked Questions

1. How does a centrigual pump work?
2. Should I use gauges on my pump?
3. What is a cavitation and how is it caused?
4. What are the common causes of pump vibration?

1. How does a centrigual pump work?

A centrifugal pump is the simplest of all pumps. It consists of one moving part, a rotary impeller and a stationary casting, called a volute, casing, or diffuser. The operation of a centrifugal pump is very simple. The pump volute is filled with liquid and the impeller is rotated, causing the liquid to rotate, creating a high velocity to the liquid. The outward flow of the liquid through the impeller reduces the pressure at the eye or center of the impeller, causing more liquid to be forced into the impeller eye by external or atmospheric pressure. The liquid is thrown into the volute and converted to pressure.

The pressure a centrifugal pump will develop is in direct relation to the velocity created by the impeller, thus the larger the diameter of the impeller, or the faster the impeller is rotated, the more head pressure the pump will develop. The width of the impeller vanes will determine how much liquid the pump will pump.

The pump speed and impeller size, will both affect the horsepower size of the motor required. The more water you pump, or the higher pressure you develop, the more horsepower you will need.

2. Should I use gauges on my pump?

A resounding YES!

When dealing with pumps, it is necessary to be able to measure the performance. Gauges, on the suction and discharge of the pump, provide those measurements. By using gauges, we can determine what the actual total dynamic head is. If we also measure the speed, we can then find the flow the pump should be producing. Gauges are your eyes inside the pump and, without the gauge readings, the solution to a performance problem becomes nearly impossible.

3. What is cavitation and how is it caused?

Cavitation is the term used to describe a rather complex phenomenon that can exist in any pumping installation. In a centrifugal pump this may be explained as follows: when a liquid flows through the suction line and enters the eye of the pump impeller an increase in velocity takes place. This increase in velocity is, of course, accompanied by a reduction in pressure. If the pressure falls below the vapor pressure corresponding to the temperature of the liquid, the liquid will vaporize and the flowing stream will consist of liquid plus pockets of vapor. Flowing further through the impeller, the liquid reaches a region of higher pressure and the cavities of vapor collapse. It is this collapse of vapor pockets that causes the noise and damage incident to cavitation.

4. What are the common causes of pump vibration?

1. Mechanical Vibration causes:
   • Unbalanced rotating components
     
   • Bent or warped shaft
     
   • Pump and drive misalignment
     
   • Pipe strain (by design or due to thermal growth)
     
   • Mass of the pump base is too small
   • Rubbing parts
     
   • Worn or loose bearings
     
   • Loose hold down bolts
     
   • Loose parts
     
   • Product attaching itself to a rotating component
     
2. Hydraulic Vibration causes:
   • Pump operating to the left or right of the curve
     
   • Vaporization of the product
     
   • Impeller vane running too close to pump cutwater
     
   • Internal recirculation
     
   • Air getting into the system through vortexing
     
   • Turbulence in system
     
   • Water hammer/Hydraulic shock
3. Other Vibration causes:
   • Harmonic vibration from nearby equipment
     
   • Operating pump at critical speed