OVERSIZING OF A PUMP

Selection of a pump with a bigger head and flow than necessary
WHAT SYMPTOMS CAN SAY THAT THE PUMP IS OVERSIZED?
- APPLICATION OF THE THROTTLE CONTROL. 
- VIBRATION AND NOISE OF PUMPS, VALVES, PIPES. 
- CAVITATION
- EXTRA MAINTENANCE COST. 
- SHUT DOWN OF ELECTRIC MOTORS.

HOW DOES PUMP OPERATE IF IT OVERSIZED?

Pump operates beyond the allowable operating range or overloaded !!! 
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CONTROL PANEL SWITCHES OFF THE PUMP BECAUSE OF EXCESSIVE CURRENT OR MOTOR OVERLOADING.  
PRESSURE GAUGES INDICATION.
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Having the Pressure gauges pump user can define the position of an operating point relatively the operating range.  there is another way to define that the pump is oversized. 
If the pump is oversized it will have pressure (head) less than the pressure within the operating range. 
Try to close the discharge valve and watch what happens. How changes pressure vibration noise current. 

CAVITATION
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The presence of cavitation is another evidence of the pump oversizing. The operating point lays far in the region of the big flow sometimes beyond the right border of the operating range.

WHY USERS SELECT A PUMP WITH THE MORE HEAD?

The typical arguments for the selection of a pump with excessive head.
A Pump with BIGGER HEAD  is less problematic than the pump with NOT ENOUGH  HEAD.
A pump with a bigger head will deliver liquid, pump with not enough head will not.
  • Poor design of a pumping system

  • Wrong calculation of hydraulic parameters of a pumping system.

  • Excessive safety factors.

  • Deviations from the project which can influence hydraulic parameters.  

  • Designing systems for the future  growth of required parameters.

  • System curve changes in time (water consumption changed).

  • Sediments and corrosion can increase the pipe's restriction.

THE POSSIBLE  SOLUTION

The replacement of a pump by the pump with appropriate parameters. This solution can be expensive.
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If we understand that the pump has a bigger head then necessary how we can correct the situation.
We can replace the installed pump by the pump with a lower head. 

THROTTLE CONTROL.
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This will allow adjusting of a system curve by using the valve so that the pump will operate within the preferred operating range with high efficiency and reliability but energy will be wasted across the valve. See it in the graph. As a negative consequence, the increased valve wear should be taken into account.  

APPLICATION OF VFD.
Application of  VFD to adapt the pump curve to the system requirements.
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Application of VFD allows the pump curve to be reduced as you can see in the drawing how an operating point moves and get inside the allowable operating range. But it is necessary to understand whether parameters at a lower speed satisfy the system requirements?

IMPELLER TRIMMING 

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