How to size a water centrifugal pump

How to size a centrifugal pump

 

Pump sizing is to select an appropriate pump whose flow and pressure match with the flow rate and pressure necessary to transfer a liquid through a piping system from one point to another.

 

How to select a pump

 

Total flow rate, Q

 

First the flow rate, Q of the pump must be determined by adding all the flow rates at each outlet of the piping system. Quantity of fluid delivered by the pump in the unit of time, generally expressed in m3/h.

 

Q = A x v

 

A (area of the pipe): π x (d/2)2 [m2]

 

v: speed of liquid (water) in the pipe [m/s]

 

MINIMUM WATER CONSUMPTION IN SINGLE-FAMILY DOMESTIC SYSTEMS:

 

Kitchen + bathroom = 1,7 m3 /h

Kitchen + bathroom + WC = 1,8 m3 /h

Kitchen + 2 bathrooms = 2 m3 /h

Kitchen + 3 bathrooms = 2,2 m3 /h

 

APPROXIMATE CONSUMPTION FOR GARDENS IN ACCORDANCE WITH SURFACE AREA Surface (m2 )

 

Garden area /m2 Flow rate m3/h
100 0.75
200 1.5
300 2.25
400 3

 

 

Example:

The water flow rate required for a home with 1 KITCHEN and 2 BATHROOMS and 200 m2 of garden space.

 

KITCHEN + 2 BATHROOMS + 200 m2 GARDEN = 2 m3 /h + 1.5 m3 /h = 3.5 m3 /h

 

 

Domestic Water Utilities FLOW RATE (l/min)
Toilet with rapid flow valve 90
Bath 15
Shower 12
Washing machine 12
Dishwasher 10
Sink  9
Toilet with flush tank  6

TOTAL WATER PRESSURE HEAD IN METERS (HT)

 

  • DELIVERY HEAD (hi)

The maximum possible height between the delivery port of the pump and the water outlet point (normally a tank) (m).

 

  • SUCTION HEAD (hs)

The height between the water level in the sump and the suction port of the pump (m).

 

  • GEOMETRICAL HEIGHT (hg)

The geometrical height from the water level in the sump to the highest water outlet point (m).

 

  • TOTAL MANOMETRIC HEAD (Hmt)

It is considered as the sum between the geometric head existing between the fluid levels and the head loss due to frictions from the fluid passage in the pipework, into the pump and relevant hydraulic accessories.

 

The expression is the following:

 

Hmt = hg + ∆p

 

∆p = sum of head loss of the system calculated from the following data:

 

  • Diameter, length and material of the suction and delivery piping
  • Number and type of elbows in the piping and hydraulic accessories such as foot valves, gate valves, non-return valves and strainers etc...
  • Type, temperature, viscosity and density of fluid (if different from that of water)

 

HEAD LOSS, ∆p

 

Absolute roughness is a measure of the surface roughness of a material which a fluid may flow over. Absolute roughness is important when calculating pressure drop.

 

K value
exampe pipe
example 2
pump characteristic
c1
c2
c3
head lossss
c6
c7

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