Sump Sizing

8/2/2019 Sump Sizing

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Pump Sump Sizing

Dewatering Pumps


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Pump sump sizingThree functions of the sump:A volume V1 to certify the function of the pump/s

Prevent snoringPrevent cavitation (NPSH rec)

Cooling of the motorA working/live volume V required between start and stopA spare volume/surge capacity to take sudden inrush of water V2


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Pump cycle time

The minimum pump cycle time Tc min is determined by the number ofstarts M allowed per hour with regards to temperature rise in themotor.

For a Flygt pump the maximum numbers of starts/hour are 30.

Pump sump sizing


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Pump capacity, Qp Inflow, average, Qin

Pump sump sizing


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Filling phase:

Emptying (pumping) phase:

i.e.

i.e. has a minimum for

and therefore

Pump sump sizing


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Example:

Qp = 40 l/s

M = 30 starts/h =>

Tc min = 3600/30 = 120 s

i.e. V min = Tc min x Qp/4

= 120 x 40/4

= 1200 l or 1,2 m3

Pump sump sizing


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Clarifying / SedimentationPump sump sizing


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Clarifying / Sedimentation


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Sedimentation in water depends on:

The surface of the basin Acl (m2)

The inflow to the basin Q (m3/h)

The settling velocity of the particles - vs (m/h)

which depends on:

The size of the particles and their shape

Spec. weight of the particles

Concentration of particles (< 10 kg/m3)

Acl > Q/vs



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Calculation example:(according to graph on previous side)

Flow Q = 30 l/s or 108 m3/h

Spec.weight of the particle = 2,5 kg/dm3

Smallest particle to settle out 74 micron gives a settling velocity of 18 m/h

Clarifying surface:

Acl = Q/vS x 1,3 (safety factor)

= 108/18 x 1,3 = 7,8 m2



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Sump Sizing

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