SIMAQ School · Calculator

Site dewatering

The pump that “won't pull” is almost never broken. It's fighting a total head nobody calculated.

Head, not litres

A pump is rated by the total head it can overcome: the lift from water to pump, the rise from pump to outlet, and what friction eats along the way. Nameplate flow only happens when that sum is zero.

The suction ceiling

No pump “pulls” water: the atmosphere pushes it. At sea level that pressure holds a column of about 10 m, and in practice friction leaves you 7 or 8. Above that no surface pump works — you move it down.

Diameter rules

Friction loss falls with the fourth power of diameter. Going from 2″ to 3″ cuts it about sevenfold. That's why a big pump on narrow hose beats less than a small one on the right hose — and hose is cheaper than pumps.

Cavitation

Choke the suction — narrow hose, clogged strainer, too much lift — and pressure drops so low the water boils cold. The bubbles collapse against the impeller and pit it. That rattling sound isn't wear, it's an install error.

Run your case

Move the four variables of your job and the calculation tells you which SIMAQ pump holds up, with how much margin, and what to fix if it falls short.

Suction lift3 mFrom the water surface up to the pump.Discharge head6 mFrom the pump up to the outlet.Total hose30 mSuction + discharge, added up.

Hose diameter

This decides almost everything: friction falls with the fourth power of diameter.

SQWP30 PRO

Enough

3″ · 30 m³/h · max head 13 m

Static head: 9.0 m
Friction loss: 1.8 m
Total head: 10.8 m
Margin: +2.2 m

SQWP40 PRO

Enough

4″ · 40 m³/h · max head 16 m

Static head: 9.0 m
Friction loss: 3.0 m
Total head: 12.0 m
Margin: +4.0 m

The SQWP30 PRO works with 2.2 m of margin.

Losses use Hazen-Williams (C = 120, sound site hose) at each pump's rated flow. Old hose, extra couplings or tight bends make it worse — which is why margin matters.

The four recurring mistakes

Narrow suction hose
Whatever was lying around. The number-one cause of cavitation and of pumps returned “faulty”.
Strainer resting in the mud
It sucks solids, clogs, and starves the suction. Suspend it, don't drop it.
Starting without priming
The casing must be full of water. Running dry burns the mechanical seal in minutes.
Long runs out of habit
Every metre of hose is head the pump must beat. A shorter route outperforms a bigger pump.

The pumps