Well pump · cycle protection
WellMate pressure-tank sizing
Size drawdown first, then tank volume. This prevents the common mistake of treating a tank’s nominal volume as the water delivered between pump starts.
Recommended catalogue model
WM-14WB
What it means:
The trap
A 178 L tank does not deliver 178 L per cycle.
Compressed air occupies most of the vessel. Between 30 and 50 psi, a WM-14WB publishes about 55.3 L drawdown. The calculator recomputes drawdown for your selected pressures.
Worked example · 3 m³/h
WM-14WB
A 3 m³/h pump delivers 50 L/min. One minute requires 50 L drawdown. At 2.07/3.45 bar, f = 0.309 and minimum nominal volume is 161.8 L. WM-12 is too small; 178 L WM-14WB gives about 55 L and 1.1 minutes.
- Use measured pump delivery at operating pressure.
- With pump power off and the tank fully drained, set air-cell precharge 4 psi (0.28 bar) below cut-in.
- Install a correctly sized relief valve that cannot be isolated from the tank.
- Not for VFD/constant-pressure sizing.
Check the assumptions
Method and primary references
The equations are shown so the result can be checked. Product data and site conditions still govern final selection.
- Pentair WellMate WM SeriesTank capacities, published 30/50 psi drawdown and sizing equation.
- Pentair WellMate FAQPrecharge: pump off, tank drained, 4 psi below cut-in.
From answer to equipment
Bring the duty point, not just a product name.
Watermart can check the calculation against the actual water analysis, pressure, valve, pump and installation constraints.
Discuss this calculation →Educational preliminary calculation—not a stamped design, quotation, or treatment-performance guarantee.