Dewatering
Prime-assisted dewatering pumps: lift, hose friction, and elevation
Last reviewed 21 October 2026.
A prime-assisted dewatering pump is a centrifugal pump with a separate air mover: a compressor and a venturi, or a diaphragm vacuum pump, that evacuates the casing and the suction hose before liquid arrives. A float valve should close once liquid is there so the primer stops pulling water. A wet-prime self-primer does the same job with a charge of liquid kept in the casing. The vacuum primer does not add head to the centrifugal curve, and it does not raise the atmospheric ceiling.
The Lakeshore illustration is an 18 ft lift, a 6 in suction hose 40 ft long with no foot valve, and 250 ft of 6 in DR 17 HDPE with a swing check. The duties below are CurvePoint’s intersection at three sites. The 1,000 gpm row is a friction check at a stated flow. It is not the operating point.
| Elevation | Water at 10°C | Water at 30°C |
|---|---|---|
| 0 m (0 ft) | 33.5 ft (10.21 m) | 32.6 ft (9.94 m) |
| 300 m (984 ft) | 32.3 ft (9.85 m) | 31.4 ft (9.58 m) |
| 600 m (1969 ft) | 31.2 ft (9.50 m) | 30.3 ft (9.23 m) |
| 1000 m (3281 ft) | 29.7 ft (9.04 m) | 28.8 ft (8.77 m) |
| 1500 m (4921 ft) | 27.9 ft (8.50 m) | 27.0 ft (8.23 m) |
Illustrative Lakeshore Process Equipment figures from CurvePoint’s own evaluation. Not a sealed calculation.
| Case | Operating point | NPSH available |
|---|---|---|
| Sea level, 10°C, 1800 RPM | 1486 gpm (93.7 L/s) at 98.9 ft (30.13 m) | 6.70 ft (2.04 m) |
| 1,500 m, 30°C, 1800 RPM | 1504 gpm (94.9 L/s) at 97.6 ft (29.74 m) | 0.12 ft (0.04 m) |
| Sea level, 10°C, affinity estimate at 1620 RPM | 1267 gpm (79.9 L/s) at 84.3 ft (25.69 m) | 9.06 ft (2.76 m) |
Illustrative Lakeshore Process Equipment figures from CurvePoint’s own evaluation. Not a sealed calculation.
| Item | US | SI |
|---|---|---|
| Air volume | 60.0 gal | 227.2 L (0.227 m³) |
| Suction loss at 1,000 gpm, 10°C sea level | 4.06 ft | 1.24 m |
| Hose velocity at the sea-level duty | 16.5 ft/s | 5.03 m/s |
| 50,000 L/day, as an average flow | 9.17 gpm | 50,000 L/day |
| 750 gpm, a filter-bag pump-rate cap in the DC strategy | 750 gpm | 47.3 L/s |
Illustrative Lakeshore Process Equipment figures from CurvePoint’s own evaluation. Not a sealed calculation.
Lift against elevation
The budget table is atmospheric head minus vapour-pressure head. That remainder still has to pay for static lift, suction-hose friction, and the NPSH the pump requires. At sea level and 10°C the illustration has an operating point with a few feet of available NPSH left. At 1,500 m and 30°C the head curves still meet and available NPSH is essentially gone. Slowing the illustration from 1,800 RPM to 1,620 RPM is an affinity estimate. Read that row as an estimate, then read the new intersection. Static lift does not scale with speed. A 2-vane open impeller tracks the affinity ratios less cleanly than a radial-vane impeller. The affinity-law guide is the longer version of that warning.
The sea-level duty sits far to the right on this curve, and the hose-velocity row is high for a suction line. That is the honest result of asking a 6 in hose to carry the intersection. A larger hose, or a duty held nearer the friction-check flow, spends less of the NPSH budget. The air volume of the 40 ft hose is in the same table, from the Schedule 40 inside diameter.
What the discharge has to satisfy
In Ontario, a Qualified Person prepares the water-taking report and the discharge report before a taking starts. Groundwater or combined takings over 50,000 L/day self-register on the Environmental Activity and Sector Registry. The registry notice of 1 July 2025 removed the 400,000 L/day cap. Surface-water-only takings stay outside that registry. Storm water alone, once it is over 50,000 L/day, still needs the Qualified Person’s discharge report. The table converts 50,000 L/day into gallons per minute with CurvePoint’s flow factor so a pump curve and a daily limit can sit on the same page. Include the storm allowance in the flow you size, not only the dry-day seepage.
Filter bags are sized to the pump rate and the soil, and they are replaced when they are about half full. Indiana’s filter-bag sheet is a draft measure. DC’s dewatering strategy caps a bag at 750 gpm or at half the bag maker’s maximum, whichever is lower, and it asks for a floating, screened intake. The 750 gpm row is that cap, converted to litres per second. It is not a pump rating. Ohio’s dewatering measures describe sediment traps with about 24 hours of detention and no more than about 4 ft of depth, plus weir tanks, sand media, and flocculants such as chitosan or anionic PAM. Draw from near the surface so the intake does not pull fines off the floor. EPA’s 2022 Construction General Permit inspection guide covers dewatering inspection and, for impaired waters, turbidity sampling. States administer that permit in most places.
A mine conveyance, and a city’s bypass pumps
Surface conveyance on a mine or a treatment site is often HDPE. The OSMRE pumping module sizes that pipe from flow, total dynamic head, velocity, and friction, which is the same system-curve question as the table above. One sealed-area decision describes a 500 gpm pump sending water to a surface settling pond. Cite that as the case. It is not a typical range. The same decision’s inlet depth is submergence, discussed on the NPSH calculator, and it is not NPSH.
MSHA’s program bulletin P11-32 is about loss-of-flow protection so a pump cannot sit dead-headed and overheat. Flow switches, undercurrent trips, and temperature sensors are the kinds of devices that bulletin is aimed at. Underground coal has a separate electrical rulebook in 30 CFR Part 75. That part is not a pump-curve method. Seattle’s sewer-bypass specification asks for automatic self-priming pumps with no foot valves and no vacuum pumps, a run-dry rating, 3 in solids, and 100 percent redundancy. Those are requirements for that city’s bypass pumps. A prime-assisted machine that depends on a vacuum primer is a different tool, and it does not satisfy that sentence by itself. Bypass plans are written up on the wastewater example.
Open the sea-level study in the calculator, then change elevation, temperature, and hose diameter to the pit you are dewatering. The suction lift guide compares the three priming methods on one page.