Big Dog Mining

Dewatering Pump & Pipe Sizing

Total dynamic head, brake horsepower and the motor draw for a dewatering line. Tells you when the pipe is too small, when the water is moving too slowly to keep solids up, and when the pump is set too high above the water to prime at all.

Step 1: The water

What you are moving, and how far up.

Units ?

Source equations are imperial. Metric is converted.

Flow rate ?gpm

What the sump actually has to shift.

Static lift ?ft

Water surface to discharge. Vertical only.

Specific gravity ?

1.00 is clean water. Higher for silty or slurry duty.

Step 2: The pipeline

Every fitting counts as a length of straight pipe.

Pipe material ?

Sets the roughness coefficient.

Roughness coefficient C auto ?

Higher is smoother. Old pipe is rougher than new.

Inside diameter ?in

Inside, not nominal. This one matters most.

Pipe length ?ft

Along the run, not point to point.

Fittings. Each one is worth a length of straight pipe. A side-outlet tee on a 6 in line costs 30 ft of head.

90° elbows ? 45° elbows ?

Tees, straight through ? Tees, side outlet ?

Gate valves, open ? Swing check valves ?

Step 3: The pump and where it sits

Altitude and suction lift decide whether it primes at all.

Pump efficiency ?

Handbook rule of thumb is 0.70.

Motor ?

Sets motor efficiency for the kW draw.

Site elevation ?ft

Thinner air lifts less water into the suction.

Suction lift ?ft

Pump above the water. Zero means flooded suction.

Energy cost (optional) ?$ / kWh

Gives running cost per day at 24 h.

What this checks

Three ways a dewatering line goes wrong that a head figure alone will not show.

Priming. Suction lift against the atmospheric head actually available at your elevation.
Velocity. Too slow and solids drop out and silt the line; too fast and you wear the pipe out.
Friction share. When friction outweighs the lift you are paying to push water through a pipe that is too small.

total dynamic head

brake power

motor draw

Step	Value	Where it comes from

System profile

Head and suction margin

Equivalent feet of straight pipe for fittings

Fitting	2 in.	4 in.	6 in.	8 in.

SME Mining Reference Handbook, Table 15.2, p. 276. The 2nd edition carries the identical table on p. 380. Between published sizes the calculator scales the equivalent length with the diameter, which is what the table itself does.

Published pipe friction loss, and what this calculator computes

Flow, gpm

SME Mining Reference Handbook, Table 15.1, p. 276, in feet of head per 100 ft of pipe. Identical in the 2nd edition on p. 380. The calculator does not read this table. It works Equation 15.2, the Hazen-Williams formula, so it handles any diameter and flow rather than only the published ones. The table is here because it is the check: C = 150 for HDPE and C = 120 for steel reproduce every column of it to within its own rounding, which is how those two values were confirmed rather than assumed.

Suction head available at elevation

Elevation, ft	Elevation, m	Head of water, ft

SME Mining Reference Handbook, Table 15.3, p. 277. Note: the printed table gives the 6,000 ft row as 1,028.8 m. 6,000 ft is 1,828.8 m, so that is a typo in the book, shown corrected above. It changes nothing here: the calculator interpolates on the feet column, and a metric elevation is converted to feet before lookup.

Head is only half of a pump selection. This gives you the duty point, flow and total dynamic head, that a pump has to meet. Which pump meets it comes off the manufacturer's curve, and where that curve crosses your system curve is the flow you will actually get, not the flow you asked for. Velocity head is ignored throughout, as the source does, because on a properly sized line it is negligible.

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Terms of use and disclaimer

Estimating aid only. This calculator is an educational tool. It is not an engineering design and it is not a substitute for the judgment of a competent or qualified person.

No warranty. It is provided "as is", without warranty of any kind, express or implied, including any implied warranty of merchantability or fitness for a particular purpose. Equations and constants are cited to their published sources above, but transcription, implementation and the values you enter can all be wrong. Verify every result against the cited source and against your own site conditions before it informs a decision.

Not a statutory document. Nothing produced here is a ground control plan, ventilation plan, blast design, haul road design or hoist design. Those must be prepared, signed and approved under the regulations that apply to your operation. Compliance with MSHA, or with your own jurisdiction's mining regulations, is the operator's responsibility and remains so.

Assumption of risk. You use this tool entirely at your own risk. Mining is hazardous, and errors in ground support, ventilation, blasting or haulage can cause serious injury or death.

Limitation of liability. To the maximum extent permitted by law, Big Dog Mining and its owners, operators and contributors accept no liability for any loss, damage, injury, death, cost or claim, whether direct, indirect, incidental or consequential, arising out of or in connection with the use of this tool or reliance on its output.

Indemnity. By using this calculator you agree to indemnify and hold harmless Big Dog Mining and its owners, operators and contributors against any claim, demand, loss, liability or expense, including reasonable legal fees, arising from your use of it or from any decision taken in reliance on it.

If you do not accept these terms, do not use this calculator.