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.
Step 2: The pipeline
Every fitting counts as a length of straight pipe.
Fittings. Each one is worth a length of straight pipe. A side-outlet tee on a 6 in line costs 30 ft of head.
Step 3: The pump and where it sits
Altitude and suction lift decide whether it primes at all.
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.
| 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. |
|---|---|---|---|---|
| 90° elbow | 5.0 | 10.0 | 15.0 | 20.0 |
| 45° elbow | 2.5 | 5.0 | 8.0 | 10.0 |
| Tee straight | 3.5 | 7.0 | 10.0 | 14.0 |
| Tee side | 10.0 | 20.0 | 30.0 | 40.0 |
| Gate valve, open | 1.5 | 2.6 | 4.0 | 5.0 |
| Swing check valve, open | 9.0 | 17.0 | 25.0 | 35.0 |
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 | ||||||||
|---|---|---|---|---|---|---|---|---|
| 25 | 1.3 | 2.0 | 0.0 | 0.1 | ||||
| 50 | 4.8 | 7.1 | 0.2 | 0.2 | ||||
| 75 | 10.1 | 15.1 | 0.3 | 0.5 | 0.0 | 0.1 | ||
| 100 | 17.3 | 25.8 | 0.6 | 0.9 | 0.1 | 0.1 | ||
| 125 | 26.1 | 39.1 | 0.9 | 1.3 | 0.1 | 0.2 | ||
| 150 | 36.7 | 55.0 | 1.2 | 1.9 | 0.2 | 0.3 | 0.0 | 0.1 |
| 175 | 48.9 | 73.2 | 1.6 | 2.5 | 0.2 | 0.3 | 0.1 | 0.1 |
| 200 | 62.6 | 93.8 | 2.1 | 3.2 | 0.3 | 0.4 | 0.1 | 0.1 |
| 300 | 4.5 | 6.7 | 0.6 | 0.9 | 0.2 | 0.2 | ||
| 400 | 7.7 | 11.5 | 1.1 | 1.6 | 0.3 | 0.4 | ||
| 500 | 11.6 | 17.4 | 1.6 | 2.4 | 0.4 | 0.6 | ||
| 750 | 24.7 | 36.9 | 3.4 | 5.1 | 0.8 | 1.2 | ||
| 1,000 | 42.1 | 63.1 | 5.8 | 8.7 | 1.4 | 2.1 | ||
| 1,500 | 12.3 | 18.5 | 3.0 | 4.5 | ||||
| 2,000 | 21.0 | 31.5 | 5.1 | 7.7 | ||||
| 2,500 | 31.8 | 47.7 | 7.8 | 11.7 | ||||
| 3,000 | 44.7 | 67.0 | 10.9 | 16.4 | ||||
| 4,000 | 76.3 | 18.7 | 28.0 | |||||
| 5,000 | 28.3 | 42.4 |
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 |
|---|---|---|
| 0 | 0 | 34.0 |
| 2,000 | 609.6 | 31.6 |
| 4,000 | 1,219.2 | 29.4 |
| 6,000 | 1,828.8 corrected | 27.3 |
| 8,000 | 2,438.4 | 25.2 |
| 10,000 | 3,048 | 23.4 |
| 15,000 | 4,572 | 19.1 |
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.
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Book a 20 min callWorked example
Worked with the values this page loads with, so the method can be checked against the cited source without entering anything. Change any input above and the calculator recomputes; the numbers below stay as a fixed reference case.
- 170.3 ft
- 30.7 hp
- 25.5 kW
| Static lift | 120.0 ft | elevation head, Eq. 15.1 p. 275 |
| Pipe length | 2000.0 ft | your input |
| + 4 × 90° elbow | 60.0 ft | 15.0 ft each at 6.00 in, Table 15.2 p. 276 |
| + 2 × 45° elbow | 16.0 ft | 8.0 ft each at 6.00 in, Table 15.2 p. 276 |
| + 2 × gate valve, open | 8.0 ft | 4.0 ft each at 6.00 in, Table 15.2 p. 276 |
| + 1 × swing check valve, open | 25.0 ft | 25.0 ft each at 6.00 in, Table 15.2 p. 276 |
| = equivalent length | 2109.0 ft | pipe plus fittings |
| Friction loss | 2.38 ft per 100 ft | Eq. 15.2: 1,045 × (500 gpm ÷ 120)^1.852 ÷ (6.00 in)^4.87, p. 275 |
| × equivalent length ÷ 100 | 50.3 ft | |
| = total dynamic head | 170.3 ft | Eq. 15.1: lift + friction, p. 275 |
| Pipe velocity | 5.7 ft/s | Eq. 15.5: Q = V × A, p. 278 |
| Water power | 21.5 hp | flow × head × SG ÷ 3,960, where 3,960 is 33,000 ft·lb/min per hp ÷ 8.33 lb/gal |
| ÷ pump efficiency | ÷ 0.70 | Eq. 15.3 p. 278; handbook rule of thumb 0.70 |
| = brake power | 30.7 hp | Eq. 15.3 p. 278 |
| ÷ motor efficiency | ÷ 0.90 | Eq. 15.4 p. 278 |
| = motor draw | 25.5 kW | Eq. 15.4: bhp × 0.746 ÷ motor efficiency, p. 278 |
| Suction head available | 34.0 ft | at 0.0 ft elevation, Table 15.3 p. 277 |
| Suction lift used | 10.0 ft | pump above the water |
Estimating aid only. This is not an engineering design and not a substitute for the judgment of a competent or qualified person. Verify every result against the cited source and your own site conditions. Full terms and disclaimer.