A pump curve is a field decision tool, not a brochure graph. It tells you where the pump can operate, what it will cost in horsepower and where the duty becomes unstable or destructive.
The five lines that matter
| Curve item | Meaning | Why it matters |
|---|---|---|
| Flow | Horizontal axis, usually gpm or m3/h | Defines the process capacity |
| Head | Vertical axis, usually ft or m | Independent of fluid density until converted to pressure |
| Efficiency | Energy conversion quality | Controls shaft HP and heat loss |
| Power | Brake horsepower or kW | Must be checked at actual SG |
| NPSHr | Suction head required by the pump | Must be lower than site NPSHa with margin |
Step 1: convert process pressure to head
Hydrocyclone and manifold duties are often specified as pressure. Pump curves usually use head, so convert using actual mud specific gravity.
Head (ft) = Pressure (psi) × 2.31 / SGExample: 40 psi at SG 1.25 equals 73.9 ft. At SG 1.00 the same pressure equals 92.4 ft, so comparing pressure without SG correction is misleading.Step 2: add system losses
The downstream process may need 74 ft at the manifold, but the pump must also overcome suction losses, discharge pipe losses, fittings, valves and elevation. Those losses are not optional; they shift the required operating point.
TDH = static head + pressure head + friction loss + minor lossesIf calculated TDH is 96 ft, selecting a pump that gives 900 gpm at 74 ft will underperform after installation.Worked selection example
| Input | Value | Use |
|---|---|---|
| Required flow | 850 gpm | Process capacity target |
| Manifold pressure | 38 psi | Hydrocyclone energy requirement |
| Mud SG | 1.22 | Pressure-to-head correction |
| Line loss | 18 ft | Installed piping penalty |
| TDH | 90 ft | Curve must pass near 850 gpm at 90 ft |
Best efficiency is a range, not a decoration
Running far left on the curve can create recirculation, vibration and heat. Running far right can overload the motor and increase cavitation risk. The useful selection is the one that satisfies the process while remaining in a stable efficiency region.
Power line check
Brake HP ≈ Hydraulic HP / pump efficiencyIf hydraulic demand is 24 HP and pump efficiency is 0.58, brake demand is about 41 HP before service factor and motor margin.Engineering depth: curve reading sequence
Read the curve in a fixed order. First define required flow. Second calculate TDH. Third locate the operating point. Fourth check efficiency. Fifth check brake horsepower at actual SG. Sixth check NPSHr at the same flow. Reversing the order is a common reason for wrong selections.
| Step | Question | Reject if |
|---|---|---|
| Flow | What process flow is required? | Duty is based only on pump size |
| TDH | What installed head is required? | Friction and fittings are omitted |
| Efficiency | Where is the BEP region? | Point is far left or far right without reason |
| Power | Can the motor carry actual mud? | Water horsepower is used for heavy mud |
| NPSH | Is suction margin adequate? | NPSHr is not checked at duty flow |
This sequence prevents a dangerous shortcut: choosing the pump from flow, then discovering after installation that head, power or suction margin were the real limits.
Related reading
Pump Curve Field Envelope
The pump curve should be read as a decision map, not a sales graphic. The field point moves when mud density changes, when the route plugs, when screens blind, when valves throttle, and when the impeller wears. A single clean-water curve must be corrected by field observation.
Operating point = intersection of pump curve and system curveIf either curve is wrong, the selected operating point is only apparent.| Pump Curve for Drilling Fluid Pumps check | Required field evidence | Stop or redesign trigger |
|---|---|---|
| Duty definition | flow, head, speed, density correction, motor load and the installed system curve are recorded with units and operating state. | The duty is described only by equipment name or nameplate capacity. |
| Installed-route confirmation | Line length, elevation, valves, receiving point and material condition are checked. | The route cannot be restarted or isolated safely after a stop. |
| Process acceptance | The downstream process becomes stable after the correction. | One gauge improves while flow, quality or reliability gets worse. |
