drilling · hydraulics
Pump (Volumetric) Efficiency
click formula to derive ↑
Inputs
gpm
gpm
Description
Computes volumetric pump efficiency — the ratio of a mud pump's actual delivered flow rate to its theoretical (ideal, geometry-only) output — from Pump Output's theoretical figure and a measured actual flow rate. Real triplex pumps typically run 85-99% efficient; the shortfall comes from valve leakage, fluid slippage past piston/liner seals, and entrained gas or air, not from the cylinder geometry itself.
Variables
| Symbol | Unit | Description |
|---|---|---|
| Ev | % | Volumetric Pump Efficiency |
| Qtheo | gpm | Theoretical (ideal, 100% efficient) pump output from cylinder geometry and stroke rate, from Pump Output. |
| Qactual | gpm | Actual measured flow rate delivered by the pump, from a flowmeter or strapped displacement measurement. |
Assumptions
- Actual output is a genuine independent measurement (flowmeter, strapped pit-level rate, or equivalent) — not itself back-calculated from theoretical output, which would make this ratio circular
- A single steady-state operating condition — pump efficiency can vary with stroke rate, discharge pressure, and fluid properties, so a figure measured at one operating point may not carry over exactly to another
- Mechanical condition (valves, liners, packing) is representative of normal operation, not a transient fault in progress
Limitations
- A snapshot efficiency at the conditions it was measured under — does not itself predict how efficiency will change as stroke rate, discharge pressure, or mud properties change
- Does not diagnose which specific mechanism (valve leakage vs. liner wear vs. gas entrainment) causes a low efficiency reading — only that the actual output falls short of theoretical
- Assumes Qtheoretical is accurate for the pump's actual liner size and stroke length as currently configured — a liner change without updating the theoretical figure will produce a misleading efficiency result
Use Cases
- → Rig pump acceptance/condition check: Compare measured output against theoretical displacement to confirm a pump is performing within its expected efficiency range before relying on it for a planned hydraulics program.
- → Corrected flow rate planning: Apply a previously measured efficiency figure to Pump Output's theoretical result to plan a more realistic expected flow rate at a candidate stroke rate.
- → Maintenance trending: Track volumetric efficiency over time to catch gradually worsening valve or liner wear before it becomes a lost-circulation or hole-cleaning problem from under-delivered flow.
Related Calculations
Region Notes
Global
A well-maintained modern triplex mud pump typically runs 95-99% volumetric efficiency; older or poorly maintained pumps, or pumps handling gas-cut mud, can fall well below 85% — always measure rather than assume a default efficiency for critical hydraulics planning.
References
Need geoscience support? BauerCalc is just one of the tools we build. If you're looking for independent expertise in well planning, geosteering, reservoir characterization, or opportunity evaluation, visit BauerSubsurface.com.