Rated curves and datasheets
Rated Cv tables, pump curves with NPSHr, and meter calibration factors. Screening ends where the datasheet begins.
Methodology
How FlowCalc calculates.
Explicit-input models with visible formulas, machine-checked test cases, and a stated verification boundary. Screening-grade arithmetic for process engineering, not detailed design.
The principle
Every result must be reproducible from the inputs on the page.
Each calculator is a fixed formula over labeled inputs. There are no hidden scores, no black-box adjustments, and no location lookups: the numbers you type, plus the stated defaults, fully determine the outputs. Every calculator page shows its formula, and every calculator ships with automated test cases that fixed inputs must reproduce before publication.
Units and conventions
One consistent SI system across all thirty-two tools.
Mass vs volume flow
Mass flow is density times volume flow. Enter density at flowing conditions; gas duties additionally need compressibility judgment the screening tools do not provide.
Pressure, head, and drop
Pressure in bar, head in metres of fluid, drop across the valve alone. System totals never stand in for valve drop: that substitution is the most common sizing error.
Margins and defaults
Every margin is shown, never buried: 15-20% on valve Cv, 15% on motor rating, 1 m on NPSH. Defaults are starting points and stay editable and labeled.
Precision statement
Outputs are screening-grade: good enough to rank options, size a first pass, or check a vendor quote. They do not replace datasheets, detailed hydraulics, or custody-grade metering.
Method by category
What each tool family models, and what it assumes.
Valves
Liquid Cv to flow at actual valve drop and SG, required Cv from duty, Cv/Kv conversion, opening-curve estimates gated on datasheet data, and choked-flow flags for gas.
Piping and head loss
Velocity from flow and diameter, diameter from velocity targets, Reynolds regime, Darcy-Weisbach friction, fitting K losses, equivalent length, and the system curve the pump rides on.
Pumps
Hydraulic and shaft power with efficiency, affinity-law speed changes, NPSHa margin against the curve NPSHr, parallel/series combinations, specific speed, and suction-energy screening.
Metering and tanks
Mass/volume conversion, flow-unit conversion, calibrated orifice dP readings, batch totalizers, vertical and horizontal tank strapping, dished-head add-ons, and fill-time planning.
Control loops
PID form conversion, first-order settling estimates, signal-damping trade-offs, and split-range valve positions. Loop tuning itself stays a field exercise.
What the tools assume
Water-like Newtonian fluids at steady state unless stated; smooth-pipe Blasius screening unless roughness is entered; manufacturer curves required for any opening-to-flow claim.
Sources and baselines
Dated numbers, named sources, annual review.
Fluid properties
Density, viscosity, and vapor pressure come from the fluid datasheet at flowing temperature. The tools never look these up: wrong properties in means wrong answers out.
Standards as context
IEC 60534 for control valves, ISO 5167 for differential-pressure metering, and API 610 for high-energy pumps appear as context for why a check exists, never as a substitute for the standard or the purchase spec.
Equipment figures
Typical velocities, roughness values, and efficiencies are labeled as starting points. Nameplate data and manufacturer sheets replace them during verification.
Verification protocol
Replace these five before relying on any result.
Fluid data at flowing conditions
Density, viscosity, and vapor pressure at operating temperature, exactly as the fluid datasheet states them.
Measured duty point
Actual flow, pressures, and levels at the operating point, plus one known duty to calibrate the system curve.
Installed geometry
True inner diameters, equivalent lengths, static heads, and suction conditions that no generic model can see.
Qualified review
A responsible process or rotating-equipment engineer confirms the conclusion before money is spent.
Defaults are starting points, not field data. Calculator results are screening outputs, not datasheets, quotes, permits, or guarantees.
Known limits
What these tools deliberately do not do.
No detailed design
Nothing here replaces line sizing, stress analysis, relief sizing, or instrument specification. Selection and construction remain engineering work under the applicable codes.
No transient modeling
Steady-state screening only. Water hammer, startup surges, and control-loop dynamics need dedicated analysis the tools do not perform.
No custody measurement
Orifice and totalizer tools screen operations; money measurement follows full ISO 5167 with calibrated hardware, not a web page.
No account data
Saved Workspace content belongs to you and is never published. Inputs you type are processed only to produce the requested result.