About FlowCalc

FlowCalc (flowcalculators.com) is an independent screening library for fluid-system arithmetic: control-valve sizing, piping head loss, pump duty and NPSH, flow metering, tank strapping, and control-loop checks. Thirty-two calculators, eight worked guides, every formula on the page, every default labeled, every margin shown.

Who this site is for

Three distinct readers use the same tools differently, so the pages are written to serve all three without dumbing down for any of them. Process and project engineers use FlowCalc as a fast first pass: checking a vendor Cv against actual drop, screening a line size against velocity limits, or confirming an NPSH margin before a HAZOP action closes. Plant maintenance, reliability, and instrument technicians use it as a field reference: verifying a replacement trim, re-rating a pump after a VSD retrofit, or converting a PID form between DCS platforms. Operators and junior engineers use it as a learning surface: each guide pairs a hand calculation with the tool that reproduces it, so the arithmetic is never a black box.

Why it exists

Fluid systems fail on arithmetic that looks right. A valve sized against system total head instead of valve drop arrives one trim too small. A suction line upsized for "safety" drops velocity into settling range. An NPSH margin of 0.3 m passes a spreadsheet and cavitates by summer. FlowCalc exists to make these numbers checkable in minutes: enter the duty as measured, read the result with its formula and substituted values, and see the margin or the warning next to it — not buried in a footnote.

What you will find here

• 46 screening calculators in 6 families. Control Valves (7): liquid Cv to flow, required Cv, opening-curve estimator with datasheet gate, Cv/Kv conversion, valve drop, gas-valve screening with choked-flow flag, actuator margin. Piping & Head Loss (7): velocity, diameter from velocity, Reynolds regime, Darcy-Weisbach friction, fitting K losses, equivalent length, system-curve builder. Pumps (6): hydraulic/shaft/motor power, affinity laws, NPSHa margin, parallel/series compare, specific speed, suction-energy screen. Metering (4): mass/volume conversion, flow-unit conversion, calibrated orifice dP reading, batch totalizer. Tanks & Level (4): vertical volume, horizontal table-factor volume, dished-head add-on, fill time. Control Loops (4): PID form conversion, first-order settling, signal damping, split-range positions.
• 8 worked guides with full arithmetic. Each guide states the governing relation, works a numeric example end to end (e.g. DN100 x 100 m water: Re 127000, f 0.0167, 0.135 bar), lists the exact inputs the calculator needs, and links to the tools that reproduce the result. Every guide carries at least three in-links to calculators and a three-question FAQ emitted as FAQ schema.
• Machine-checked publication. Every calculator ships with declared test cases; fixed inputs must reproduce fixed outputs through the real calculation engine before the page is published. The current suite runs 46 calculators with zero failures, and the release checksum gates every served result.
• A private Workspace. Save duties, assumptions, and PDF reports per job or turnaround without exposing plant data. Workspace content belongs to the account holder, is never published, and can be deleted at any time.

How content is produced and reviewed

Definitions live in versioned JSON catalogs (calculator bundle contract calculator-core/1.0), synced additively into WordPress — content edits in WP get overwritten by design, so corrections land in the catalogs, not in the database. Review follows three gates: schema parse against the engine BundleParser, numeric pass of every declared test through the real compiler and calculation service, and an editorial read for units, margins, and verification steps. Reader reports via Contact enter the same queue: verified errors are fixed in the catalog, re-tested, re-synced, and noted on the page.

What this site is not

FlowCalc is a screening and reference tool. It is not detailed design, not a code compliance determination, not custody-grade measurement, not a vendor quote, and not a guarantee of performance. A calculator output is not an approval, a permit, or a basis for procurement on its own. Read the Disclosure before relying on any result, and the Methodology before citing one.

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Read the methodology · Read the disclosure · Contact the site