# Frequently asked questions

Source: https://meptools.com/tools/water-pipe-pressure-drop-pump-head/docs/faq/

## Do I enter the nominal pipe size or the internal diameter?

The **internal diameter (actual bore)**. The tool has no pipe-size or schedule tables, so it uses
exactly the diameter you type. Look up the real internal diameter for your pipe material and
schedule.

## What happens if I leave roughness blank?

The tool assumes a **smooth pipe (ε = 0)** and shows a note saying so. Enter an absolute roughness
(in `mm`, `m`, or `in`) to model a real wall.

## Where do the fitting K values come from?

You supply them. There is no built-in fitting-K library — each row is your engineering assumption.
Record where you got them in the **source note** field. The editor sums the rows into ΣK, which
drives the minor-loss term ΣK·(v²/2g).

## Why does transitional flow say the result is approximate?

Between Re 2300 and 4000 the flow is unstable between laminar and turbulent behaviour, and the tool
applies the Swamee-Jain turbulent approximation there. The result panel adds a warning so you treat
the number as indicative, not precise.

## Why is shaft power showing a dash?

Shaft power needs a **pump efficiency**. Leave the efficiency field blank and only hydraulic power
(P = ρgQH) is reported; enter an efficiency between 0 and 100 % to get an estimated shaft power.

## Can I model zero flow?

Yes. Zero flow is valid — friction and minor losses become zero and the report shows only the
static and residual head. A warning notes this.

## How do I get a PDF report?

Two ways. **Print** (rail or File menu) opens your browser's print dialog — choose "Save as PDF"
there — and is **free on every plan**, though the free copy carries a **DRAFT** watermark.
**Export PDF** produces a branded PDF with your project header and no watermark; it is a **Pro**
feature, and the action shows a `pro` badge and prompts an upgrade if your plan doesn't include
it. See [Saving, sharing & exporting](/tools/water-pipe-pressure-drop-pump-head/docs/exporting-and-saving)
and [Plans & payments](/docs/plans-payments).

## What does Share do?

**Share** (rail or File menu "Copy share link") copies a link that restores your entered values —
including the fitting schedule — for whoever opens it. It does not share your saved project, and
nothing is calculated on the other end until they press Calculate.

## Why isn't there a result yet? Do I have to recalculate after every edit?

Yes. This tool never recalculates on its own — press **Calculate** to run the numbers. If you edit
any field after a run, the result on screen is marked **STALE** until you press **Recalculate**
(or Enter). See
[Getting started](/tools/water-pipe-pressure-drop-pump-head/docs/getting-started).

## Do I need an account?

No account is needed to run the calculator — it's free and works for guests. You do need to be
**signed in** to save, autosave, rename, or manage projects.

## Is this an approved design or code check?

No. It is a preliminary, formula-only aid for a single pipe path. It does not check code compliance,
pump selection, NPSH, surge, or manufacturer data. A qualified engineer must verify the final design
— see [Warnings & limits](/tools/water-pipe-pressure-drop-pump-head/docs/warnings-and-limits).