# Warnings & limits

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

The tool reports two kinds of feedback: **validation errors** that block a result, and
**calculation warnings** that annotate a result you can still read. This page explains both and the
scope boundary you must respect.

## Validation errors (no result produced)

If any input fails its rule, the result panel shows the message(s) below instead of a report:

| Message                                                  | Cause                                                                                          |
| -------------------------------------------------------- | ---------------------------------------------------------------------------------------------- |
| Flow rate must be zero or greater.                       | Negative or non-numeric flow.                                                                  |
| Internal pipe diameter must be greater than zero.        | Diameter ≤ 0 or blank.                                                                         |
| Pipe length must be zero or greater.                     | Negative length.                                                                               |
| Absolute roughness cannot be negative.                   | Negative roughness (blank is fine — it means smooth).                                          |
| Static head must be a number.                            | Non-numeric static head (blank is fine; negative is fine — it means gravity assists the flow). |
| Density must be greater than zero.                       | Density ≤ 0.                                                                                   |
| Dynamic viscosity must be greater than zero.             | Viscosity ≤ 0.                                                                                 |
| Required residual pressure cannot be negative.           | Negative residual pressure.                                                                    |
| Pump efficiency must be greater than 0 and at most 100%. | Efficiency out of the 0–100 range.                                                             |
| Fitting K must be zero or greater: `<label>`.            | A fitting row has a negative K.                                                                |

## Calculation warnings (result still shown)

These appear in the **Warnings & assumptions** card. Informational notes (`.`) confirm an
assumption; warnings (`!`) flag something to check.

| Level   | When it appears         | Meaning                                                                                                                   |
| ------- | ----------------------- | ------------------------------------------------------------------------------------------------------------------------- |
| Info    | Always                  | Formula-only preliminary calculation — no material, roughness, fitting-K, pipe-size, or fixture-unit tables are embedded. |
| Info    | Roughness left blank    | Using the smooth-pipe assumption (ε = 0).                                                                                 |
| Info    | ΣK = 0                  | No fitting/valve minor losses were included.                                                                              |
| Info    | Static head is negative | Gravity assists the flow.                                                                                                 |
| Warning | Flow = 0                | Zero flow: friction and minor losses are zero; only static/residual head is shown.                                        |
| Warning | 2300 ≤ Re ≤ 4000        | Transitional flow: the result is approximate and may be unstable between laminar and turbulent behaviour.                 |
| Warning | Total head ≤ 0          | A pump may not be required for these assumptions — verify the system hydraulics.                                          |

## Scope — what the tool does not do

This is an independent preliminary engineering aid for a **single pipe path**. It does **not**
verify or account for any of the following:

- Code compliance, authority approval, or local amendments
- Pipe-material suitability, pressure class, or temperature rating
- Manufacturer data or proprietary fitting-loss tables
- Fixture-unit loading or diversity
- Water-quality requirements
- Pump selection, **NPSH**, transient/surge, or acoustic limits
- Commissioning requirements
- Velocity limits — the tool reports velocity but applies **no maximum-velocity check** (no
  erosion, noise, or water-hammer threshold). Compare the reported velocity against your own
  project criteria.

Pipe roughness and fitting K are **user-entered assumptions**, and the tool does not certify their
suitability. Final design must be verified by a qualified engineer against the adopted codes,
project specifications, manufacturer data, and the authority having jurisdiction. Treat the report
as a transparent preliminary calculation — not an approved design, a code-compliance check, or a
pump selection.

See also [Inputs & units](/tools/water-pipe-pressure-drop-pump-head/docs/inputs-and-units) for the
per-field rules and
[Methods & formulas](/tools/water-pipe-pressure-drop-pump-head/docs/methods) for what each number
means.