Product limitations

Rated limits versus sizing — whether an instrument survives the process, and whether it can read the duty.

Two different questions, often collapsed in conversation:

Question	Answered by	Example
Does this instrument survive the process?	Product limitations (rated temperature, pressure, viscosity, conductivity, phases)	Conductivity ≥ 5 µS/cm on an EMF
Can this instrument read the duty?	Flow sizing tables	DN50 at this m³/h is inside the published band

A wrong bore is often correctable (quote DN80 instead). A duty no published size in the family reaches rules the family out (R29).

Where the limits come from

Flowtech’s Product Limitations & Restrictions Guide states hard limits in a consistent grammar, with a qualifier when the bound depends on phase, construction, or flow band:

Temperature (Liquid) versus (Gas) versus (Steam)
Pressure (Standard SS) versus (PTFE-Lined)
Pressure (WE < 10,000 LPH) versus (WE >= 10,000 LPH)

Absence of a figure is not a free pass: switch datasheets leave temperature and pressure blank, so family-level figures are used and a specific model may be tighter. Verify against the latest datasheet before final selection.

Kinds

Guide section	What it means for quoting
Hard limits	Numeric or categorical bounds. A stated breach excludes
Not suitable for	Duties this family is not for
Key limitations	Constraints that are not a simple bound
Installation	Orientation, run-up, probe length

A breach of an assumed value warns; a breach of a stated value excludes (R24).

Sizing tables

The flow-range tables are not one shape. Some families key by line size, some by tube × float, some by connection, steam by line size × pressure as mass flow. Steam rows are not converted as if they were water.

For a size-axis family the sizing table’s size column is the variant axis — that is how the table drives which item codes exist.

What the business does here

Keep the guide and the sizing reference current; a corrected limit changes the next recommendation without a code change.
Do not invent a rating where the guide is silent — the option stays unconfirmed (R23).