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:

A wrong bore is often correctable (quote DN80 instead). A duty no published size in the family reaches rules the family out, unless it rests on an assumed value (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), each held as a limit that applies when that datasheet option is chosen
• 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.

The reflex level gauge serves steam and liquids, on the client’s word of 2026-10-15, overriding the guide’s “Liquid”. Its ideal use is unchanged: steam up to 20 bar.

The side and top mounted magnetic level indicators take pressures from full vacuum, -1 bar g, up to the guide’s 40 and 16 bar, where the guide writes “0 to 40 bar” and “0 to 16 bar”. A vessel under vacuum, such as a flash vessel at -0.8 to 1.5 kg/cm² g, keeps them. Flowtech is to confirm that its magnetic gauges are built for vacuum service.

The families the guide does not cover take their limits from the web instead, filed under the document name Web-sourced limits. Flowtech’s own product pages are used first; where they state nothing, the same product type in two other makers’ published datasheets. A rating stated per size is held at its lowest figure. The top mounted level switch takes a liquid of specific gravity above 0.7 and a stem of at most 3 m, and the cable float switch a specific gravity of at least 0.8, each from Flowtech’s own page. Each limit is stored with the address it was read from, the sentence that states it and the date it was read; the limit’s own wording shows on the family, but the address and the date are not shown on any screen yet. Editing a web-sourced limit’s title on the Limitations screen keeps its sources. Clearing its document name is refused, and so is an edit that would join its sources to another limit’s, move a limit onto a title another limit already has, or rename a limit whose sources another limit shares.

Kinds

Any limit can also be set to apply when a datasheet option is chosen, such as a PTFE lining. It is judged as usual when the line states that option, set aside when the line states another, and when the line states none a breach warns and takes the option off the menu (R23). A limit or table can’t be linked to the Custom option.

A breach of an assumed value or phase, a guessed fluid or a limit with a single outside source warns. Among limitation entries, only a trusted hard limit or not-suitable entry, breached by a known value, excludes (R23, R24). A value within 0.0005 of a bound counts as on it, so a stated 5 kg/cm² meets a maximum of 5 kg/cm². A categorical bound other than not-suitable or ideal use can’t be checked and rules nothing out. A categorical ideal use lists what suits the family: an opacity of CLEAR matches a fluid the library holds as clear.

Flowtech selection rules

Thirteen rows filed under the document name Flowtech selection rules are Flowtech’s own and carry no source: the side mounted level switch is limited to one set point (parameter Number of Set Points), the displacer level switch is ideal for two, the top mounted level switch for three or more and needs a process connection of at least 25 NB, the electromagnetic flowmeter is not suitable for DM, deionized or distilled water (R99), and each of the glass tube, by-pass glass tube, tiny glass tube and acrylic body rotameters carries a Hazardous fluid row ruling it out for a fluid whose health rating is 3 or 4 and a Moderately hazardous fluid row warning at 2 (parameter Health Hazard, R104). They are judged like any other row (R23, R28) and edited on the Limitations screen.

Provisional ideal use

Sixteen families carry an ideal use, filed under the document name Ideal use (provisional). Each comes from Flowtech’s own product page or another maker’s, stored with the sentence that states it, and stays provisional until Flowtech confirms or corrects it on the Limitations screen.

The electromagnetic flowmeter has two: slurries, from Flowtech’s page, and conductive liquids. Flowtech’s page names conductive liquids without a minimum; the 5 µS/cm figure is another maker’s. It leads on a conductive liquid when the client names no type, because an electromagnetic flowmeter is ideal for measuring the flow of electrically conductive fluids.

An ideal use is checked only against what a line holds. A pressure, phase or line-size ideal use can be read from the line’s own figures and wording, with no match in the fluid library. A conductivity ideal use reads the line’s conductivity figure; when the line states none, a fluid the fluid library rates conductive counts as meeting 5 µS/cm, shown as assumed. That is why plain water leads with the electromagnetic flowmeter. One that reads a fluid’s opacity, solids, toxicity, corrosion or oil category matches only when the line’s fluid is matched to the fluid library and the library rates that trait; otherwise the family keeps its place. Families whose stated duty only repeats their own hard limits, or names nothing a line states, such as a portable or open-channel meter, carry none; the electromagnetic flowmeter’s conductive liquids is the exception, since it repeats its own 5 µS/cm minimum. So do the turbine, acrylic and by-pass rotameters, transmitters and full view sight glass: no maker’s page states a duty for them narrower than their limits in terms a line holds.

The page

Product Limitations opens on a family view with two more tabs beside it. Someone without the right to edit sees everything, read-only.

Families

The families are listed on the left, grouped by category, with a search. Each shows how many rules and sizing tables it holds (“5 rules · 2 tables”) and a flag where something is missing:

• No datasheet: the family has no datasheet to choose options from.
• No flow range: no flow range is held for this family yet.
• Rules off: some of the family’s rules are switched off.

A family that can’t read a flow also shows the family to try next.

The picked family fills the right side. It opens with how it is sized, in plain words, then When FlowOS suggests it, whose changes are kept with Save, then its rules, each a sentence with the condition and the datasheet option it holds under, such as “Temperature at most 121 °C, when Gas” or “Pressure at most 100 bar, when Liner MOC = PTFE”. A not-suitable rule reads as where the family fails: “Not suitable for Temperature above 120 °C”. Beside each sentence are its effect (rules out, warns, note, ideal use, or off) and its source. A rule is added or changed in a side panel that opens beside the list. Below the rules come the family’s sizing tables, its try-next list and its notes.

When FlowOS suggests it sets whether the family is suggested whenever it fits the line, or only on demand, when the enquiry asks for it. The words that ask for it are listed and can be removed or added. A word added here counts in the item and type cells of lines of the family’s category. Marked counts anywhere in the enquiry, it also asks for the family on every line of its category when it appears anywhere in the email the lines were read from, as R27 describes. Its own name always counts. The words FlowOS knows already are shown read-only, and so is Also suggested on steam lines where it is set. A word another family also holds says so; removing it, or adding a word another family already holds, asks first, because lines saying it would then name the other family alone or both. A built-in word another family’s word overrides is marked as such. The Readout beside it marks the family Analogue, Digital, Both or Not set, and applies at once with Save: a line that asks for analogue is not offered a digital family, and the reverse (R124). Both and Not set are offered either way. The flow meters and rotameters start marked: analogue for the acrylic body, by-pass glass, by-pass metal, glass tube and tiny glass tube rotameters and the manometer; both for the metal tube rotameter, whose datasheet has a digital or analogue row; digital for the electromagnetic, vortex, IBR vortex, turbine, ultrasonic, digital oval gear and open channel flowmeters and the IoT device; the orifice plate and ORF flange assembly are not marked. The marks are applied once, at rollout, to every family still Not set; after that the page’s choice stands. The on-demand choice applies at once, on every line without a reviewer’s pick; changes to the words, and to whether each counts anywhere, apply to enquiries read afterwards. Save is enabled only while something has changed, and Discard returns the section to what was saved. Editing needs the right to edit items.

Fields

Below the sizing tables, Fields lists the text, number and range fields of the family’s current datasheet, under its headings, with where each value comes from (R122). Menus, yes/no rows and accessories are always the buyer’s and are not listed:

• Buyer, the default: requirement gathering reads it from the enquiry, and a person can edit it on the line.
• Flowtech: the product provides it. Its value is the limitation linked to it with Flowtech’s figure for (several are listed with their conditions), else the datasheet’s default or, for the Flowtech flow range, the family’s sizing.
• After order: Flowtech’s engineers work it out once the order is confirmed.

Each row shows the value Flowtech gives the field, where it has one, with On quotation (Auto prints it when the line holds a value, Always, Never) and Quotation heading (the default, one of the quotation’s three headings, or one of the datasheet’s own, which prints as a section of its own). A change is kept at once, with no publishing of the datasheet, and applies to every line of the family read afterwards and to every line’s datasheet the next time it is opened. Changed only shows just the fields set away from Buyer. Editing needs the right to edit items.

All rules

Every rule of every family as a sentence, with a search and filters by family, kind and on or off, and by whether the rule is linked to a datasheet option. The list exports to CSV. A row opens its family with that rule’s panel already open. A rule of a family that is switched off stays listed, but does not open, and its effect reads family off.

All sizing tables

One row per sizing table across all families. A row opens its family at that table. The export holds the ranges of the tables the search leaves shown, each under its table’s name.

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.

The electromagnetic flowmeter table also carries the ten released sizes the sizing reference leaves out, 550 to 2200 NB. They are worked out from the reference’s own velocity basis, 0.3 to 5 m/s. Each of the ten rows carries a note saying it is derived; the note appears in the flow-sizing export. The reference’s printed figures are otherwise kept as printed, except six cells that break their own table’s rule: five vortex steam cells are held at the size’s volume range times the column’s steam density, and the standard metal tube rotameter’s 15NB minimum at the 2.5 LPH its row gives. Each table’s note lists the cells and the figures printed.

Editing them

Sizing tables are edited on the family view of the Product Limitations page (see The page). Each family shows the tables it uses, and its try-next list and notes are edited there too.

• Tables. A table has a phase, a layout and its rows, and says how its figures read: as actual volume, a velocity range, water or air equivalent, or saturated steam in kg/h. The layout is one range per size, per size and connection type, per tube with its connection range, or per size and pressure for steam. Changing how a table reads or its layout re-checks every row held, and is refused if a row no longer fits. The table editor is a full dialog.
• Families using a table. A table can serve several families. A family uses it when a datasheet option is chosen, such as the wetted material, so one family can hold a table per option. Two tables of one family may not apply to the same option, and a family may not hold two active copies of one table.
• Try next. The families to follow first when this family is named and ruled out, in order (R88). A family can’t list itself or list another twice. A family offered only when named, such as a bypass rotameter, is reached this way only from a family whose table lies wholly below the line’s flow.
• Notes. The family’s source notes and those on its tables, each with its source and an optional reference, shown with the sizing. A remark on one row is that row’s own note.

Each table also shows what a line must state before it can read the line (Needs). That is worked out from how the table reads, not edited.

Which table reads a line is R29’s.

In the datasheet’s price preview, entering a line’s operating pressure or line size narrows the range options. The pressure ranges of the smart and miniature pressure transmitters are limited to those that cover the operating pressure, and the sensor sizes of the clamp-on ultrasonic flowmeter to those that cover the line size. Both transmitters’ ranges start at -1 bar, so a line under vacuum, down to -1 bar, fits them. The pressure transmitters’ Custom option is always offered.

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 can’t be checked and rules nothing out (R23).

Related: Product suggestion · Reference data · Limitations.