Control-valve data we need for independent evaluation

We select control valves (aeration and comparable low-Δp gas duty) by recomputing their performance at our site conditions, not the conditions of your example sheet. As a publicly owned organisation every number in an evaluation must be traceable and reproducible from the supplier's own data. This page shows the dataset that makes that possible, and the check we run on it before a valve enters evaluation.

Applies to — quotations and datasheets for gas/air control valves submitted for comparison.
Does not apply to — on/off valves, liquid duty, and commercial terms; those follow the inquiry itself.

What we compute from your data

Fictional example — every number and curve on this page describes an invented DN200 valve. It is illustrative only and is not any manufacturer's product.

upstream pressure 1.70 bar(a) temperature 100 °C

values as a table

An example table pins us to your chosen pressure and temperature. A resistance coefficient ζ per stroke lets us regenerate this entire figure at any condition — move the sliders above: that recalculation is exactly what we must be able to do ourselves, for every valve in a comparison, on identical terms.

The dataset

Tier 1 · required

ζ versus stroke

Resistance coefficient at ≥ 10 points from 10 % to 100 % stroke, with the reference area named (nominal bore or seat area).

Kv versus stroke

Kv in m³/h at the same stroke points. Deliberately redundant with ζ — the redundancy is our cross-check.

Geometry

DN / flow area, face-to-face length, and any installation assumptions (upstream straight length, orientation).

One worked example

Flow versus pressure loss per stroke at fully stated conditions: medium, absolute pressure, temperature, humidity, and the Nm³ reference basis — or simply mass flow in kg/h, which needs no basis at all.

The formula, named

Which sizing relation produced the example — IEC 60534-2-1, a ζ-based relation, or a house formula written out. Named, not implied.

Tolerance

The uncertainty band on ζ/Kv (± %). A coefficient without a tolerance cannot carry a guarantee.

Tier 2 · welcome, not blocking

leakage class at 0 % stroke (EN 60534-4) minimum controllable stroke positioner hysteresis / dead band x_T / choked-flow data for high-Δp duty

Submit: fill in, self-check, send

Step 1 — pick the medium class. The coefficients are the same either way (ζ is dimensionless); what changes is which conventions are mandatory.

Step 2 — fill the template below (it is pre-filled with the fictional DN200 valve so the checker demonstrably passes; replace every value with your own). Flows in kg/h are always unambiguous; Nm³/h is accepted only together with the declared basis. Step 3 — run the self-check: it is the same set of checks we run on receipt, so anything red here becomes a clarification round later. Step 4 — return the JSON with your quotation, through the inquiry that pointed you to this page.

How we verify it

Before a valve enters evaluation we rebuild your worked example from your own coefficients and conventions. The example is the checksum: if we cannot reproduce it, we cannot reproduce anything else either.

Three consistency checks sit inside that recomputation:

ζ ↔ Kv agree — for the same reference area, ζ ≈ 1.6·10⁹ · D⁴ / Kv² (D in m, Kv in m³/h) must hold across the stroke range.
The example follows √Δp — subcritical gas flow at fixed stroke scales with the square root of the pressure loss; rows that do not are typing errors or an unstated correction.
The physical constant closes — flow, coefficient and stated conditions must reproduce each other through the named formula, not just internally.

Conventions that silently change the numbers

These are the ambiguities we most often have to write back about. Stating them costs one line each; leaving them out changes results by more than typical differences between competing valves.

convention	please state	effect when unstated
Nm³ reference basis	0 °C / 1.01325 bar, or 20 °C, or other	≈ 7 % on density and flow
ζ reference area	nominal bore or seat area	up to several % near full stroke
pressure basis of the example	absolute upstream pressure	Qₙ ∝ √p — 1.49 vs 1.7 bar(a) ≈ 6.8 %
gas-sizing formula variant	the exact relation and constants	1 – 3 % between common variants
humidity basis	dry air or a stated RH	up to ≈ 1 % on density