Instrumentation
DP → Flow Wizard
A guided, step-by-step walkthrough for turning a DP transmitter reading into an engineering flow value — built for the field, not for re-typing 15 fields into a flat form. Uses the same calculation engine as the Thermal Plant Estimator's Flow Calculator (Mode 4).
Standard method — stated scope limits apply
Step 1 of 10 — Fluid
What's flowing through the line?
About This Calculation
Every differential-pressure flow element — orifice, venturi, flow nozzle — shares the same underlying physics (Bernoulli's principle: accelerating a fluid through a restriction drops its pressure, and that drop scales with the square of flow rate) but each element type has its own discharge coefficient, permanent pressure loss, and accuracy characteristics. This wizard walks through selecting an element type for your service and duty, then sizing it, rather than assuming you've already decided which element you need — the right choice genuinely depends on available pressure drop budget, required accuracy, and installation space.
Frequently Asked Questions
Why does flow scale with the SQUARE ROOT of differential pressure, not linearly?
Bernoulli’s equation relates velocity squared to pressure drop — doubling flow rate requires roughly quadrupling the differential pressure across a fixed restriction, which is why a DP transmitter’s calibrated range and a flow element’s turndown ratio are tightly linked: the same transmitter range gives much better resolution at low flow than the square-root relationship might suggest.
When should I choose a venturi over a plain orifice plate?
When permanent pressure loss matters — a venturi recovers most of the pressure it temporarily drops (typically 10–20% permanent loss vs. an orifice’s 40–80%), at several times the cost and a longer required installation length. It’s the right trade when pumping/compression energy cost over the element’s life outweighs its higher purchase price.
What does turndown ratio mean for a DP flow element?
It’s the ratio between maximum and minimum flow the element can measure at acceptable accuracy — typically only about 3:1 to 4:1 for a single DP element and transmitter, since accuracy degrades badly at low flow (small DP, more affected by transmitter zero error) even though the physics theoretically supports a wider range.
Do I need straight upstream and downstream pipe runs for any DP element?
Yes, for all three types — published standards (ISO 5167 for orifice/venturi/nozzle) specify minimum straight-run lengths depending on the upstream fitting (elbow, valve, tee), since the accuracy of every DP element depends on a settled, symmetric velocity profile arriving at the element.