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Fluid Systems Engineering & Management Blog

by Swagelok Northern California

"Sizing Pressure Regulators" Q&A Recap; Slide Deck Now Available

by Jeff Hopkins, on 1/23/13 8:00 AM

This post has 5 answers to technical questions about pressure regulators and a link to download slides from last week's technical briefing


swagelok pressure regulator
Now posted: The slide deck used in our technical briefing on selection and sizing of pressure reducing regulators. Test your knowledge: The deck includes an example involving Argon gas supply to two pieces of welding equipment enclosed in a cleanroom. More »

Last week Swagelok field engineer Eric Kayla was at our Fremont office to lead a briefing on match the right regulator to a particular job. If you didn't come to the technical briefing last Thursday, you can still benefit in a couple of ways.

One is to download the slide deck that Eric used during the webinar. It's available for free on our website. The slide deck includes tips on interpreting flow curves, the graphs that illustrate how a regulator will perform with different combinations of flow and pressure.

The other is to check out these answers to the questions Kayla fielded after the presentation:

Q: Can you interpolate below the lowest published flow curve?

A: When interpolating flow curves it’s easier when you have a higher boundary and a lower boundary. However, when you’re interpolating below the flow curve you don’t have that floor or that sense of what’s low enough.  Interpolating below the line is more difficult and less scientific.

Q: What happens if you operate a regulator outside its optimal flow range?

A: If you’re on the low side of the flow range you’ll be operating in the area of seat load drop -- also called lock-up -- and you’ll get an erratic reading.  If you operate to the high side of the flow range, you’ll begin to operate toward the choke flow point. At that point, the poppet is fully out of the seat, and it’s literally operating as a restricting orifice, and you’re not able to adjust the regulator much.

Q: How can you minimize droop?

A: Droop is characteristic of the regulator based on its mechanical operation. Different loading mechanisms can improve the droop.  So if the droop of your spring-loaded regulator is too severe, you could change to a dome-loaded regulator and that will push the curve flow towards horizontal, reducing the droop.

Q: What if some of our regulators were sized using Cv method?

A: Cv is calculated at the choke flow point. So if you were to operate on far right of the flow curve, with the poppet pushed as far as it can go, it’ll be more like a restricting orifice and less like a regulator.

Q: Why would someone use a left-to-right flow curve over a right-to-left flow?

A: The flow path depends on the installation point of the regulator. That is, where does the high pressure come in, where does the low pressure need to be delivered, and where is the regulator physically installed in the system?

Additional resources

pressure regulator  pressure regulator pressure regulator 
Technical Bulletin and Article on Pressure Regulator Flow Curves Slide Deck: Theory & Operation of Pressure Reducing Regulators Swagelok Pressure Regulators Catalog

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Topics:Regulators

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