Q&A: What is a two-stage regulator's effect on supply pressure?

Written by Jeff Hopkins | 11/9/12 8:32 PM

Answers to more regulator questions fielded by Eric Kayla; free Essentials download.

So many participants sent in questions during the Q&A portion of our event, "The Theory and Operation of Pressure Regulators" with Swagelok Field Engineer Eric Kayla, that this week we are posting a second follow up post capturing Kayla's answers. If you'd like to replay the webinar and get this slides, those are available here:

Q: In choosing a regulator, how important is it to know the flow that I need?

A: You need to know three characteristics:

The flow required through the regulator
Your inlet pressure, and
Your control pressure

If you know those three things, along with the basics of your system such as fluids and temperatures, you are well on your way to properly sizing a pressure reducing regulator.

Q: What is a two-stage regulator's effect on supply pressure?

A: You are going to have the supply pressure effect operating on both regulators. With supply pressure effect, there is an inverse reaction on the outlet pressure to a change in inlet pressure. For example, when the inlet pressure decreases the outlet pressure increases. Conversely, when the inlet pressure increases the outlet pressure decreases.

In two-stage pressure reduction you will typically have a decrease in inlet pressure to the first regulator resulting in an increase in outlet pressure of the first regulator. The outlet pressure of the first regulator is also the inlet pressure to the second regulator, so you will have an increase in inlet pressure to the second regulator resulting in a decrease in outlet pressure of the second regulator. You still have supply pressure effect affecting both regulators, but you use them together to manage the effect on your outlet pressure.

Here is how the math works:

In a typical single stage regulator the supply pressure effect may be about 1%, so a 2000 psig decrease in inlet pressure would result in a 20 psig (1% of 2000 psig) increase in outlet pressure.

In a typical two stage regulator, the supply pressure effect is approximately .01%. The 2000 psig decrease in inlet pressure to the first stage regulator would result in a 20 psig (1% of 2000 psig) increase in outlet pressure. That increase would be a 20 psig increase to the inlet of the second stage pressure regulator resulting in a 0.2 psig (1% of 20 psig or .01% of 2000 psig) decrease in outlet pressure.

More on Swagelok pressure regulators (types, photos, one-step literature download)

At our Regulators page we offer photos, descriptions, and details on regulators to fit almost any situation: back-pressure dome-loaded; back-pressure spring-loaded; pressure-reducing dome-loaded; pressure-reducing spring-loaded; high purity; sanitary; and tank-blanketing regulators.

At the same page you can get our handpicked collection of Swagelok and Swagelok Northern California literature on regulators in one step:

Swagelok regulator assemblies save time and are warrantied

If you're interested in saving time and ensuring you have exactly the right regulator for the job, you have a few options. One is to have an assembly designed and built for you by our Assembly Services team. Another is to take advantage of the quick-turn regulator assemblies offering at Swagelok Northern California.

Learn more about our regulator assemblies here: