Edmonton Valve & Fitting Blog

Weekly posts for northern and central Alberta engineers, plant operators, and buyers.

An Inside Look at Swagelok's Pressure Reducing Regulators

by Katie Reid, on Thu, Jul 28, 2016 @ 14:07 PM

They do only one thing, but they can do it in several different ways


To get all the technical information on Swagelok's Pressure Reducing Regulators, download a copy of the K Series Catalogue here.

The name says it all. A pressure reducing regulator reduces pressure. That's it. It doesn't regulate flow, it doesn't regulate back pressure, it doesn't regulate anything else. It just makes sure that the downstream pressure stays constant.

But how does it do that?

It starts with a poppet and a seat. That's where the pressure drop takes place. When the poppet moves away from the seat, it opens up a space. A large space means a small drop in pressure. A small space creates a large drop in pressure. The poppet will move up and down as conditions change to give you the outlet pressure you've asked for.

Each regulator is designed to work best within a certain range of conditions. Bump up against one end of the range, and the pressure will build up enough to close off the inlet. That’s called lockup. Go all the way to the other end of the range, and the regulator will be wide open, and is no longer regulating pressure. That’s called choke flow.

Feel the force

Regulator operation — that is, moving the poppet as conditions change — is all about balancing forces. There are four forces.

The first is the loading force. In analytical systems, most regulators are spring loaded. There's a coiled spring in the top of the regulator pushing down. That's the part we can control, increasing or relaxing the force of the spring to get the outlet pressure we want.

Second is the force of a much smaller inlet spring. It's down under the poppet pushing up. It holds the valve against the seat and closes it off if there's no flow.

Third is the outlet pressure force, and fourth is the inlet pressure force.

The regulator automatically tries to maintain balance. If the flow rate suddenly increases, you'd have a higher pressure drop if no other elements changed. So the regulator will balance that by moving the poppet away from the seat and creating more area.

Not all regulators are spring loaded. Some are dome loaded, meaning that there's pressurized gas in a dome on top of the regulator. There are even designs that use a combination of spring and dome loading. And there is a type called a ratio regulator, which works off a set ratio of the dome pressure.

Righting droop

Regulators can be subject to droop, which means the outlet pressure increases somewhat as flow increases. Spring-loaded regulators are more susceptible to droop than other types. That's because as the spring lengthens, the loading force gets weaker. Using a longer spring will minimize this effect.

Dome loaded regulators also can experience droop. The use of a pilot regulator can help, adjusting the pressure in the dome as needed. Even better performance can be obtained by sampling the pressure downstream, called external feedback, and sending it to the pilot regulator.

There's no hard and fast rule about how far downstream you can tap. In general, try to stay within 10 or 15 diameters of the main regulator.

There's a lot more to be said about regulators, more than we have room for in a blog post. We'll be glad to talk with you about them; tell us what you want your regulator to do, and the conditions in which it has to operate, and we can help you pick out the best one for your needs. If in the meantime you would like to get your hands on the technical information for Pressure Regulators, K Series - download the catalogue.


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