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Swagelok Southwestern Ontario

Your Authorized Swagelok Sales and Service Center

Terminology

Accumulation — An increase in inlet pressure caused by an increase in flow rate to a back- pressure regulator.
Creep — An increase in outlet pressure typically caused by regulator seat leakage.
Dependency — See supply pressure effect (SPE).
Droop — A decrease in outlet pressure caused by an increase in flow rate to a pressure-reducing regulator.
Lockup — An increase in outlet pressure that occurs as the flow rate is decreased to zero.
Self-venting — A feature that reduces outlet pressure in a pressure-reducing regulator when the regulator set point is decreased and there is no flow through the regulator.
Sensitivity — The degree to which the regulator responds to force balance changes.
Set pressure — The desired outlet pressure of a pressure-reducing regulator, normally stated at a no-flow condition.
Supply pressure effect (SPE) — The effect on the set pressure of a pressure-reducing regulator as a result of a change in inlet pressure, normally experienced as an increase in outlet pressure due to a decrease in inlet pressure. Also known as Dependency.
Threaded vent — A connection that allows monitoring of the diaphragm or piston sensing mechanism.

Q: How do you read and size regulators using flow curves?

A: Please reference the flow curves in catalogue MS-06-114, "Pressure-Reducing Regulator Flow Curves Technical Bulletin". If further assistance is required; please contact your Swagelok Southwestern Ontario Sales Rep for further assistance.

Q: How do the venting options work on K series regulators?

A: The self-vent option allows excess outlet pressure to vent through the body cap. This can occur when downstream flow is suddenly reduced or when the handle is adjusted to a lower pressure with little or no flow downstream.
The captured-vent option includes a 1/8 in. female NPT connection and stem seal in the body cap➀ to allow monitoring of the diaphragm or piston sensing mechanism. It also allows containment of hazardous gas or liquid media should a diaphragm or piston rupture.
Self-vent and captured-vent options can be ordered together so that hazardous gas or liquid media can be contained if vented.

Q: What happens if you oversize a regulator?

A: If it's too big for the application, your poppet and seat will be too large, allowing too much flow. Every time that regulator opens, it will allow more flow than you expect. The regulator will do more work than it should need to. You'll see more fluctuations and spikes in your downstream pressure.

Q: What about if you undersize it?

A: Instead of having a seat and poppet too large, you'll have one too small. It will open as much as it can to let through as much flow as it can. You are probably going to operate closer to the choke flow range. You are also probably going to erode the seat faster than with a properly sized regulator.

Q: Does a pressure regulator control flow?

A: No, a pressure regulator responds to changes in flow demand to maintain a pressure setpoint. As a regulator responds, its throughput changes as a consequence of its adjustments for pressure. The best way to understand this effect is to look at the flow curve of a regulator. For any given pressure setting, there is a flow rate that falls on the flow curve. As the flow rate changes, the regulator will follow along the flow curve to establish a new balance and flow. For more details, refer to page 1 of our MS-06-114, "Pressure-Reducing Regulator Flow Curves Technical Bulletin"

Q: Discuss the difference between liquids and gasses in regulators.

A: Liquids are more straightforward because they are not compressible. Gasses are a little different, so there are different sizing methodologies. And if you are using a liquid with some particulates, it could increase wear on the seats over time.

Q: Does the supply pressure effect happen with both liquids and gasses?

A: Yes. If we aren't changing anything on the loading force, our sensing mechanism will work to balance out against that loading force. If the inlet pressure force goes down, the only way to counterbalance it is an increase in outlet pressure force.

Q: What type of regulator is best suited to applications with pressure pulsations?

A: A piston sensing regulator is best suited to applications with pressure pulsations. Pumps typically create rapid impulses that can cause a metal diaphragm to fail due to fatigue. Piston sensing regulators replace the diaphragm with a machined piston that is not subject to fatigue in high cycle applications.

Q: Do I remove the inlet gauze inlet filter prior to installation?

A: Regulators are susceptible to damage from system particles. Swagelok pressure-reducing regulators include a 25 μm filter held in the inlet port by a retaining ring. It can be removed easily for cleaning or to use the regulator in liquid service.

Q: Are CAD files available for your products?

A: Yes, they can be found here: Swagelok CAD files