Video: Key pressure reducing regulator terms explained

Enjoy this clip from our technical briefing on the theory and operation of pressure reducing regulators, then, sign up for our next webinar on how to choose the right pressure reducing regulator for your application. 

Droop

The flat part in the middle is not perfectly flat. Usually, it slopes downward. This is called droop. As flow increases, outlet pressure will drop some—or a lot, depending on the regulator
design. While droop is relatively modest along the flat part of the curve, it is quite steep at the far ends of the curve.

Proper selection is crucial 

Supplying a regulator with pressures substantially lower than the inlet pressure rating results in a flow curve with more droop than flow curves for regulators whose inlet pressure rating closely matches actual system pressure. In addition, selecting a regulator that closely matches inlet pressure requirements provides the best handle resolution (smaller amount of pressure change per turn of the handle) and control, enabling a broader ideal operating range.  

Seat-load drop

Seat-load drop occurs on the far left of the regulator curve, where there is initially a steep drop in pressure. If reading the curve from left to right, imagine that the system is in a no-flow state. The regulator is set to a certain pressure, but there is no flow. Then, imagine that an operator slowly opens a downstream valve to initiate flow. Immediately, there is a sharp drop in pressure because it is difficult for a regulator to maintain pressure at this location. A regulator operating along this steep drop in the curve may emit chattering or pulsating sounds as it fluctuates between flow and no-flow conditions.

Lockup 

Now read the curve from right to left. Imagine that the system is operating along the flat part of the curve. Then, imagine that an operator slowly closes a downstream valve, reducing flow to near zero. We are moving up the curve. As the no-flow state nears, the regulator has difficulty maintaining the set pressure. Again, the regulator may emit a chattering sound.  Eventually, the regulator snaps shut, stopping flow. This is called lockup. The terms seat-load drop and lockup are essentially interchangeable. Sometimes, lockup is used to describe both conditions. It is not advisable to operate a regulator under these conditions.

Next webinar: How to select and size a pressure reducing regulator

On January 17th, in a live technical webinar, customers of Swagelok Northern California will receive a 30 minute briefing from Swagelok field engineer and regulator expert Eric Kayla.  Kayla will discuss how to properly select and size a pressure reducing regulator and cover:

• Understanding pressure reducing regulator flow curves
• How to use a flow curve to size a pressure reducing regulator 
• How to size a pressure reducing regulator for different types of media

In a hurry or have a question? Please call our office at 510-933-6200.

Additional resources:

Related articles:

Webinar Replay: The Theory and Operation of Pressure Reducing Regulators

Related downloads:

Technical Bulletin and Article on Pressure Regulator Flow Curves

Slide Deck: The Theory and Operation of Pressure Reducing Regulators

Q&A from The Theory and Operation of Pressure Reducing Regulators

Swagelok Pressure Regulators Catalog