If you have a high pressure source and need to adjust it down to a lower working pressure, you may think, “Oh, well I reckon I need to buy a pressure-reducing regulator.” Problem solved, right? Well not so fast. There are multiple regulator manufacturers to choose from, and within each manufacturer, several different types of regulators with individual characteristics. Lucky for you, Swagelok purchased Kenmac in 2003 and RHPS in 2010 to expand their product offering of fluid system components to include regulators.
All regulators will exhibit behavior known as droop. No, the regulator itself doesn’t droop due to gravitational forces. Regulator droop is the phenomenon where your outlet pressure doesn’t equal your set pressure. More specifically, the outlet pressure drops below the set point pressure as your flow increases. Here’s an example flow curve for a regulator:
If you’ve ever driven a car up an incline, you’ve experienced droop in the real world. Here’s how:
Let’s say you’re driving on a flat highway at 70 mph (outlet pressure is set at 70 psig). Your foot on the gas pedal is your set point to achieve an even velocity (regulator handle is set and left alone). You’re regulating just enough gas in your engine to match your set point. All is well until you start driving up a hill (valve down stream is opened further). If you leave your foot in the same position (set point unchanged), you will start slowing down (outlet pressure decreases, aka ‘droop’). Eventually the incline will increase to a point where you’ll slow to a crawl (choked flow). Here’s my artistic attempt to draw the analogy:
I’m not the best artist, but Swagelok has a great marketing team that developed an awesome video about reducing the effects of regulator droop:
Filter Funnel 