Natural Gas Pressure (Self-contained) Regulator Chatter 1

[GoHawkbeaks]

Hello all,
I am designing a natural gas pressure reducing valve system which is utilizing self-contained pressure regulators to reduce the pressure of incoming gas. The flows through the system are such that I cannot size a single regulator to control over the full range of flow (the turndown is greater than 100:1). So, I must design both a "High-flow" and "Low-flow" pressure reducing train and install them in parallel.
I believe this is commonly accomplished, however, my question is this: During cases of low flow, what will keep the larger, "High-flow" valves from chattering and trying to control pressure when the "Low-flow" valves should be operating and controlling pressure.
I believe this can be done by setting the “Low-flow” valves to a control to a higher pressure (say 130 psig) and set the “High-flow” valves to a slightly lower pressure (say 125 psig). This way, during periods of low flow, the “High-flow” valves will be closed since the “Low-flow” valves will be controlling to a higher pressure downstream. Once the system demands more flow, the pressure will drop and the “High-flow” valves will open.
Any thoughts or previous experience is always appreciated.
Regards,
GHB

 

[pmover]

yes, your analysis/thoughts are commonly practiced.

the lower flow regulator should have the higher pressure setpoint than the high-flow regulator as you so describe. the difference in setpoints may need be verified/tested, but 5-7-psi is adequate for similar systems i'm aware of.

good luck!
-pmover

 

[TD2K]

Include the "droop" in your analysis of the regulators if it's significant. Droop isn't significant for all regulators but if it is, you can get a surprisingly wide range between what the regulator will 'control' the pressure at between min flow and max flow compared to set point.