Hello list members: We're planning to install a butterfly-type valve for automatic flow control of a gaseous substance in one of our processes. Because of space restrictions, we need to place this valve no more than 10 inches (preferably less) downstream from the gas regulator; this regulator steps down gas pressure from the 20-30 psig or so on the supply side to the 3-4 psig required on the process side. Our question is, are there any restrictions, guidelines or recommendations for the distance required between a regulator and a throttling valve? Our flow sensing devices, for example, clearly state the amount of diameters of straight pipe before and after the sensor for accurate measurement, but we have seen no such recommendations for throttling valves. We normally have our regulators a considerable distance upstream from our control valves, but in this case as I mentioned we are more space restricted, and haven't placed a valve that close to the regulator before. Any comments will be much welcome. By the way, pipe diameter is 4 inches. Regards Bob Gantt

 

At this kind of low pressure, the recovery profile for gaseous fluid is almost immediate. Unless, the system chokes itself from underdesign. It might be wise using globe valve instesd of butterfly. It will be less sensitive to upstream inconvenience. I don't see a problem. That installation looks home made.