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FAQ: What is the straight run of pipe needed when installing a mass flow controller or variable area flow meter (rotameter)?

Variable Area Flow Meters (Rotameters):

As an Applications Engineer at Brooks Instrument, I talk to a lot of customers and am frequently asked this question, “What is the straight run of pipe needed when installing a metal or glass variable area flow meter (rotameter)?”

Answer: There is no straight run of pipe needed. The meter can be installed immediately before and after a valve or elbow.  It’s important to remember this is a measurement device and should be plumbed accordingly. It is not a good idea to install short radius reducing elbows on the inlet side as this can cause swirling.

Mass Flow Controllers (MFCs):

I am asked the same question when it comes to mass flow controllers (MFCs). “What is the straight run of pipe needed when installing an MFC?”

Answer: When installing a mass flow device with a full-scale rate of 10 SLPM or greater if possible, have at least 10 pipe diameters or greater of straight tubing upstream of the device. This is not required for devices with integrated filters. 

About The Author

Tim Romanik
Senior Applications Engineer

Tim is a senior applications engineer at Brooks Instrument.

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