upstream and downstream pipe length of rotameter flow meter

Question

upstream and downstream pipe length of rotameter flow meter

navycaptain (Chemical)

(OP)

20 Jul 20 09:17

Dear Engineers:
I'd like to ask a question: what is the minimum length of upstream and downstream for rotameter flow meter?

Normally,upstream is 5D of the diameter and downstream is 3D of the diameter, but I met with one possible problem: sometimes, it's hard to make perfect flange coaxiality and parallel during site installation construction, so basically, they prefer to make it 10D upstream and 5D downstream,and also inproper flange gasket installation can make a contribution to swirl.

Do you have any experience on it? is it necessary to ask design institution to design 10D upstream and 5D downstream? are there any code od standard on this?

thank you!

Youth is not a time of life, it's a state of mind.

LittleInch (Petroleum) · Answer 1 · 2020-07-20 10:01:03

Do you mean something like this? https://www.omega.co.uk/prodinfo/rotameters.html

They state upstream and downstream configuration isn't an issue.

All the flow goes through the meter and swirl isn't really an issue for this type of meter.

Unless you mean something else?? If so please send a link or attach photo.

Generally you need to follow vendor recommendations in order to get to their required accuracy / uncertainty / repeatability limits. There aren't usually any code issues, but something like AGA 8 might state the requirement for fiscal metering.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Compositepro (Chemical) · Answer 2 · 2020-07-20 19:46:40

As LittleInch said, rotameters are not sensitive to laminar vs turbulent flow. Many small rotameters have needle valves right on the inlet. They do have relatively large pressure drops compared to many other types of flow meters.

navycaptain (Chemical) · Answer 3 · 2020-07-21 01:45:23

Hi Little Inch,thank you a lot for your detailed reply and informative link, then it's clear that there is no requirement of upstream and downstream of straight length pipe for rotameter.

Youth is not a time of life, it's a state of mind.

navycaptain (Chemical) · Answer 4 · 2020-07-21 01:52:53

Hi Compositepro, thank you for your professional explanation, I'm clear on this. thank you!

Youth is not a time of life, it's a state of mind.

EdStainless (Materials) · Answer 5 · 2020-07-21 13:54:38

The control valve goes before them with liquids, after them with gasses.
Many of these can be rebuilt to change tubes, floats, and kind and location of valves.
Ultrasonic flowmeters and differential pressure types are usually very sensitive to flow disturbance, where turbine and float type meters are not.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

danw2 (Industrial) · Answer 6 · 2020-07-21 14:39:18

The inlet/outlet process connections are either in-line with the tube at the top and bottom or at 90° to the tube orientation, on the backside of the tube. Sometimes there are elbows right at the inlet/outlet.

There's no reason to condition the flow with upstream or downstream straight runs when the meter's performance is not affected by it.

bimr (Civil/Environmental) · Answer 7 · 2020-07-21 15:10:23

"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."

Brooks

navycaptain (Chemical) · Answer 8 · 2020-07-22 01:00:28

Hi EdStainless, thank you for your professional comments

Youth is not a time of life, it's a state of mind.

navycaptain (Chemical) · Answer 9 · 2020-07-22 01:02:07

Hi danw2, thank you for your clear pictures, they help a lot!

Youth is not a time of life, it's a state of mind.

navycaptain (Chemical) · Answer 10 · 2020-07-22 01:02:51

Dear Bimr, thank you for your professional reply.

Youth is not a time of life, it's a state of mind.

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upstream and downstream pipe length of rotameter flow meter