Vortex Flowmeter Problem

Hi,

there is a vortex flowmeter. There are two valves at the front and behind side of these flowmeters. Flowmeter is mounted vertical and flow direction is from down to up. When the valves are closed, some fluid stays in it. But no flow occurs when the valves are close. But not everytime, sometimes flowmeter give full output (20 ma). How can I solve this problem?
 
How long is the pipe length before and after the flow meter?
Flow meters are generally very picky to the length of pipe before and after the meter. What's inte the pipe, Oil? water?
 
There is 50 cm straight pipe after and before the flowmeter. The fluid is caustic.

It works fine when the valves are open, but makes problem when the valves are closed. Flowmeter is dn50.

> How long is the pipe length before and after the flow meter?
> Flow meters are generally very picky to the length of pipe before and
> after the meter. What's in the the pipe, Oil? water?
 
Hi Zapotek67,

This commonly occurs when you have vibration in the process fluid.
Vibration can be generated by nearby equipment, pumps, agitiators, rotating machinery, reciproating compressors etc

My theory is when there is no vortex shedding (from flow) to damp out background vibrations (noise sources as above) - then background noise is considered to be flow and the result is often mid to full scale.

Possible solution:

* Install damping / isolation around piping

* Add pipe supports fixed to solid foundations, i.e.; concrete, bund floor, earth, separate supports

* Change the orientation of the flow meter

* Force flow meter to read zero in PLC/DCS when you know there is no flow (valve closed etc)

* Review model style/age and trial modern vortex flow meter with better noise rejection

* Change flow meter style - mag flow / coriolis, orifice etc

FYI - we use Mag flows for caustic (50%) - never had any issues.

Regards,
PB
 
Hi.

Despite the signal problem, please note that your installation doesn't look fine:

- You need more than 50 cm before a DN50 vortex!...have a look in the manual. For the outlet, it's fine

- If flow is downward, pls be sure the pipe is ALWAYS full.

Going to the problem, its looks like vibrations . You can check this simply hitting the pipe wit a hammer when the flow is zero. Try rotating 90° the meter, or decrease the vortex amplifier gain.

Anyway remember you have to check the installation
 
Hi zapotek67,

When changing instruments I have to consider a lot of factors. In your case I'd look at the list of recommendations, add budget & time as factors, and work through them in order of what is easiest for your application and customers.

For example; Right now I have a couple of problematic vortex flow meters on HP air lines used for batching, which we have been ignoring for 10+ years due to other priorities, we now need reliable consistent measurement.

The shutdown time and cost is my biggest factor so I'm going straight to DP flow replacement - i.e.; guaranteed to work.

Good luck!
Regards,
PB
 
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