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Anonymous Poster #1

Flow Measurement Using Air Bubbler System in Sewage Applications

07/15/2020 2:16 AM

Hi does anyone know of reliable flow measuring bubbler systems and if there are any limitation in relation to maximum depth and flow velocity.

I would like to find how the system would be installed and if possible the air line not been inserted directly in the flow and how to prevent potential blockages in the pipeline.

All responses welcome.

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#1

Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 3:18 AM
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#2
In reply to #1

Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 4:01 AM

Thanks greatly appreciate the early response and the links .

The Lesman video very informative and interesting.

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#3

Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 4:41 AM

Height over a weir is a non-contact method of flow measurement.

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#4
In reply to #3

Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 5:07 AM

Agreed but to install in live sewer causes hydraulic restrictions, construction costs, additional, operational inspections and as already pointed sewers are zone 0 so the least operations and maintenance access and activities the better.

Thanks for the response

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#5
In reply to #4

Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 5:24 AM

Zoom out a bit, please.

  • Why is the flow needed to be measured where previously it hasn't been?

The water industry is full of standardised arrangements for doing things. In the UK, in particular, there is a thing called WIMES [Water Industry Mechanical and Electrical Standards].

  • Why is a previously-trusted and standardised arrangement for doing things not applicable in this case?
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#6
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Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 6:02 AM

I obviously did not provide sufficient information in the question.

The measurement of flows in this case is required for many different reasons.

The main reason being that the new sewer is to accommodate all of the previous flows which were pumped from numerous sewage lifting and sewage pumping stations to the sewerage treatment plant.

1- The previous pumping stations (PS) are being diverted and will become gravity flows. The previous PS provided the flow data. The flow diversion chamber will measure and provide the flow data.

2- The gravity flows enter into the new sewer at the interface points which will also be measured.

3- The flows in each sections of the new sewer will also be measured at specific shaft locations.

4- All of the flows will be used to provide the flow data which will be analysis and used compare the accurate of previous network hydro-graphs and hydraulic modes and to identify abnormal flows and potential leaks in the system. models to to a into each section.

The flows will then be pumped from one PS to the STP's

Appreciated there will be errors due to the inaccuracies and uncertainties of the flow measurement and the data exchange etc. However flow trends will be established for the network and the new sewer which will identify abnormalities in the flows and lead to further investigation.

Agreed WIMES has been used for the ME and partially for the ICA for decades and continually being updated to take in technological advances, and will catch up at some point and include the MEICA requirements for major and link sewers networks.

Thanks again for your input as it has made me rethink some areas and obviuosly be a little bit more explicit in the question.

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#7
In reply to #6

Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 7:14 AM

This link should be of some help in making your decision:

https://macemeters.com/solutions/wastewater/

And these folks:

http://mcrt.com/partially-filled-flowmeter.html

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#8
In reply to #6

Re: Flow measurement using air bubbler system in sewage applications

07/15/2020 11:46 AM

The snippet <...The previous PS provided the flow data....> indicates that there is equipment already installed that is a viable solution and worthy of cloning into the new arrangements.

<...leaks...> will be self-evident. Too many measurements will cascade a lot of effort recalibrating flow instruments.

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#9

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/15/2020 1:57 PM

A potential level measurement error when using a bubbler is the pitot effect of a flow stream near the discharge point of the bubbler dip tube.

One open tank bubbler I encountered had a discharge port within several inches of the bottom of the dip tube and when the discharge valve opened to allow flow, the level dramatically shifted in excess of the change in actual level due to the forces/pressure at the bottom of the dip tube. Moving the dip tube to the other side of the tank solved the problem.

I heard a report of a commercial waste water bubbler issue when used in an underground sewer line in an open flow stream, that is, not for level behind an open channel flow element, like a weir but just inserted in an unobstructed flow stream. It was not clear what the flow velocity was, but the report was that that the level readings from the commercial bubbler box were not at all reasonable.

An early 1950's study by the State of Illinois on bubbler errors that could be encounter when used as a field tool for well depth measurement covered the pitot effect. In summary,

"If high velocities in the well were present moving either towards or away from the nozzle discharge area, an additional correction for a velocity head would be necessary. This error is caused by the Pitot effect. Velocities causing a measurable head are generally not present in an observation well and seldom in a pumped well unless the nozzle is located very near the pump intake. Reasonable effort should be made to locate the nozzle out of turbulent regions that usually occur at the pump intake."

Bubbler System Instrumentation For Water Level Measurement by Gerald H. Nelson
https://www.isws.illinois.edu/pubdoc/ri/iswsri-23.pdf

Be aware.

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#12
In reply to #9

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/16/2020 4:25 AM

Thanks this is very interesting already knew there were potential errors in accuracy but this report throws a different light on the subject .

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#10

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/16/2020 2:26 AM

I used ISCO sampling equipment years ago for some EPA studies. Grabs, composites, timed and flow weighted sampling can be done. The flow weighted method, uses a sealed collar(which is easily installed) and a weir plate, with a bubbler. At that time, we used strip chart recorders, but now it's all logged digitally.

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#11
In reply to #10

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/16/2020 4:22 AM

Thanks for the response. Yes have also used ISCO and other sampler units for composite sampling, however we cannot use a weir due to the hydraulic restriction access etc.

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#13

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/16/2020 5:05 AM

Do you need to sample?...or just measure flow? Lift station run times can give accurate results.

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#14

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/16/2020 7:11 AM

Ultrasonic level measurement is very accurate,if the appropriate module or setting,according to pipe diameter is used.

A radar type is suggested if foaming is a problem.

Zero is set by measuring the distance from the probe to the bottom of pipe,and span is calculated using the distance to the top of the pipe,then with the appropriate "K Factor" program,based on pipe diameter (GPM,LPM,GPD,LPD,MGPD,ETC).
The probe is not in contact with the liquid,and can be located far above the pipe.

If your area is subject to frequent lightning storms,then appropriate surge protection is suggested.

A small bore hole above and into the pipe could allow mounting of the instrument to be located above ground with no electronic components in the "zero" zone.

A PVC pipe inserted into this hole,with the sensor mounted at the top would be relatively cheap to implement.

This may be more expensive initially,but total cost of ownership will be lower,due to reduced maintenance costs,and no hazard to personnel entering a very hazardous zone.

Of course,a seal at the entry point of the cable to the transceiver will be required, according to local codes.

Do it right,and do it once.Do it wrong,and it is like walking around with a hole in your pocket,it will "Penny you to death." Typical systems may be found here:

https://www.pulsar-pm.com/Instrumentation/Product-Types/Transducers

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#16
In reply to #14

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/17/2020 4:23 AM

One point to bear in mind with the use of a standpipe is the beam spread of the transmitted signal. Blanking can be applied but the signal contacting the standpipe walls can be reflected at angles and give a false reading in the valid signal range.

We had to use large diameter standpipes to prevent the signal interference in coal bins and ensure the bottom of the standpipe was just above the blanking max setting else the ultrasonic level detector will latch onto the tube entry point..

On sumps the turbulence of the inflows generated erroneous signals of the actual depth that were in the valid depth range.

Depending on the sewer profile at the measuring point an F of X function can be used in a PLC to accurately do the volumetric conversion from depth to volume..

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#15

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/16/2020 9:38 AM

Back to the other points in your original question -

There is no maximum depth limitation on a bubbler other than supporting the dip pipe/tube and supplying a pressure higher than the hydrostatic pressure to be measured.

The pitot effect when using a bubbler in a flow stream is an issue with a bubbler in a flow stream.

The conventional means of dealing with clogging is to use smooth pipe/tube, like PVC and periodically
- hold or freeze the level reading
- blow the dip tube down with one or more blasts of air at line pressure.
- resume flow from the constant flow regulator and allow the dip tube pressure to stabilize
- release the hold on the level reading and resume normal readings

If clogged, the dip tube pressure increases with a resulting false high level reading. In a critical service nuclear application, the differential relay's constant flow rate output was measured by a mass flow meter to monitor and confirm a continuous flow stream.

I'm not sure what "the air line had not been inserted directly in the flow" means. A bubbler dip tube that discharges into air will have no pressure in the dip tube (other than a miniscule pressure drop at a very low flow rate, maybe 1 SCFH) so the level reading will be zero.

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#17

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

07/17/2020 4:34 AM

Have tried to use bubblers in coal washing jigs but they failed often with blockages caused by the sudden pressure fluctuations forcing product into the orifices of the bubbler so we reverted to direct pressure measurements with diaphragm sensors.

With the bubblers apart from the air supply requirements they were a high maintenance item requiring checking weekly for flow. Each one had its own air regulator, filter drier which also required checking weekly.

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#18
In reply to #17

Re: Flow Measurement Using Air Bubbler System in Sewage Applications

11/15/2020 6:42 AM

This is not a bubble tube system,but seems to be a better solution to your concerns.

Here is what I think may be a solution to your problem:

A magnetic flow meter that uses capacitive measurement for level,and electromagnetic effect for velocity, and when combined,they give an accurate measurement of flow in a partially filled pipe.

They require very little maintenance and can operate in manual or automatic mode.

The present very little obstruction to the flow in the pipe.

It is clog proof and is not affected by solids or foam or debris in the flow.

This link presents an application solution to a lingering problem in a STP.

https://www.waterworld.com/technologies/flow-level-pressure-measurement/article/16194107/new-meter-accurately-monitors-flow-in-partially-full-pipe

There are also many links here that you may find beneficial.

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