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Old February 5th, 2020, 12:45 PM   #1
Charbel
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Level switches for sewage tanks

Dear,

I am looking for level switches that perform properly in sewage water where there is possibility of flocs and some objects (maybe bags, baby napkins), sewage pumps are located in an airport.
Float switches are not functioning properly specially the one related to low low level because of the presence of some foreign objects in the pit as stated above. Kindly share ideas based on your experience if you have some alternatives.
Thank you
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Old February 5th, 2020, 04:35 PM   #2
Tom Jenkins
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Floats are usually the old reliable standby. There are different styles, so you might consider alternates.

If float switches are not doing the job I suggest you look at ultrasonic or pressure based switch. And there is always the old reliable bubbler system. https://www.brooksinstrument.com/en/...bubbler-method Just substitute a pressure switch for the pressure transmitter.
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Old February 5th, 2020, 05:16 PM   #3
Dryhops
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You can get fancy and use radar, or ultrasonic sensors that are never actually submerged.

This document is useful as it describes many level measurements options:

https://www.emerson.com/documents/au...s-en-76356.pdf
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Old February 5th, 2020, 05:54 PM   #4
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Last week I was at a couple location and one has this
in their waster water transfer tank and the other location had this in their treated water holding tank. The pressure switch was for low and low low level and the high and overflow levels had float switches.



I have zero experience with either and read about them to have an overall understanding of the system.
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Old February 6th, 2020, 02:25 AM   #5
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If it is a transfer station, the solids need sucked out once in a while too. Then the floats will work correctly.
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Old February 6th, 2020, 07:08 AM   #6
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Ultrasonic and radar sensors work great if you can stay within their working range. There are typically deadbands that need to be avoided at all costs. Because they are electronic, it is good to have them wired and configured in such a manner that will tell your controller if a valid signal is not present (failsafe). Backup or verification sensors are always a good idea in critical processes.
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Old February 6th, 2020, 10:33 AM   #7
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Why not use a Float switch which travels up and down on a pole, then take some plastic wire mesh and make a tube around it to prevent foreign objects effecting it travel.
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Old February 6th, 2020, 06:26 PM   #8
mad4x4
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Speak to these guys https://www.pulsar-pm.com/ they handle dirty water all the time sure they will be able to help
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Old February 7th, 2020, 03:52 AM   #9
JERA
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For sewage water applications I use VEGAPULS WL S 61

https://www.vega.com/en/home_cu/prod...gapuls-wl-s-61
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Old February 7th, 2020, 02:30 PM   #10
Tom Jenkins
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Some cautions with ultrasonics:
- you can't be too close to a tank wall, or you will get echos off the wall and false readings
- when mounting outdoors wind can cause the echo to drift and cause loss of signal
- if you have foam or floating debris you will get a level reading from them that isn't exactly correct

Bubblers have fallen out of fashion, but they are cheap and reliable.
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Old February 7th, 2020, 02:50 PM   #11
mylespetro
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Are the floats rod-mounted from the top, or are they mounted on the side of the tank? I've had lots of success using Vega ultrasonic tuning fork switches, but that was in oil, they might not work if something got hung over the top of the fork.
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Old February 7th, 2020, 03:24 PM   #12
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Pulsar (as mentioned above) and very good in waste application's, we use them almost exclusively in our sewerage pump station's (lift station's). We also use the Vega WL S61 radars and they are very good, loop powered instrument with Bluetooth (for easy maintenance). I would recommend the Vega personally.
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Old February 7th, 2020, 03:43 PM   #13
lesmar96
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Quote:
Originally Posted by Tom Jenkins View Post
Some cautions with ultrasonics:
- you can't be too close to a tank wall, or you will get echos off the wall and false readings
- when mounting outdoors wind can cause the echo to drift and cause loss of signal
- if you have foam or floating debris you will get a level reading from them that isn't exactly correct

Bubblers have fallen out of fashion, but they are cheap and reliable.
This is good advice. I have an application personally right now in a lift station that foam seems to be throwing it off. How do you recommend handling a problem like that? Do you use float backup in case something makes the sensor inaccurate?
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Old February 7th, 2020, 03:48 PM   #14
OkiePC
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Quote:
Originally Posted by lesmar96 View Post
This is good advice. I have an application personally right now in a lift station that foam seems to be throwing it off. How do you recommend handling a problem like that? Do you use float backup in case something makes the sensor inaccurate?
At least one low level float to keep the pumps from running dry.
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Old February 7th, 2020, 04:00 PM   #15
Oceansoul
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Quote:
Originally Posted by lesmar96 View Post
This is good advice. I have an application personally right now in a lift station that foam seems to be throwing it off. How do you recommend handling a problem like that? Do you use float backup in case something makes the sensor inaccurate?

Radar.
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