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Old 01-20-2019, 03:22 PM   #1
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Default Smith and Loveless electrode vacuum sensor

I looked at a S&L lift station this week and I have most of the control scheme figured out .
Once a high level is detected a small vacuum pump starts and pulls the main pump into a vacuum this allows the main pump to prime and start.
The vacuum sensor electrode is located in a small glass dome on the pump volute and the electrode hanges in the middle of the glass dome. there is a single wire feeding voltage to the electrode and the electrode conducts to the grounded pump assembley.
In the circuit feeding the electrode are some control logic contacts a resistor (of unspecified value) a diode, a relay coil with a capacitor (of unspecified value )in parallel to the coil and electrode which conducts to ground.
What S&L calls a electrode relay may have some circutiry in it besides coil and contacts that I do not know.
The more and more I look at the drawing the electrode may not detect a vacuum so much as it detects when the pump is flooded and that lets the pump start. However I always thought you were never allowed to use the grounded case as of equipment as a circuit conductor.
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LC
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Old 01-20-2019, 05:47 PM   #2
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Is this a B/W liquid level control? I have a couple on water heater tanks to control the water inlet valve.When they touch water they activate a set of contacts, they're pretty tough.
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Old 01-20-2019, 06:09 PM   #3
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No this is a Smith and Loveless design you can go to their website and look at their pumps. You can see the glass dome on the pump. The mount is cast into the volute of the pump.
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Old 01-21-2019, 10:01 AM   #4
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Maybe they are sinking the ground for the relay,
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Smith and Loveless electrode vacuum sensor-electrode.jpg  


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Old 01-21-2019, 10:05 AM   #5
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Having a control signal pulled to ground is not the same as using the ground as a circuit conductor. Nanoamps or less.
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Old 01-21-2019, 10:36 AM   #6
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No it is a single #12 or #14 wire that is pulled in with motor circuit conductors and exits the motor lead junction box and is connectrd to the electrode on the glass dome on the pump volute.
The more I think about it I believe what they are doing is not detecting a vacuum but detecting a liquid level in the glass dome . That would confirm that the pump is primed and the pump will start.
Just my theory.
LC
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Old 01-21-2019, 10:49 AM   #7
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I changed my mind after seeing the picture of the domes,


in the parts ,...


https://www.smithandloveless.com/parts-catalogs
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Old 01-21-2019, 01:56 PM   #8
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I have worked on many liquid level probes that go to case ground, I could see a vacuum working the same way. It would just have to be ultra sensitive to read the impurities in the air
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