Mercury Float Switches

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Old 03-16-07, 07:06 PM
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Mercury Float Switches

Post after post here talks about things getting stuck in switches causing pump failure.

Doesn't anyone use mercury switches rather than mechanical switches? They work even if there is a little stuff floating in the water. In industry, that's all I ever see used.
 
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Old 03-16-07, 08:05 PM
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We use sensor type mecury switchs all the time for our control panel pump systems. We also use them in residential applications but not as much as the mechanical types. They seem to be a better switch as we get very few back.
 
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Old 03-17-07, 07:57 AM
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Mercury switches

I am all for a more reliable switch..Do you have any links for this type of switch? I see quite a few NON-mercury switches out there.
 
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Old 03-17-07, 10:37 AM
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I don't think there is actual mercury in them anymore. Same concept though.
Just google "mercury float switch" and you will get many links.
 
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Old 03-17-07, 10:52 AM
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just a quick perusal of the internet showed many actual mercury switches. For those that aren't they like to attempt to claim superiority over mercury switches.

For my money, it's hard to beat a mercury switch. they are the simplest system you can use and you don;t have to worry about burned contacts so life expectancy is extremely long.

as far as things getting stuck in the switch, not sure what you are referrring to. A float switch is going to act the same whether it is a mercury switch or other type of contact. If neither is allowed to float, they will not change status, if they float, they change status, as long as the internal mechanicals are functioning correctly.

Now there may be some legal restrictions to using mercury switches in certain applications. Where potable water is involved, I can see a limitation but I rarely see float switches used in potable water situations. Most of the time with potable water, I use a neutral lead contact that hangs in the water that when the water contacts the lead, it completes a circuit. The downfall of these is as when minerals build up on them, they lose the ability to make the neccessary contact to complete the circuit.
 
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Old 03-17-07, 02:47 PM
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So the majority of the mercury swittches are "tether" type switches?
 
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Old 03-21-07, 08:04 AM
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They are tethered. The "little stuff" I was thinking about were things like kitchen matches from lighting the furnace. They can float around until they finally work themselves into a spot where the mechanical switch can't move.

From a practical point, I wouldn't care what is inside as long as it works the same way. I would have some environmental concerns as to disposal.

The only bad thing I have ever heard about these switches is that scale builds up on the outside. They are so reliable that nobody looks at them and over a period of many, many years, the scale buildup becomes so heavy the float won't float anymore.
 
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Old 03-21-07, 08:25 AM
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I've actually had a couple of these type switches that took on water and shorted out through the years. However, I still use them wherever I can. I always try to use a pump without a builtin switch, and control it with a tethered "mercury" switch. The failure rate is considerable less than integral switches.
Ron
 
 

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