# Mercury Switch Replacements



## wildleg (Apr 12, 2009)

mercury free level switches ?


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## ace24wright (Jul 10, 2012)

magnetic micro switches, (reed switches)


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## glen1971 (Oct 10, 2012)

Some older level switches have retrofit kits available.. Or you can try a different style of limit switch and maybe a minor bracket modification, if replacement is too difficult..


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## millelec (Nov 20, 2010)

Stang, are these pressure switches? Penn makes some.
http://www.johnsoncontrols.com/cont...ration/commercial_refrigeration/pressure.html
(altho just had a HVAC tech removing mercury switches from a unit we're scrapping so he can use them in another machine since he hates new stuff)


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## wildleg (Apr 12, 2009)

there is a push to remove mercury switches from places like wwtp. I believe that is why he is asking this question. There are manufacturers that make suitable replacements with non-mercury devices. Maybe if he posts what the application is, someone can help him


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## JRaef (Mar 23, 2009)

For check valves they must be limit switches, vertically oriented. They used mercury because it is VERY reliable, never wears out and can carry relatively high current. But with the move away from mercury for anything anywhere, you have to find a replacement with comparable reliability and capacity. That's the challenge. Reed switch based limit switches and solid state prox switches are the most reliable, but can't carry much current so you end up with interposing relays, which drops the reliability factor. 

But really before you go much further with this, you need to fully understand the nature of the control system. If for example this was upgraded to PLC controls years ago and the mercury switches just left in place because they were there and worked reliably, then I would use solid state prox switches into the PLC inputs. But if it is still all done with direct 120 or 240V control and the motor control circuit is piped directly through the mercury switches, you need a different solution.


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## Fixastang (Sep 4, 2012)

The mercury switches are used on check valves throughout the plant to indicate if the valve is open or closed. We are currently providing 120vac to the switch with a PLC monitoring the feedback (whether the valve is open or closed.) We have been able to determine the ones we have were made by Consolidated Electronics, which was bought out by Siemens. We have attempted to contact them regarding these items, but have yet to receive a response. The switches are mounted on the arms of the check valves, which provides us with plenty of room to make/modify mounting plates to accommodate different switches.

Thanks for the suggestion regarding reed switches. I am curious if we would need an amplifier on the reed switch signal or would it pass the 120vac signal back to the plc without any problems. The distance from the check valves to the plc is generally less than 100 ft.

Thanks again for all the suggestions you have been providing.


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## JRaef (Mar 23, 2009)

No amplifier necessary, the PLC input is not looking for current, just voltage and the tolerance is usually pretty wide. Go with reed (sealed) switches, lots of options there. Just be aware they are not "forever" switches like the mercury were, they will need to be put into a PM schedule to be checked, even if it's only once a year or every other year.


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