Replacement of Mercury Switches in Industrial Settings

[CuriousElectron]

Hi All,
How prevalent is replacing field devices(level/pressure switches) with non-mercury containing devices in your area of work?
Some vendors offer substitutes, presumably the functionality of the device would not change, just achieving the same function without using mercury as part of its workings.

Thanks,
EE

 

[JohnRBaker]

It's been a few years (like close to 40) since I was working where this was an issue. However, back when I was, we used a lot of mercury switches because some of our machines were gas-fired (large commercial bakery ovens) and as such we needed pressure switches and air-flow detectors that used them, both in the temperature control and safety circuits. Now I recall that there was a period where we decided to look at alternatives because we were installing machinery into bakeries where food was being produced. Nothing came of it since no regulatory agency was making an issue of it, at least not back then. However, we were very careful to not install any controls with mercury switches near where food products and/or raw ingredients could be exposed if one of controls were damaged and a glass vial broken allowing mercury to leak out or be exposed to the atmosphere.

That being said, I would think that with solid-state devices that someone should have come-up with something that could be used in pressure and position detectors, where mercury switches have traditionally been the standard.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

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[hacksaw]

Practically all plants from the 70's on have avoided use of mercury containing instruments and electrial equipment, due to the subsequent liabilities beyond their control.

There may be what is referred to as a "grand fathers clause" where existing equipment need not be replaced, unless it fails, at which point it is replaced by mercury free devices. Additionally, you'll find few supplierswho will sell mercury containing devices, due to shipping liabilities.

 

[John2025]

We replaced mercury contactors with SSRs in the 90s or so and we were probably late doing it. Don't forget to dispose responsibly, too.

 

[CuriousElectron]

I heard that mercury containing switches are more susceptible to vibration versus snap action switches. Is that true?
Thanks,
EE

 

[Turn_of_the_Screw]

Yes. We used to use them in a miniature portable boiler product. There were some problems that would occasionally occur when the pump kicked on since they were not mechanically isolated. We moved to snap action and eventually solid state. Also took the pressure off from a liability standpoint as well.

 

[Hoonya]

Of course, it would be much better to use non-mercury containing devices. Just because of safety