mercury in boiler controls

michelle gaither

what is the weight of mercury in these typical boiler
switches?

> High Temperature Limit Controls
> Firing Rate Controls
> Limit Controls
> Low Water Cutoff

Also, there are non-hg alternatives for low water cutoff, but are there alternatives for the other 3?

thanks much.

Michelle Gaither
Tech Lead, PPRC
www.pprc.org

Steamhead

Michelle, that depends

on the age of the control and who made it.

There was a company called Mercoid that used merc switches almost exclusively. I believe they lasted thru the 1950s- I still occasionally see their equipment in service on older boilers. Most other manufacturers also used these switches in some of their gear.

Today, the only place I see mercs in new boiler equipment is in Vaporstats and higher-line Pressuretrols. This type of switch is almost mandatory since these safety controls need to be extremely sensitive. These units have rather large mercury tubes- about the size of my thumb- but are very well made and should not break easily.

You also find them in Low-Water Cutoffs for larger boilers. Here they are used for their durability. A standard LWCO cannot be used to operate a feed pump the way the heavy-duty ones can.

I'm not sure if liquid-filled Aquastats and similar units contain mercury or something else.

You might be interested to know that at least one supply house chain in the Baltimore area will accept old mercury thermostats and other equipment to be recycled.

P.S. Have you visited the Vintage Telephone Equipment Museum on Marginal Way? It's crammed full of working antiques. I don't think the old dial-switching systems used mercury, but I'll bet some of the radio and long-distance transmission equipment did. Might be an interesting tour. Here's their link- http://www.scn.org/tech/telmuseum/

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Yvon Blais

mercury switches

You can use the following: For a High Limit Steam Pressure Control with manual reset, the P7810D1008 is the electronic version of the L404C and can be used as a substitute.

For a boiler feed pump controller, the MM 150SMD can be used for the pump controller. It has a snap switch in it (S).

For a LWCO, the MM 63M has a No. 2 switch in it and is already a snap switch.

Many locations are now forbidding use of mercury type switches for boiler applications. Here in Massachusetts, State Buildings have supposedly become "mercury free".

Yvon Blais

mercury switches

You can use the following: For a High Limit Steam Pressure Control with manual reset, the P7810D1008 is the electronic version of the L404C and can be used as a substitute.

For a boiler feed pump controller, the MM 150SMD can be used for the pump controller. It has a snap switch in it (S).

For a LWCO, the MM 63M has a No. 2 switch in it and is already a snap switch.

Many locations are now forbidding use of mercury type switches for boiler applications. Here in Massachusetts, State Buildings have supposedly become "mercury free".

Unknown

Hi Yvon,

Nice to see you here, again. Do you know the pressure range of that electronic pressuretrol? I'm interested, but I haven't found it, yet.

Noel