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 Tech TalkMercury Legislation and Float Switches 
Currently, mercury-added products are used in many applications. As of today, there is no perfect substitute for mercury in terms of non-mechanical design or reliability of usage. Still, growing environmental concerns over the last ten years have created several pieces of legislation throughout the county prohibiting many types of mercury products.In particular, the following states prohibit the use of mercury float switches: Connecticut, Rhode Island, Maine, California, Vermont, and Illinois. New York will prohibit their use effective on 01/01/08, and Massachusetts on 05/01/09. Mercury always must be properly disposed of, and local codes and regulations followed. Choosing a Float Switch When selecting a float switch, you must decide between mercury-activated or mechanically activated float switches. Considerations include the liquid you are measuring, electrical requirements, turbulence present, and other factors. In most cases, either type of float switch will work well. Mercury-Activated Float Switches Mercury float switches are usually constructed of a watertight material filled with either foam or air to surround the actual mercury tilt switch within. The foam or air provides buoyancy to the float switch, and also serves as additional protection for the mercury tilt switch. Mercury tilt switches are small tubes with electrical contacts at one end of the tube. When the tube tilts, the mercury collects at the lower end and creates a conductive path to complete the circuit. When the switch is tilted back, the circuit is broken. Mercury-activated float switches are generally cited as the most reliable, since they have no moving parts or mechanical operations. Additionally, they are well suited for hazardous environments where a low voltage operation is required. Note: mercury floats switches are not acceptable for potable water applications. Upon replacement or disposal, mercury switches should be discarded as hazardous material dictated by local codes or regulations. Mechanically-Activated Float Switches Mechanical float switches use a similar construction method for the outside shell, but contain a series of mechanically activated parts. Typically, a steel ball is enclosed within an hourglass-shaped cavity, which lets the ball travel to the lower end of this cavity when the float switch is tilted. This action lets the ball depress against one or two levers, which activate a micro-switch within the float itself. The micro-switch handles the current and completes the circuit. While mechanical float switches are generally more vulnerable to impact/shock and will likely fail sooner than a mercury model due to their moving mechanical parts, they can be very effective in particular situations. They are well suited to turbulent applications and they are the recommended type of float switch for potable water. Whether you choose mercury or mechanical models, float switches are the preferred method of level measurement in today’s market. Their ease of use in both installation and eventual replacement coupled with affordable cost make them the first choice for most applications.
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