Frequently Asked Questions

Unless otherwise specified, most stock Madison float switches ship in the Normally Closed (NC) position. 

Vertical: the float's witness mark (stainless steel models) or magnets (plastic models) indicate the NO/NC operation

NO is indicated by circle up (stainless steel) or magnets down (plastic)

NC is indicated by circle down (stainless steel) or magnets up (plastic)

Horizontal: the direction of the arrow on the hex indicates the NO/NC operation

NO is indicated by arrow up

NC is indicated by arrow down

Use an ohm meter or continuity meter to verify the switch setting and operation. For vertical switches, connect the meter to the leads and measure the switch with the float hanging down away from the fitting. If the meter reads a short, the switch is normally closed and will open on the rise.

To change the contact operation for vertical switches, remove the retaining clip and float and reverse the float on the stem. 

The only exception is the operation of the subminiature switch (M3326/M3326-NO), which must be specified when ordered since the float is not reversible on this model. 

For horizontal switches, rotate the switch 180° in the tank installation.

316 Stainless Steel: For high temperature (to 250°C), high-pressure (to 300 psi), and corrosive conditions. Commonly used in food processing, medical, heating, and cooling equipment.

Polypropylene & Polysulfone: For acidic conditions, such as those found in electroplating and metal cleaning. Another choice for lower-temperature (to 105°C) food processing applications (Madison Company uses only polypropylene that is FDA-approved for food contact). Also a good choice for general-purpose applications in commercial or consumer appliances and equipment.

Brass & Buna-N, PBT & Buna-N: The selection for petroleum-based liquids, such as lubricating oils, gasoline, and diesel fuels. Widely used in storage tanks of vehicles, generators, transmissions, and hydraulic systems. Other uses are in lubrication, recovery, refining and fuel processing equipment. PBT is not suitable for use at temperatures above 130°C.

Kynar: Chemical- and solvent-resistant properties make this material a problem solver for many applications. Its high-purity nature is ideal for food handling and sensitive laboratory or test equipment.

In many applications, a relay is required to isolate the float switch from the device. The float switch will be connected in series with a relay input coil that typically draws less than 500 mA. When the switch is closed, the relay coil is activated and closes the output contacts. These contacts turn on or off the high current required by the device.

Madison sensors can control the liquid level between a high and a low point. By combining a controller with two float level switch points, a pump or valve can be switched on/off automatically. Two single point float switches, or a custom multi-level float switch with the levels set an appropriate distance apart in the tank can be utilized for this application.

A double pole double throw (DPDT) relay can be combined with two level switches as shown below for "pump-up" or "pump-down" applications.

Madison offers R2-120V AC pump controllers that can be used with float switches or conductivity probes; relays and controllers to activate pumps, solenoid valves, motors and alarms. 

Catalog float switches are accurate to within 1/8” of the center of the float travel, with a hysteresis of 1/16”.

Each individual switch will switch repeatably within 1/32”.

Madison can furnish an interface float that, given two mediums, is designed to sink in one medium and float in the other. A typical application would be one where oil and water accumulate in one tank, and sensing of only a fall in water level is required (oil level is not an issue). Since a standard float of any material will float in any liquid with a specific gravity higher than the specific gravity of the float, Madison would "weight" the float to a specific gravity of 0.95. Since the specific gravity of the oil is 0.8-0.9 and that of the water is 1.0, the float will sink in the oil and float in the water. Both full-size Buna-N and polypropylene floats can be modified in this manner.

American National Standard Taper Pipe Threads, most commonly called “NPT Threads”, are often pipe thread fittings that seal using a thread-to-thread connection with a matching tapered diameter. The male and female fittings bind together to make a pressure tight seal. To assist with proper engagement of these threads, the use of a thread sealant or Teflon tape that is compatible with the application is highly recommended

Proper installation steps are below;  

STEP 1: Inspect the port and fitting to ensure that both threads are free of contaminants and excessive burrs or nicks.

STEP 2: Apply Teflon Tape 1-1/2 to 2 turns in a clockwise direction, or a thread pipe sealant, around the male threads leaving the first thread uncovered.

STEP 3: Screw in the thread finger or hand tight into the port depending on size. 

STEP 4: Wrench tighten the fitting an additional 1-2 turns past Finger or hand tight. If a leak occurs, add ¼ to ½ turn and recheck for any leaks till sealed.

•Note:  Properly assembled NPT fittings will engage in 3.5 to 6 threads. Excessive torque can crack the fittings or bind/gall them together, preventing removal or reinstallation.