Introduction: A magnetic float level gauge may appear straightforward from the outside – typically a vertical tube attached to the side of a vessel with a column of colored flags or a moving indicator – but it comprises several key components working together. Understanding these components is important for specifying, operating, and maintaining the device. Below CN BOILER describes the main parts of a magnetic float level gauge and their functions, as well as common variations in design.
Primary Components and Their Functions
1. Float: The float is the heart of the gauge inside the chamber. It is a hollow (or sometimes foam-filled) body that floats on the process liquid. The float contains a permanent magnet assembly sealed inside. As the liquid level changes, the float moves up or down accordingly, following the liquid surface. Floats are often engineered from stainless steel (316/304 SS) for general use, but other materials like titanium, Hastelloy, or even engineered plastics are used for special applications (e.g. corrosive fluids or very low specific gravity liquids). The float must be designed with suitable buoyancy for the operating liquid’s specific gravity (density) and to withstand the process pressure and temperature. For instance, floats for very low-density fluids need to be larger or lighter to provide enough buoyant force, and floats for high-pressure service may be of thicker construction or pressurized internally to avoid getting crushed. The magnet inside the float can be of different designs (e.g. a circular toroidal magnet or a series of bar magnets). The choice of magnet configuration affects the strength and orientation of the magnetic field that will couple to the indicator.
2. Chamber (Measuring Tube): The chamber is the vertical tube or column attached to the process vessel that houses the float. It is also commonly called the gauge body or bypass chamber. This chamber is connected to the vessel by process connections (flanged, threaded, or welded nozzles at the top and bottom), allowing liquid to flow in and out so that the level in the chamber matches the level in the vessel. The chamber is typically made of a non-magnetic metal – often stainless steel – to allow the magnetic field to pass through to the outside indicator with minimal attenuation. It must be pressure-rated for the process; thus, for high-pressure applications, the chamber is a heavy-wall pipe or tube designed according to pressure vessel codes. Chambers often include an upper vent and lower drain (or simply use the process connections as vent/drain) to facilitate maintenance (e.g. to flush the chamber). Inside the chamber, the float must have clearance to move freely over the entire level range. Some designs incorporate guide rods or centralizers inside if needed to keep the float properly aligned (though many floats are “guide-free” and rely on geometry to stay oriented). The length of the chamber is usually custom-fabricated to span the measurement range required (some gauges can be very long – multiple meters – built in sections if needed). In summary, the chamber provides the pressurized enclosure that isolates the float and process liquid, acting as the structural component of the gauge.
3. Indicator Assembly: The indicator is the externally mounted display that shows the level to the observer. There are two main types of indicators: flag indicators and follower (shuttle) indicators. The flag indicator type is extremely common – it consists of a column of small pivoting flags (often 10–30 mm tall each) that are magnetically flipped by the float’s magnet. These flags are typically colored (for example, one side painted red and the other white, or other high-contrast color combinations) to denote liquid vs. gas. They are housed in a narrow enclosure running alongside the chamber. Each flag contains a little magnet or is magnetized so that it will rotate when the float’s magnetic field passes by. The flags above the float show one color, and those below show the opposite color, creating a sharp boundary indicating the fluid level. The entire indicator assembly is often enclosed in a protective housing (glass, polycarbonate, or metal with a viewing window) to shield it from weather, dust, or damage. An alternative indicator style is the magnetic follower: a lightweight magnetized capsule (often painted bright color) that rides in a transparent tube on the outside of the chamber. The float’s magnet “drags” this follower up and down, directly pointing to the liquid level on a scale. Both flag and follower indicators perform the same role – providing a clear visual level reading – and are chosen based on visibility and client preference. Modern designs often use wide flag indicators for better long-distance visibility (e.g. flags 1.5 inches wide, viewable from over 60 meters away). The indicator usually has a graduated scale or ruler attached, marked in engineering units (feet/inches, meters, etc.) or percent, so operators can take quantitative readings. The indicator is a critical component as it translates the float’s movement into a human-readable form, with high visibility and minimal maintenance.
4. Magnets and Magnetic Coupling: While not a standalone “part” you hold separately (the magnets are embedded in the float and flags), the magnetic system is worth noting as a key component of function. The float’s internal magnet is typically a permanent magnet (made from materials like ceramic ferrite or rare-earth alloys) configured to project a magnetic field outward to the indicator. High-quality gauges use magnets designed to maintain strength over time and temperature. Some floats use a single cylindrical magnet, others use an annular ring, and some use arrays of bar magnets – each approach balances field strength and weight. The indicator’s flags each have small magnets so that when the float’s field is near, it forces them to flip. There is careful engineering here: the field must be strong enough to reliably actuate the flags or shuttle even across a thick chamber wall, but not so strong that it causes flags to flip too far above or below the actual float position (which would blur the reading). Also, using non-magnetic chamber materials (e.g. austenitic stainless steel or non-metallic) ensures the magnetic flux isn’t shunted away or weakened by the chamber wall. The magnets essentially form the coupling link between the float and indicator – a “contactless” connection that is fundamental to the gauge’s operation.
5. Process Connections and Mounting: The gauge typically has two process connection points (at least) to the vessel – one near the bottom of the gauge chamber and one near the top. These are often flanged connections (e.g. ANSI or DIN flanges) or could be threaded or socket-welded, depending on the design and vessel nozzle available. The arrangement of these connections can vary: some gauges mount to the side of a vessel with one top and one bottom connection (Style A or B side-mounted configurations), while others might have a single connection with an internal stilling well (for top mounting in a tank), but side mounting is most common for continuous level measurement. Valves are usually installed between the vessel and the gauge connections – this allows the gauge to be isolated for maintenance or in case of float failure. In high-pressure or hazardous service, these are often block valves with safety features. The gauge assembly will have supports or bracing to fix it to the vessel or nearby structure, ensuring it remains vertical (proper vertical alignment is important for accuracy and smooth float travel. Many gauges also include a vent plug at the top and a drain at the bottom of the chamber for commissioning and servicing
6. Optional Components: Many magnetic float gauges are outfitted with optional components for enhanced functionality:
Level Switches: Magnetically actuated switches can be clamped or mounted at specified elevations on the outside of the chamber. These switches (often reed switches in a small housing) are tripped by the presence of the float’s magnetic field. They provide electrical contact outputs for high-level or low-level alarms, pump control, etc. Because they are external, they can often be added or adjusted without breaking into the process.
Level Transmitters: For remote monitoring, a transmitter can be added. One common type is a reed chain (reed-chord) transmitter – this is essentially a long chain of resistors and reed switches in a stick that runs alongside the chamber, producing a variable resistance (or a 4–20 mA output) proportional to level, with typical resolution of around 1/2 inch or better. Another type is a magnetostrictive level transmitter, which can give very high resolution (a couple of millimeters). These devices allow the magnetic gauge to output to control systems while still providing a local visual readout.
Insulation or Heating Jackets: For applications involving cryogenic fluids or fluids that solidify at ambient conditions, the chamber can be insulated or heat-traced. Some gauges have a steam jacket or electrical heater option to keep viscous fluids flowing freely inside the chamber (preventing the float from sticking in cold, waxy fluids).
Calibration Scale and Accessories: Some gauges include a calibration scale or markers that can be adjusted to mark specific levels (like minimum operating level, alarm points, etc.). There are also accessories like float stop alarms or flag fault indicators (for example, some manufacturer designs includes an “automatic float failure warning” flag that changes color if the float were to sink to the bottom
Summary :
To recap, CN Boiler will do the conclusion, a magnetic float level gauge is composed of a float with a magnet (the moving sensor element), a chamber that interfaces with the process fluid, an external indicator (flags or follower) that visually displays the level, and the necessary connections and mounting hardware to attach it to a vessel. The synergy of these components yields a level gauge that is robust, self-contained, and easy to read, bridging the internal process conditions to an external, safe indication through magnetic coupling. Understanding each part – float, chamber, indicator, magnets, and accessories – helps in selecting the right configuration and caring for the gauge to ensure long-term accurate service.
