【Weekly Question 20090803】Application issues of float level switches
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This post was last edited by stevenyjz on 2009-8-3 09:18. Do people use float level switches in daily maintenance or design work? What factors should be taken into account when selecting float level switches to be installed on equipment? For example, the length of the short-circuit tube on the device, etc. Tell us about the problems you have encountered when using float level switches, how you resolved them, whether you have used other types of level switches as well, and what considerations are necessary when using them. Everyone is welcome to share their thoughts freely.
I encountered a situation where the float could not be fitted into the flanged short pipe; the reason was that the diameter of the float was too large. After measurement, it turned out that the increase in diameter wasn’t significant, and it was found that the welds inside the short pipe could be filed down to level them out. I have also used RF admittance level switches; they work well and require few installation requirements.
Common problems encountered with float level switches during use include incomplete closure, malfunctioning floats, and leakage. As control switches, they rely on the weight of the float being equal to the weight of a certain volume of liquid in order to determine whether to open or close; as a result, their accuracy is quite poor. There are many reasons for their malfunctioning: changes in the specific gravity of the liquid, wear and tear on the float and the openings, etc., can all lead to malfunctions.
First, consider the corrosiveness of the medium (don’t use it; otherwise the float won’t be visible after a few days). Another factor is aesthetics. Generally, float-level switches cannot be used in vacuum tanks (I’ve encountered this situation: as the vacuum level increases, the float stops moving, resulting in multiple overflows from the tank). That expert could also please explain the reasons for this. Next, consider factors such as impurities, fluctuations, the size of the float, the location of the alarm point, the alarm status, and the specific gravity of the medium. There are also cable-mounted floats, rod-mounted floats, and side-mounted floats; each case requires a specific analysis
Float-type switches: These instruments are flexible and can easily adapt to conditions such as the temperature, pressure, and viscosity of the medium. However, due to the length of the lever, the measurement range is limited. When selecting other level (fill level) switches, factors such as the particle size of the material, its angle of repose, electrical conductivity, the structure of the silo, and process requirements must be taken into consideration
The main issues encountered were stuck float balls and corrosion problems; radio frequency admittance level switches, fork-type switches, and others were also used
Due to their simple structure, float level switches are widely used. However, after being in use for a long time, they often get stuck at a certain angle; knocking on them or removing and moving the moving parts usually resolves the issue. As for installation, I don’t think there are any special requirements; just ensuring leak prevention and no jamming is sufficient. I have never used the radio frequency admittance level switch mentioned upstairs; I wonder if there is any material on this topic? Thank you~
A rod-type float switch features a float ball with an internal ring magnet that is fixed in place on a sealed, non-magnetic rod as required. When the float ball rises or falls with the liquid level due to the buoyant force of the liquid, the reed switch inside the rod generates an on/off signal under the influence of magnetic force, thereby indicating the actual level of the liquid being measured. A set of reed switches can be used for continuous measurement, or reed switches can be placed at the upper and lower limits for switch control; in this case, it is best to connect two reed switches in parallel at the same location to increase the safety factor.
Float switches offer the advantages of simplicity and convenience. However, there are also cases where the locking mechanism does not function properly, and the balls tend to crack under vacuum conditions.
Float switches have a simple structure, are easy to maintain, and are cost-effective. The value for money is quite good. It can be used in most ordinary situations.
Our unit has encountered several instances where the magnetic steel inside the float switches used for steam bubble level detection lost its magnetism (the temperature inside the bubbles was no more than 150 degrees at that time; it was later found that the quality of the magnetic steel in these products was poor, causing them to lose their magnetism even at temperatures below those specified for operation), which led to false alarms. We later switched to products from another manufacturer, and they have been functioning properly ever since.