Float flowmeter: See the beauty of small flowmeter in 5 minutes
Regarding flowmeters, the most common ones are electromagnetic, turbine, vortex, and slightly more complex ones such as orifice flowmeters, which have been mentioned in previous articles. Today our topic is still flowmeters, but what is different from the past is that this flowmeter is a small and beautiful example of flowmeters - float flowmeter .
Principle of float flowmeter
The float flowmeter is also a type of variable area flowmeter. In a vertical cone that expands from bottom to top, the gravity of the float with a circular cross section is borne by the liquid power, so that the float can rise and fall freely in the cone. When the fluid flows through the cone from bottom to top, the thrust S generated by the kinetic energy of the fluid on the float and the buoyancy A of the fluid cause the float to rise. As the annular flow area between the inner wall of the cone and the float increases, the thrust S generated by the kinetic energy of the fluid on the float decreases accordingly. When the sum of the thrust S and the buoyancy is equal to the float's own gravity G, the float is in a state of equilibrium and stabilizes at a certain height. The scale corresponding to the height position indicates the flow value.
Types of Variable Area Flow Meters
The float flowmeter can be divided into transparent tapered tube float flowmeter and metal tube tapered tube float flowmeter according to the tapered tube material.
1. Glass/Plastic Float
The most commonly used material for transparent conical tubes is glass, which is also the common glass tube float. Its advantages are mainly low cost, transparent material, convenient reading of measurement data, and suitable for measurement comparison at multiple sites. The disadvantage is that there are strict requirements for the corrosiveness of the medium and the environmental pressure and temperature. If you are not careful during operation, the glass tube is easy to be broken; therefore, transparent engineering plastics such as polystyrene, polycarbonate, plexiglass, etc. are often used in some occasions, which have the advantage of not being easy to break.
Although the price is relatively cheap, the float flowmeter can generally only read the instantaneous value of the flow rate.
Compared with transparent conical tube float flowmeter, metal tube float can be used for higher medium temperature and pressure, and there is no potential danger of glass tube float flowmeter cone tube being broken. It has the characteristics of small size, large detection range, and easy use. It can be used to measure the flow of liquid, gas and steam, especially suitable for low flow rate and small flow rate medium flow measurement.
In addition, according to whether there is a remote signal output, it can be divided into: local indication type float flowmeter and remote signal output type float flowmeter. Transparent tube float flowmeter is mainly for local indication, equipped with a proximity switch, and outputs the upper and lower limit alarm signal of the flow. Some local indication metal tube float flowmeters have the same appearance as the remote signal output, but the float displacement is transmitted through magnetic coupling, and the local indication is performed after being processed by linearization mechanisms such as connecting rod cams.
The conversion part of the remote signal output type instrument converts the float displacement into current or air pressure analog signal output, which becomes an electric remote float flowmeter and a pneumatic remote float flowmeter respectively.
Application and main production areas of float flowmeter
90% of float flowmeters are widely used in process industries such as electricity, petrochemicals, chemicals, metallurgy, and medicine, as well as utilities such as sewage treatment.
1 In some applications, it is sufficient to monitor the flow rate not exceeding or falling below a certain value. For example, an increase in the flow rate of the cable inert shielding gas indicates a new leak.
2 Glass tube float flowmeters with upper or lower limit flow alarms can be used in places such as circulating cooling and culture tanks where water or air flow reduction and interruption alarms are required.
3. Continuous sampling of analytical instruments for environmental protection atmosphere sampling and process industry online monitoring, and flow monitoring of sampling are also the major service objects of float flowmeters.
4 As an auxiliary instrument for measuring and controlling constant flow in the process industry, such as liquid level, density and other parameters, it is widely used and occupies a considerable share. Remote metal float flowmeter with signal output is often used as flow control detection instrument or pipeline mixing ratio in process industry, such as controlling the ratio of raw water to chemical solution in water treatment process.
