Metal float flowmeterUsed for small diameters and low flow rates. Commonly used instruments have a diameter of 40-50mm or less, with a minimum diameter of 1.5-4mm. They are suitable for measuring low flow rates and small flow rates. Taking liquids as an example, the nominal diameter of a glass tube float flowmeter with a diameter of 10mm or less for full flow rates is only between 0.2-0.6m/s, or even below 0.1m/s; Metal tube float flow meters and glass tube float flow meters with a diameter greater than 15mm are slightly higher, with flow rates between 0.5-1.5m/s.
Float flow meters can be used for lower Reynolds numbers, using floats with viscosity insensitive shapes. As long as the Reynolds number at the flow annulus is greater than 40 or 500, the flow coefficient remains constant when the Reynolds number changes, meaning that changes in fluid viscosity do not affect the flow coefficient. This value is much lower than the low Reynolds number requirement of standard orifice plate and other throttling differential pressure instruments of 104-105.
Most float flowmeters do not require an upstream straight pipe section, or in other words, do not have high requirements for the upstream straight pipe section.
Float flow meters have a wide flow range, generally 10:1, with a low of 5:1 and a high of 25:1. The output of the flow detection component is close to linear. Low pressure loss.
The glass tube float flowmeter has a simple structure and is inexpensive. As long as the flow indicator is convenient to use on site, the disadvantage is the risk of glass tubes being fragile, especially for unguided floats used for gas.
The metal tube float flowmeter has no risk of cone tube rupture. Compared with glass tube float flow meters, it has a wide range of temperature and pressure usage.
Most structural float flow meters can only be used for pipeline installation with vertical flow from bottom to top.
The application of float flow meters is limited to small and medium-sized pipe diameters. Ordinary full flow float flow meters cannot be used for large pipe diameters. The maximum diameter of glass tube float flow meters is 100mm, while metal tube float flow meters are 150mm. For larger pipe diameters, only shunt type instruments can be used.
When the fluid used is different from the factory calibrated fluid, flow indication correction should be performed. Float flow meters for liquids are usually calibrated with water, while those for gases are calibrated with air. If the actual fluid density and viscosity are different, the flow rate may deviate from the original division value and require conversion correction.