pOSITIVE dISPLACEMENT fLOW METERS
Method
Positive displacement flowmeters measure flow rates by filling an internal chamber with a known volume of liquid, then releasing it downstream before refilling. Each fill-and-release cycle generates an electrical pulse, which is counted to calculate both the total volume and the flow rate. These meters are especially accurate at low flow rates and can handle a wide range of liquids, including those that are unusually light or heavy, which might not be detected by other measurement methods.
Oval Gear Flow Meters
Oval gear flow meters consist of two oval-shaped gears in a specialized cavity. As the liquid pressure increases, it forces the liquid between the gears, causing them to rotate. Sensors detect this rotation and generate pulses proportional to the flow rate, offering high accuracy, especially at low flow rates.
Piston Flow Meters
Piston flow meters feature a precisely measured chamber and a mechanical piston. As liquid pressure builds in the chamber, it pushes the piston back, allowing the chamber to empty. A spring then resets the piston, readying it for the next cycle.
Advantages
- Capable of handling very high-viscosity liquids
- Accurate even at extremely low flow rates
- Ideal for lubricating systems and oil flow applications
Disadvantages
- High cost for larger sizes
- Requires very clean, filtered, or strained liquids
- Can cause high-pressure losses
- Risk of seizing or clogging, potentially blocking flow; however, many models include emergency bypass valves to allow some flow through a clogged meter