The term swirl is used to describe the rotational velocity or tangential velocity component of fluid flow in a pipe or tube. Depending on its degree and direction, swirl will change the angle of attack between the fluid and the Precision Turbine Flow Meter (PTF) rotor blades, causing a different rotor speed at a constant flow rate to non-swirling conditions at the same flow rate.
Liquid swirl and non-uniform velocity profiles may be introduced upstream of the PTF by variations in piping configurations or projections and protrusions within the piping. Swirl may be effectively reduced or eliminated through the use of sufficient lengths of straight pipe or a combination of straight pipe and straightening vanes or a straightening plate installed upstream of the PTF. 10 upstream diameters and 5 downstream diameters of straight pipe are recommended as part of the installation process.