Viscosity
Turbine meters are viscosity sensitive. As the metered fluid increases in viscosity, meter
linearity declines. This effect on linearity is primarily due to a change in the fluid's velocity
profile and skin friction between the fluid and the rotor blades.
Viscosities of 3 centipoise or less are seldom cause for concern. Consider all influential
factors of higher levels. By anticipating the viscosity, maximum flow rate, flow range and
desired linearity of the flow system, the user is able to determine the appropriate turbine
meter for the application.
Back pressure
Maintain sufficient back pressure on the turbine meter to prevent flashing and cavitation.
This is particularly important when measuring liquids with high vapor pressures, such as
LPGs.
Equation 2-1: Back pressure calculation
P
b
≥ 2Δp + 1.25p
e
P
b
Minimum back pressure, pounds per square inch gauge (psig)
Δp
Pressure drop through the meter at the maximum operating flow rate for the liquid
being measured, pounds per square inch (psi).
P
e
Equilibrium vapor pressure of the liquid at the operating temperature, pounds per
square inch absolute (psia), gauge pressure plus atmospheric pressure.
illustrates the effects of back pressure. Insufficient back pressure leads to measurement
inaccuracy. The resulting flashing and cavitation is extremely damaging to the flow meter
and pipe work.
Operating conditions and specifications User manual
March 2019 P/N 3-9008-515
44 Daniel Series 1500 Liquid Turbine Meter, NPS 3-24
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