28
www.Daniel.com
SERIES 1200 LIQUID TURBINE METER
Table 2-2: Environmental conditions
(continued)
Parameter type
Description
Proximity to open flame
Provide fire prevention measures and equipment per local
regulations.
Proximity to vehicular traffic
The design of the turbine meter has not been assessed for the
effects of traffic loads.
2.1.3
Operating parameters for the LTM
Turbulant flow is detrimental and affects turbine meter linearity
(1)
. It can cause non-
homogeneous fluid cross-section and inconsistant back pressure, possibly resulting in
cavitation
(2)
. To correct the flow characteristics, use upstream and downstream piping
lengths per
Figure 2-3
).
Pipe fittings such as elbows and tees, and piping components such as valves and strainers
should be located far enough upstream to dissipate any flow disturbance before it reaches
the turbine meter. The use of flow straighteners or a flow conditioning plate greatly
influences turbine meter performance.
Specific gravity
The turbine meter is affected by specific gravity which may influence performance. The
effect of specific gravity on the turbine meter may be evidenced when it is below 0.7. As
specific gravity decreases, the lift forces on the turbine blade decreases. Likewise as
velocity decreases, lift forces decrease. These reduced lift forces are overtaken by bearing
friction as low rates are approached. Subsequently, linearity deteriorates at low flow rates
while measuring light fluids.
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
(1)
Linearity is the total range of deviation of accuracy, expressed as a curve, between minimum and maximum flow rates.
The ideal accuracy curve of a volumetric meter, such as the turbine, is a straight line denoting a constant meter factor.
(2)
Cavitation is the formation and collapse of vapor-filled cavities that result from a sudden decrease and increase in
pressure. Refer to
Back pressure calculation
for more information.
User manual
Operating conditions and specifications
P/N 3-9008-513
September 2020
User manual
31