Technical Guide
August 2007
In some circumstances, the use of a Flow Conditioning Plate (FCP) is possible. The flow conditioning plate is available from 3” to 6” for the Daniel Series 1500 Liquid Turbine Flow Meter, and is standard on the Daniel Series 1200 Liquid Turbine Flow Meter (with the exception of the 1”). When supplied, the FCP is an integral part of the turbine meter. The FCP serves to reduce swirl in the same way as flow straightening sections, and is of particular significance where piping installations do not permit long upstream sections, such as in load racks where space is at a premium.
BACK PRESSURE
It is essential to 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.
The necessary back pressure required is given by the equation:
BP = (meter ∆P X 2) + (VP X 1.25) BP = Back pressure required
∆P = Meter pressure drop at maximum flow
VP = Equilibrium vapor pressure of the liquid at the operating temperature, pounds per square inch absolute (psia), (gauge pressure plus atmoshperic pressure.)
The pulses per unit volume / flow range curves below illustrate the effects of back pressure. Not only does insufficient back pressure lead to measurement inaccuracy, the resultant flashing and cavitation is extremely damaging to the flow meter and pipework.
Figure 14 - Effects of Back Pressure
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