Badger Meter Vortex Meters - Manual (Page 20)

20 09-VRX-UM-00408 07/12
Velocity Profi le for RNL Insertion Meters
When using an RNL series insertion fl ow meter, it is necessary to consider the eff ects of the velocity profi le across the pipe or
duct to optimize accuracy.
In large pipes, the fl ow moves slowly at the pipe walls but is at maximum velocity in the center of the pipe creating a continuously
variable velocity across the pipe. This velocity variation is called the velocity profi le of the pipe, and can be measured and plotted
by using the insertion fl ow meter to measure velocities at various noted positions across the pipe. As the maximum velocity is
in the center of the pipe, it follows that if the fl ow meter is positioned in the center, it will not measure average fl ow. The “rule
of thumb” position is 25% of the pipe ID into the pipe, but the optimum position can only be obtained by measuring the profi le
and working out the correct position from that.
Straight-Run Piping Considerations
The sensor should be installed with 20 diameters, or more, of straight, unobstructed, full area pipe upstream of the fl ow meter
installation and 10 diameters, or more, downstream. This condition provides a fully developed, symmetrical fl ow profi le that is
necessary to obtain accurate and repeatable results. The fi rst obstruction up and downstream should be a full area elbow. If the
minimum straight run is not possible, the general rule is to have 80% of the straight run upstream and 20% downstream from
the fl ow meter installation.
High intensity ultrasonic noises should not be located upstream or downstream from the sensor. Common ultrasonic noise
sources include the following:
● Slightly cracked valves operating with large pressure drops.
● Small pipe leaks in high pressure systems.
● Venturies operating at near-sonic fl ow rates.
● Sonic nozzles.
If these ultrasonic noise sources cannot be eliminated, the meter should be mounted with at least one elbow between the fl ow
meter and the noise source.
Temperature and Pressure Tap Locations
User supplied pressure and temperature sensors should be mounted downstream from the fl ow meter. The pressure sensor
should be approximately 3-5 pipe diameters and the temperature sensor approximately 4-8 pipe diameters downstream.
RNL Insertion Style Meter Installation
The RNL series fl ow meter is shipped completely assembled, tested and ready to install and operate in its permanent location.
If the main line can be depressurized easily without undue user inconvenience, then a simple installation, consisting of a 2 inch
(51 mm) nozzle and a standard ANSI 150 pound, 2 inch pipe fl ange may be used. This permits the shortest shaft length to be used,
which keeps clearance space requirements for insertion and removal to a minimum. Gaskets (not provided) are necessary between
the sensor and ANSI fl ange. It is recommended that the customer conduct a fl ow profi le survey prior to installing fl ow meter.
DANGER - Caution should be used when inserting or retracting at pressures exceeding 60 PSIG (4.14 BARg).