Badger Meter Vortex Meters - Manual (Page 6)

6 09-VRX-UM-00408 07/12
INSTALLATION
MECHANICAL INSTALLATION
The fl ow meter is shipped completely assembled, tested and ready to install and operate in its permanent location. See Figure
3 for the applicable outline dimensions for the fl ow meter. See the Appendix for additional installation information.
Installation Location
The RNL series fl ow meters use a combination of ultrasonic and vortex shedding technologies to measure volumetric fl ow. An
ultrasonic noise source can interfere with this technique, therefore the meter should not be installed near high intensity ultrasonic
noise sources. Common ultrasonic noise sources include the following:
» Slightly open valves operating with large pressure drops.
» Small pipe leaks in high pressure systems.
» Venturis 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 remembering to keep in mind the straight pipe run requirements as described next.
The sensor should be installed with at least 20 pipe diameters of straight pipe upstream and 10 pipe diameters downstream.
This condition provides a fully developed, symmetrical fl ow profi le that is necessary to obtain accurate and repeatable results.
Shorter upstream/downstream piping may be used, although a shift in calibration may occur. If severe turbulence or distorted
fl ow profi les are present, fl ow straighteners should be used. Consult factory for shorter upstream/downstream confi gurations.
When installing the fl ow meter in a newly constructed process line, a strainer should be installed upstream of the meter to
prevent foreign material from damaging the meter strut or obstructing the fl ow. Damage to the strut could aff ect the accuracy
of the meter.
In order to prevent cavitation, it is important that the required back pressure be maintained. The minimum required back pressure
varies with temperature. See the back pressure calculations in Figure 2. The sensor should be installed using the minimum piping
requirements indicated in Table 1.
Maximum volumetric fl ows are determined by the inside diameter of the pipe and the velocity of the fl uid being measured.
Calculations of minimum and maximum fl ow ranges are based on the pipe being full at all times. See Table 2 for fl ow ranges in
common pipe sizes.
BACK PRESSURE CALCULATIONS
At high fl ow rates, cavitation may occur, causing a fl ow meter to be inaccurate. Cavitation can be prevented by increasing the
back pressure. The following equation determines the minimum back pressure required to prevent cavitation:
P
1
= P
VP
+ 0.03 V ²
where: P
1
= line pressure at the meter PSIA
P
VP
= vapor pressure of the liquid PSIA
V = line velocity FPS
EXAMPLE: In water at 65° F fl owing with a speed of 25 fps, the vapor pressure is 0.3 PSIA.
P1 = 0.3 + 0.03 (25) 2 = 19.05 PSIA If atmospheric pressure is 14.69 PSIA,:
Then P1 = 19.05 PSIA - 14.69 PSIA = 4.36 PSIG
Maintaining a back pressure of 5 PSIG or greater will prevent cavitation.
FIGURE 2 - BACK PRESSURE CALCULATIONS