Meriam 70H_72H High Pressure Wet Tap Accutubes with Integral 3-Valve Head and Optional RTD - Manual (Page 5)

6
1 SYSTEM CONSIDERATIONS
1.1 Selection of the proper location and position of the Accutube flow sensor within the
piping system is important. The first consideration is to locate the Accutube with proper
upstream and downstream straight pipe runs. This is required to assure a fully developed
symmetrical flow profile at the Accutube. Accuracy can be affected if sufficient piping
is not provided. Table 1 shows recommended straight run requirements with various
types of upstream flow disturbances. For inline series sensors the straight pipe run must
be of the same schedule/I.D. as the Accutube.
TABLE 1
RECOMMENDED STRAIGHT RUNS OF PIPE
(Upstream Length in Terms of Internal Diameter of Pipe - See Notes)
UPSTREAM
FLOW
DISTURBANCE WITH
STRAIGHTENING
VANES
WITHOUT
STRAIGHTENING
VANES-IN-PLANE
WITHOUT
STRAIGHTENING
VANES-OUT-PLANE
ONE ELBOW
OR TEE 6 - 8 8 - 10
TWO 90 ° BENDS IN
SAME PLANE
8 - 10 12 - 15
TWO 90 ° BENDS
DIFF. PLANE
10 - 12 24 - 28
REDUCERS OR
EXPANDERS 8 - 10 8 - 10 8 - 10
ALL VALVES
(SEE NOTE 3) 10 - 12 24 - 28 24 - 28
Note 1: Downstream straight run of pipe should be a minimum of 4 to 5 internal diameters.
Note 2: The values listed in Table 1 are acceptable for most applications. Additional lengths are
recommended where precise measurements are desired.
Note 3: Recommendations for valve disturbances are for non-throttling (fully open) position
only. The Accutube should not be located downstream of a throttling valve.
Note 4: Straightening vanes (where used) shall be installed 2 diameters downstream of the
upstream flow disturbance.
Note 5: Deviations from the above recommendations will normally not affect repeatability of the
flow signal.
Note 6: Combination of various types of fittings can cause severe flow distortion, the results of
which are unpredictable. Installations with fitting combinations other than those listed
above should be approached with caution. Flow straightening vanes are strongly
recommended to insure accurate flow measurement.