Requirements | 8695 Orifice Plate
Bulletin 8695 Page 4
STRAIGHT PIPE RUN REQUIREMENTS The minimum straight pipe lengths required are the lengths between various fittings located upstream or downstream of the orifice plate itself. Additional uncertainty or loss of accuracy cannot be predicted when straight lengths are shorter than the values listed in Table 1 (values expressed as multiples of internal diameter, D). It is recommended that control valves are located downstream of the orifice plate. The valve listed in Table 1 is a full bore valve in the wide open position. Per Table 1, straight lengths are to be measured from the downstream end of the curved portion of the nearest (or only) bend, or of the tee, or the downstream end of the curved or conical portion of the reducer or expander. The bends on which the lengths in this table are
based on had a radius of curvature equal to 1.5 D . Column A for each fitting gives lengths corresponding to "zero additional uncertainty" values. Column B for each fitting gives lengths corresponding to "0.5% additional uncertainty" values. Values are based on International Standard Table 3-ISO 5167-2:2003(E) and are for reference only. For more precise measurement or for other fittings and the limitations of the separation between the two bends and appropriate lengths of reducers and expanders see the ISO 5167-2 standard. A flow conditioner will permit the use of shorter upstream pipe runs. For specific installation conditions not covered in this literature please contact North American.
Table 1
Single 90º tee with
Full bore ball valve
Single 90º bend
Single 45º bend
β ratio
or without extension Mitre 90º bend
Two 90º bends in the same plane
Down- stream (outlet) side
Abrupt symmetrical reduction
Concentric expander
Concentric reducer
Two 90º bends in any plane
Two 45º bends in the same plane
Gate valve fully open
d/D
A B
A
B
A 3 9
B 3 3
A
B
A
B 6 6 6 7 9
A 5 5 8 9
B 5 5 5 5 6 8
A
B 6 8 9
A
B
A 4 6 6 7 7 8
B 2 3 3
<=0.20 6 3 0.40 16 3 0.50 22 9 0.60 42 13 0.67 44 20 0.75 44 20
10 10 10 10 18 10 30 18 44 18 44 18
7
7
12 12 12 14 18
6
30 15 30 15 30 15 30 15 30 15 30 15
30 9 30 18 30 18 44 18 44 18
12 20 26
19 9 29 18 36 18 44 18
11
3.5 3.5
12 13
28 14 36 18
24 12
4
ORIFICE PLATE SIZING Differential pressure transmitters are frequently used for measuring differential pressure across an 8695 orifice plate. When sizing an 8695 plate for use with a transmitter, be sure to size the plate for the maximum design flow conditions. When selecting an appropriate span for the differential pressure transmitter add 10% to the maximum design flow. Next, find the differential pressure for the 10% added flow. That differential pressure will be the span you will want to select for your transmitter. To prevent the transmitter from being “saturated” at the maximum expected flow (See the 8246-A bulletin for more information on transmitters).
Another parameter to consider when sizing an orifice plate is the required flow turndown of the system. To reliably measure the differential pressure across the orifice plate at the minimum flow setting the differential pressure transmitter has to be capable of reading that value. So, when sizing the plate make sure the differential pressure at maximum flow is high enough that an accurately measureable differential is available at low fire.
CONTACT fna.sales@fivesgroup.com T +1 800 626 3477 - F +1 216 373 4237
Fives North American Combustion, Inc. 4455 East 71st Street - Cleveland, OH 44105 - USA www.fivesgroup.com
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