2000 Hook-up Book

Steam Meters

Meter Location Meters need to be installed in defined lengths of straight pipe to ensure accurate and repeatable performance. These pipe lengths are usually described in terms of the number of pipe diameters upstream and downstream of the meter. For example, an Orifice Plate with a Beta ratio of 0.7 installed after a 90° bend requires a minimum of 28 pipe diameters of straight pipe upstream and 7 downstream. If the pipe diameter is 6", this is equivalent to 14 feet upstream and 3-1/2 feet down stream. If the meter is located down stream of two 90º bends in different planes, then the mini mum straight length required upstream of the meter is 62 pipe diameters or thirty one feet. This can be difficult to achieve, partic ularly in fairly complex pipework systems, and there may not in fact be a location that allows these criteria to be met. This is an important consideration when selecting a meter.

Table 19 shows the minimum pip ing requirements for Orifice Plates as laid down in the US standard ASME MFC-3M togeth er with the manufacturers recommendations for vortex and spring loaded variable area meters. See Figures II-93, 94, 95, 96 (pages 131 and 132).

SYSTEM DESIGN

Table 19: Recommended Minimum Straight Lengths (D) for Various Meter Types

On Upstream (inlet) side of the primary device

Downstream

Meter Type

ß Single Two 90° Bends Two or more 90° Bends Reducer Expander Globe Valve Gate Valve All Fittings Ratio (3) 90° Bend Same Plane Different Planes 2D to D 0.5D to D Fully Open Fully Open in this table

Orifice Plate 0.30 Orifice Plate 0.35 Orifice Plate 0.40 Orifice Plate 0.45 Orifice Plate 0.50 Orifice Plate 0.55 Orifice Plate 0.60 Orifice Plate 0.65 Orifice Plate 0.70 (4) Orifice Plate 0.75 Orifice Plate 0.80

10 12 14 14 14 16 18 22 28 36 46

16 16 18 18 20 22 26 32 36 42 50

34 36 36 38 40 44 48 54 62 70 80 40 12 12 12 12

5 5 5 5 6 8 9

16 16 16 17 18 20 22 25 30 38 54 12 12 12 12

18 18 20 20 22 24 26 28 32 36 44 50

12 12 12 12 12 14 14 16 20 24 30

5 5 6 6 6 6 7 7 7 8 8

11 14 22 30

Vortex (1) Spiraflo (2)

N/A 20 - 40 20 - 40

10 - 20 10 - 35

20 - 40 5 - 10

N/A N/A N/A N/A

6 6 6 6

6 6 6 6

6 6 6 6

6 6 6 6

6 6 6 6

3 - 6 3 - 6 3 - 6 3 - 6

Gilflo (2)

Gilflo SRG (2) Gilflo ILVA (2)

Notes: 1. The table shows the range of straight lengths recommended by various Vortex meter manufacturers. 2. Downstream requirements are 3D and 6D when upstream are 6D and 12D respectively. 3. ß ratio = Orifice diameter (d) divided by Pipe diameter (D) 4. Most Orifice Plates are supplied with a ß ratio of around 0.7 which gives the best pressure recovery without compromising signal strength.

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