Page 59 - Instrumentation Reference Book 3E

44 Measurement of flow

Appendix 1.1 Continued
Miniinurn number of pipe diameters for Cases A to F listed below
(a) Miniinurn length of straight pipe iininediately
upstreaiii of device (b) Minimuin length
between first
Diameter ratio dlD less than: 0.22 0.32 0.45 0.53 0.63 0.7 0.77 0.84 uustreain fitting
_
"
and next upstream
Area ratio m less than: O.Oji 0.1 0.2 0.3 0.4 0.5 0.6 0.7 fitting
X
Case Ht. Gate valve up to
i closed5 (for fully
open see Case B) 40 40 40 41 46 52 60 70 26
Case J$. Globe valve up to
$ closed$ (for fully
open see Case C) 12 14 19 26 36 60 80 100 30
Orher firtifigs
Case K. All other findings
(provided there is
no swirling motion) 100 100 100 100 100 100 100 100 50

See Subclauses 47b and 41c.
t For area ratio less than 0.015; or diameter ratios less than 0.125 see Subclause 47b.
f If swirling motion is eliminated by a flow straightener (Appendix F) installed downstream of these fittings they may be treated as Class F, E,
and C respectively.
0 The vahe is regarded as three quarters closed when the area of the opening is one quarrel- of that when fully open.
NB: Extracts from British Standards are reproduced by permission of the British Standards Instirution, 2 Park Street, London WIA 2BS from
whom complete copies can be obtained.