Special Operating Conditions | Metering Orifice
IF LIMITED PRESSURE IS AVAILABLE If 3½"w.c. cannot be spared for metering, larger orifice plates can be selected to take less pressure drop. (See graph on page 4). Part of the pressure drop across an orifice may be recovered. Net recovery, in % of the drop, varies from about 15% for the smallest orifice for any pipe size to about 33% for the largest orifi ce .
Drop across a 2000 plate for 4500 scfh would be about 13"w.c., as read on graph* from the intersection of 2848 equivalent scfh air and the #2000 capacity line.
Or it can be calculated:
( 2848 ) 2 3.5 = 11.84"w.c. 1548†
Chart 1. Temperature Correction Factor
Chart 2. Pressure Correction Factor
1.1
2.2
1
2
0.9
1.8
0.8
1.6
0.7
1.4
0.6
1.2
0.5
1
0
200
400
600
800
1000
1200
0
5 10 15 20 25 30 35 40 45 50 Pressure, psig
Temperature, F
ALTITUDE CORRECTION FACTOR FOR AIR OR GAS
Altitude
Altitude
feet 1500 2000 2500 3000 3500 4000 4500
meters
Factor = √ G
feet
meters
Factor = √ G
457.2 609.6 762.0 914.4
0.983 0.975 0.965 0.958 0.947 0.939 0.932
5000 5500 6000 6500 7000 7500 8000
1524 1676 1829 1981 2133 2286 2438
0.921 0.913 0.905 0.898 0.886 0.878 0.870
1067 1219 1372
Bulletin 8697 Page 20
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