Combustion Catalog | Fives North American

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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