McQuay IM 685, Installation & Maintenance Manual

Page: 6 / 32

Page 6 / IM 685
Valve and Regulator Venting
Valve diaphragm vents, pressure regulator vents, and pressure switch vents are located in the outdoor
burner vestibule and therefore vent tubing is not run to the outside of this vestibule. If local regulations
require that this be done, it is a part of the field gas piping hookup. Remove any plastic protector plugs
from regulator and valve vents.
Normally Open Vent Valve
Vent valves such as required by IRI for over 1000 MBH input units must always be routed to the
outdoors. This is field piping.
Table 1. Capacity of Pipe Natural Gas (CFH)
WITH PRESSURE DROP OF 0.3" W.C. & SPECIFIC GRAVITY OF 0.60
PIPE
PIPE SIZE–INCHES (IPS)
LENGTH (FT.)
1 ⁄
2
3 ⁄
4
1 1 1 ⁄
4
1 1 ⁄
2
2 2 1 ⁄
2
3 4
10 132 278 520 1050 1600 2050 4800 8500 17500
20 92 190 350 730 1100 2100 3300 5900 12000
30 73 152 285 590 890 1650 2700 4700 9700
40 63 130 245 500 760 1450 2300 4100 8300
50 56 115 215 440 670 1270 2000 3600 7400
60 50 105 195 400 610 1150 1850 3250 6800
70 46 96 180 370 560 1050 1700 3000 6200
80 53 90 170 350 530 990 1600 2800 5800
90 40 84 160 320 490 930 1500 2600 5400
100 38 79 150 305 460 870 1400 2500 5100
125 34 72 130 275 410 780 1250 2200 4500
150 31 64 120 250 380 710 1130 2000 4100
175 28 59 110 225 350 650 1050 1850 3800
200 26 55 100 210 320 610 980 1700 3500
Note: Use multiplier below for other specific gravities and pressure drops.
Table 2. Specific Gravity Other than 0.60
Table 3. Pressure Drop Other than 0.3"
PRESSURE
MULTIPLIER
PRESSURE
MULTIPLIER
DROP DROP
0.1 0.577 1.0 1.83
0.2 0.815 2.0 2.58
0.3 1.000 3.0 3.16
0.4 1.16 4.0 3.65
0.6 1.42 6.0 4.47
0.8 1.64 8.0 5.15
SPECIFIC GRAVITY MULTIPLIER
0.50 1.100
0.60 1.000
0.70 0.936
0.80 0.867
0.90 0.816
1.00 0.775