How to Trap Steam Distribution Systems - Armstrong International, Inc.

How to Trap Steam Distribution SystemsFor traps installed between the boiler and the end of the steammain, apply a 2:1 safety factor. Apply a 3:1 safety factor fortraps installed at the end of the main or ahead of reducingand shutoff valves that are closed part of the time.The inverted bucket trap is recommended because it canhandle dirt and slugs of condensate and resists hydraulicshock. In addition, should an inverted bucket fail, it usuallydoes so in the open position.Installation. Both methods of warm-up use drip legs andtraps at all low spots or natural drainage points such as:Ahead of risersEnd of mainsAhead of expansion joints or bendsAhead of valves or regulatorsChart CG-7. Btu Heat Loss CurvesBTU PER SQ FT PER HOUR PER °F TEMPERATURE DIFFERENCETEMPERATURE DIFFERENCE150° 160° 180° 200° 240° 300° 400° 500° 700° 900° 1050°1110987654.54.03.53.33.02.82.62.52.42.32.22.15PSIG5.31"2"3"5"6"10"10.315.3FLAT SURFACES25.350.375.3100.3150.3250.3450.3600.3900.31500.32400.3PRESSURE IN LBS PER SQUARE INCH1110987654.54.03.53.33.02.82.62.52.42.32.22.152.10Install drip legs and drain traps even where there are nonatural drainage points (See Figs. CG-29, CG-30 and CG-31).These should normally be installed at intervals of about 300'and never longer than 500'.On a supervised warm-up, make drip leg length at least1-1/2 times the diameter of the main, but never less than10". Make drip legs on automatic warm-ups a minimum of28" in length. For both methods, it is a good practice to usea drip leg the same diameter as the main up to 4" pipe sizeand at least 1/2 of the diameter of the main above that, butnever less than 4". See Table CG-13.Table CG-13. Recommended Steam Main and Branch Line Drip Leg SizingMSteam MainSize (in)Chart CG-8. Recommendation Chart(See Page CG-2 for “Feature Code” References.)Equipment BeingTrappedSteam Separator1st Choice andFeature CodeIBLVB, M, L, E, F, N, Q*DC is 1st choice where steam quality is 90% or less.DDrip LegDiameter (in)Drip Leg Length Min. (in)SupervisedWarm-UpAutomaticWarm-Up1/2 1/2 10 283/4 3/4 10 281 1 10 282 2 10 283 3 10 284 4 10 286 4 10 288 4 12 2810 6 15 2812 6 18 2814 8 21 2816 8 24 2818 10 27 2820 10 30 3024 12 36 36HAlternate Choice*DCSteam MainsMMDDrip leg sameas the headerdiameter up to4''. Above 4'',1/2 header size,but never lessthan 4''.HH24CG-19Figure CG-29.Trap draining strainer ahead of PRV.Figure CG-30.Trap draining drip leg on main.Figure CG-31.Trap draining drip leg at riser. Distance“H” in inches ÷ 28 = psi static head forforcing water through the trap.Armstrong Steam and Condensate Group, 816 Maple St., P.O. Box 408, Three Rivers, MI 49093 – USA Phone: (269) 273-1415 Fax: (269) 278-6555www.armstrong-intl.com