Document 06E22jYnm79Eza9o36ND4LL5n

438 CHAPTER 23 " 1948 Guide Table 10. Return Pipe Capacities for 30 psi Steam Systems3 Capacity Expressed in Pounds pier Hour Pips Sizb Inches x -1 iX , 2 2H3 3H 4 5 6 M 115 230 485 790 1,580 2,650 . 4,850 7,200 10,200 . 19,000 31,000 Drop inPressure--Pounds per 100 Ft in Length H 170 340 710 1,160 2,360 3,900 7,100 10,600 15,000 27,800 45,500 M 245 490 1,025 . 1,670 . 3,400 5,600 10,300 . 15,300 21,600 40,300 65,500 H . 308 615 1,290 2,100 4,300 7,100 12,900 19,200 : 27,000 , 55,500 83,000 -1 365 730 1,530 2,500 5,050 8,400 15,300 22,800 32,300 60,000 98,000 Note: The above table is based on strain at pressures of 0 to 4 psi. the main riser on a down-feed system from Column B, the dry return from Column O, and the wet return from Column N. Notes on Gravity One-Pipe Air-Vent Systems 1. Pitch of mains should not be less than } in. in 10 ft. 2. Pitch of horizontal runouts to risers and radiators should not be less than in. per foot. Where this pitch cannot be obtained runouts over 8 ft in length should be one size larger.than called for in the table. 3. In general, it is not desirable to have a main less than 2 in.. The diameter of the far end of the supply main should not be less than half its diameter at its largest part. 4. Supply mains, runouts to risers, or risers, should be dripped where necessary. 5. Where supply mains are decreased in.size they should be dripped, or be provided with eccentric couplings, flush on bottom. Example 4. Size the one-pipe gravity steam system shown in Fig. 19 assuming that thjs is all there is to the system or that the riser and main shown involve the longest run on the system. Solution. The total length of run actually shown is 215 ft. If the equivalent length of irun is taken at double this, it will amount to 430 ft, and with a total drop of ii psi the drop-per 100 ft will be slightly less than He psi. It would be well in this case to use Pie psi, and this would result in the theoretical sizes indicated in Table 12. These theo- Table 11. Return Pipe Capacities for 150 psi Steam Systems3 Capacity Expressed in Pounds per Hour,. Pips Size Inches . X. l . ix, , ih: 2: 2H; ." '3 3H 4' 5 .6 : M 156 313 650 ;i,070 2,160 3,600 6,500 9,600 13,700 25,600 42,000 Drop in Pressure--Psi per 100 Ft in Length H 232 462 960 1,580 3,300 5,350 9,600 14,400 20,500 38,100 62,500 : a 360 690 1,500 2,460 4,950 8,200 15,000 22,300 31,600 58,500 96,000 H 465 910 1,950 3,160 6,400 10,700 19,500 . 28,700 . 40,500 76,000 125,000 1 560 1,120 2,330 3,800 7,700 12,800 23,300 34,500 49,200 . 91,500 150,000 2 . 890 1,780 3,700 6,100 12,300 20,400 37,200 55,000 78,500 146,000 238,000 Note: The above-table is'based on steam at pressures of 1 to 20 psi.- Steam Heating Systems and Piping: Table 12. Pipe Sizes for One-Pipe Up-Feed System Shown in Fig. 19 Part or Ststem -Section or Pipe Radiation Supplied EDR Sq Fr Theoretical ; Pipe bob - (Inches) Practical Pipe amt (Inches) . Branches to radiators.. 100 2 2 Branches to radiators.. 50 l X IX Riser a to b ' 200 2 2 Riser............................. . b to c 300 m 2X Riser_____ ctod 400 , 2M 2X Riser...................... ......... d to e 500 3 3 Riser............................. e to/ 600 3 3 Runout to riser._______ / tog 600 m m Supply main_______ __ g to h 600 3.. 3 xBranch to supply main h to/ 600 m 3 Dry return main........... / to k 600 i 2 Wet return main_____ ktam 600 i 2 Wet return main_____ tn to n 600 i 2 Wet return main ........ n to,p 600 i . 2. 439 Fig. 19. Riser, Supply Main and Return Main . retical sizesi however, should be modified by not using a wet return less than 2 in. while the main supply, g-h, if from the uptake of a boiler, should be made the full size.of the main, or 3 in. Also the portion of the main k-m should be made 2 in. if the wet return is made 2 in. SIZING PIPING FOR ONE-PIPE VAPOR SYSTEMS Piping for orie-pipe vapor systems is sized so as to permit orily'a'few . ounces pressure drop in the system.' Otherwise, the method follows that outlined for sizing one-pipe gravity systems. SIZING PIPING FOR TWO-PIPE HIGH PRESSURE SYSTEMS ; Steam piping for two-pipe high pressure can be sized for greater pressure drops than that of the return piping. . For a system using steam at 30 psi, the total pressure drop can be 5 to 10 psi and for 150 psi systems, 25 to 30 psi. ' It has been observed that the maximum total pressure in the returns of, a 30-psi system is about 5 psi, and that of a 150-psi system is about 20-psi. The pressure in the return mains is, of course, caused by the discharge of traps, or by leaky traps and by flashing of condensate into steam due to the lower pressure in the return line. The usual practice in the sizing of high pressure returns has been to size on the basis of psi per 100 ft of pipe for 30-psi systems, and 1 psi per 100 ft for 150-psi systems. This is an average figure which corresponds generally to several of the previously published tables for the design of high pressure return piping. Notes on Two-Pipe High Pressure Systems Pitch of mains should riot be less than X inch in 10 feet. ' Pitch of horizontal runouts to risers and heating units should be not less than H indi per foot. .