Document DvXD09QQ6bwEv5Ln381M9DpOB

American Society of Heating and Ventilating Engineers Guide, 1934 Cr o p y r.ig. .h.t j A merican Hewing, P Society iping and or Ai A r bating and Conditioning Ventilating Engineers Contractors National Auociation N J o t tof l b R evp rin te d W ith o u t S p e c ia l Perm ission Chapter 32--Steam System Piping Example 2. What pressure drop should be used for the steam piping of a system if the measured length of the longest run is 500 ft and the initial pressure is not to be over 2 lb gage? Solution. It will be assumed, if the measured length of the longest run is 500 ft, that when the allowance for fittings is added the equivalent length of run will not exceed 1,000 ft. Then, with the pressure drop not over one-half of the initial pressure, the drop could be 1 lb or less. With a pressure drop of 1 lb and a length of fun of 1,000 ft, the drop per 100 ft would be Mo lb, while if the total drop were M lb, the drop per 100 ft would be Mo lb. In the first instance the pipe could be sized according to Column D for Ms lb per 100 ft, and in the second case, the pipe could be sized according to Column C for Yu lb. On completion of the sizing, the drop could be checked by taking the longest line and actually calculating the equivalent length of run from the pipe sizes determined. If the calculated drop is less than that assumed, the pipe size is all right; if it is more, it is probable that there are an unusual number of fittings involved, and either the lines must be straightened or the column for the next lower drop must be used and the lines resized. Ordinarily resizing will be unnecessary. SIZING ONE-PIPE GRAVITY AIR VENT SYSTEMS One-pipe gravity air vent systems in which the equivalent length of run does not exceed 200 ft should be sized as follows: 1. For the steam main and dripped runouts to risers where the steam and condensate flow in the same direction, use Ye lb drop (Column D). 2. Where the riser runouts are not dripped and the steam and condensation flow in opposite directions, and also in the radiator runouts where the same condition occurs, use Column L. 3. For up-feed steam risers carrying condensation back from the radiators, use Column J. 4. For down-feed systems the main risers of which do not carry any radiator con densation, use Column H. 5. For the radiator valve size and the stub connection, use Column K. 6. For the dry return main, use Column U. 7. For the wet return main use Column T. On systems exceeding an equivalent length of 200 It; it is suggested that the total drop be not over 34 lb- The return piping sizes should correspond with the drop used on the steam side of the system. Thus, where M4 lb drop is being used, the steam main and dripped runouts would be sized from Column C; radiator runouts and undripped riser runouts from Column L; up-feed risers from Column J; the main riser on a down-feed system from Column C (it will be noted that if Column H is used the drop would exceed the limit of Ml lb); the dry return from Column R; and the wet return from Column Q. With a Mrlb drop the sizing would be the same as for M4 lb except that the steam main and dripped runouts would be sized from Column B, the main riser on a down-feed system from Column B, the dry return from Column 0, and the wet return from Column N. Example 3. Size the one-pipe gravity steam system shown in Fig. ! assuming that this is all there is to the system or that the riser and fun shown involves .the longest run on the system. Solution. The total length of run actually shown, is 215 ft.' If the equivalent length of run is taken at double this, it will amount to 430 ft, and with a total drop of M lb the drop per 100 ft will be slightly less than M6 lb.' It would be well in this case to use Hi lb, and this would result in the theoretical sizes indicated in. Table 9. These, theo-