Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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CV Factor 4 5 13.5 15 22.5 Table VI: Recommended Valve Sizes quantity of steam used for a specific coil size varies with the steam pressure (see Table V) and the heat released is the heat of evaporation (latent heat) only. The values in the table are in BTUs per pound of steam. So the quantity of steam required equals the design heating requirement, divided by the heat of evapora- tion of the steam. Design heating requirement(BTUH)/Heat of evaporation (from Table IV) The result, in pounds of steam per hour, can be equated to pipe size as shown in Table V. The condensate generated (condensed steam) must be "trapped," that is, equipped with a steam trap. Steam traps are sized based on pounds per hour times a safety factor. Since the amount of condensate varies with the temperature of the solution, it is wise to use a safety factor of four or better. Trap capacity equals the steam required times four. The condensate piping is smaller than the steam pipe since the condensate is liquid. Some of the condensate will convert back to steam because of condensate temperature and pressure. The use of piping smaller than in. nominal is not rec- ommended since scale and buildup inside the pipe is a factor in all steam lines. We recommend using in. nominal pipe for condensate lines. This size will han- dle up to 1,920 lb/hr with a modest pressure drop. Steam coil valve sizing is usually smaller than the pipe size since a pressure drop across the valve is required for proper operation. Some typical sizes for diaphragm solenoid valves are shown in Table VI. Since the performance of the valve and trap can be affected by foreign matter in the steam, it is wise to place a 100-mesh strainer of the same pipe size as the steam pipe ahead of the valve. Metal steam heaters, when suspended in electrified tanks, may conduct cur- rent through the steam lines to ground so it is a good practice to install non- conductive couplings between the heater and the pipe lines. This can be accom- plished using a proprietary insulating coupling, dielectric union, or section of steam hose. Finally, because some steam heaters may be buoyant (tend to float) when in ser- vice, it is necessary to secure these heaters through the use of ballasts or proprietary Nominal Pipe Size (in.) Flow Rate (gal/min) ½6 ¾ 1 1¼ 1½ Table VII: Water Flow Rates for Various Nominal Pipe Sizes 670 10 20 30 45 Diaphragm Valve Pipe Size (in.) ½ ¾ 1 1¼ 1½ Steam Required (lb/hr) 120 150 400 450 675

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