Document 3ex2a3VzRBz2OG6dVeby9RXgy

HEATINC VENTILATING AIR CONDITIONING GUIDE 1942 and the normal size of drop required is 1 in. or less. The bottom of each steam drop should terminate with a dirt pocket and be dripped as shown in Fig. 10. The returns on a down-feed vapor system are the same as on an up-feed system. The runouts to the radiators and the radiator con nections of. the down-feed system are the same as those for the up-feed system already described. CONDENSATION RETURN HEATINC SYSTEMS When automatic condensation return pumps are substituted for the gravity return of a two-pipe vapor system they are known as return systems or return pump heating systems. A typical installation of a motor driven automatic condensation unit is illustrated in Fig. 11. It will be noted that the returns are graded to cause flow by gravity to the vented receiver. As the receiver is filled, the float mechanism operates either a pilot or an across-the-line switch to start the pump and, upon emptying CHAPTER 14. STEAM HEATING SYSTEMS pump withdraws the air and water from the system, separates the air from the water and expells it to atmosphere and, pumps the water back to the boiler, or other receiver, which may be a.feed-water heater or hot well. It is essential that no connection be made from the supply side to the return side at any point except through a trap. The desirable practice demands a return flowing to the vacuum pump by an uninterrupted down ward slope. In some instances local conditions make it necessary to drop the return below the level of the vacuum pump inlet, before, the pump can be reached. In such an event one of the advantages of the vacuum system is the ability to raise the condensate to a considerable height by the suction of the vacuum pump by means of a lift connection or fitting inserted in the return. The height the condensate can be raised depends on the steam pressure and the amount of vacuum maintained. It is Fig. 10. Detail of Drip Connections at Bottom of Down-Feed Steam Drop. the tank, to disconnect the power and stop it. The pump may be used to deliver the condensate direct to the boiler, to a feed water heater or to raise the water to any higher elevation or pressure than that of the return line. A useful application is a small condensation unit to handle a remote section of radiation that otherwise would be difficult to grade to the main return; VACUUM SYSTEMS In the vacuum system, a vacuum is maintained in the return line practically at all times. The pump is usually controlled by a vacuum regulator which operates the pump to maintain the vacuum within limits and operates in response to a pressure difference between-the atmosphere and the return.to control the vacuum in the return main, The source of steam supply may be a low pressure boiler as shown in Fig. 12,'or a high pressure line through a pressure reducing valve. The piping and other details are the same as for the vapor systems. The return risers are connected in the basement into a common return main which slopes downward toward the vacuum pump. The vacuum 274 Fig. 11. Typical Installation Using Condensation Pump preferable to limit lift connections to a single lift at the vacuum pump. A still more preferable arrangement is the use of an accumulator tank, or receiver tank, with a float control for the pump at the low point of the return main located adjacent to the vacuum pump. When the vertical lift is considerable, several lift fittings should be used in steps as shown in Fig. 13. This permits a given lift to be secured with a somewhat lower vacuum than where the vertical distance is served by a single lift. Where several lifts are present in a given system at different locations, the lifting cannot occur until the entire system is filled with steam. A lift connection for location close to the pump, where the size may be above the commercial stock sizes, is shown in Fig. 14. . It is desirable that means be provided for manually draining the low point of the lift fittings to eliminate from the return piping all water in danger of freezing-in case the system is shut.dowri for a considerable length of time.- 275