Document zoBwdXJqwGL5mzkr7O69v56n3

American Society of Heating and Ventilating Engineers Guide, 1929 tOAm M# Steam driven pumps can be economically used with steam pressures of 15 lb. or over and where the exhaust steam can be completely utilized. Where the supply of exhaust steam from engines or other sources is continuously in excess of that necessary to supply the heating system the electric driven pump is generally the most efficient and is also pre ferable when the steam pressure is too low to operate a steam driven pump. Steam cylinder sizes of reciprocating vacuum pumps should include the effect of frictional resistance of the piping system, the pump resistance and the possible drop in steam pressure under unusual conditions. When this analysis is not feasible the following formula may be used: 4S = 3 ^~2 ~ fd^ in which Ab = area of steam piston in square inches. Aw = area of water piston in square inches. Pb = boiler pressure in pounds per square inch. Pd = discharge pressure in pounds per square inch. V = vacuum at pump expressed in inches of mercury. -- = approximate vacuum in pounds per square inch (2 in. mercury = approximately 1 lb. per square inch). Water cylinder sizes of steam driven reciprocating vacuum heating pumps may be determined from Table 14. The discharge from reciprocating vacuum heating pumps should be pro vided with means for releasing the entrained air. This may require water 298 Chapter XVIII--Pumps and Traps for Heating, and Ventilating Equipment surface area in either a tank having a large horizontal cross section or a stand pipe of sufficient sectional area to permit a low velocity of downward water flow while the entrained air is escaping to the surface against the water current. For removal of air in a separating tank 1 sq. ft. of hori zontal cross section for each 2100 lb. of water per hour should be provided. When a stand pipe is used for air separation, one with a diameter equal to that of the pump cylinder is usually sufficient. The freely vented air separating tank is preferable wherever a suitable location is available. The tank should be located at such a height that the pressure produced by the water column in its discharge pipe will be sufficient to overcome that in the low-pressure boiler feed water heater or other point of disposal. Fig. 5 shows an arrangement which may be used for vacuum pump, air separating tank and feed water heater. This arrangement provides means for the air to escape through a vent in the top of the tank and for the water to flow by gravity to the. feed water heater, through the loop seal attached to the discharge outlet of the tank. If the rate of flow of returns to the tank exceeds the rate of discharge from the tank the excess is permitted to overflow through an opening in the end of the tank, near the top. The hydro-pneumatic type separating tank may be used whenever an open tank cannot be located at a height sufficient to provide gravity head to discharge the tank contents against the maximum pressure in the heater or boiler. A float controlled valve is placed on the air outlet of the separating tank and so arranged that when the water of conden sation has insufficient head to flow by gravity to the point of use, the air will be confined in the upper part of the tank. Its operation is such that when the pump continues to deliver water and air to the tank the pres sure within the tank increases until it becomes sufficient to discharge the water, thus lowering the water line and eventually permitting escape of the surplus air through the float-controlled air valve. The confined air pressure in the tank plus the gravity head in the tank discharge pipe must be sufficient to cause flow to the place of disposition. This confined ^Discharge from VacuumPump ObbeWifve t'Lubncaior Globe Valve By-pass Globe Valves andUnions ^andDripPgn BoilerfeedPump andReceiver Specials (hdsVafve \ , c LiftFfhnq Dra,n *0 Sewer Floor Line Fig. 6. Method of Connecting Vacuum Pump and Automatic Boiler-Feed Pump and Receiver 299