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American Society.of Heating and Ventilating Engineers Guide, 1924-25 Vent toAtmosphere Run to Air above Roof Pump Control Valve Discharge from Pump to Tank Steam to (J. Vacuum Pump Globe Valve Globcr Valve . Lubricator, Globe \hlve' dorterFeedPump CastIron 8ase Plate *+ and Drip Pan Lubricator ' Ofobe Valve Globe Valve By-pass s' GateVatve/' Suetton Strainer Lift Fitting ' ToSewer -Vacuum Pump CastIron Base Plate , and Drip Pan Floor Line Fig. 19. Method of Connecting Vacuum Pump, Boiler-Feed Pump and Steam-Control Receiving Tank Fig. 20. Method of Making Connection to Steam-Operated Vacuum Pump 82 American Society of Heating and Ventilating Engineers Guide, 1924-25 water current. For removal of air, allowance of 1 sq. ft. of horizontal cross section for each 2100 lb. of water per hr. should be made. A stand pipe with diameter equal to that of the pump cylinder is usually suf ficient. I Wherever a suitable location may be obtained the freely vented air separating tank is generally used. The tank must be located high enough so that the pressure produced by the water column in the discharge pipe will be sufficient to overcome that in the low pressure boiler feed water heater or other point of disposal. Where an open tank cannot be located at a height sufficient to provide gravity head to discharge the tank contents against the maximum pres sure in the heater or boiler, the hydro-pneumatic tank can be used. A float controlled valve is placed on the air outlet of the separating tank and so arranged that when the water of condensation has not sufficient head to flow by gravity to the point of use, the air will be confined in the upper part of the tank. As the pump continues to deliver water and air to the tank the pressure within the tank increases until sufficient to discharge the water, thus lowering the water line and eventually per mitting 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 air pressure plus the column of mixed air and water in the pump discharge to the tank is the total head against which the pump must act. Figs. 18, 19 and 20 show vacuum pump connections for several different conditions of service. In no case should the head against the discharge of reciprocating pumps exceed 15 lb. unless the pump stroke exceeds the bore and thus reduces the bad effect of clearance. Where the pressure on the heater, boiler, etc., varies materially from time to time but in general is near the minimum, a substantial saving in energy may be obtained by using a hydro-pneumatic tank instead of a plain tank set at a higher elevation to overcome the peak pressure in the boiler or heater. The use of a plain tank keeps the pump operating against the maximum head, where the hydro-pneumatic tank set lower operates as a plain tank whenever the gravity head in the tank is sufficient to cause flow from its elevation, and employs the combination of air pressure and gravity head, with air vent closed, only at times of peak load. Only then is the air pressure load added to the pump discharge. Where the head on the delivery side of steam driven pumps exceeds 15 lb. it is good practice to deliver the condensation to a vented receiver located close to the level of the vacuum pump outlet. This receiver should be connected to a separate steam or power driven water pump capable of delivering against the maximum head and controlled by a throttle valve, actuated by the water line in the receiving tank. Table 64 gives the sizes of plain or hydro-pneumatic tanks for air separating purposes and also those for storage of returns. In the latter case the tanks are based upon storing the quantities of water which will be discharged during five minutes at the basis of hourly rates given in the first column. 83