Document NN2Epg24oVjDwJbkxeb7YQmMR

492 CHAPTER 23 ; . 1949 Golds Steam Heating Systems and Piping ; . \ 493 high to allow gravity flow of the condensate, to the boiler. If the boiler pressure is too high for such gravity feed, then an additional steam pump for feeding the boiler is desirable! The extra pump is sometimes avoided by using a closed separating tank with a float controlled vent... In. both arrangements, the air taken from the system must be discharged against the full discharge pressure of the vacuum pump. In the case of high or medium pressure boilers, it is better to use the atmospheric separator and the second pump. : ' ,. ,! . In .figuring the required displacement, for such pumps,, a value, of from 6 to 10 times the volumetric flow of. condensate.is.used for, average vacuums and systems. . ... ; ........ . STEAM TRAPS ' Steam traps,- as the name implies, are automatic devices'used to trap or hold steam in an apparatus or piping system until-it has given up its latent heat, and to allow condensate and air to pass as soon as it accumu lates. In general traps consist of a vessel jn which to accumulate' the condensate, an orifice through which the condensate is discharged; a valve to close the orifice: port, mechanisms to operate the valve, and inlet and outlet openings for ,the entrance,and discharge of the condensate from-the trap vessel.. t .... Steam traps are classified according to the type of operating; device by which they function. The traps which are available on the market today may be classified as (1) float, (2) thermostatic, (3) float and thermostatic, (4) upright bucket, (5) inverted bucket; (6) flash, (7) impulse, (8)- tilting, (9) lifting, and (10)! boiler return-trap or alternating receiver. - ' Float Traps. Float traps operate by the rise and fall of a float due to a change of condensate level in the trap. When the trap is empty,' the float is in its lowest -position and .the discharge valve is closed. As condensate accumulates in the'trap Fio. 25. Typical Float And Thermostatic Trap V ... ' . ' . chamber, the float rises and gradually opens the valve and the pressure of the steam pushes the condensate out .of the valve. .The discharge from a float trap is generally continuous, since .the opening of the valve is proportioned to the flow of condensate through the trap. A gage glass may be usea to indicate the height of condensate . in the trap chamber. . Unless float traps .are1 well made and proportioned, there is danger, of considerable steam leakage through the discharge valve due to unequal- expansion, of the valve and Beat and the sticking of moving parts. Float traps are made in sixes from I to 3 in., and for pressures varying from vacuum conditions to 200 psig. Float traps are used for draining condensate from steam separators, steam headers, blast coils, heating systems, steam water heaters, laundry equipment, sterilizers, and other - equipment. When used for draining low pressure systems, float traps should be equipped with a thermostatic air vent (See Float and Thermo static Traps). Figs. 21'ana 22 illustrate types of float traps which are in use at the present time. Thermostatic Traps.-, Thermostatic traps function by means of elements which expand and contract under the influence of heat and cold. Early types of thermo static traps employed carbon posts and bi-metallic elements for expansion. In general, the modern type, of thermostatic trap consists of thin corrugated metal bellows or-discs enclosing a hollow chamber. The chamber is either filled with a liquid or a small amount.of;a volatile liquid such as alcohol is introduced. - The liquid expands or becomes.a.gaswhen steam comes in contact with the expansive element. The pressure created in either case expands the element and closes the valve of the trap against the escape of steam. When condensate or air comes in contact with the element, it cools and contracts, opening the valve and allowing the escape of water and air. - The discharge from;this.type of .trap is intermittent. Thermostatic traps find their use. generally for, the draming of -condensate from radiators, convectors,-pipe coils, dnps, unit .heaters,- water heaters, cooking kettles, and other equipment. . Except, for radiators and convectors, it is recommended that a strainer be installed on the inlet connection to the trap.to prevent dirt; pipe scale, and other foreign sub stance from entering.the trap. A cooling leg of a length of pipe should also be pro vided ahead of the trap on unit;heaters and similar apparatus to cool'the condensate ,Fm. 23.. Thermostatic Trap ... ;.Fig". 24. Thermostatic.Trap Bbllows.TtpE; . .. ; , Dis<: Type :