Document MGxR9mGQw4xYNO6Qa8DxgRaqk

American Society of Heating and Ventilating Engineers Guide, 1936 proposed American Standard containing dimensions of steel welding-neck flanges for pressures up to 1500 lb per sq in. has been developed in A.S.A Sectional Committee B16. Tables 10 and 11 give these dimensions for welding-neck flanges suitable for 150 and 300 lb per sq in. gage pressure. VALVES Valves are made with both threaded and flanged ends for screwed and bolted connections just as are pipe fittings. The. material used for valves of small size is generally brass or bronze for low pressures and forged steel for high pressures, while in the larger sizes either cast-iron, cast-steel or some of the steel alloys are employed. Chapter 34--Pipe, Fittings, Welding sizes the rising stem is more commonly used. The rising stem valve is desirable because the positions of the handle and stem indicate whether the valve is open or closed, although space limitations may prevent its use. The globe valve is less expensive to manufacture 'than the gate valve, but its peculiar construction offers a high resistance to flow and Table 10. Proposed Dimensions of Steel Welding Neck Flanges for Maximum Steam Service Pressure of 150 Lb per Sq In. (Gage) at a Temperature of 500 F, and 100 Lb at 750 F a. Typical Short Radius Elbows =5!-- =ass^= ; ZZZZZ^ b. Tee c. Forged Cap d. Concentric Reducer e. End , Closure Fig. 3. Typical Welding Fittings '\ Practically all iron or steel valves intended for steam or water work are bronze-mounted or trimmed. Brass, bronze, and iron valves are generally designed for standard or extra heavy service, the former being used up to 125 lb and the latter up to 250 lb saturated steam working pressure, although most manufacturers also make valves for medium pressure up to 175 lb steam working pres sure. The more common types are gate valves or straightway valves, globe valves, angle valves, check valves and automatic valves, such as reducing and back-pressure valves. Gate valves are the most frequently used of all valves since in their open position the resistance to flow is a minimum. These valves may be secured with either a rising or a non-rising stem, although in the smaller 622 Nominal Pipe Sob Diameter Thickness Diameter Hub Diam. 07 or or Beginning Flange Flo. Min. Hub or Cbauteb Length Thbu Hub 0 0 X. H Y DUU. FOB Standard Pipe A Diam. or Bolt Circle No. or Bolts Size or BOLT8 i i% 2 2% 3 3% 4 5 6 8 10 12 14 0. D. 16 0. D. 18 0. D. 20 O. D. 24 O. D. w We 5 6 7 m m 9 10 11 13% 16 19 21 25% 25 32 He % He H We % We We We 1 m We 1% 1% We We IWe. We IWe We We We We 4% 4We We We We 9We 12 U% 15% 18 19Ye 22 26K 1.32 1.66 1.90 2.38 2.88 3.50 4.00 4.50 5.56 6.63 8.63 10.75 12.75 14.00 16.00 18.00 20.00 24.00 We 2% We 2% 2% 2% 2We 3 3% 3% 4 4 4% 5 5 5% 5^8 6 1.05 1.38 1.61 2.07 2.47 3.07 3.55 4.03 5.05 6.07 7.98 10.02 12.00 13.25 15.25 17.25 19.25 23.25 3% 3% 3% 1% 5% 6 7 7% m 9% 11% 14% 17 18% 21% 22% 25 29% 4% 4% 4% 4H 4% 4 Ye 8% 8 Ye 8% 8% 8% 12 Ve 12 Ve 12 1 16 1 16 1% 20 1% 20 1% All dimensions given in inches. --------------------- "* *" *o iuuuucu *4* uj mnnrnum. It is recommended that the taper of the hub should not exceed 6 degrees for a reasonable distance back oi the chamfer in order to reduce the heat transfer while welding. may'prevent complete drainage of the pipe line. These objections are of particular importance in heating work. Check valves are automatic in operation and permit flow in only one direction,, depending for operation on the difference in pressure between the two sides of the valve. The two principal kinds of check valves are the swing check in which a flapper is hinged to swing back and forth, and the lift check in which a dead weight disc moves vertically from its seat. Valves commonly used for controlling steam or water supply to radi ators constitute a special class since they are manufactured to meet 623