AWWA Manual M75:2020 pdf download.Elastomers for Waterworks: Pipes, Valves, and Fittings
element and provide a seal. The seal is highly reliable because the groove and mating surface hold the O-ring in place, which prevents the O-ring from dislodging and leakage from occurring. The groove and mating surfaces are typically bolted together, creating metal-to-metal contact with low bolt torque to provide the necessary compression on the O-ring. As shown in Figure 2-3, the O-ring gland and groove are designed to compress the O-ring in one direction, provide volume for compression and thermal expansion, and allow the O-ring to move to one side of the groove when pressure is exerted. Because of the imposed compression, an O-ring can seal from zero to very high pressures (i.e., 0–5,000 psig or 0–34.5 MPa). While O-rings are typically static seals, they can also be used on moving parts, such as rotating shafs and oscillating cylinders, to contain the line fuid within the pressure boundary. When used in dynamic applications, the mating metal surfaces must be very smooth to prevent wear. O-rings are available in many standard circular cross sections and diameters but can also be custom-molded to suit a particular valve application. The standard sizes used by O-ring manufacturers in the United States are defned by standards such as Aerospace Standard AS-568. Typical cross-sectional diameters range from 0.040 to 0.275 in. (1.02–6.98 mm). Typical inside diameters range from 0.029 to 25.940 in. (0.74–658.9 mm). There are more than 300 standard sizes. O-rings are typically molded from high-tensile elastomers to a hardness of 70 Shore A, which is similar to that of automobile tires. O-rings are readily available in many diferent compounds to be compatible with hundreds of chemicals and fuids.
Pipelines are ofen assembled using sections of pipe, ftings, and valves joined together with standardized bolted fange connections. In general, the fange connection consists of two circular fat rings of a specifed thickness (T) integrally cast, welded, or threaded to the ends of the pipe with a series of bolt holes around a bolt circle (BC) with a specifc diameter to compress the seal and withstand the hydrostatic and pipe loads during service (see Figure 2-4). Flanged connections are commonly used for aboveground water and wastewater service requiring a fxed restrained joint but are also used below ground in buried applications (with corrosion protection where required) and nonburied applications such as vaults. They are popular in treatment plants and industrial piping systems, in both interior and exterior applications, as well as bridge and other elevated crossings. Flanged joints allow for easier access to the piping system and associated pipeline equipment, such as valves and pumps (see Figure 2-5).AWWA Manual M75 pdf download.