This chapter presents various types of pipe fittings. Of all the fittings, the elbow is the one most often used. Simply put, the elbow, or ell, is used when a pipe changes direction. Elbows can turn up, down, left, right, or any angle in between. When one finds it necessary to draw a 90° elbow or calculate how much space it will occupy in a routing configuration, knowing its length becomes essential. An elbow's length is commonly referred to as the center-to-end dimension and is measured from the centerpoint of its radius to the end of either opening. Dimensional sizes of fittings are typically provided by the manufacturer of the fitting. Manufacturers issue dimensioning charts containing lengths for a particular fitting. Another elbow that may be used under certain circumstances and with permission from the customer is the 90° short-radius elbow. The 90° short-radius ell makes a much sharper turn than does the long-radius ell.
Emissions from Pipe Fittings and Gaskets
Threaded pipe fittings in the seal flush line can be significant leak sources, with readings above 1,000 ppm.4,17 Similar emission levels may be measured near the gasket region on the seal chamber face. Any leakage from these areas may drift into the emission measurement area for the mechanical seal. The mechanical seal may then be erroneously implicated as a leaker. It should be standard practice to sniff nearby hydraulic fittings and the flange gasket area if excessive VOC concentrations are detected adjacent to the mechanical seal.
Leak-tight threaded pipe fittings can be more easily attained using anaerobic paste-type sealants rather than PTFE tape. The seal chamber face must be smooth to be emission tight. Gaskets and O-rings must be free of nicks and scratches.
32.16.2 Thermoplastic Fittings Manufacturing
Thermoplastic pipe fittings may be injection-molded, fabricated, rotomolded, or thermoformed. Injection-molded fittings are generally made in sizes through 12-in. nominal diameter. Typical molded fittings are tees, 45-degree and 90-degree elbows, reducers, couplings, caps, flange adapters, stub ends, branch saddles, service saddles, and self-tapping saddle tees. Electrofusion couplings and fittings are either made by injection molding or machined from pipe stock. Electrofusion fittings and couplings are made with a coil-like integral heating element incorporated into the fitting. Joining with other fittings uses an electrical fusion device that provides electricity into the heating element, which melts the adjacent thermoplastic material and creates a fusion-welded joint.
Larger-diameter fittings exceed the capabilities of injection molding and are typically fabricated. Rotomolding is used for the manufacture of polyethylene large-diameter (up to 60 in.) and custom fittings for polyethylene corrugated drainage piping applications.