but are usually of thinner and lighter construction because the weight of the materials conveyed is less. Vacuum-system designs share with DWV designs the need to eliminate internal ridges, burrs, sharp turns, or other obstructions which might create clogs. Non-return or check valves allow free flow of a fluid in one direction, but prevent its flow in a reverse direction. They are often seen in drainage or sewage systems, but may also be used in pressurized systems. Isolation valves are used to temporarily disconnect part of a piping system, to allow maintenance or repair, for example.
PTFE tape and pipe joint compound (also known as “pipe dope”) should only be used on “IPS” (“iron pipe size”) threads, which are normal pipe threads. IPS threads make their seal along the threads themselves; when a piece of IPS-threaded pipe is screwed into a fitting, PTFE tape and/or pipe dope is used to assist that seal on the threads. Flare fittings, on the other hand, seal on the beveled ends of the fittings, and so using pipe dope or tape on flare threads could actually prevent the fittings from making an adequate seal. The chief advantage of these connectors is that they can be installed after cutting the pipe to length in the field. This can save time and considerable expense compared to flange connections, which must be factory- or field-welded to pipe segments. However, mechanically fastened joints are sensitive to residual and thickness stresses caused by dissimilar metals and temperature changes.
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Flanges used in piping (orifice, threaded, slip-on, blind, weld neck, socket, lap-joint, and reducing) are available with a variety of facings, such as raised, flat, and ring-joint. A barb , which connects flexible hose or tubing to pipes, typically has a male-threaded end which mates with female threads. The other end of the fitting has a single- or multi-barbed tube—a long tapered cone with ridges, which is inserted into a flexible hose. The nipple is a short stub of a pipe that has a male pipe thread at each end or at one end. The swage is like reducers but small in size and used to connect pipes to smaller screwed or socket welded pipes. Like reducers, they are also available in concentric & eccentric types.
Wye tee allows one pipe to be joined to another at a 45° angle. This type of tee reduces friction and turbulence that could hamper the flow. A barred tee which is also known as a scrapper tee is used in pipelines that are pigged. The branch of the tee has a restriction bar welded internally to prevent the pig or scrapper to enter the branch. The bars are welded in the branch in a way that it will allow restriction free passage of the pig from the run pipe.
Although reducers are usually concentric, eccentric reducers are used as needed to maintain the top- or bottom-of-pipe level. Gaskets are mechanical seals, usually ring-shaped, which seal flange joints. Commonly used gaskets are non-metallic (ASME B 16.21), spiral-wound (ASME B 16.20) and ring-joint (ASME B 16.20). Non-metallic gaskets are used with flat- or raised-face flanges. Spiral-wound gaskets are used with raised-face flanges, and ring-joint gaskets are used with ring-type joint flanges. Stress develops between an RTJ gasket and the flange groove when the gasket is bolted to a flange, leading to plastic deformation of the gasket.