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4.1: Piping & Fittings

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    Installing, maintaining, and troubleshooting plumbing systems requires specific knowledge of industry standardized measurements, construction codes, and specialized components of plumbing systems. While locally adopted plumbing codes apply to these systems and components, manufacturer installation and use instructions should be followed. Many common plumbing parts and materials like pipes and fittings do not come with instructions and should be sized and installed to comply with locally adopted plumbing and building codes.

    A pipe or fitting’s ability to hold pressure, survive hot or cold temperatures, and endure natural elements is limited by it’s chemical composition, wall strength, and integrity of the sealing method used to join individual components. Schedule is the term used in referring to “plastic” (PVC, ABS, CPVC) pipe’s wall thickness, with lower numbers representing thinner walled pipes. The most common sizes used in residential construction are Schedule 40 (thinner wall used in drain, waste and vent applications) and Schedule 80 (thicker wall used in pressurized water applications). Several material types are approved for use in piping system that serve different purposes in a complete plumbing system to include water supply, and waste, drain and vent (DWV). The following table indicates the type of plumbing system that various types of piping are generally allowed in residential and light commercial construction:

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    Fitting are used to join and redirect pipes and components to form complete plumbing systems. Due to the variety of designs of plumbing system components, fittings also facilitate adaptations from one size diameter of pipe or fitting to another. While many styles of fittings are used in most all types of systems, plumbing codes only allow some fittings to be used in particular type of plumbing system (supply or DWV) and have strict requirements as to how they are to be incorporated into the system (ex: compression fittings and unions should never be used inside of walls).

    Fitting Terminology

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    Fittings by Clifford Rutherford, Rosemary Rutherford & Gwen Arkin is licensed under CC BY 4.0

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    Solvent Cleaners, Primers, & Cements or Glues

    Pipe glues and primers

    Pipe Glues & Primers by Gwen Arkin is licensed under CC BY 4.0

    The use of cleaners, primers, and glues is specific to slip fitting applications and the chemical composition of the “plastic” piping being used. Chemical resistant gloves should be worn when using these chemical process adhesives as prolonged skin contact can result in irritation or chemical burn. Latex and vinyl gloves are not chemically resistant when used with some solvents, primers, and glues.

    Always consult manufacture directions for set times of cements and glues before pressurizing any glued plumbing assembly. When assembling fittings and pipes, cleaners, primers and glues should be swabbed over the entire joint surface of both the male and female slip fitting. Although manufacturer directions may vary, in most cases a cleaner should be used, followed by a primer and then the solvent cement. Additionally, after application of the primer, the solvent cement should be applied immediately before the primer dries. Before the glue begins to set up, the male pipe or fitting is inserted fully into the female socket with a slight twisting motion. It is important to hold the joint firmly together until an initial setting of the glue is achieved, as glued fittings have a tendency to push apart as the chemical heats and expands.

    Color and Material

    Most manufacturers of these chemically reactive products have adopted colors in their products that identify the composition of material it is to be used with.

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    Color Blocks by Jonathan Kevan is licensed under CC BY 4.0

    Difference Between PVC Cement Types & Primer

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    Differences Between CPVC, DWV PVC, Schedule 40 PVC, and Schedule 80 PVC

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    Threaded Pipe Fitting Assembly

    Most pipe threads by themselves are not sufficient to create a complete seal in pressurized piping systems.

    Thread Tape

    Teflon Tapes

    Teflon Tapes by Gwen Arkin is licensed under CC BY 4.0

    IPS and NPT pipe threads require Polytetrafluoroethylene (PTFE) tape (Teflon™ by Chemours) to be applied to the male threads of fittings in order to obtain a complete seal. PTFE tape is available in widths of 1/2″, 3/4″ and 1″ and different weights or thicknesses (white-standard duty, pink-high density). The standard duty tape should be wrapped completely and evenly across the male threads approximately three to four times in the direction the threads turn to tighten the fitting. The easiest way to accomplish this is to place the tape roll in the left hand with the tape feeding toward the right from the bottom. While holding the male fitting with the right hand, place the end of the tape across the top of the fitting and turn the fitting clockwise. After securing the first 1 to 1-1/2 wraps, gently stretch the tape, continuing to turn while overlapping layers up and down the threads until 3 to four complete wraps are achieved evenly across the length of the male threads. Pull the tape firmly to break and thread male fitting into female fitting, securing with an appropriate wrench.

    Standard or high density PTFE thread pipe cannot, by codes, be used for natural gas and propane applications. A chemically resistant yellow version is used for these flammable gas systems.

    Pipe Dope

    Pipe Dope

    Pipe Dope by Gwen Arkin is licensed under CC BY 4.0

    As with thread tape, pipe dope comes in PTFE and other compositions designed for water lines and for gas lines. While some people use pipe dope on top of thread tape but many manufactures claim that the is minimal or no benefit to using both products simultaneously. Some pipe dopes cannot be used on plastic piping, be sure to check manufacturer directions prior to use. Pipe dope is applied with a brush to the male threads of a piping joint and then the pipe is tightened into the female fitting and secured with an appropriate wrench.

    Copper Pipe Fitting and Soldering

    Due to the ever rising cost of copper material, soldering of copper pipes and fittings in residential construction is rapidly becoming obsolete as PEX flexible water supply tubing and similar solderless products, that use crimping system technologies, are being recognized and approved for installation by industry codes. However, plumbers and building maintenance technicians should always be prepared to use soldering techniques to install and repair copper supply lines of all sizes in commercial and older residential systems.

    Simple Steps for Soldering

    1. Clean the pipe well.
    2. Clean the fitting well.
    3. Apply an even coat of flux.
    4. Don’t get the fitting too hot.

    How to Solder Pipe

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    4.1: Piping & Fittings is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Clifford Rutherford via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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