Basic Concepts of Plumbing. There are no difficult concepts in plumbing “Sewage don’t run uphill and payday is Friday” There can be some complicated implementations, particularly in vacuum systems, particularly if you let physicists design them!. NPT: National Pipe Thread.
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Basic Concepts of Plumbing There are no difficult concepts in plumbing “Sewage don’t run uphill and payday is Friday” There can be some complicated implementations, particularly in vacuum systems, particularly if you let physicists design them!
NPT: National Pipe Thread • “Black” and “galvanized” pipe: dimensions and fittings. • Galvanized pipe is zinc-plated and used for water and compressed air, which often contains considerable quantities of water • Black pipe is used for gas (Natural gas), it rusts easily when wet. • Pipe is typically rigid; it doesn’t bend easily
Pipe Terminology • Pipe is measured on the ID (inside diameter), approximately. • Actually it’s measured on the OD (outside diameter), but that number makes no sense! (See below) • The naming standard used to be IPS (Iron Pipe Size), but has been supplanted by NPS (Nominal Pipe Size). • “Schedule” refers to the wall thickness • “Schedule 40" is the normal/common thickness • All schedules of the same nominal size must have the same OD to be compatible with the same size fittings • “In Europe, pressure piping uses the same pipe IDs and wall thicknesses as Nominal Pipe Size, but labels them with a metric Diameter Nominal (DN) instead of the imperial NPS.” (Wikipedia: pope (material))
Pipe Terminology • ½" schedule 40 pipe has an OD of 0.840", thickness of 0.109" and ID of 0.622“ • ½” schedule 80 has a wall of 0.147" and ID of 0.546", schedule 160 has a wall of 0.187" and ID of 0.466". • Remember that all schedules of the same nominal size must have the same OD to be compatible with the same size fittings • Is that all perfectly clear and is it now obvious why it’s called ½" pipe? (You recognize sarcasm, yes?) • Other sizes of pipe don’t make any more sense than this. • Plastic sprinkler pipe also comes in schedules; the pipe is typically schedule 40 but fittings are typically schedule 80.
Noel Denevers, Fluid Mechanics, Addison-Wesley, Reading MA, p. 471-474 (1970)
Nomenclature of Pipe Fittings • Fitting • a joint or connector, as an elbow, union, or tee, used in a pipe system. (Dictionary.com) • Couplings: require significant motion of pipes, particularly along the axis of the pipe. Typically used during installation of a plumbing system. • Unions: Require minimal longitudinal motion of the pipe. Typically used to install and exchange appliances after plumbing system has been constructed. • Bushings: used to change pipe size. • Tees • Elbows: 90º and 45º • “Street” fittings are asexual • Nipple: a short piece of pipe, threaded on both ends, used to connect two fittings.
Pipe Fittings • “Iron” pipe fittings have a tapered thread • Typically “sealed” with Teflon tape. • The taper half-angle is 1º 47', which corresponds to 3/4" decrease in diameter per foot of thread. • Demo of threaded pipe joint. How tight do you make it? Tight enough that it doesn’t leak!
Tubing • Tubing is measured on the OD and is exact...well sort of. An alleged piece of 1" x 1/8" wall stainless tubing was measured to be 1.050". As usual, caveat emptor! • Tubing available in many materials • Copper • Flexible: used extensively refrigeration, water and many other applications • Rigid (aka “pipe”, but measured on OD!): used extensively for water, especially in homes • Brass • Stainless • High quality vacuum systems often made with welded stainless tubing • All sorts of exotic metals (including platinum!)
Pipe and Tubing • Pipe is rigid: Changes in direction are made with elbows and tees • Tubing can be bent • Copper tubing can be easily bent by hand • Benders available for other metals • Electrical Metallic Tubing (“EMT”) • Used extensively for commercial wiring • EMT benders are common • Replacement car exhaust systems are now custom-made for each model in each installation
Pipe and Tubing • Tube fittings typically “slip” together • Plastic pipe fittings are made permanent with glue • Metal fittings are made permanent with solder (“sweated”) or welding (stainless)
Soldering • Types of solder • Soft • Lead/tin alloys • Different alloys have different melting points and strengths • Apply with iron or propane torch • Solid core is typically used for plumbing • Rosin core is used (without flux) for electrical connections • Silver • Much stronger and higher melting than lead/tin solders • Apply with oxy-acetylene torch • Many specialty typed for special applications • Types of flux • Green Streak contains acid and is very corrosive to electronics but fine for copper pipe • Superior 90 is great for electronics and adequate for copper pipe
Swagelok: Plumbing for Physicists • Fittings, nuts and ferrules. • Demo: the Swagelok catalog • Standard Swagelok is not appropriate for applications that need to be changed often. • Definitely ditto for tapered pipe fittings.
Swagelok: Plumbing for Physicists • UltraTorr compression O-ring fittings. • Excellent for repeated changes; should last forever with occasional change of O-rings • Great for vacuum • Will not tolerate high pressure! • VCO fittings • O-ring fittings that can be changed repeatedly • Will tolerate moderate pressures • VCR fittings: • Typically used on welded stainless steel systems for extremely high vacuum or where leaks absolutely cannot be tolerated like silane and arsine lines. • Like mini-conflat fittings: they come with a gasket that is single-use. • Intended as removable fittings in bakeable, welded all-metal systems. • It makes no sense to put Teflon tape on a Swagelok or conflat fitting. (Ditto for the joint between a regulator and gas cylinder.)
Plumbing with Glass • “Glass” comes in numerous “grades” • “Fused silica” is high purity SiO2 typically about 99.99% pure • Usable to 1200 C • Very low coefficient of thermal expansion • Can be thrust into water for 1500 C! • “Vycor” is a trade name for 96% pure silica • “Pyrex” • Approximately 81% SiO2, 2% Al2O3, 4% Na2O, 0.5% K2O and 13% B2O3 • Very common for labware • Low coefficient of thermal expansion • Usable in flames and on hotplates • Flint glass is commonly used for lenses
Plumbing with Glass • Ground joints and ball joints: nomenclature and sizes • Ground joints are classified by a “standard taper” size • 24/40 is quite common for intermediate-sized joints • The maximum diameter of the taper is 24 mm • The taper is 40 mm long • Ground glass fitting is typically sealed with vacuum grease • Grease can be removed with piranha solution • Frozen joints can be loosened by Coca Cola®! • Stopcocks are sized by the diameter of the hole (mm) • Connections made by “welding” in a flame: “glassblowing”
Plumbing with Glass • Ace and Fisher – Porter • Grease-free couplings and connectors • Grease is a place for volatile contaminants to adsorb and outgas forever • Greased fittings cannot be baked • Gas handling systems in OEML are completely grease-free • Glass, Teflon and metal parts only • Suitable for use with reactive gases • Swagelok can be connected to glass by using teflon or nylon ferrules • Ace also has fittings that directly connect to Swagelok