Basic Terminology and Definitions Used for Pipe Fittings:
Every industry has it’s own “code language”, sometime terms are a short-hand way to communicate faster and more accurately, some are just a way to identify “insiders” from “outsiders.” The following will help you to speak “Irrigation” (as well as “Plumbing” which uses most of the same terms.)
SSS, SST, SS, ST, etc…
These are terms used in describing the connections for PVC fittings. “S” stands for “SLIP” “socket”, or “spigot”, which means that the connection is a solvent weld (or glued) type. By the way, both sockets and spigots CAN be threaded also, which is why we use the term SLIP to specify that the connection is solvent welded. I’ve been told that slip really only means a socket, but common usage is for both sockets and spigots. In case you hadn’t guessed by now, there is a bit of confusion on this subject! (Webster’s Unabridged Dictionary doesn’t have the plumbing definition among it’s 69 definitions for the word slip.) At any rate, if you go to the hardware store to get a 3/4″ tee with solvent weld inlet and outlet and a 1/2″ threaded side outlet, you would ask for a “three quarter by three quarter by half tee, slip, slip, thread” and you would write it as “3/4 x 3/4 x 1/2 TEE SST”. (You can say “one-half” if you want to be technically correct, but most of us lazy people just say “half”.)
Lock, Loc, Push-Fit, etc…
There are an assortment of different terms used for these easy to assemble, glue-free fittings, most often the names in some way imply that the tube is “locked” into place. In irrigation most PEX connections are made using these push in and lock type fittings, where the tube is pushed into the fitting and a sharp metal clip locks it in place. At the time I am writing this article, the lock type fittings are starting to be made for all types of plastic tube and pipe, including poly tubing, PVC, and drip tubing. One note, when assembling using these locking fittings, be sure you press the tube or pipe very firmly into the fitting forcing it all the way in, it needs to go fully into the fitting in order to form a tight connection and not leak.
Spigots, Sockets, and Slip.
A spigot is the equivalent of a male end. A socket is a female end. In other words a spigot fits into a socket. Slip can mean either a spigot or socket, but normally means socket, and normally means the connection is solvent welded. For more on the subject see “SSS, SST, SS, ST, etc..” above.
Male and Female.
Oh come on now. Surely you can figure this one out! (Hint: many plumbing terms were originated by sex-crazed males.) Well all-right, male means spigot, female means socket. What do you mean that didn’t help?
You can say “glued” if you want, but that’s not totally correct (you do get partial credit). The cement (glue) used for connecting PVC parts is sticky like standard glue, but in addition it actually melts the plastic, creating a true weld. Thus the term “solvent weld”. By the way, the solvent for PVC is acetone (nail polish remover), so you can remove the PVC cement if you spill it with acetone. (I saved the front seat of my truck from disaster this way after knocking over a complete can of purple color pvc cement onto it. It was a lot of work and took a lot of acetone, but it all came out of the seat fabric eventually.) You can also use acetone to clean PVC pipe, but be careful as the acetone will melt the pipe if you use too much!
Abbreviation used for galvanized steel. Always avoid screwing a male metal fitting into a female plastic fitting. The plastic fitting will split when you tighten the joint. Always work male plastic into female metal when going from metal to plastic parts. If you absolutely must use a plastic female fitting place a worm-gear clamp around the very end of the female fitting and tighten it slightly before you insert the male end. Use lots of Teflon tape or pipe dope and don’t over tighten!
Cu, Type M, Type L, Type K.
All are abbreviations used for copper tube and fittings. Type M, L, and K describe the thickness of the copper pipe wall. M has the thinnest wall and K has the thickest. K is the strongest of the three. K is the only one that should have threads cut into it, the others are weakened too much by cutting threads. K is a good choice for use where physical strength is required, such as supporting the weight of a backflow preventer, although L will support a smaller 3/4″ or 1″ backflow preventer in most situations. L is the most common choice for standard uses, especially if the tube will be in or under buildings. Type M is more likely to develop pin holes in it over time. Widespread use of type M in homes during the 60’s and 70’s has lead to the creation of an entire industry devoted to replacing or rehabilitating failed copper pipe in homes.
A type of fitting used with polyethylene pipe. Insert fittings have barbs that are inserted into the open end of the tube. You must use a clamp placed over the tube and tightened to physically hold barbed fittings in place. Do not rely on the barbs to hold the tube on the insert fitting. Crimp and worm gear clamps are both used.
SCH 40, SCH 80.
Terms used with PVC fittings that indicate the specification standard the fitting was constructed to meet. SCH 80 is usually a gray color and is stronger than SCH 40 which is usually a white color.
Uniform Plumbing Code, National Sanitation Foundation. Indicates that the PVC fitting complies with standard code requirements. An indication of a top-quality PVC fitting.
Female Iron Pipe Thread, Male Iron Pipe Thread. Specifies the end is threaded and the thread pattern used is standard iron pipe style.
Poly Vinyl Chloride. The material most plastic fittings are constructed out of. See SCH 40, SCH 80 above.
The other plastic that some fittings are made of. Marlex is actually a brand name of a specific High Density Poly Ethylene. Normal PVC threaded joints “seize up” and will not turn freely. The HDPE has a oily surface which acts as a lubricant. HDPE fittings are used in situations where the threaded connection needs to remain flexible, such as swing joint risers. (A swing joint allows the sprinkler to move up and down for adjustment and to protect it from being damaged if run over by a vehicle. Swing joints are the standard type of sprinkler riser used in parks and golf courses.)
Teflon Tape, Pipe Dope
Most threaded joints need a sealer placed on the threads before the connection is made. The sealer serves two purposes. First it seals the joint (like you couldn’t figure that out). Second, it lubricates the joint, which makes it much easier to thread the pieces together. Teflon tape is my preferred product , it is easy to use and clean. Wrap 3 layers around the male threads, wrapping in the same direction as the threads (so it doesn’t unwrap when you start threading the fittings together). Don’t cover the end thread, that will help avoid “cross-threading” the joint. Be careful not to allow “strings” of Teflon tape to get into the pipes where they can clog sprinklers or emitters. Never use pipe dope with sprinklers, it can gum up the nozzles, and in gear-driven sprinklers it jams the turbines. Most sprinklers say “no pipe dope” on them, the manufacturer is not calling you a derogate name and saying not to use pipe!
The Basic Fittings (drawings are of PVC fittings but names also apply to polyethylene and PEX.)
Bell Reducer. A bell reducer has female threads on both ends. Bell reducers are generally not available in PVC (so, despite what the caption says above, this drawing is not of a PVC fitting).
Cap. A cap may have a solvent weld socket end or a female threaded end. The other end is closed off. If a solvent weld cap is used to provide for a future connection point, be sure to leave several inches of pipe before the cap! When the cap is cut off for the future connection there will need to be enough pipe present to glue a new fitting onto! I can’t begin to tell you how many times I’ve seen a solvent weld cap butted right up against another fitting, making it impossible to ever use the capped connection again!
Coupling. A coupling connects two sections of pipe together. Couplings may have solvent weld socket ends or female threaded ends.
Cross. A cross connects four pipe sections together. Crosses may have solvent weld socket ends or female threaded ends (no female threads available for PVC). Crosses are special order parts at many suppliers. Crosses create a great deal of stress on the pipe because they have four connection points. In theory this is the same principle that makes a 3 leg stool (a “tee”) more steady than a 4 leg stool (a “cross”). I recommend that you avoid using crosses in most situations. Use two tees.
Female Adapter. Female adapters are used to add a female threaded pipe connection on a solvent welded pipe. Never use female adapters when converting to a metallic pipe. The metal male pipe threads tend to split the PVC fittings. Place a metal coupling on the metallic pipe then use a PVC male adapter. Metal male threads should never be inserted into any female threaded PVC fitting!
Male Adapter. Male adapters are used to add a male threaded pipe connection to a solvent weld pipe section.
Plug. Used to plug a unused fitting outlet. May have female threads or a solvent weld spigot. In most cases a threaded plug is used to provide a connection point for future use. If solvent welded in place the plug is never going to be removed!
Side Outlet Ell. Side outlet ells are an ell with a side outlet. (Well duh…) They most commonly have two 3/4″ or 1″ solvent weld sockets, with a 1/2″ side outlet having female threads. Side outlet ells are common in residential sprinkler systems, but are seldom used in commercial installations. The side outlet is listed last when stating the side outlet ell size. Example: 1x1x1/2 SO ELL SST has a 1/2″ threaded side outlet.
Tee.The most common fitting! Available with all female thread sockets, all solvent weld sockets, or with opposed solvent weld sockets and a side outlet with female threads. Many configurations of “reducer tees” are available, meaning that one or more of the sockets is smaller than the others. Tees are always labeled as “NxNxN TEE with the side outlet as the last size. The largest of the other two sockets is always listed first. Thus a 1×3/4×1/2 TEE SST has a 1/2″ threaded side outlet (T for threaded) with the remaining sockets being 1″ and 3/4” solvent weld sockets (SS for slip, slip). On a “bullhead tee” the side outlet is the largest socket on the tee (thus it looks somewhat like a bull’s head I guess). The side outlet is referred to as the “bullhead”.
Q: The pressure is blowing off the pipes/tubes from the barbed fittings on my drip irrigation system. This is only happening on hot days (30°C=86°F in the shade). Pipe temperature could be as high as 45°C=113°F. Our water pressure varies between 2.5 and 3.1 bar (35 and 45 PSI.)
A: Drip tube should not blow off the barbs, even on a hot day when the temperature softens the plastic tubing (however the heat does make it easier for them to blow off!) There are three common reasons the tubes blow off.
1. The most common problem is that the water pressure is too high. This is probably your problem. The water pressure should be around 1.3 to 2.0 bars (20 – 30 PSI). You should install a pressure reducer after your valve to lower the pressure.
2. The pipe and fittings may not be the same size. This is one of the pitfalls I warn about in my Drip Guidelines. 16mm and 18mm tube are both commonly referred to as 1/2 inch in the USA! The fittings for these two are not interchangeable.
3. Pressure spikes can pass through the less expensive pressure reducers often sold for drip systems. If you have high water pressure this may be the problem. The solution is to install a high quality brass pressure reducer valves. These generally are sold in the plumbing department rather than the irrigation department of stores and cost $50.00 or more.
Common sizes are 12 mm (0.455″ or 3/8″), 16mm (0.620″ or 1/2″), 18mm (0.720″ or 1/2″), and 24mm (0.940″ or 3/4″). Do you see the problem? Two sizes are commonly referred to as “1/2 inch” in the USA! The fittings for these two are not interchangeable.
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