If you’ve been to the hardware store, you’ve likely walked down the aisle looking at all those black things that appear identical. They’re elbows. One bend this direction, and another bends that direction. There’s a tee that splits flow, and a coupling connects two pipes. These thing look alike but serve different structural functions. Get the wrong fitting, and you’ll have a leak. You’ll also lose your confidence and perhaps ruin your day. Understanding how these fittings work will help before you grab that wrench. Here’s how the key categories break down (see the chart up top). So now when you’re choosing the correct piece, you don’t have to guess.
Couplings connects two pieces end-to-end. Tees create branches. Elbows turn corners. That is what they are for.
How to Choose the Right Pipe Fittings
How you connect them matters as well. Threaded fittings can be unscrewed apart for future disassembly. This is great because it lets you take things apart later for repairs. Connections that are glued or soldered together are permanent. Only use this type of connection if you’ll never need to access it again. It’s not a cost issue; it’s an accessibility issue. If there’s any possibility you may want to remove a length of pipe in the next few years, don’t glue it into place.
Material selection is where homeowners tend to trip over themself. “All pipe is the same,” they think. Nope, copper has that antimicrobial thing going for it, which makes it excellent for drinking water. Brass? It is great for gas lines and very resistant to corrosion. What about black iron? It is darn cheap and heavy. It is perfect for oil/gas. But if not covered, it’ll rust like crazy in a moist environment.
And you don’t want to mix any of these things willy-nilly, because you get galvanic corrosion if you have two dissimilar metals touching each other in the presence of water. You need to avoid this with a dielectric union. It’s basically an insulator between one metal and another. It is small, but it saves your system from slow, hidden death.
The other wrinkle is that there are different pressure ratings too. For example, water lines used in homes is typically Schedule 40 pipe. This isn’t rated for high pressure like air or steam lines. For those situations you want Schedule 80 or 160. The higher number means thicker walls. That makes the inside diameter smaller. But it also makes the pipe stronger and less likely to burst. Again this is a compromise based off the material being moved by the line. Fail to account for the Schedule number and if your pipe gets pressurized you run the risk of a disaster.
Attention should be paid to threads. With National Pipe Taper (NPT) threads, you have a mechanical seal due to the taper of the threads. By themselves, they are not pressure tight. Instead, they must be filled with PTFE tape or pipe dope to fill tiny gap between them. This is where many people goes wrong. Water gets in, weeping joints occur, and all sorts of havoc ensues.
Not only that but you have to get the thread angle right. Trying to force an NPT fitting onto a BSP fitting will result in cross-threading. That messes up the connection. Size isn’t everything. Geometry is too. What size? It’s a mess if you don’t know.
First of all, the actual outside diameter is not equal to the nominal (label) pipe size. What?! Yes, a half-inch pipe isn’t half an inch… this goes back to old iron pipe specifications. In those days, the nominal size indicated the internal diameter. Now, regardless of wall thickness, the outside diameter remains unchanged. That makes fitting interchangeable. Always use calipers and check the outside diameter. Don’t trust what it says on label.
The tricks to avoiding that are attention and patience. Brass and plastic fittings must not be over-tightened (they’ll crack) and under-tightened (they’ll leak). It’s usually a couple turns with a wrench after hand-tight. That’s a fine line. You should of used more caution.
Understanding why all parts exist makes the hardware store aisle look more like a toolbox. No longer do you see random shapes. Instead, you begin to see solutions. That clarity transforms a stressful project different than a successful installation.
