Although thermal couplings are cheaper than compression joints and much faster to install, they do have their limitations. Chief among these are restricted spaces where it is not safe to use a gas torch, and the proximity of flammable materials and gases. Moreover, they cannot directly connect to plumbing fittings with threaded attachments, for example taps.
Thus, one inevitably ends up using a combination of different types. We assemble pipe runs with thermal couplings, while using compression couplings at the beginnings and ends. To help you determine what type of plumbing fittings you are working with, the numbers in the image opposite refer as follows:
Plumbing Fittings: Nerijp: GNU
# 1: Copper pipe with soldered joints
#2: Iron or brass threaded connectors
#3: Brass compression couplings
#4: Brass compression / solder joiners
#5 Brass adapters
The Types of Plumbing Fittings We use Most
That said, there are six plumbing fittings you are most likely to use around the house, and in a combination of soldered and compressed joints as I mentioned. In no particular order these are:
Elbows allowing a 90° or 45° degree change in direction. Some of these connect similar diameter pipes while other are reducers.
Straight Couplings for joining pipes where the run is longer than a standard length. Once again, these may also act as reducers.
Copper Fittings: Torsten Bätge: GNU 1.2
Compression Unions placed at points where periodic separation is necessary for maintenance. Some have insulation to interrupt an electric path
Tee Pieces allowing a division of water flow in different directions. The pipe diameters can step up or step down, or remain consistent
Crosses allowing divided water to enter three different sub-systems. They are unstable and can stress pipes. A series of tee pieces is safer.
Online Valves permitting temporary or permanent closure of a pipe end. I call them the ‘plumber’s friend’ for when we need to get the water back on unexpectedly.
I always keep a small stock of the most common plumbing fittings handy, and a spare length of pipe. This is a small capital outlay compared to having what I need available in an emergency.