Soft Copper Tubing, Hard-Drawn Copper Tubing, Cutting Copper Tubing, Flaring Copper Tubing, Constricting Tubing, Swaging Copper Tubing, Forming Refrigerant Tubing and Fitting Copper Tubing by Compression
Tubing
Several types of tubing are used in plumbing, refrigeration, and air-conditioning work. Air conditioning and refrigeration, however, use special tubing types. Copper, aluminum, and stainless steel are used for tubing materials. They ensure that refrigerants do not react with the tubing. Each type of tubing has a special application. Most of the tubing used in refrigeration and air conditioning is made of copper. This tubing is especially processed to make sure it is clean and dry inside. It is sealed at the ends to make sure the cleanliness is maintained.
- Stainless steel tubing is used with R-717 or ammonia refrigerant.
- Brass or copper tubing should not be used in ammonia refrigerant
- Aluminum tubing is used in condensers in air- conditioning systems for the home and
This calls for a special type of treatment for soldering or welding. Copper tubing is the type most often used in refrigeration systems. There are two types of copper tubing—hard-drawn and soft copper tubing. Each has a particular use in refrigeration.
Soft Copper Tubing
Some commercial refrigeration systems use soft cop- per tubing. However, such tubing is most commonly found in domestic systems. Soft copper is annealed. Annealing is the process whereby the copper is heated to a blue surface color and allowed to cool gradually to room temperature. If copper is hammered or bent repeatedly, it will become hard. Hard copper tubing is subject to cracks and breaking.
Soft copper comes in rolls and is usually under 1/2 in. in outside diameter (OD). Small-diameter copper tubing is made for capillary use. It is soft drawn and flexible. It comes in random lengths of 90 to 140 ft. Table 1-1 gives the available inside and outside diameters. This type of tubing usually fits in a 1/4 in. (OD) solder fitting that takes a 1/8 in. (OD) diameter tubing.
Table 1-1 Inside and Outside Diameter of Small Capillary Tubing*
Inside Outside
| Diameter (ID), in. | Diameter (OD), in. |
| .026 | .072 |
| .31 | .083 |
| .036 | .087 |
| .044 | .109 |
| .050 | .114 |
| .055 | .125 |
| .064 | .125 |
| .070 | .125 |
| .075 | .125 |
| .080 | .145 |
| .085 | .145 |
*Reducing bushing fits in 3/8 in. OD solder fitting and takes 3/8 in. OD tubing.
There are three types of copper tubing—types K, L, and M.
- Type-K tubing is heavy It is used for refrigeration, general plumbing, and heating. It can also be used for underground applications.
- Type-L tubing is used for interior plumbing and Type-M tubing is used for light duty waste vents, water, and drainage purposes.
- Type-K soft copper tubing that comes in 60-ft rolls is available in outside diameters of 5/8, 3/4, 7/8, and 11/8 It is used for underground water lines. Wall thick- ness and weight per foot are the same as for hard copper tubing.
Copper tubing used for air-conditioning and refrigeration purposes is marked “ACR.” It is deoxidized and dehydrated to ensure that there is no moisture in it. In most cases, the copper tubing is capped after it is cleaned and filled with nitrogen. Nitrogen keeps it dry and helps prevent oxides from forming inside when it is heated during soldering.
Refrigeration dehydrated and sealed soft copper tubing must meet standard sizes for wall thickness and outside diameter. These sizes are shown in Table 1-2.
Hard and soft copper tubings are available in two wall thicknesses—K and L. The L thickness is used most frequently in air-conditioning and refrigeration systems.
Hard-Drawn Copper Tubing
Hard-drawn copper tubing is most frequently used in refrigeration and air-conditioning systems. Since it is hard and stiff, it does not need the supports required by soft copper tubing. This type of tubing is not easily bent. In fact, it should not be bent for refrigeration work. That is why there are several tubing fittings available for this type of tubing.
Hard-drawn tubing comes in 10 or 20 ft lengths. See Table 1-3. Remember, there is a difference between hard copper sizes and nominal pipe sizes. Table 1-4 shows the differences. Nominal sizes are used in water lines, home plumbing, and drains. They are never used in refrigeration systems. Keep in mind that Type K is
Table 1-2 Dehydrated and Sealed Copper Tubing Outside Diameters, Wall Thicknesses, and Weights*
50-Foot Coils
Outside Diameter (in.) Wall Thickness (in.) Approximate Weight (lbs)
| 1/8 | .030 | 1.74 |
| 3/16 | .030 | 2.88 |
| 1/4 | .030 | 4.02 |
| 5/16 | .032 | 5.45 |
| 3/8 | .032 | 6.70 |
| 1/2 | .032 | 9.10 |
| 5/8 | .035 | 12.55 |
| 3/4 | .035 | 15.20 |
| 7/8 | .045 | 22.75 |
| 11/8 | .050 | 44.20 |
| 13/8 | .055 | 44.20 |
*The standard soft dehydrated copper tubing is made in the wall thickness recommended by the Copper and Brass Research Association to the National Bureau of Standards. Each size has ample strength for its capacity.
Table 1-3 Outside Diameter, Wall Thickness, and Weight per Foot of Hard Copper Refrigeration Tubing
Outside Diameter (in.) Wall Thickness Weight Per Foot
| Type-K Tubing | ||
| 3/8 | 0.035 | 0.145 |
| 1/2 | 0.049 | 0.269 |
| 5/8 | 0.049 | 0.344 |
| 3/4 | 0.049 | 0.418 |
| 7/8 | 0.065 | 0.641 |
| 11/8 | 0.065 | 0.839 |
| 13/8 | 0.065 | 1.040 |
| 15/8 | 0.072 | 1.360 |
| 21/8 | 0.083 | 2.060 |
| 25/8 | 0.095 | 2.930 |
| 31/8 | 0.109 | 4.000 |
| 41/8 | 0.134 | 6.510 |
| Type-L Tubing | ||
| 3/8 | 0.030 | 0.126 |
| 1/2 | 0.035 | 0.198 |
| 5/8 | 0.040 | 0.285 |
| 3/4 | 0.042 | 0.362 |
| 7/8 | 0.045 | 0.445 |
| 11/8 | 0.050 | 0.655 |
| 13/8 | 0.055 | 0.884 |
| 15/8 | 0.060 | 1.114 |
| 21/8 | 0.070 | 1.750 |
| 25/8 | 0.080 | 2.480 |
| Type-M Tubing | ||
| 1/2 | 0.025 | 0.145 |
| 5/8 | 0.028 | 0.204 |
| 7/8 | 0.032 | 0.328 |
| 11/8 | 0.035 | 0.465 |
| 13/8 | 0.042 | 0.682 |
| 15/8 | 0.049 | 0.940 |
Table 1-4 Comparison of Outside Diameter and Nominal Pipe Size
Outside Diameter (in.) Nominal Pipe Size (in.)
| 3/8 | 1/4 |
| 1/2 | 3/8 |
| 5/8 | 1/2 |
| 3/4 | — |
| 7/8 | 3/4 |
| 11/8 | 1 |
heavy-wall tubing, Type L is medium-wall tubing, and Type M is thin-wall tubing. The thickness determines the pressure the tubing will safely handle.
Cutting Copper Tubing
Copper tubing can be cut with a copper tube cutter or a hacksaw. ACR tubing is cleaned, degreased, and dried before the end is sealed at the factory. The sealing plugs are reusable.
To provide further dryness and cleanliness, nitrogen, an inert gas, is used to fill the tube. It materially reduces the oxide formation during brazing. The remaining nitrogen limits excess oxides during succeeding brazing operations. Where tubing will be exposed inside food compartments, tinned copper is recommended.
To uncoil the tube without kinks, hold one free end against the floor or on a bench. Uncoil along the floor or bench to the desired length. The tube may be cut to length with a hacksaw or a tube cutler. In either case, deburr the end before flaring. Bending is accomplished by use of an internal or external bending spring. Lever-type bending tools may also be used. These tools will be shown and explained later.
The hacksaw should have a 32-tooth blade. The blade should have a wave set. No filings or chips can be allowed to enter the tubing. Hold the tubing so that when it is cut the scraps will fall out of the usable end. Figure 1-61 shows some of the tubing cutters available. The tubing cutter is moved over the spot to be cut. The cutting wheel is adjusted so it touches the copper.
Fig. 1-61 Three types of tubing cutters. (Mueller Brass)
A slight pressure is applied to the tightening knob on the cutter to penetrate the copper slightly. Then the knob is rotated around the tubing. Once around, it is tightened again to make a deeper cut. Rotate again to make a deeper cut. Do this by degrees so that the tubing is not crushed during the cutting operation.
After the tubing is cut through, it will have a crushed end. The crushed end is prepared for flaring by filing and reaming. See Fig. 1-62. A file and the deburring attachment on the cutting tool can also be used. After the tubing is cut to length, it probably will require flaring or soldering.
Fig. 1-62 The three steps in removing a burr after the tubing has been cut with a tubing cutter. (A) The end of the cut tubing.
- Squaring with a file produces a flat (C) The tube has been filed and reamed. It can now be flared.
Flaring Copper Tubing
A flaring tool is used to spread the end of the cut cop- per tubing outward. Two types of tools are designed for this operation. See Fig. 1-63. The flaring process is shown in Fig. 1-64. Note that the flaring is done by holding the end of the tubing rigid at a point slightly below the protruding part of the tube. This protruding part allows for the stretching of the copper.
Fig. 1-63 Two types of flaring tools for soft copper tubing.
A flare is important for a strong, solid, leak-proof joint. The flares shown in Fig. 1-64 are single flares. These are used in most refrigeration systems. The other type of flare is the double flare. Here the metal is doubled over to make a stronger joint. They are used in commercial refrigeration and automobile air conditioners. Figure 1-65 shows how the double flare is made. The tool used is called a block-and-punch.
Fig. 1-64 Flaring tools. (A) This type of tool calls for the tubing to be inserted into the proper size hole with a small amount of the tube sticking above the flaring block. (B) This type of tool calls for the tubing to stick well above the flaring block. This type is able to maintain the original wall thickness at the base of the flare. The faceted flaring cone smoothes out any surface imperfections.
Adapters can be used with a single-flare tool to pro- duce a double flare. See Fig. 1-66.
Figure 1-67 shows joints that use the flare. The flared tubing fits over the beveled ends. The flare tee
uses the flare connection on all three ends. The half- union elbow uses the flare at one end and a male pipe thread (MPT) on the other end. A female pipe thread is designated by the abbreviation FPT.
Double flaring is recommended for copper tubing 5/16 in. and over. Double flares are not easily formed on smaller sizes of tubing.
Constricting Tubing
A tubing cutter adapted with a roller wheel is used to constrict a tubing joint. Two tubes are placed so that one is inserted inside the other. They should be within
- when inserted. This space is then constricted by a special wheel on the tube cutter. See Fig. 1-68. The one shown is a combination tube cutter and constrictor. The wheel tightens the outside tube around the inside tube. The space between the two is then filled with solder. Of course, proper cleanliness for the sol- der joint must be observed before attempting to fill the space with solder.
Both pieces of tubing must be hot enough to melt the solder. Flux must be used to prevent oxidation during the heating cycle. Place flux only on the tube to be inserted. No flux should be allowed to penetrate the in- side of the tubing. It can clog filters and restrict refrigerant flow.
Swaging Copper Tubing
Swaging joins two pieces of copper without a coupling. This makes only one joint, instead of the two that would be formed if a coupling were used. With fewer joints, there are fewer chances of leaks. Punch- type swaging tools and screw-type swaging tools are used in refrigeration work. The screw-type swaging tool works the same as the flaring tool.
Fig. 1-65 Double flares formed by the punch-and-block method. (1) Tubing is clamped into the block opening of the proper size. The female punch, Punch A, is inserted into the tubing. (2) Punch A is tapped to bend the tubing inward. (3) The male punch, Punch B, is tapped to bend the tubing inward. (4) The male punch is tapped to create the final double flare.
Fig. 1-66 Making a double flare with an adapter for the single-flare tool. (1) Insert the tubing into the proper size hole in the flaring bar. (2) Place the adapter over the tubing. (3) Place the adapter inside the tubing. Apply pressure with the flaring cone to push the tubing into a doubled-over configuration. (4) Remove the adapter and use the flaring cone to form a double-thickness flare.
Fig. 1-67 A half-union elbow (A) and a flare tee (B). Note the 45° angle on the end of the half-union elbow fitted for a flare. Also, note the 45° angles on both ends of the flare tee. Note that the flared end does not have threads to the end of the fitting.
Fig. 1-68 Tubing cutter adapter with a roller wheel to work as a tubing constrictor.
Tubing is swaged so that one piece of tubing is enlarged to the outside diameter of the other tube. The two pieces of soft copper are arranged so that the inserted end of the tubing is inside the enlarged end by the same amount as the diameter of the tubing used. See Fig. 1-69. Once the areas have been properly pre- pared for soldering, the connection is soldered. Today, most mechanics use fittings, rather than take the time to prepare the swaged end.
Forming Refrigerant Tubing
There are two types of bending tools made of springs. One fits inside the tubing. The other fits outside and over the tubing being bent. See Fig. 1-70. Tubing must be bent so that it does not collapse and flatten. To pre- vent this, it is necessary to place some device over the tubing to make sure that the bending pressure is applied evenly. A tube bending spring may be fitted either inside or outside the copper tube while it is being bent. See Fig. 1-71. Keep in mind that the minimum safe distance for bending small tubing is five times its diameter. On larger tubing, the minimum safe distance is ten times the diameter. This prevents the tubing from flattening or buckling.
Make sure the bending is done slowly and care- fully. Make a large radius bend first, then go on to the smaller bends. Do not try to make the whole bend at one time. A number of small bends will equalize the applied pressure and prevent tubing collapse. When using the internal bending spring, make sure part of it is outside the tubing.
Fig. 1-69 Swaging tool and swaging techniques. The swaging punches screw into the yoke and are changed for each size of tubing. Swages are available in 1/2, 5/8, and 7/8 in. OD, or 3/8, 1/2, and 3/4 in. nominal copper and aluminum tubing sizes.
Fig. 1-70 Bending tools for soft copper tubing.
Fig. 1-71 Using a spring-type tool to bend tubing.
This gives you a handle on it when it is time to remove it after the bending. You may have to twist the spring to release it after the bend. By bending it so the spring compresses, it will become smaller in diameter, and pull out easily. The external spring is usually used in bending tubing along the mid- point. It is best to use the internal spring when a bend comes near the end of the tubing or close to a flared end.
The lever-type tube bender is also used for bending copper tubing. See Fig. 1-72. This one-piece open-side bender makes a neat, accurate bend since it is calibrated in degrees. It can be used to make bends up to 180°. A 180° bend is U-shaped. This tool is to be used when working with hard-drawn copper or steel tubing. It can also be used to bend soft copper tubing. The springs are used only for soft copper, since the hard- drawn copper would be difficult to bend by hand. Hard-drawn copper tubing can be bent, if necessary, using tools that electricians use to bend conduit.
Fig. 1-72 A tube bender.
Fitting Copper Tubing by Compression
Making leak-proof and vibration-proof connections can be difficult. A capillary tube connection can be used. See Fig. 1-73. This compression fitting is used with a capillary tube. The tube extends through the nut and into the connector fitting. The nose section is forced tightly against the connector fitting as the nut is tightened. The tip of the nose is squeezed against the tubing.
If you service this type of fitting, you must cut back the tubing at the end and replace the soft nose nut. If the nut is reused, it will probably cause a leaky connection.
Fig. 1-73 A capillary tube connection.
