How to Make a Copper Press Joint

Why this matters

A press joint takes seconds, works on a line that will not drain dry, and needs no flame in a finished house. Those are the reasons shops love it, and the reason it fails: because it is fast, it gets made without the two checks that prove it. A tube that was not fully inserted, or that backed out when the next joint was pressed, can hold a test at static pressure for weeks with a partial grip, then let go on a water hammer. The mark on the tube is the only evidence of insertion that survives the press, and it only works if it was drawn before the tube went in. When to use press rather than solder is owned by The Joining Method Standard SOP; this card is how to make the joint once that call is made.

What the fitting does

A copper press fitting has a bead near each end holding an O-ring, EPDM on fittings for water. The press jaw closes over the bead and deforms the fitting and the tube together: the O-ring is compressed into a seal, and the copper of fitting and tube is crimped into a mechanical grip. Both depend on the tube being inside the fitting to its full socket depth and being round, clean and unscored where the O-ring lands. Fittings for fuel gas use a different seal and carry their own color marking; a water fitting does not go on gas, and the other way round.

Most fittings are made so that an unpressed joint leaks visibly during a pressure test within a range the maker states, which catches the joint that was assembled and forgotten. It does not catch a joint that was pressed with the tube short of full depth, which is why the mark matters more than the leak feature.

Hazards at the tool and the line

Pinch. A press tool closes with several tons of force. Both hands stay on the tool, nobody steadies the pipe near the jaw, and you never press with a finger between the jaw and a joist or a wall. Keep the tool's trigger finger off until the jaw is seated.

Cutting and deburring. The tube cutter's wheel and a sharp burr both cut. Deburr away from your hand.

Wet lines. Press is chosen on wet lines, so expect water at the cut. Keep it off any receptacle or appliance below the work; if water reaches an electrical device, switch off and lock out its circuit before going near it, and leave it off until the device is dry and has been checked; a device that got wet inside goes to an electrician.

One joint, start to finish

1. Inspect the tube. Look at the last inch or two of the tube end for dents, out-of-round, deep scratches running along its length, or hard deposits. Why: the O-ring seals against the tube's outer surface. A lengthwise scratch is a leak path under the seal. Cut back to good tube if needed.

2. Cut square. Tubing cutter, light pressure, increase a little each revolution. Why: a skewed end bottoms on one side only, so the socket depth on the short side is less than the fitting needs.

3. Deburr inside and outside. Ream the inside, and take the sharp edge off the outside with a deburring tool. Why outside: a sharp outer edge can slice or roll the O-ring as the tube slides past it, and a cut O-ring will pass a short test and weep later.

4. Mark insertion depth. Use the fitting maker's depth gauge, or measure the socket depth of that fitting, and mark the tube with a fine marker at that distance from the end, all the way around or at least on the side you will see after the joint is made. Why: once pressed, nothing else tells you where the tube end is.

5. Check the fitting. O-ring present, seated in its bead, no grit, no stray flux or cutting chips. Use only the lubricant the maker allows, if any. Why: a missing or displaced O-ring is uncommon and impossible to see after pressing.

6. Insert to the mark. Push the tube in with a slight twist until the mark meets the fitting face. Why the twist: it eases the tube past the O-ring rather than pushing the ring ahead of it.

7. Seat the correct jaw square on the bead. Use the jaw for that size and that fitting's profile, as the fitting maker lists. Center it on the bead and hold the tool perpendicular to the pipe. Why: a jaw off the bead presses the wrong part of the fitting, and a jaw at an angle presses one side harder than the other.

8. Press one full cycle. Pull the trigger and let the tool complete its cycle without interruption; most tools finish the stroke on their own and signal when done. Why: a cycle stopped partway leaves a partial press, which can look like a full one.

9. Check the mark, and the indicator. The mark should still sit at the fitting face. Remove any press indicator tag or check the indicator the maker uses. Why now: pressing the next joint can spring the pipe and pull a tube back out of the last one, and that only shows in the mark.

10. Test before the wall closes. The pressure test the adopted code requires (IPC 2021 Section 312.5 or the UPC 2021 test provisions, as adopted), within the range where the maker's unpressed-joint feature works if you want it to show.

  GOOD                        BACKED OUT
  fitting face                fitting face
       |                           |
  =====|mark=========    =====|         mark=====
       |                           |<-- gap -->|
  mark meets the face         tube pulled back;
                              grip and seal short

A worked job

The scope. A corroded section of 3/4 in type L copper above a gas water heater, inside a finished utility closet with drywall above. The line could not be drained dry because the house's lowest drain was blocked by a stuck boiler valve, so solder was off the table. The work: two press couplings joining a new 14 in piece, plus a press ball valve on the heater's cold side that was missing. Five press ends in all: two per coupling and one where the valve's upstream end meets the cold line, the valve's downstream end taking an existing threaded adapter.

Preparation. Main off, heater gas control turned to pilot, a hot tap opened upstairs. The cuts weeped water steadily into a bucket. Each tube end was inspected, cut, reamed and edge-deburred, then marked from the maker's depth gauge for 3/4 in fittings.

Pressing. The first coupling went on and both ends were pressed. The new 14 in piece was then pushed into the second coupling, and in getting it lined up the installer had to flex the tube. After pressing the second coupling, a check of every mark showed the downstream end of the FIRST coupling with its mark about 1/4 in back from the face: the tube had pulled out when the piece was flexed. The joint had been pressed with the tube at full depth, then the tube had moved. Nobody could say what grip the deformed copper still had, so the whole coupling was cut out, leaving a gap of about 3 in that was closed with a short new piece and two new couplings, each tube end marked and checked again after every press.

The tally. Nine ends pressed in all: the original five plus four on the repair. One failed its mark check, the backed-out end; its mate came out with the same coupling though its mark was fine. Seven ends remain in the finished line, every mark at the face.

Test and return. The main was opened slowly with the upstairs tap open to bleed air, then the tap was closed. The system came up to its 60 psi static and held with all seven press ends dry under a paper towel for 15 minutes. The gas control went back to its setting and the main burner lit with a steady flame.

What the case shows. The joint that failed was pressed correctly. The step it failed was step 9, applied to the previous joint rather than the one in hand. A crew that checks only the joint it just pressed will miss exactly this.

When the call forks

Tube that is not round. Annealed (soft) copper that has been bent or crushed near the end may need a sizing tool, or more often a cut back to round tube, depending on the maker's instructions. Do not press over an oval.

Old tube with heavy scale or paint. Clean the seal area with sand cloth to bare metal, but do not sand a groove into it. If the surface is pitted, cut back.

Mixed makers. Fittings and jaws are a system; a jaw that fits another maker's bead is not necessarily listed for it. Use the combinations the fitting maker publishes.

Tight to a wall or a joist. The jaw needs clearance all the way around the bead. Where a standard jaw will not seat square, the maker's compact jaws or a ring-and-actuator set may fit; if nothing seats square, move the joint rather than press it crooked. Plan joint locations before cutting on a retrofit, because once the tube is cut short against a wall there is no moving it.

Sizes over 1 in. Larger fittings generally take a press ring wrapped around the bead and closed by an actuator jaw, rather than a direct jaw. The steps are the same; the ring has to be fully closed around the bead and latched before the press, and the depth mark matters more, because a larger tube is harder to push fully home and easier to stop short.

Air test instead of water. Some makers allow an air test of their press systems and some limit it. Compressed air stores far more energy than water at the same pressure, so a joint that lets go on air throws the tube and the fitting; nobody stands in line with an open pipe end, and the test pressure and medium are the ones the maker and your code allow.

Tool service. Press tools have a service interval set by the maker, often counted in cycles. A tool past its interval can lose force without obvious signs. The shop's tool log is where that number lives.

How to verify it on someone else's work

• Marks visible at every fitting face, or at least on the side you can see. No mark at all on a press job means nobody can prove insertion.
• No leftover indicator tags on any fitting, if the system uses them.
• Jaw impressions centered on each bead and even all the way around.
• A test record with the pressure, the medium and the time held, written before the wall closed.

References

• Fitting and tool makers' installation instructions, which are part of the listing, including the jaw combinations and test ranges
• IPC 2021 or UPC 2021 water supply test provisions, as adopted by your jurisdiction
• See related: The Joining Method Standard SOP
• See related: How to Sweat a Copper Water Joint That Passes First Time