The tips library
PEX by the numbers
PEX forgives a lot, but every joint on it lives or dies on a number. Here they are, from the tool and tubing makers' sheets and the PEX design guide.
Tip 1
Cut PEX square with a PEX cutter, never a hacksaw
The trick
A clean, square cut with no burrs or shavings, made with a cutter meant for PEX and approved by the tubing maker. Boshart's sheet says it flat out: do not use a hacksaw.
Why. Every PEX joint seals over the fitting's ribs, right up to the shoulder. A slanted end sits short on one side, and the PEX design guide says a ragged end risks a leak at the fitting.
The tell. Sight straight across the end. A slope or a squashed oval means cut it again. Sioux Chief adds: don't crush the tube with the cutter.
When to stop. No room left at a stub-out to cut it square again? That's a coupling and a new piece of tube, not a crooked joint.
Sources
- Plastics Pipe Institute and Plastic Pipe and Fittings Association, PEX Plumbing Design and Installation Guide, 3rd ed., Chapter 9
- Boshart, How to make a copper crimp ring PEX connection
- Sioux Chief, 305-649 Ratcheting Cinch Clamp Tool instruction sheet
Tip 2
Crimp ring sits an eighth to a quarter inch back from the end
The number
Ring on the tube, fitting in until the tube hits the shoulder, then set the ring 1/8 to 1/4 inch from the end of the tube. Tool square to the fitting, and close the jaws all the way.
Why. Boshart says that distance is what puts the ring right over the fitting's ribs. Too close to the end and it misses ribs. Too far back and it squeezes bare tube.
The tell. A ring that isn't centered over the ribbed part, or a crimp squeezed oval because the tool was cocked.
Boshart also says to make a test crimp before the job, because normal wear on a crimp tool opens the crimp up over time. The gauge on that test crimp tells you if the tool needs adjusting before it touches the house.
When to stop. Fails the go/no-go gauge? It doesn't get a second squeeze. Take the joint apart and start over with a fresh cut and a new ring.
Sources
- Boshart, How to make a copper crimp ring PEX connection
- PEX Universe, How does a go/no-go gauge work
Tip 3
Gauge every crimp. The tool doesn't get a vote
The trick
Hold the gauge square to the ring. The GO slot has to slide over it and the NO-GO slot must not pass over any part of it. On a single-slot U gauge, a good ring goes in to the line between GO and NO-GO and stops there.
Why. The ring has to land in a narrow window. Short of it, the ring is loose on the ribs. Past it, the ring is squeezed harder than the joint was built for.
The tell. On the U gauge: ring won't go in the first step, it's under-crimped. Ring goes all the way to the bottom, it's over-crimped. Boshart: stopped at the line and the gauge turns all the way around the ring, the joint is right.
No gauge on hand? Boshart says a micrometer or a caliper on the outside of the crimped ring will tell you the same thing, if you have the maker's number to measure against.
When to stop. Any fail: no re-crimp. Take the joint apart, start over at the cut with a new ring, and make a test crimp to check the tool first.
Sources
- Boshart, How to make a copper crimp ring PEX connection
- PEX Universe, How does a go/no-go gauge work
Tip 4
Cinch clamps sit 3/16 to 1/4 inch back, and the ear closes all the way
The number
Stainless cinch clamp 3/16 to 1/4 inch from the tube end so it covers both sealing barbs. The ear gets closed all the way, and Sioux Chief's sheet says its ratchet tool won't let go until it is.
Why. A cinch clamp seals by closing its ear to a fixed size. What drifts is the tool, so Sioux Chief has you gauge the tool's jaws, not the clamp.
The tell. An ear that isn't pinched fully closed. Sioux Chief says look at every clamp for the right closed-ear shape.
When to stop. Check the tool with its gauge before the first clamp and after the last one, every job. Out of adjustment at the end of the day? Every clamp since the last good check is suspect.
Sources
Tip 5
Expansion PEX: rotate between pumps and don't hold the last one
The number
Ring up to its stop edge, or no more than 1/16 inch past the tube end if it has none. Expand, release, turn the head 1/8 turn, expand again, only as many times as the fitting needs. Don't hold the last one open. Fitting in right away.
Why. Turning the head spreads the stretch. Skip it and Uponor says you cut deep grooves in the tube that can become leak paths. Then the tube's memory shrinks it back down onto the fitting.
The tell. You should feel some drag as the fitting goes in. No drag at all, the tube may be over-expanded and needs extra time to shrink down.
Uponor's sheet says some tool and head combinations turn the head for you and some don't, so watch that the head actually turns on every pump.
When to stop. Fitting won't go all the way to the stop? Pull it right away and expand one final time. Don't force it in.
Tip 6
Cold day expansion: fewer pumps and warm rings
The number
Below 40 F, Uponor says fewer expansions. Keep the rings and fittings in your pockets so they're warm when they go on.
Why. The colder it is, the slower the tube shrinks back down. Give it the summer pump count in January and it's stretched more than it can close in a hurry.
The tell. Same drag test as any day: the fitting should go in with some resistance. In the cold, a joint that went in easy needs more time before you call it done.
When to stop. Done shrinking, ring still more than 1/16 inch off the fitting shoulder? It gets cut out and made again. Cold is no excuse.
Tip 7
Look at the shoulder: more than a sixteenth gets cut out
The number
The finished ring sits snug against the fitting shoulder. More than 1/16 inch (1 mm) of gap and the connection gets replaced. Uponor's manual: square cut 2 inches from the fitting on 1/2 to 1 inch pipe, 3 inches on 1-1/4 to 2 inch.
Why. A gap at the shoulder means the tube and ring never covered the whole sealing surface of the fitting.
The tell. Daylight between the ring and the shoulder.
When you cut one out, Uponor says its brass fittings can be used again, but its plastic ones get thrown away.
When to stop. Not enough tube left to cut back and remake? Stop there. That's a coupling and a new piece of tube, or a plumber.
Sources
Tip 8
Bend PEX no tighter than six times its outside diameter
The number
Minimum bend radius is 6 times the tube's actual outside diameter: 3.8 inches for 1/2 inch PEX, 5.3 inches for 3/4 inch, 6.8 inches for 1 inch. On certain coiled tubing, bending against the coil takes three times that.
Why. PEX is bigger outside than its name: 1/2 inch PEX measures 0.625 inch across. The radius goes by that real size, because bending tighter is what flattens the wall and kinks it.
The tell. A flat spot or a kink at the bend. For a tight turn close to a fitting, the design guide calls for a bend support, which also takes stress off the joint.
The radius is measured to the middle of the bend. The guide says the tubing maker can specify otherwise, so if your tube's sheet gives a different number, the sheet wins.
When to stop. A kink gets cut out and joined with fittings. Never take a torch near it: open flame is on the design guide's list of things PEX must not touch.
Sources
- Plastics Pipe Institute and Plastic Pipe and Fittings Association, PEX Plumbing Design and Installation Guide, 3rd ed., Chapter 9
Tip 9
Leave 1/8 inch of slack per foot, and bore the holes big
The number
Leave 1/8 inch of slack per foot of run. Bore holes at least 1/4 inch bigger than the tube's outside diameter: 7/8 inch for 1/2 inch PEX. Support horizontal runs of 1 inch and under no more than 32 inches apart.
Why. PEX grows and shrinks a lot with temperature. The design guide puts it at about 1.1 inches per 10 F per 100 feet. Slack and loose holes let it move without pulling on the fittings.
The tell. Tube pulled dead straight between fittings with no droop, or tube jammed in a hole the size of the tube.
The guide also says don't use supports that pinch or cut the tubing, and keep PEX away from pipe dope, solder flux and open flame.
When to stop. Boring or notching joists past what code allows weakens the framing. That's a builder's or a plumber's call, not yours.
Sources
- Plastics Pipe Institute and Plastic Pipe and Fittings Association, PEX Plumbing Design and Installation Guide, 3rd ed., Chapter 9
The Old Tradesman is a cartoon character. Every tip on this page stands on the sources listed under it. He is the voice. They are the authority. The drawings are diagrams, not photographs.
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