Internal PVC Pipe Repair Coupling - 40mm (1.5") & 50mm (2") - Class 9 & Class 12 - Pool & Spa Pressure Pipe

Internal PVC Pipe Repair Coupling - 40mm (1.5") & 50mm (2") - Class 9 & Class 12

An internal repair coupling for PVC pressure pipe. Unlike an ordinary coupling, this one glues inside the two pipe ends rather than over them, so the repair adds nothing to the outside diameter of the pipe.

That is the whole point of the fitting. It is the repair for a cut or cracked pipe you cannot pull apart: pipe cast into a slab, run through a wall, buried hard against something, or sitting tight behind equipment.

Get The Class Right Or It Will Not Fit

This is the part people get wrong. Because the coupling seats inside the pipe, what matters is the pipe's internal diameter, and the internal diameter changes with the pressure class. Same 40mm pipe, different class, different bore.

Australian PVC pressure pipe to AS/NZS 1477 is sized by its outside diameter, which stays the same across every class. The class sets the wall thickness, and the thicker the wall the smaller the bore. So a Class 12 pipe has a noticeably tighter bore than a Class 9 pipe of the same nominal size, and the couplings are not interchangeable.

Dimensions are from the AS/NZS 1477 Series 1 PVC-U pressure pipe tables and agree with the published Vinidex and Iplex pipe data.

How To Tell Which Class You Have

• Read the pipe. Pressure pipe is printed along its length with the standard and the class, as "AS/NZS 1477" and "PN9", "Class 9", "PN12" or "Class 12". This is the reliable method. Wipe the pipe down and look, including on the offcut you just removed.
• Measure the wall. Once the pipe is cut you can measure the wall thickness on the cut face with vernier calipers. On 40mm, roughly 2mm is Class 9 and roughly 2.8mm is Class 12. On 50mm, roughly 2.6mm is Class 9 and roughly 3.3mm is Class 12. The gap between the classes is large enough to call with confidence.
• Measure the bore. Compare against the ID column above. Measure across the cut end, not down a socket.

Not sure after all that? Send us a photo of the pipe print and the cut end with a tape or calipers across it, and we will tell you which one you need.

What These Do Not Suit

• DWV pipe. Waste pipe to AS/NZS 1260 is a different size system, with different outside and inside diameters, and it carries no pressure class. If the print says AS/NZS 1260, or there is no class marked at all, this is not the fitting.
• Class 6 and Class 18 pressure pipe. 40mm and 50mm pipe is also made in Class 6, which has a wider bore, and Class 18, which has a much tighter one. Neither variant here will make a sound solvent weld in those.
• Flexible spa pipe. SpaFlex and similar flexible PVC have their own bore and need a fitting made for them.
• Imperial schedule pipe. US Schedule 40 and Schedule 80 share some outside diameters with the metric range but not the bores.

Internal Or External Coupling

Use an ordinary external coupling wherever you can. It is cheaper, the joint is visible, and it is more forgiving to glue. An internal coupling earns its place only when the pipe cannot move.

• Pipe ends can be sprung apart, or one run can be pulled back: use a standard coupling, such as our 50mm PVC coupling joiner.
• Neither end will move, or there is no clearance around the pipe: use the internal coupling on this page.
• You have room to cut out a section and want flexibility: a length of 40mm or 50mm flexible pipe with couplings is often the easier repair.

Fitting

1. Isolate the pump and drain the line. Solvent cement will not take on a wet surface and a joint made on a pressurised line will fail.
2. Cut the damaged section out square. In a tight spot a PVC wire saw will cut pipe where no cutter or hacksaw will reach.
3. Deburr both pipe ends inside and out, and clean the inside of each end back far enough to take half the coupling. The inside of the pipe is the gluing surface here, so it has to be clean and dry.
4. Dry-fit first. The coupling should push in firmly by hand. If it drops in loosely you have the wrong class, and if it will not start you have the other wrong class. Do not force it and do not sand it to fit.
5. Apply solvent cement to the coupling and to the inside of the pipe, then push home with a slight twist and hold for 30 seconds. Work quickly, because you get one attempt.
6. Keep the cement off the far end of the coupling. Excess inside the bore has nowhere to go and can end up carried into the pump or filter.
7. If your coupling has a centre stop, each pipe end butts against it, so set the gap between the pipe ends accordingly. If it has no stop, slide it fully into one end first, bring the pipes together, then draw it back to centre.
8. Let the joint cure before you pressurise it. Follow the cure time on the cement for the pipe size and the day's temperature, and leave it longer in the cold.

An internal joint cannot be inspected once it is made and cannot be cut out and redone without losing more pipe. If the repair is on a buried line or anywhere a leak would be expensive to find again, this is work for an experienced hand.

Choosing Your Variant

• 40mm Class 9 suits 40mm pressure pipe with a 44.05mm bore
• 40mm Class 12 suits 40mm pressure pipe with a 42.75mm bore
• 50mm Class 9 suits 50mm pressure pipe with a 55.15mm bore
• 50mm Class 12 suits 50mm pressure pipe with a 53.65mm bore

You Will Probably Also Need

• 747 PVC solvent cement, 118mL or the 473mL tin
• PVC wire saw, for cutting pipe in tight spots
• 50mm PVC coupling joiner, the standard external coupling

Frequently Asked Questions

Why does the class matter on an internal coupling?
Because the coupling seals against the inside of the pipe. Pressure pipe keeps the same outside diameter across all classes and changes its wall thickness instead, so the bore is different in every class. A 40mm Class 9 pipe has a 44.05mm bore and a 40mm Class 12 pipe has a 42.75mm bore, a difference of more than a millimetre.

How do I find the class of my pipe?
It is printed along the pipe with the standard, as "PN9" or "Class 9". If the print has worn off, measure the wall thickness on the cut face. On 40mm pipe Class 9 is about 2mm and Class 12 about 2.8mm.

Will this fit 40mm or 50mm DWV waste pipe?
No. DWV pipe is made to a different standard with different diameters. Pool and spa plumbing is pressure pipe, not DWV.

Can I use an internal coupling instead of a normal one?
You can, but there is no reason to. A standard external coupling is cheaper and easier to glue. The internal coupling exists for repairs where the pipe cannot be sprung apart or there is no room around it.

What if my pipe is Class 6 or Class 18?
Neither of these will fit. Contact us with the pipe size and class and we will tell you what the options are.

Do I need primer as well as cement?
Clean, dry, deburred surfaces matter more than anything else on this joint. Use the solvent cement according to its own instructions, and remember the inside of the pipe is the surface being welded, so it needs the same preparation you would give a socket.

Common search terms: internal pipe repair coupling, internal pipe joiner, PVC internal coupling 40mm, PVC internal coupling 50mm, class 9 internal joiner, class 12 repair coupling, pool pipe repair coupling, slab pipe repair, repair cut PVC pipe no movement, internal joiner with stop.

Before ordering: confirm both the pipe size and the pipe class. These are not interchangeable and an internal coupling cannot be adjusted to fit. If you are unsure, seek professional assistance or contact us with photos of the pipe print and the cut end. As with all products, this must be diagnosed and fitted by a qualified and experienced person.