Unlike other plastics, polyethylene (PE) is not solvent-welded with glue. The method you choose to join poly pipe depends on the pressure, permanence and pipe material it is being joined to. Compression fittings seal with a captive O-ring the moment they go on the pipe and can afford a tool-free installation depending on diameter and material. Electrofusion permanently fuses pipe and fitting into one part, ideally for highly demanding scenarios, particularly in civil, industrial and mining applications. And threaded fittings simply screw into place.
Method
Compression
Electrofusion
Threaded
How it seals
Captive O-ring compressed between the fitting body and the pipe
Embedded wires heat and fuse the pipe and fitting into one part
Screwed connection e.g. to BSP
Reversible
Yes – undo and reconfigure
No – permanent
Yes
Typical use
Water‚ irrigation‚ rural‚ general plumbing
Gas‚ fire mains‚ civil water and waste water
Conversions and take-offs to threaded systems
Compression
Compression fittings are tough, light black fittings with nuts you do up to connect pipe in the configuration you need. PLASSON compression fittings seal the instant they go on the pipe: the O-ring is held captive in a machined groove in the fitting body, so it can’t fall out, get contaminated or be damaged. Tightening the nuts only holds the pipe in place and prevents blow-outs – it is not what makes the seal.
Smaller diameters and rural barbed fittings can be pushed on by hand; larger metric fittings need only a wrench to bring the nut up. Because the joint is mechanical it can be undone and reconfigured, which suits repairs, extensions and any run that may change. It is the default across water, irrigation, rural and general plumbing.
Electrofusion
Electrofusion is permanent. Wires embedded in the fitting heat up when current is applied, melting and mixing the plastic so the pipe and fitting become one continuous part. The result is a joint as strong as the pipe itself, which is why it is specified for the most demanding work – buried, large-diameter and critical infrastructure across civil, industrial and mining. PLASSON SmartFuse electrofusion fittings run from 16 mm up to 1000 mm and cover yellow-stripe gas, some red-stripe fire mains, and blue-stripe civil water and waste water. Each weld can be recorded and traced through the SmartFuse system.
Threaded
Threaded fittings screw into place and connect poly to a threaded system – a male or female BSP take-off to a meter, valve, tap or another pipe material. They are the simplest join where a mechanical seal onto the pipe is not needed at both ends.
How PLASSON compression fittings seal
PLASSON compression fitting uses the same captive O-ring design. The O-ring sits in a specially machined groove and compresses against the pipe as it is inserted, sealing before the nut is tightened. The mechanical fittings are flexible and stable enough to hold that seal through ground movement. Body and nut are polypropylene, high-grade copolymer, and the fittings are rated to PN16.
Fitting types
Fittings do more than lengthen a run. They divert, combine, reduce, cap, monitor or take off flow.
Fitting
Tee & Wye
Elbow
Coupling
Adaptor
Cap
Plug
Bushing
Nipple
Flange
Ag pipe
What it does
Connect three pipes. A tee splits or combines at 90° in a “T”; a wye joins at about 45° in a “Y” for drains.
Change flow direction. Common bends are 90°‚ 60°‚ 45° and 22½° and can be combined around obstructions.
Slip over two pipe ends to join them; can also reduce one size to another.
Connect two different pipe types – poly to copper or poly to a threaded connection.
Fit over a pipe end to stop flow permanently or as a temporary cut-off.
Seal into a threaded pipe opening (a cap fits over a plug fits in); common at sewer cleanouts.
Reducer that connects two pipe sizes one seated inside the other.
Short section male-threaded at both ends joining two female-threaded ends.
Bolted flat fitting for wall floor and ceiling pass-throughs and for connecting valves to mains in electrofusion installs.
Rural couplings and clamp saddles for imperial ¾″ to 2″ pipe. Red barbed inserts connect ag pipe without tools.
Joining different pipe sizes
Reducing fittings join two different-diameter metric HDPE pipes. Reducing sets are inserts that adapt an existing PLASSON compression fitting to a smaller outlet while keeping its pressure rating and leak-free seal. A reducing tee takes a smaller off-take off a main line. Reducing fittings match common pipe sizes, are rated to PN16 (up to 16 bar, varying with ambient and fluid temperature) and suit PELD, PEHD, PE40, PE80 and PE100 pipe.
Joining different pipe materials
Standard PLASSON compression fittings adapt to other materials with conversion kits: copper, galvanised, PVC and PEX, plus threaded connections. Universal slip repair fittings and adaptor kits cover mixed-material joins and repairs. The Barrel Union Threaded Male Adaptor converts the end of a Line 7 metric compression fitting straight to a male BSP thread.
Sizes
PLASSON compression fittings start at 16, 20, 25 and 32 mm for domestic plumbing and run up through 40, 50 and 63 mm to above 1000 mm for civil and industrial work.
Install guides
View our installation guides page for video explainers and easy to follow installation sheets, including:
- Metric compression fittings
- Compression joiners 75–125 mm
- Rural fittings, no tools
- Poly-to-copper fittings
- Slip repair couplings
- Metric MineSafe couplings 63–125 mm
- Joining pipe of different diameters
FAQ
How do you join poly pipe?
Three ways: compression fittings, threaded fittings, or electrofusion. Compression and threaded are mechanical and reversible; electrofusion is a permanent fused joint.
Do you glue poly pipe?
No. Polyethylene is not solvent-welded like PVC. It is joined by compression fittings or by fusion.
Can you undo a compression fitting?
Yes. Compression joints can be undone and reconfigured.
Can you join poly pipe to copper?
Yes, with an adaptor or conversion kit. PLASSON fittings also connect galv, PVC, PEX and threaded systems.
How do you join two different-size poly pipes?
With a reducing fitting, or a reducing set that adapts an existing fitting to a smaller outlet while keeping its pressure rating.
What pressure are PLASSON compression fittings rated to?
PN16 – up to 16 bar, varying with ambient and fluid temperature.
