A compression fitting joins polyethylene (PE) pipe with a captive O-ring that seals against the pipe the moment it is inserted – no glue, no heat. The nut only holds the pipe against blow-out; it does not make the seal. PLASSON compression fittings are rated to PN16 and run from 16 mm for domestic plumbing to over 1000 mm for civil and industrial work.
How the seal works
Every PLASSON compression fitting seals the same way. The O-ring sits captive in a groove machined into the inside of the fitting, which holds it in the optimum sealing position. As the pipe passes through the O-ring, the ring compresses against it and the joint is watertight – before the nut is touched. The nut is then tightened only to stop the pipe pulling out, or blowing out, under pressure.
Because the seal comes from the O-ring and not the nut, 16 mm to 32 mm fittings go on hand-tight, and rural fittings need no tools at all. The captive groove also means the O-ring can’t fall out, be lost, damaged or contaminated during installation – a common failure point on fittings where the ring sits loose.
The mechanics are straightforward: compression deforms the O-ring into the gap between the fitting and the pipe, closing off any leak path. Fluid pressure then pushes the ring against the groove wall on the low-pressure side, and at higher pressures the ring deforms toward a “D” shape, increasing the contact area and the sealing force. More pressure, tighter seal.
What makes them reliable
Four things separate a PLASSON compression fitting from a generic one:
Feature
Instant sealing
Material flexibility
Long body
Pull-out resistant
What it means on the job
The captive O-ring seals before you tighten the nut. Smaller and rural fittings go on by hand – faster installs fewer leaks to chase.
Convert the same fitting to join metric poly (blue line) rural poly‚ PVC‚ steel and copper. One system across a mixed site.
The extended body keeps the seal intact through bending loads and ground movement where a short fitting would let go.
Every PLASSON fitting exceeds the pull-out requirements of the Australian Standard which is why they suit submersible bore work.
O-ring materials
The seal can be specified in three elastomers, depending on what the pipe carries:
O-ring
Nitrile (NBR)
EPDM
Viton (FKM/FPM)
Chemical resistance
Standard
Better than NBR
Best of the three; high temperature
Typical use
Water and general service
Wider chemical range
Oils‚ fuels‚ hydraulic fluids‚ aromatics and solvents
Materials and ratings
PLASSON compression fittings are rated to PN16 and work across high and low pressure. The bodies are corrosion resistant, UV stabilised, light and strong, so they hold up outdoors and in aggressive fluids without the corrosion that ends the life of metal fittings.
Sizes
The range starts at 16, 20, 25 and 32 mm for domestic plumbing and runs up through 40, 50 and 63 mm to above 1000 mm for civil water and waste water.
Where the O-ring came from
The O-ring is older than it looks. It was first patented in Sweden in 1896 by J.O. Lundberg, and again in the US in 1937 by Niels Christensen. It became the standard hydraulic seal, and the military set the standard sizes still in use today. PLASSON’s contribution was simple: machine a groove that holds the ring in the exact position it needs to seal, every time. That is the whole reason a PLASSON fitting seals on contact.
Fitting types
Couplers, tees, elbows, reducers, adaptors, caps, plugs, bushings, flanges and rural fittings all use this same seal. For more information on how to join poly pipe, click here.
Visit our installation guides page for more video explainers and easy to follow installation sheets.
FAQ
What is a compression fitting?
A mechanical fitting that joins PE pipe with a captive O-ring. The O-ring seals against the pipe as it is inserted; no glue or heat is used.
Do you tighten the nut to make the seal?
No. The O-ring makes the seal on contact. The nut is tightened only to hold the pipe against blow-out under pressure.
Can you install PLASSON compression fittings by hand?
Yes for 16 mm to 32 mm fittings, and for rural fittings, which need no tools.
What O-ring materials are available?
Nitrile (NBR) for general service, EPDM for a wider chemical range, and Viton (FKM) for oils, fuels and high temperatures.
What pressure are they rated to?
PN16, across high and low pressure.
Can compression fittings join poly to copper or PVC?
Yes. The same fittings convert to metric poly, rural poly, PVC, steel and copper.
Not sure which fitting?
Use the Product Finder, or call the team on 1300 752 776.
