Push-fit plastics first deskilled drainage and new improvements look set to convert water supply and central heating. Mark Brinkley visits a Westbury site to review one of Wavin OsmaGold’s first applications.
Plastic hot and cold plumbing is not new - Acorn, precursor of Hep2O, was launched in 1979 - but the launch of Osma and Marley systems this year opens a new chapter. It may also mark the beginning of the demise of copper plumbing. To date copper’s market share in hot and cold water supply and central heating has been no more than mildly dented - it still has about 85%. There has been little cost advantage to encourage plumbers to switch to plastic and early systems failed to establish a reputation for reliability; there were well-reported failures, usually resulting from joints springing.
But plastics technology never stands still and early adopters Hepworth and Speedfit have improved their systems and the lessons learned seem to have been taken on by new entrants into the market. OsmaGold reckons to have designed out every conceivable installation error and early feedback from a Westbury Homes site supports this view. Peter Shepherd of PSS Midland is first-fixing houses on the Westbury Village site in Bicester and reckons OsmaGold is the best designed and easiest to use of the three systems he has used. What is more, he admits that the time taken for first fixing a house is reduced from around 12 hours using copper pipe down to about 6 hours. “It’s not really something plumbers want to shout out from the rooftops because it’s going to do us all out of a job. Personally I have never had a problem with any plastic system but this one is particularly easy; the pipe is more flexible and the fittings are ever so well designed.”
Copper is still used in places in these houses. Westbury specify exposed radiator tails and bath and sink connections in copper and, of course, boiler connections and gas piping have to be copper.
Marley’s Equator system is very different to OsmaGold, principally in using a different plastic, cross-linked polyethylene - better known as PE-X - which is used in underfloor heating. Marley is also keen to advance the principle of manifold plumbing whereby every outlet is connected directly to a central point, rather than linked in a multi-jointed circuit. Advocates of PE-X point to its reputation for reliability: critics say it is less flexible than polybutylene, making it less forgiving to work with.
Industry divide over ring location
The two key elements contained within the fittings are the rubber O ring, which provides the water seal, and the metal grab ring, which locks the pipe in place. To make a permanent watertight connection both the O ring and the grab ring have to be fully penetrated by the pipe; failure to do this is the principal cause of leaks. The question which still taxes manufacturers is which of the two rings should be on the outside. Of the five main manufacturers, two chose one method, two chose the other while Hepworth recently changed on their latest fittings, the O ring is on the inside. Hepworth’s George Bell explains: “We have experienced a small number of catastrophic failures caused by apparently watertight joints coming apart many months or even years after installation, precisely because the pipe was never inserted deep enough into the fitting to penetrate the grab ring. In some cases, this installation fault hasn’t even been uncovered by a pressure test. By placing the grab ring on the outside, any assembly fault will show up immediately water is run through the system. We are now convinced that this is the correct arrangement and we have redesigned our fittings so that the grab ring is on the outside.” In contrast, Osma remain confident that the place for the grab ring is on the inside. They believe they have designed out the problem with a better watertight seal which they refer to this as an M ring rather than an O ring. Osma’s Norman Spencer comments: “We believe that Hepworth’s problem stemmed from the outer O ring being quite difficult to penetrate. It could take quite a push to break through and this sometimes led plumbers to think they had made a good connection when in fact the pipe had never even got to the grab ring. Our M ring system requires only the softest push: there is no noticeable resistance until you get to the grab ring.” Currently the plastic plumbing industry lines up like this. O rings first: OsmaGold, Polyplumb, Legacy Hep2O. Grab rings first: John Guest, Marley Equator and the new Hep2O BiTite fittings. What isn’t disputed is that if the joints are properly assembled, both types of fitting will remain watertight.
