Pipes, valves & fittings
The ‘most useful’ tool in the box
Nigel Sanger, technical manager at JG Speedfit discusses the unsung heroes of plastic plumbing, analysing the various components which comprise their renowned plastic push-fit fittings
T
he benefits of plastic push-fit technology are becoming known to the plumbing industry. Not only do they facilitate a faster installation without the need for specialist tools, but they can also guarantee the most accurate pipe connection when working in challenging tight spaces. Less well-known, however, is how plastic push-fits are being designed to provide this versatility.
O-rings
I’m often asked about the lifespan of an O-ring. These are present in most power steering systems and also become an integral component of any push-fit piping system, when it comes to making a secure seal. While I have seen damaged O-rings, I’ve never seen one which has failed because it got old and started falling apart. The problem with O-rings is that they can be found in a large number of everyday products, and many plumbers often associate them with the type used in low cost products such as garden hoses, where they are inserted to prevent leaks. However, these O-rings are made from cheap and unreliable materials, which is why they are so prone to failure. O-rings, such as those you will find in Speedfit push-fits, are created with a highly-engineered material, known as EPDM (ethylene propylene diene monomer). It’s the same material used for O-rings which provide the primary pressure seal for disc brake calipers in cars, and should have a working life of up to 50 years. EPDM O-rings are incompressible. Therefore they are able to perform at high
pressure. However, they can be distorted, and it is this ability to change shape and conform to the outside face of the pipe and inside surface of the fitting that allows them to create a leak-proof seal. It’s this balance between distortional properties and seal strength that makes O-rings so effective in push-fit design. When designing a fitting, there should be scope for the O-ring to change shape. This enables the pipe to be pushed easily into the fitting helping the plumber design a reliable connection, as the O-ring cannot dislodge from its position.
Collets
This is actually the product that John Guest first invented back in 1974 and is a design that all our fittings are based upon. The collet allows you to create a secure connection easily with minimum insertion force. In the early days of push-fit plumbing, stainless-steel rings were used in place of collets. These would have teeth that had to be pushed apart when inserting the pipe. However, while the action of pushing the pipe through the teeth would stop it from falling out, it would often leave scratches on the surface of the pipe. To counter this, manufacturers had to place the O-ring first, seal, and then grip the ring in place. It was impossible to make the seal once the pipe had been pushed through the stainless-steel ring
22 August 2017
and had been scratched. The problem associated with this type of fitting is that installers would not always push the pipe in far enough to make a secure seal. They may have pushed the pipe through the O-ring, but often not through the grip ring. This would create a joint initially, but within six months, it would come apart and lead to catastrophic failure. The collet reversed this mechanism because it has been specially designed to have a very low insertion force so it doesn’t damage the surface of the pipe. Today, plumbers can insert the pipe into the collet which grabs the pipe, and then push it through the seal, guaranteeing a secure, leak- proof connection.
Twist and lock mechanism
When you consider the composition of a push-fit, the O-ring element of the fitting is fairly industry standard, and the metal gripping the pipe will either be a stainless-steel collet, or an old-fashioned grab-ring. Having an O-ring with a large surface seal means a high insertion force, and a risk of rolling the O-ring out of the fitting. Having a low insertion force means having a small area of the O-ring seal to the pipe surface and greater risk of leaks. To counter this, Speedfit fittings are engineered to have a strong seal and a low insertion force, through the use of a twist and lock mechanism. Once you push the pipe into the fitting, the collet tightly clamps onto the pipe, gripping it firmly. It also pushes the spacer washer against the O-ring, giving a greater seal on the outside of the pipe. This ensures that when plumbers tighten the outer cover, they end up with a more secure joint, which is part push-fit, part compression.
Inserts
Plain inserts and Superseal inserts give additional protection against side loading and provide a perfectly round pipe with a tapered leading edge to further ease the pressure needed to make a joint. However, a Superseal insert has two seals on it. One on the stem that pushes into the pipe, and one on the leading edge of the insert that fits into a pocket in the fitting to create a secondary seal. When you double the seal, you double the integrity of the fitting, whilst maintaining a low insertion force. All of these components play a vital role in creating a push-fit/twist and lock
compression mechanism, without the use of specialist tools. As the plumbing sector continues to pioneer new technologies, investigate new methods for first fix plumbing, and face pressures to further reduce installation times, the convenience and effectiveness of plastic push-fit fittings is going to continue to become the most useful – and sometimes, only tool – in the plumber’s toolbox.
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