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  • Writer's pictureTodd Engle

PEX what is this stuff?

PEX Plastic Tubing

PEX is polyethylene cross-linked plastic tubing. The cross-linked structure prevents the pipe from rupturing over a wide range of temperatures and pressures. PEX is resistant to solvents and cannot be joined by solvent cementing. PEX is flexible and can be bent. PEX can be hot-bent with a hot-air gun. The minimum hot-bending radius is 2½ times the outside diameter. PEX can be cold-bent, too (at room temperature) to a minimum radius of 6 times the outside diameter.

PEX manifold by CPI® Paul Haug

Gridded and parallel water distributions systems use individual supply pipes that extend to each fixture from a central supply point. The central point is a manifold to which the individual supply pipes connect. These systems have advantages over the traditional branch distribution system. Individual shutoff valves installed at the manifold should be identified as to the fixture being supplied, since the control function of valves at the manifold would not be apparent.

A manifold with parallel-connected individual water distribution lines is a system that provides a centralized distribution point (manifold) for all fixture supply piping, both hot and cold. The system gets its name, “parallel-connected,” from the fact that the hot and cold distribution pipes for each fixture run “parallel” from the central manifold to each fixture. Such systems are analogous to a main (centralized) electrical panel where parallel wires (a hot and a neutral) are routed to an appliance (a fixture).

A gridded water distribution system involves water distribution pipes that are fed from each end or possibly from multiple points in the system. Such systems allow greater design flexibility and can provide the required flows and pressures with smaller diameter piping (as compared to conventional “trunk and branch” systems). The prohibition of gridded distribution systems for supplying the hot water distribution system is because these types of systems delay the arrival of hot water to the outlets, wasting water and energy.

Fixture valves can be installed either at the fixture or at the manifold. However, where valves are installed at the manifold, they must be labeled to identify the fixture served. This is analogous to the requirement that circuit breakers in an electrical panel be labeled.

If an inlet or outlet will not be used at the manifold, it must be capped.

The main service line to the manifold may include a main shutoff valve if required by local code. There should be a valve shutoff key readily accessible at the manifold.

One securing clamp should be installed for each tube. The clamps and tubing supports should be only plastic or plastic-coated, no metal. Clamps should not be installed more than 6 inches from the end of the port. The tubes at the manifold should exit the port at a 90° angle to the centerline of the manifold. It should come out of the manifold straight, not at a curve or angle.

PEX tubing should not be connected to the water heater directly.

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