Inner-ducting is the process by which you make pipe interiors smaller by installing smaller pipes inside the larger ones. You may be wondering why anyone would do that, since all they would have to do is remove the larger pipes and replace them with smaller pipes, but there are several good reasons, certainly not the least of which is insulating the cables or wires that pass through the smaller conduits. Since you can use either PVC pipe or HDPE pipe, however, you should be very careful about which type of couplers you use to install the inner-ducting. Here are three reasons why you should never mix HDPE couplers with PVC pipe (and vice versa).
HDPE Expands and Contracts
HDPE, or High Density Polyethylene, is favored for its ability to expand and contract under pressure and when heated. While these qualities are favored in certain industries, they may not work quite as expected if you connect couplers and pipes of HDPE to PVC. PVC pipe and couplers are very rigid and will not expand or contract quite like HDPE does. Therefore, connecting pipes and couplers of both materials together could result in several leaks and breaks in the line.
HDPE Couplers Handle Being Compressed inside Larger Conduits
When you need to fit HDPE pipe inside larger pipes, it is rarely a problem. When you need to encase the couplers inside the pipes as well, they are able to take a compression fitting and make it work, but ONLY if you are using them with HDPE pipe. You will not get that kind of acceptance from a PVC fitting, which is so rigid that applying pressure to it may cause it to crack or fracture completely, never mind what it will do if you actually get it inside the larger pipe. HDPE couplers also offer some flatter, smoother coupling options that make the transition between one section of pipe and the next barely noticeable. It is as though you had one continuous piece of pipe slide right into and through the larger conduit.
HDPE Couplers Can Handle More Intense Heat
HDPE overall can handle more intense heat than PVC. If you place a pipe or coupler made from HDPE on the end of a PVC pipe or coupler and then set it over an extremely hot surface, the PVC is likely to melt while the HDPE piece expands and either cracks the PVC coupler or drops the PVC pipe out of the end of HDPE coupler. The PVC turns into a puddle of unpleasant-smelling plastic while the HDPE just sweats and expands. Eventually the HDPE would melt too, if temperatures were hot enough, but this just shows one more reason why you do not want to be mixing these two options for inner-ducting.
For more information, talk to a professional like Cabletec.