By Patrick Gordon – Consultant
A question that merchants often get asked is why do the fittings that I bought not work on my existing pipes?
The short answer is because they are made differently. But why are they made differently?
Let us first differentiate what the different uses are for these pipes. The Low-Density Polyethylene (LDPE) pipes should only be used for irrigation purposes and come in different pressure classes namely Class3 and Class6.
The High-Density Polyethylene (HDPE) piping is used to convey potable water over great distances and is available in variety of classes, but the popular ones are Class10 and Class12. But what do the different classes indicate? These are indicative of the rated pressure of the pipe. As an example, Class3 is rated at 300kPa. Here is a list of the classes and their ratings.
Images courtesy of SPLASHWORKS who is the proud distributor of the IDEAL brand of pipe fittings.
LDPE pipes are designed to work with an insert fitting and have a constant internal diameter (ID). This means that a 20mm pipe measures 20mm on the internal diameter.
In the pictures it can be clearly seen that these fittings have a swaged profile on the external on the fitting. When inserting the fitting into the pipe it will fit very snugly, and the pitches of the swaging will expand the pipe.
The fittings could be swaged on all sides, or it could have a male or female BSP thread on one end to facilitate an interconnection to another piping system. All the swaged connection joints must be clamped with a hose clamp to prevent the fitting from pulling off the pipe.
This type of fitting restricts the flow in the pipe as it makes the inner dimensions smaller. To compensate for this, you would have to increase the pipe size by at least one size, or you can use a FULL FLOW type fitting that fits over the outside of the pipe.
As with the previous type of fitting there are multiple fitting configurations. An added feature is that they are colour coded for fast size identification.
The HDPE pipes are designed to work with fittings that fit over the pipe and compress using a mechanical type seal. For this reason the pipes have a constant outside diameter (OD) that seals on a neoprene seal inside the fitting. The connection is held in place with a crimping cone that compresses on the pipe when the connection nut/ring is tightened. These fittings also have a large insert depth to give a better rigidity to the joint. An added advantage of the fitting is that it can easily be disassembled if you want to change the reticulation design.
As with the other type of fittings for LDPE pipe, these are also available in a wide range of types and sizes. They are also available with BSP threads so that you can connect to other types of pipes.
Remember that no “plastic” pipe is allowed to be used in exposed installations for potable water.
For any further information on this topic please contact the writer: PA Gordon on patrickg@splashworks.co.za.
