LDPE or HDPE : when do I use what ?
By Patrick Gordon - Consultant
TECHNICAL 35
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 .
CLASS WORKING PRESSURE TYPE OF PIPE Class 3 300kPa LDPE Class 6 600kPa LDPE Class 10 1000kPa HDPE Class 12 1200kPa HDPE Class 16 1600kPa HDPE Class 20 2000kPa HDPE
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 .
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 .
Images courtesy of SPLASHWORKS who is the proud distributor of the IDEAL brand of pipe fittings .
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
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 . PA
For any further information on this topic please contact the writer : PA Gordon on patrickg @ splashworks . co . za .
November 2024 Volume 30 I Number 9 www . plumbingafrica . co . za