FAQ - Network characteristics

What are the advantages of using push-fit PVC pipe systems?

The push fit joint with rubber seals on PVC-U pipes provides a number of advantages:

  • PVC pipes, fittings and ancillary parts are manufactured with tight tolerances on dimensions, which means that the elastomeric seal in the joint provides leak-free transportation of potable water as well as sewerage.
  • The push fit joint system makes PVC pipe systems easy to assemble.
  • The joints are superior to most other pipe connection systems due to quick and easy handling in the trench with no need for special tooling.
  • The pipes are easily cut and layed in the trench, making them a winner on installation cost.
  • Push-fit PVC pipes allow thermal expansion and contraction of the PVC pipelines.
  • In practise installation can be carried out with the minimum open length of trench enabling very limited transportation of excavation equipment.
  • Push-fit joints allow small changes of direction in a pipeline and for larger changes of direction there exists a huge range of PVC fittings which can provide the necessary solution.

What is the choice of stiffness and maximum allowable depth of bury for PVC pipes

Stiffness is the property of pipes that defines their resistance to deformation under exterior loads, mainly vertical loads associated with buried pipe conditions. In non-pressure applications, this is a basic property to ensure the right performance of the installation.

Stiffness depends mainly on two factors: E modulus, which is a physical property of every material, and the geometry of the profile of the pipe.

The behaviour of the pipe, and the deformation it reaches over time, is not only dependant on stiffness, but on soil and installation conditions. A higher stiffness gives a better performance, but the following graph shows the behaviour and influence of both stiffness and installation conditions.
Under a qualified installation, stiffness is not so relevant and all stiffness classes are suitable to be used.

Some organisations for plastic pipes have proposed or developed methods to rapidly evaluate the behaviour of buried pipes.

Figure 1: Design graph for determining the pipe deflections immediately after installation and after settlement of the soil

The diagram proposed by Teppfa (The European Plastic Pipes and Fittings Association) clearly shows that SN4 or SN8 piping systems present very good behaviour when the level of workmanship is good or at least standard.

On the vertical axis, the pipe deflection is shown and on the horizontal the pipe stiffness classes. For each installation group an area is given in which the deflection after installation is expected. The upper edge of the area represents the maximum deflection to be expected. The lower edge of the area shows the average deflection to be expected.

The graph shows the deflections immediately after installation. It does not include the effect of traffic load, depth of cover or groundwater.

The soil will further compact in the course of time. This further compaction is caused by the weight of the soil, the percolation of rain and ground water through the soil and by traffic load.

In order to obtain the final deflection including the effect of traffic, one shall add a consolidation value to the initial deflection. These consolidation values are listed in the table in the graph. Hence the final deflection becomes:

Final deflection = Initial deflection + C f

PVC4Pipes recommends SN 8 as a standard pipe that covers a depth of burial ranging from 0.6 to 6 metres in most soil conditions. Other depths of burial can be employed for PVC pipes (up to 15m) but, for these depths, specific conditions have to be studied on a case by case basis.

Many other calculation methods are listed in different European countries, but all of them agree on the wide versatility of PVC systems.

What is the reason for selecting the correct pressure class?

The criteria for choosing the correct pressure class are established in the standard EN-805: "Water supply - Requirements for systems and components outside buildings".

The pipe system designer must calculate all the conditions that affect a water network, including static and transient effects, to obtain the basic parameters, as for example, the allowable operating pressure (PFA) and the allowable maximum operating pressure (PMA)

After calculations, the designer will choose between the several classes that are possible in rigid PVC pipes.

The pressure classes for conventional rigid PVC pipes are defined in the standard EN 1452: "Plastic piping systems for water supply. PVC-U" and the pressure classes for molecular oriented (PVC-O) pipes are defined in ISO 16422: "Pipes and joints made of oriented unplasticised Polyvinyl chloride for the conveyance of water."

The following classes are available for PVC piping and; the most used in Europe are for PVC-U 10 and 16 and for PVC-O 16 and 25:

Can PVC pipes withstand a vacuum? If so, what is the maximum vacuum that PVC pipes can withstand?

PVC pipe systems can withstand a vacuum and can operate under pressures as low as -0.9 bar in regard to the pressure class of the PVC -system PN 10. For non-pressure and vacuum to -0.3bar, PVC sewer systems can be used.

Length of pipes

It is conventional to use rigid PVC pipes of lengths between 3m and 6m in all applications although it is also possible to use pipes in lengths of up to 12 m on special projects. These relatively short lengths allow rigid PVC pipes to be stored and transported easily and also ensure that they are very easy to install. The short lengths also eliminate any problems associated with longitudinal bending.

Rigid PVC pipes are easy to handle manually as the weight of each section is relatively low. The assembly of rigid PVC pipe sections and their connections to other pipe fittings can be undertaken by using a sealing ring or, for some industrial applications, by the use of an adhesive; this depends for which application the pipes will be used, or on the different traditions country by country.

Short section lengths of rigid PVC pipes make it easy to install and to adjust the length at junctions etc. Rigid PVC pipes can also be repaired quickly and easily with only a short length of pipe needing to be removed.
In different countries when talking about the measurement of lengths of pipe there are two different measurements used and they are: "without socket" known as the working length, or "with socket" known as the overall length.

What are the main advantages of installing PVC pipes compared with other solutions?

As a result of the combination of the following characteristics, PVC is generally the most efficient, quick installing and cost-effective of all the spectrum of solutions for piping.

  • Lightweight: PVC pipes are light and easy to handle (up to 6 m length), significantly reducing the need for mechanical support for placing and fixing the pipes together, leading to a cost efficient installation.
  • Joints: PVC piping systems can be installed with different types of joints: solvent cement joints and push-fit joints. Across Europe , push-fit joints are usually preferred for municipal installations.
    The use of push-fit joints is a very important characteristic as it not only assures a watertight, safe and durable union, but permits a fast and simple mounting, an important cost saving during installation, as it avoids using complex welding operations and costly investments in sophisticated equipment and specialised skills.
  • Fittings and special operations: PVC pipe systems are normally completed with the widest range of fittings and ancillary products, allowing a modular installation and high quality of the full network. When finishing work has to be done by hand (For example making holes, installing saddles and cuts in the pipes), rigid PVC is easy to work with, and does not need complex tools or special expertise.

What is the design coefficient for PVC-U pressure pipes?

The design coefficient (safety factor) is used in the design of all pressure systems using plastics pipes. It takes into consideration service conditions as well as properties of the components of a piping system.

This coefficient is illustrated by the following graph:

Design Coefficient - PVC Pipes for Water Distribution

According to ISO 12162 the minimum value for design coefficients (C min ) are as follows:

  • PVC-U 1.6
  • PVC-A 1.4
  • PVC-O 1.4