Specification of PVC pipe
We often come across situations where a plastic pipe system has been over specified for the job, to the point where the user could make considerable savings, without compromising on the integrity of their pipework system, by selecting a different specification. We are always happy to advise on the right specification for you if you contact us and give details of your application. Here we set out some of the pitfalls that people fall into, which results in the spending more than they need to:
- Fitting US specification pipework - a lot of systems, both domestic (like hot tubs, spas etc.) and machinery (especially that manufactured in North and Central America) comes with manuals that instruct you to connect using Schedule 40 or Schedule 80 pipework (often abbreviated to SCH40 / SCH80). The North American system of pipe specification follows different standards than that in the UK, but the dimensions are the same. So a schedule 40 2" pipe will fit into a UK 2" socket etc. The only difference is the pipe wall thickness. With the UK system, pipe and fittings are manufactured to a "Class" which denotes a fixed pressure rating. For example "Class C" (the most common used) is 9 bar (or 132 psi). Whether it is 2" pipe or 6" pipe, all Class C pipe has a pressure rating of 9 bar. The US system is different, and more confusing, as pipes of different sizes have different pressure ratings. SCH40 2" pipe for example has a pressure rating of 19.3bar. Now I don't know about you, but I rarely come across systems that operate at much higher than a few bar, let alone 19! SCH40 / 80 pipe is therefore more expensive as it has a thicker wall ( to compensate for the higher pressure rating), which means more plastic is used. In addition to this it has to be shipped over from the US, which adds cost. Our advise is, where SCH40/80 pipe is specified, to use UK class C or D instead. It will do the job just as well, give just the same results and cost you a lot less. As an added complication, SCH40/80 threaded fittings have an NPT thread, which is not compatible with most UK threads - another reason to use UK inch systems.
- Selecting a higher pressure rating than is needed - There is a great temptation, when ordering plastic pipe, to go for a higher pressure rating than actually needed to "build in a safety margin". This is totally unnecessary. In all my years of supplying plastic pipe system, I have never come across a pipe that has burst through over pressure, it is usually a fitting, and that is nearly always as a result of over-tightening of a thread which has weakened it. Most systems operate at only a couple of bar pressure, despite what many users think. A pool/spa type pump operates at about 2.5bar, most water circulation/treatment pumps operate at less than 1.5bar etc. In fact the only systems that tend to operate at over a few bar are pressure washing systems or industrial venturis. Bearing in mind that the lowest pressure systems are 9 bar (Class C) for imperial and 10 bar (PN10) for metric, specifying over and above this is usually a waste of money.
- Using pressure pipe for drainage - This sounds like a "no brainer" but as pressure pipe has a thicker wall (to withstand higher pressures) it is more expensive than drainage pipe. The dimensions of the two pipe systems are the same in that they are both metric systems. A 200mm drainage pipe will fit 200mm pressure fittings and visa versa. The reason for choosing pressure pipe is often that it is being buries, however drainage pipes are designed for this purpose. Any pipe, whether pressure or drainage will be compromised in the same way, by much the same forces, if it is not buried properly ie: pea gravel surrounding the pipe and no huge boulders resting on the pipe! Drainage pipe can also often be used in low pressure systems which require large diameters (such as fish farming and waste water treatment). In these systems it is often integrated with pressure fittings, but the decision to use drainage rather than pressure pipe reduces the cost of the system, without compromising the integrity of it.
If you would like to discuss your application to make sure you are selecting the right type of pipe and making the most of your budget, please feel free to contact us and we will be happy to advise.