Understanding & Making the Right Choice of Swimming Pool Pipe & Fittings for Your DIY Swimming Pool.

BSP (British Standard Pipe) sizes do not represent what it says on the tin. If you have come from a previous FAQ we have published Understanding BSP Threads You will have quickly realised they do not represent the actual imperial measurement they are stated in. A standard domestic pressure pipe used in the vast number of UK swimming pools is stated as BSP 1.5″ but actually measures across its outside diameter  (OD) near enough 2 inches (48.3mm accurately measured in metric). BSP refers to the old measuring of the internal diameter (ID) and what would be referred to as its nominal flow rate in that size of steel pipe.

From our own help desk conversations many clients make the mistake of stating they have 2″ pipe on their installation when they placed a ruler and with Rack of Eye (Rock of Eye) guessed the measurement as 2″/50mm. When 1.5″ BSP swimming pool pipe is 48.3mm a close call for the inexperienced eye.

We at Pool Experts will always recommend swimming pool pipe & fittings manufactured to BS/EN1452. The 3 main classes of swimming pool pipe are class C-9bar, class D-12bar and class E-15bar. Although class C at 9bar is way above the standard running pressure of most swimming pool equipment 1 to 2.5bar maximum, because of the slightly thicker wall in the class D and not a large difference in price C to D we choose class D as our go-to product.  Other advantages to follow**. We do however supply Class C as some lighting products and return jet assemblies friction fit better in the thinner wall of Class C.

**Another reason for Pool Experts choosing class D is the term “Derating”. This is where the pressure rating of uPVC pipe reduces with the temperature of the water being pumped. Not to go into too much technical details but basically the heat adversely affects the chemical composition of uPVC and can weaken it structurally. This can also affect joints and although chemically bonded to each other, the affects of the cold and warm water cycle in the expansion and contraction can be a real issue in excessive water temperature. The main 12bar rating is measured at 20ºC. For a water temp of 30ºC the derating value is 0.8 so the pressure rating reduces to 8.8bar. Similarly for 40ºC you can expect a derating value of 0.6. The higher the temp the higher the Derating.

For 1.5″ class D rigid swimming pool pipe we would recommend a maximum flow rate of 11m³/hr with a flow rate of around 1.5m/sec. Class D 1.5″ pipe can be pushed upwards to around 17m³/hr but be warned this higher velocity creates higher friction loss and increased head with unacceptable noise and the potential of equipment damage if maintained.  Some consideration needs to be given if you have a long run on the suction side of your installation, i.e. the pipework before your pump, the shorter the better. The 11m³/hr quoted above should be reduced to around 8m³/hr if you cannot avoid the long run. You can also consider using 2″ pipe for this section of pipework. The pipework is under negative pressure and therefore creates turbulence that can increase inefficiencies and noise that go hand in hand.

The same goes for 2″ class D, with a desired maximum flow rate of 17m³/hr and a flow rate of around 2.0m/sec, this pipe can be pushed to 23m³/hr but with the same consequences.

There is a flexible version of uPVC pipe that is rated around 6bar. The rules if Derating still apply to this product and because of this lower pressure rating we do not recommend its use for long runs of pipe or as the first choice for inground installations.  Another main disadvantages are joints can be very problematic, they need careful preparation and once welded even with quick drying cement need to be immediately left and not moved as this can create voids in the weld leading to premature failure. A further disadvantage is in the way the pipe is manufactured. The internal surface of the pipe normally has a spiral construction described as Striations, not as pronounced as the outer surface but still there. The uneven internal surface of the flexi pipe creates turbulence within the water flow and can create quite heavy inefficiencies. You want laminar flow, this is the most efficient way to move water. This is why rigid pipe is more often than not the best option by far for swimming pool construction.

Advantages are, short runs to join mismatched alignment or repairs when it is impractical to get a straight piece of pipe correctly located. Top Tip, where a small alignment is necessary consider using rigid pipe with heat applied to bend into position.

uPVC (PVC-U) Class D normally is supplied grey in colour, not white and unless stated this often contains a mixture of uPVC and ABS plastics. In our experience uPVC offers a little more flex and reliability over the ABS versions if buried and any ground movement was to occur in your installation. To minimise any risk of cracks and splits occurring Class D swimming pool pipe manufactured from uPVC only should be used if buried or entombed in concrete bases and walls.

You will find many companies out there selling different classes C, D, E etc with PN specification thrown in for good measure. PN stands for Pressure Nominal (derived from the French Pression Nominale) PN10 is a 10 bar rated pipe, PN16 is 16 bar and so on. If manufactured from uPVC all the same rules apply.