PPR Pipe Friction Loss Chart: Head Loss per 100 m by SDR

In SDR 6 PP-R pipe carrying water at 20 °C, one metre per second of velocity costs about 11.5 m of head per 100 m at DN20, 8.6 at DN25, 6.3 at DN32, 4.8 at DN40, 3.6 at DN50 and 2.7 at DN63. The full chart, with flow rates and velocities, is below.

A second table follows because those six figures are worthless on their own. Head loss is set by the bore, the bore by the wall series, and the PN label on your quotation does not reliably tell you the series. Every free PPR friction chart on page one omits the series, the water temperature and the roughness. This page prints all three.

One clip before the numbers. Practical Engineering runs water through a physical rig and reaches the diameter term at 5:15 — watch how far the pressure drop moves for one size step, because that effect is most of what the chart below measures.

▶  Play

Flow and Pressure in Pipes Explained, Practical Engineering — an independent engineering channel, not a pipe supplier. Its demonstration uses Hazen-Williams; this page computes with Darcy-Weisbach, for the reason given below.

PPR Head Loss Chart: SDR 6 Pipe, Water at 20 °C

Flow points sit at 0.5, 1.0 and 2.0 m/s rather than round litres per second, so the table doubles as a velocity check. DN25 at 0.216 L/s runs 1.0 m/s and 8.6 m per 100 m; at 0.433 L/s it is at 2.0 m/s and 29.6 m per 100 m, where most designers size up.

Read the Chart Against SDR, Not the PN Label on the Invoice

SDR 6 is the heaviest of the three common water series, so it gives the smallest bore for a given outside diameter.

Key the chart on SDR because PN is not a dimension. The dimension standards, DIN 8077 and EN ISO 15874-2, tabulate wall thickness by pipe series and print no pressure class. ISO 4065:2018 fixes the geometry in clause 3.6 as S = (SDR − 1) / 2, then sets the label in clause 4.2 as S = design stress / PN. The wall is standardised; the class it earns is not, because design stress belongs to the compound and to the design temperature and lifetime. Run it: S 2.5, which is SDR 6, is PN20 at a design stress of 5.0 MPa and PN25 at 6.25 MPa. Same pipe, same bore, two correct labels.

That is why published charts disagree and none of them is wrong. One PP-R catalogue prints PN25 = SDR 6, PN20 = SDR 7.4, PN16 = SDR 9, PN10 = SDR 11, and a second supplier chart lists the same ladder. Our own PPR size and pressure-class chart runs one step across: PN12.5, PN16, PN20, PN25 against SDR 11, 7.4, 6, 5. So a PN20 line at OD 20 mm is a 2.8 mm wall on one convention and 3.4 mm on the other, a bore of 14.4 against 13.2 mm. Read the SDR 6 row while holding the lighter wall and you overstate head loss by about 52%.

So order by wall thickness in millimetres or by S series, never by the PN number alone. PN versus SDR versus schedule covers the three rating systems, and the PPR supplier page gives the range we hold.

How the Numbers Were Produced, and How to Reproduce Them

Darcy-Weisbach with a Colebrook-White friction factor, not Hazen-Williams, whose C value published sources put between 145 and 150 for plastic with nothing to say which is right. Colebrook takes an absolute roughness in millimetres, and PP-R has a published one: 0.007 mm, the value manufacturer hydraulic tables use, at a stated 20 °C.

Work one cell by hand. DN25 in SDR 6 has a 16.6 mm bore, so the area is 2.1642 × 10^-4 m². At 0.25 L/s the velocity is 1.155 m/s and the Reynolds number is 1.155 × 0.0166 / 1.0035 × 10^-6, or 19,108. Relative roughness is 0.007 / 16.6, that is 4.217 × 10^-4. Solving Colebrook iteratively returns a friction factor of 0.02706, and head loss is 0.02706 × 1.155² / (2 × 9.81 × 0.0166), which is 0.1108 m per metre, or 11.1 m per 100 m. Run those lines on any cell in the chart and you should land on the printed figure.

Correcting for Hot Water and for a Thinner Wall

The temperature correction runs against intuition. Warm water thins, the Reynolds number rises, the friction factor falls, and the same flow costs less head. From 20 to 60 °C kinematic viscosity drops from 1.0035 to 0.4740 × 10^-6 m²/s and head loss falls to 0.86 of the chart figure. A hot riser is a pressure-class problem, which pressure derating by service temperature governs.

The series correction is bigger. A lighter wall is a wider bore, so at the same flow SDR 11 at DN25 loses 3.2 m per 100 m against SDR 6's 8.6. That gain is paid for in pressure rating: picking SDR 11 to save pump head on a 70 °C circuit is how a system fails early.

What the Chart Leaves Out

Straight pipe only. Elbows, tees and valves add local losses no equivalent length is offered for here, because none was verified against a published PP-R loss coefficient. Static head is absent too: a water column adds 1 m of head, 0.098 bar, per metre of rise, and belongs to the riser calculation.

Assembling a system total needs no further data, only the definition. Total head = (J / 100) × straight length in metres, plus the sum of ζ × v² / 2g over every fitting and valve, plus the static lift. J and v come off the row you read; g is 9.81 m/s². The one term this page cannot supply is ζ: get it from the fitting maker for the exact moulding, because a PP-R socket elbow, a moulded tee and a compression fitting of one nominal size do not share a coefficient. Ask in writing rather than borrowing a steel-fitting table.

One caution before comparing this table with a catalogue. Across three sampled rows of a published PP-R hydraulic table at the same stated roughness and temperature, velocities matched to three decimals while tabulated head loss sat approximately 1.10 times higher. The catalogue does not state why. IFAN publishes no measured bore tolerance or flow-rig data for its own pipe, so every number here is computed, not measured.

Conclusion

Two numbers decide a PPR friction calculation and only one is on your quotation. The flow you know; the bore you have to establish, because the same nominal size spans 16.6 to 20.4 mm at DN25, worth a factor of 2.7 in head loss. Confirm the wall series in millimetres, then read the row.

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