ASFA Pipe & Fittings Sizer

01 / How the sizer works

The run of pipe

Two parts. The main carries the whole zone's flow from the pump or tank to the zone valve. The sub-main runs from the zone valve along the ends of the rows; at each row some water leaves, so the flow falls row by row. The sizer works the sub-main out stretch by stretch, from one row to the next, each with the flow still to come: an exact sum, not a single shortcut factor.

Pipe size

For each stretch, the smallest pipe in which the water moves no faster than 1.5 m/s. Faster water loses more pressure and hits harder when a valve shuts. The sizer never goes above 2.29 m/s. Along the sub-main the pipe steps down to a smaller size where one will do, but no more than 3 times.NRCS Conservation Practice Standard 430 (Irrigation Pipeline): 5 ft/s; Hunter Product Catalogue Vol. 41, pp161-163: good design practice keeps the velocity within 1.5 m/s. Rain Bird Landscape Irrigation Products Catalog (D42139, 2023), PGA valve page p66: supply-line flow not above 7.5 ft/s (2.29 m/s), to reduce water hammer. Steps: Netafim, Subsurface Drip Irrigation Guide, printed p. 12 (do not step a sub-main down more than 3 times along its length); where speed alone would step more often, the stretch that adds the least extra pipe if kept at the larger size (its length times the extra pipe area) stays at the larger size, one at a time until 3 steps are left (our rule).

Material and joints

Our rule: PE100 pipe with compression fittings up to 90 mm, PVC-U pipe with solvent-welded (glued) joints above 90 mm.Outside diameters and walls: walls computed from each class's SDR to ISO 4427-2 / EN 12201-2 (calculated minimum wall, held in the ASFA catalogue), and never less than 2.0 mm, our planning figure from the supplier's PE100 series; where that floor makes two classes the same pipe, the pipe is shown with the highest class whose minimum wall it meets; walls computed from each class's SDR to ISO 1452-2 / EN 1452-2 (calculated minimum wall, held in the ASFA catalogue).

Pressure class (PN)

PN is the pressure in bar a pipe is made to carry. A higher class has a thicker wall, so a smaller bore (inside diameter). The sizer first takes the lowest class that carries the highest pressure in that section, then the size. In the main that pressure is the pressure at the pump outlet (the pump head less the lift, which is used up below the outlet), or more at the low end of a falling main. PE pipe of 25 to 40 mm is made with a wall of at least 2.0 mm, so where that wall meets more than one class the sizer shows the highest class it meets, with its wall rather than an SDR. In PVC-U the surge of a valve shut at once is added; if the class cannot carry both, the sizer steps the class up, or the size, and says so.Surge: Rain Bird Tech Tip: surge = 0.01345 c V (psi), c = 4660 / sqrt(1 + K (SDR - 2) / E) ft/s, with K = 300,000 psi (water) and E = 400,000 psi (PVC, about 2.76 GPa). No modulus for PE100 is on file, so PE pipe surge is not worked out here: we check it with your quote.

Friction

The pressure water loses rubbing along the pipe, by the Darcy-Weisbach method with the Swamee-Jain friction factor, for smooth plastic pipe and water at 25 °C (our planning figure): the same method and figures as our own design software. 1 bar is taken as 10.2 m of water.Darcy-Weisbach with the Swamee-Jain friction factor, water at 25 °C (our planning figure); roughness 0.0015 mm. Swamee and Jain (1976), Journal of the Hydraulics Division, ASCE 102(5).

Bends and row take-offs

Each fitting loses a share of the water's speed: K times v²/2g. A 90° bend counts 0.8, a 45° bend 0.3. These are the textbook figures for 3 in (about 80 mm) screwed fittings, the smallest size the table prints. Your fittings are smaller and of a different kind, and small fittings can lose more, so the bend losses here may be a little low. That is one reason we check the design before we quote. Each row takes off the sub-main through its own start connector (a rubber grommet in PE, a saddle on PVC-U); we count the water going on past each take-off as the straight-through side of a tee, K 0.9, the nearest figure the table prints. The water that turns into the row is not counted. Reducers and couplings are not in the table: their loss is small and is not counted.USDA (2016), resistance coefficients K for fittings and valves, screwed, 3 in (the smallest size printed), as reproduced in Irrigation Systems Management (LibreTexts), Table 8.4.

Valves

The zone valve's loss is read from Hunter's printed table for its flow, in a straight line between two printed rows and never beyond the table. A valve is used only inside both its printed loss table and its printed flow range. Unless you choose one, the sizer takes the smallest Hunter PGV whose printed flow range holds your flow, the same rule as the Valve & Controller Picker (our rule); if the valve would see more than the PGV's printed 10 bar, the ICV, which Hunter prints for up to 15 bar. For dirty water, choose an ICV in the list. Hunter recommends at least 1.5 bar at the valve, so where the pipes alone would leave less, the sizer holds 1.5 bar there and adds the difference to the pump head. The ball and check valves at the pump use the maker's printed Kv for PVC-U valves: the flow in litres a minute that loses 1 bar. Their loss is (flow ÷ Kv)² bar.Hunter Product Catalogue Vol. 41, pp. 87, 88, 89, 90, 91. Ball valves: a maker's printed Kv100 for PVC-U ball valves (Cepex PVC-U ball valves, p152); on a PE100 main, our planning figure for a ball valve of the same size. Check valves: a maker's printed Kv100 for PVC-U spring check valves (Cepex UP-S.67, p193); on a PE100 main, our planning figure for a check valve of the same size.

The fittings list

Plain names, any maker: a start connector at each row (with a grommet in PE, on a saddle on PVC-U); an end cap at the far end, past the last row, that you open to flush the sub-main; a reducer wherever the sub-main steps down; an adaptor each side of the zone valve, to its thread, with a reducer first where the pipe is a different size from the adaptor; the bends you enter on the main; and the ball and check valves. Where we sell that exact item, the line links to our store.Which pipe sizes take a thread adaptor: pipe sizes made with a male-thread adaptor for each valve thread, from a maker's range: PE100 compression x BSP male thread (Cepex PP-P. 05. CPMT, p646); PVC-U solvent socket x BSP male thread, size for size (Cepex UP. 17. SFMT, p79).

Pump head

The pressure the rows need, plus what is lost on the way in the pipes, fittings and valves the sizer counts, plus the height the water climbs (less any it falls), plus the lift from the water level to the pump outlet. It is given in metres of water, with the same head shown in bar. A pump is chosen by two figures: this head and your flow. The filter, any fertiliser injector and the pipe inside a borehole are not in it: see section 02. The sub-main is fed so the row with the least pressure, usually the last, still gets what the rows need where it starts.

02 / What the sizer leaves out

• The suction sideThe pipe, foot valve and strainer between the water and a surface pump, and whether the pump can lift from that depth, are checked with your quote.
• The pipe inside the boreholeThe friction in the pipe from a submersible pump up to the surface is not counted in the head, and that pipe carries the whole pump head, more than the main. The water level also falls while the pump runs, and further in the dry season, so the lift grows. Your borehole's test pumping record tells us how far; we size that pipe and check both with your quote.
• Filters and fertiliser injectorsTheir own pressure loss is not counted: it depends on the model and on how clean the filter is. Add what the maker prints, or we work it out with your quote.
• Air valves and thrust blocksAir valves at the high points of the main, and concrete blocks at bends and tees of large PVC-U pipe, are placed with your quote.
• Water hammer in PE pipe, and the pump's shut-off pressureSurge in PE100 is not worked out. A pump pushing against a shut valve gives more than its working head: check the class against the pump's curve, as we do with your quote.
• Hot pipe and hot waterPressure classes are set for cool water. Warmer water, or pipe left in the sun, carries less, and the sizer does not lower the class for it: we check it for your site.
• Real fittingsThe figures are for 3 in screwed fittings, the smallest size the table prints. Smaller fittings, and compression fittings with a narrower bore, may lose more, so we check the real fittings with your quote. Joints between lengths, saddles and reducers are not counted.
• Valve pressure rangeThe sizer keeps the zone valve at or above Hunter's printed minimum and flags it above its printed maximum (PGV 1.5 to 10 bar, ICV 1.5 to 15 bar). The pump's shut-off pressure can be higher than that, as above.
• More than one zone at onceThe sizer takes one zone running on its own. If zones share the main at the same time, the main carries more water and needs working out again.
• FlushingThe sizer works out the pipes for normal watering only. It does not check that opening the flush end moves the water fast enough to wash dirt out of the sub-main and main. We check this with your quote.
• Inside the rowsThe pressure lost along each dripline is in the maker's row lengths, which the Drip Planner checks. For emitters and bubblers on a feed pipe along a tree row, the pressure lost along that feed pipe is not counted: the emitters at the far end get less than the start of the row, and we work it out with you. Non-compensating lines and steep rows are worked out with you too.

Next, check the pump with the ASFA Pump & Power Check, or see all the free tools. Ready to go further? Request a quote.