Page 332 - Toro Irrigation Product Catalogue August 2020

Precipitation and Infiltration Rates

Precipitation Rates Table 1: Indicative Maximum Precipitation Rates – mm/hour

To avoid run-off and water wastage, select Soil Texture 0-5% slope 5-8% slope 8-12% slope 12+ % slope
sprinklers so that the precipitation rate is
less than or equal to the infiltration rate of Cover Bare Cover Bare Cover Bare Cover Bare
the soil. The type of soil, condition of both Coarse sandy soils 50 50 50 38 38 25 25 12
soil and ground cover, and slope affect the Coarse sandy soils over 44 38 31 25 25 19 19 10
infiltration rate. The table below shows some compact subsoils
indicative average rates. Always confirm the Light sandy loams
infiltration rate with on-site tests. uniform 44 25 31 20 25 15 19 10
Where system precipitation rates are higher Light sandy loams over 31 19 25 12 19 10 12 7
than the infiltration rate, it may be possible compact subsoils
to avoid run-off by repeating the irrigation Uniform silt soils 25 12 20 10 15 7 10 5
cycle for shorter periods of time. Silt soils over compact
subsoil 15 7 12 6 10 4 7 2.5
Heavy clay or clay loam 5 4 4 2.5 3 2 2.5 1.5
The maximum precipitation rates values listed in this table are suggested by the US
Department of Agriculture. The values are indicative averages only and may vary with
respect to actual soil and ground cover condition.

Piping Flow Rates

Flow Rates

One of the selection criteria irrigation designers use to select
pipe sizing for mainline pipe is to maintain the velocity of flow Table 1
through the mainline pipe to be less than or equal to 1.5 m/s. Mainline Flow Rates for 1.5 m/s
Pressure rating and pressure loss are other criteria. Velocity ˚ PVC Pipe
Tables 1 and 2 indicate flow rates in litres per minute for PVC Pipe Size and Class Maximum Flow (Lpm)
various PVC (AS 1477) and PE (AS/NZS 4130S1) pipe sizes for a 15 mm cl 15 23
velocity of 1.5 metres per second.
20 mm cl 12 39
Pipe sizing in sprinkler laterals (pipes downstream of the
zone control valve) is based on maintaining the zone pressure 25 mm cl 12 62
to within a set tolerance. As a result, velocities in sprinkler 32 mm cl 12 99
laterals can sometimes need to be raised higher than 1.5 m/s 40 mm cl 12 130
in an effort to balance friction loss and pressure gained by
elevation differences. This decision should only be undertaken 50 mm cl 12 204
by someone experienced in hydraulic design.

Table 2 Table 3 Table 4
Mainline Flow Rates for 1.5 m/s Lateral Flow Rates for 2.0 m/s Lateral Flow Rates for 2.0 m/s
Velocity ˚ PE100 PN 12.5 Velocity ˚ PVC Pipe Velocity ˚ PE100 PN 12.5
MDPE Pipe Size and Class Maximum Flow (Lpm) PVC Pipe Size and Class Maximum Flow (Lpm) MDPE Pipe Size and Class Maximum Flow (Lpm)
DN25 30 15 mm cl 15 30 DN25 40
DN32 50 20 mm cl 12 52 DN32 68
DN40 80 25 mm cl 12 82 DN40 105
DN50 125 32 mm cl 12 132 DN50 165
40 mm cl 12 173
50 mm cl 12 272

Company policy is one of constant improvement and therefore changes in specifications may
310 be made without notice and without incurring liability. Please refer to www.toro.com.au
Toro Australia Pty Ltd, 53 Howards Road, Beverley, South Australia, 5009.
Phone 1300 130 898, fax (08) 8243 2488. A.B.N. 47 001 310 443