Page 332 - TORO PRODUCT CATALOGUE NOV_2019

Precipitation and Infiltration Rates
Table 1: Indicative Maximum Precipitation Rates – mm/hour
Soil Texture
0-5% slope
5-8% slope
8-12% slope
12+ % slope
Cover
Bare
Cover
Bare
Cover
Bare
Cover
Bare
Coarse sandy soils
50
50
50
38
38
25
25
12
Coarse sandy soils over compact subsoils
44
38
31
25
25
19
19
10
Light sandy loams uniform
44
25
31
20
25
15
19
10
Light sandy loams over compact subsoils
31
19
25
12
19
10
12
7
Uniform silt soils
25
12
20
10
15
7
10
5
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
Precipitation Rates
To avoid run-off and water wastage, select sprinklers so that the precipitation rate is less than or equal to the infiltration rate of the soil. The type of soil, condition of both soil and ground cover, and slope affect the infiltration rate. The table below shows some indicative average rates. Always confirm the infiltration rate with on-site tests.
Where system precipitation rates are higher than the infiltration rate, it may be possible to avoid run-off by repeating the irrigation cycle for shorter periods of time.
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 through the mainline pipe to be less than or equal to 1.5 m/s. Pressure rating and pressure loss are other criteria.
Tables 1 and 2 indicate flow rates in litres per minute for various PVC (AS 1477) and PE (AS/NZS 4130S1) pipe sizes for a velocity of 1.5 metres per second.
Pipe sizing in sprinkler laterals (pipes downstream of the zone control valve) is based on maintaining the zone pressure to within a set tolerance. As a result, velocities in sprinkler laterals can sometimes need to be raised higher than 1.5 m/s in an effort to balance friction loss and pressure gained by elevation differences. This decision should only be undertaken by someone experienced in hydraulic design.
Table 1
Mainline Flow Rates for 1.5 m/s Velocity − PVC Pipe
PVC Pipe Size and Class
Maximum Flow (Lpm)
15mmcl15
23
20mmcl12
39
25mmcl12
62
32mmcl12
99
40mmcl12
130
50mmcl12
204
Table 2
Mainline Flow Rates for 1.5 m/s Velocity − PE100 PN 12.5
MDPE Pipe Size and Class
Maximum Flow (Lpm)
DN25
30
DN32
50
DN40
80
DN50
125
Table 3
Lateral Flow Rates for 2.0 m/s Velocity − PVC Pipe
PVC Pipe Size and Class
Maximum Flow (Lpm)
15mmcl15
30
20mmcl12
52
25mmcl12
82
32mmcl12
132
40mmcl12
173
50mmcl12
272
Table 4
Lateral Flow Rates for 2.0 m/s Velocity − PE100 PN 12.5
MDPE Pipe Size and Class
Maximum Flow (Lpm)
DN25
40
DN32
68
DN40
105
DN50
165
Company policy is one of constant improvement and therefore changes in specifications may 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
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