Design Data

Allowable design stress for uPVC Pressure Pipes

If PVC pipe or PVC valve is used to convey fluids of excessive temperature then the allowable design stress or the pressure class ratings should be appropriately reduced in accordance with following table.

Maximum service temperature		Allowable design stress or pressure class rating
ºF	ºC	%
80	27	94
86	30	89
95	35	79
104	40	71
113	45	63

Allowable design stress for PE Pressure Pipes

If PE pipes are used to convey fluids of excessive temperature then the allowable design stress or the pressure-class ratings should be appropriately reduced in accordance with following table.

Maximum Service temperature		Allowable design stress or pressure class rating
ºF	ºC	%
40	5	120
60	15	110
80	27	100
100	38	90
120	50	80
140	60	75

Potential Evapo transpiration Rate (PET) for different Climate

Climate	Temperature (ºC)	Humidity (%)	PET (mm per day)
Cool Humid	Less than 18	50 - 85	2.54 - 3.80
Cool Dry	18 - 25	Less than 50	3.80 - 5.00
Moderate	28 - 36	50 - 65	5.00 - 6.35
Hot Humid	36 - 40	50 - 85	6.35 - 8.90
Hot Dry	40 - 45	Less than 50	8.90 - 10.00
Hot Dry Desert	45 - 50	Less than 30	10.00 - 11.50

Recommended Sprinkler Spacing

Wind velocity miles / hr.	Maximum spacing
Wind velocity miles / hr.	Square spacing	Triangular spacing
0 to 3	55 % of diameter	60 % of diameter
3 to 6	50 % of diameter	55 % of diameter
6 to 12	45 % of diameter	50 % of diameter

Maximum Precipitation Rate (mm per hour) of Sprinkler in different Soil and Ground Slope

Soil Type	0 to 5%	5 to 8%	8 to 12%	12 to 20%	Above 20%
Coarse Sandy Soil	50	50	40	40	38
Coarse Sandy Soil over compact sub soil	45	45	30	30	30
Light Sandy Loam	40	40	25	25	25
Light Sandy loam over compact sub soil	30	30	20	20	20
Uniform Silt Loam	25	25	15	15	15
Silt Loam over compact sub soil	15	15	10	10	10
Heavy Clay/ Clay Loam	5	5	3	3	3

Note: Above values are given for reference purpose and may vary with respect to actual soil and site conditions. Designer has to select and decide the appropriate value as per the prevailing conditions of site, soil, climate, type of crops, other agro climatic factors.

Calculating Precipitation Rates

Depending upon the construction of the irrigation system, the precipitation rate may be calculated by either a 'sprinkler spacing' or 'a total area method.

Sprinkler Spacing Method

The precipitation rate should be calculated for each individual zone. If all sprinkler head on the zone have the same spacing, flow rate and arc of coverage.

i. Any Arc and Any Spacing

ii. Equilateral Triangular Spacing

Total Area Method

The precipitation rate for a system is the average precipitation rate of all sprinklers in an area, regardless of the spacing, flow rate or arc for each head. The total area method calculated all the flows of all heads in any given area.

Matched Precipitation Rates

A zone or system in which all the heads have similar precipitation rates is said to have 'matched precipitation rates'. Systems that have matched precipitation rates reduce wet and dry spots and excessive run times which lead to high water consumption and increased costs. Knowing that the sprinkler spacing, flow rates and arcs of coverage after precipitation rates, a general rule of thumb is : as the spray arc doubles, so should flow.

......90º Arc (Quarter Circle) - (0.23 m3/hr, 3.81 litre/min)

…….. 180º Arc (Half Circle) - (0.45 m3/hr, 7.62 litre/min)

……...360º Arc (Full Circle) - (0.91 m3/hr, 15.24 litre/min)

The flow rate of half circle heads must be two times the flow rate of the quarter circle heads and the full circle heads must have two times the flow rate of the half circle heads.

In the illustration, the same amount of water is applied to each quarter circle area and precipitation is therefore matched.

Types of Sprinklers based on Precipitation

Type of Sprinkler	Precipitation Rate (mm per hour)
Low Volume Sprinkler	Less than 13
Medium Volume Sprinkler	13 - 25
Big Volume Sprinkler	Above 25

Solvent Cement Requirement for uPVC Pipes

Pipe Size mm	No. of Joints* per Litre	Pipe Size mm	No. of Joints * per Liter
20	330	125	45
25	270	140	36
32	225	160	27
40	180	180	20
50	135	200	15
63	125	225	12
75	103	250	9
90	79	280	6
110	54	315	5

* Each Joint represents one socket in a Fitting.

Frictional Head Losses in Valves and Fittings (As equivalent to the length of pipe in meter)

Nominal mm	45º Elbow	90º Elbow	Tee in Flow	Side Out Let Tee	Gate Valve	Sprinkler Angle Valve	Angle Valve	Globe Valve
20	0.30	0.60	0.30	1.21	0.12	0.60	2.74	5.18
25	0.30	0.91	0.60	1.52	0.15	0.91	3.65	6.70
32	0.60	0.91	0.60	1.83	0.18	1.21	4.57	8.22
40	0.60	1.21	0.91	2.44	0.24	1.52	5.48	11.58
50	0.60	1.52	0.91	3.05	0.30	1.83	6.70	13.71
63	0.91	1.83	1.21	3.65	0.36	2.14	8.53	17.76
75	0.91	2.14	1.52	4.26	0.42	2.75	10.66	21.33
90	1.21	2.44	1.83	5.48	0.55	3.35	13.71	27.43
110	1.52	3.31	2.14	7.01	0.70	4.57	18.28	36.57
140	2.00	4.26	2.90	8.50	0.85	5.33	22.09	44.19
160	2.44	5.18	3.65	10.00	1.00	6.10	25.90	51.81