Checking Drippers

To ensure a drip irrigation system is operating correctly, regular measuring and recording of dripper outputs and pressures throughout the system is essential. The discharge from a dripper, as stated by the manufacturer, is generally a nominal discharge figure at specific pressure and temperature. Most manufacturers nominate the discharge at 100 kPa (14.5 psi), which is generally the minimum recommended pressure for correct dripper operation. In a properly designed system there will be less than about 10% variation in pressure throughout, to avoid having some plants under- and others over-watered. Alternatively, self-compensating drippers, putting out a relatively constant discharge over a wide range of pressures, may be used. The discharge of some of these self-compensating drippers is normally controlled by a small rubber diaphragm, which may gradually harden when in contact with chemicals. Hardening of the rubber diaphragm causes an alteration to the discharge rate, making the replacement of the dripper necessary. To avoid over/under-watering random checks of dripper-output at several points throughout the system should be carried out on a regular basis. Following is an outline of a method suitable for checking dripper-outputs. Equipment needed Shovel 9 plastic containers of suitable size 2 litre measuring jug - measuring in millilitres Watch/timer Pressure gauge with tapered fittings Paper to record results Procedure Place one container under a dripper towards each corner of the shift and one approximately in the centre of the shift, ensuring all water from the dripper is collected in the container. Note location of the dripper on a sketch of the shift Record the start and finish times Measure and then record the amount of water collected in each container by tipping it into the measuring jug Calculate the discharge each dripper would put out in one hour Measure and record the pressure and discharge at the valve and at the end of several laterals. A variation in dripper outputs of +/- 5% indicates the system is poorly designed, control block pressure is incorrectly set or there are some partial blockage problems. Readings recorded using this system should be kept and compared each time a new set of readings is taken. This will allow any alteration in pressures and dripper outputs to be detected and rectified early on. There should be one pressure gauge on each side of the filter bank at the pump. These gauges should be used regularly to monitor the performance of the pump filter to detect problems in the system. Another gauge should be kept in a protective container in the farm vehicle and used regularly to monitor pressures at control points and at ends of laterals throughout the vineyard.

Calculating Average Discharge Add up all the discharges and divide the total by the number of discharges. Example: Emitter Litres 1 42.5 (Lowest) 2 44.4 3 45.2 4 46.9 (Highest) 5 44.9 6 45.9 7 44.8 8 44.6 9 45.6 Total 404.8 l/hr Average Discharge = 404.8 / 9 45 l/hr

Cartoon: The dog drank it, or we've got a problem

Calculating Discharge Variation To calculate this you will need the Midpoint Discharge and the Difference. To find the Midpoint Discharge, add the highest discharge and lowest discharge and divide the result by two.

Using the example above:

Highest + Lowest	46.9 + 42.5 = 89.4
Divided by	2
Midpoint Discharge	= 44.7

To calculate the Difference, subtract the Lowest Discharge from the Midpoint Discharge:

Using the same example agian:

Midpoint - Lowest	44.7 - 42.5
	= 2.2

Finally, to find the Discharge Variation as a percentage, divide the Difference by the Midpoint and multiply by one hundred.

Concluding the example from above:

Difference / Midpoint	2.2 / 44.7 = .049
By	100
Variation	= +/-4.9%

This is less than ± 5%, so it is acceptable.

(Source: Swan Hill Irrigation Management Course, Book 1, Chapter 3)

Checking Sprinklers

Measuring Sprinkler Discharge At each sprinkler the discharge is measured for 30 seconds. The output for one hour is then calculated. Each sprinkler has a specified discharge when it is new. Discharge (l/hr) = Water Collected Divided By Time collected for Multiplied by 3600 (Seconds/hr) Each sprinkler has a specified discharge when it is new. If wear and tear has effected the nozzle, the discharge figure above will be very different from the manufacturers recommendations, and will not be working efficiently (remember, worn nozzles can be checked using a drill bit). Example:

Cartoon: Lets see what its like to rely on this sprinkler for a drink

If 1.58 litres was collected in the bucket from an emitter 30 seconds, the discharge will be:

189.56 (l/hr)

=

1.58

Divided By

30

Multiplied by

3600 (Seconds/hr)

Calculating the Application Rate
Application rate is the depth of water that a pressurised system applies to the soil surface in one hour.

Application Rate (mm/hr)

=

Discharge from Sprinklers (l/hr)

Divided By

Sprinkler Spacing (m) x Row Spacing (m)

Example:

4.7 (mm/hr)

=

189.6 (l/hr)

Divided By

7.3 (m) x 5.5 (m)

Average Irrigation Depth
The average irrigation depth is found by multiplying the Application Rate by the number of hours of the shift.

Average Irrigation Depth (mm)

=

Application Rate (mm/hr)

Multiplied By

Time (hrs)

Example for a 10 hour shift:

47 (mm)

=

4.7 (mm/hr)

Multiplied By

10 (hrs)

(Source: Swan Hill Irrigation Managment Course, Book 1, Chapter 3)

Application Rate/Pressure Bench Marks

System Type	Optimum Pressure Range (kpa)	Discharge Range (l/hr)
Drippers	80 - 100	2 - 8
Microjets	100 - 150	25 - 200
Mini-sprinklers	125 - 200	35 - 350
Low-level	200 - 300	300 - 1200
Overhead	250 - 400	700 - 3000

(Source: Swan Hill Irrigation Managment Course, Book 1, Chapter 3)

Checklist
Starting at the pump shed;

1.	Check that the motor is running normally and drawing the correct amperage. Listen for unusual bearing noises.
2.	Examine the inlet side of the pump to ensure there are no obvious obstructions around foot-valves, screens etc. Replace any faulty or torn gaskets.
3.	Check for any obvious leaks that are on the delivery side of the pump, and take appropriate corrective action.
4.	Check to ensure that gate valves on the delivery side of the pump are appropriately open.
5.	Filters should be clean and operating normally. If there are pressure gauges at both ends of the filter, the difference should be within specifications.
6.	Monitor the pressure gauge on the delivery side and ensure that it is running at normal pressure. If unsure about the pressure that should be delivered, or the amperage that the pump should run at, contact the system designer.
7.	Where there are flushing points on mains and sub mains or laterals, these should be opened to clear any obstructions. Make sure that the flushing points are the correct size for the system.
8.	Ensure that the numbers of sprinklers on each shift are within the design standards of the system.
9.	Sprinkler nozzles can be checked for wear by using drill bit shanks (preferably new). Nozzles usually have a nozzle size in mm, fractions of an inch, or a manufacturer’s code stamped on them or are colour coded. Select the appropriate sized drill bit shank to fit snugly in a new nozzle.

Overhead Sprinkler Systems

1.	Replace any sprinkler washers if there is leakage down the riser, or other signs of wear.
2.	Note the speed of rotation of the sprinkler – it should to manufactures specifications.
3.	Check the knocker arm rate, this should be about 3 times per second or 180 per minute (almost too fast to count).
4.	Check sprinklers across the shift at the top, middle and end of the laterals.
5.	Check sprinklers in shifts across all sub-mains to ensure uniformity.
6.	Check the cost of refurbishment of the sprinkler to its replacement cost. It is sometimes cheaper to buy a new one.
7.	If replacing a sprinkler in a system with a different brand or type, ensure that the specifications of the new sprinkler are similar to the old one. They should have similar discharges and wetted diameters, as well as operate at the same pressure. Check with your designer before putting in a different make or model.

Low Level Systems

1.	Repair any leaks in the poly-lines, lead tubes, drag hoses or other pipe work. Check for leaks, particularly where the lead tube joins into the lateral.
2.	Check that the knocker arm or spinner is operating properly, and the sprinkler is rotating at the correct speed. Replace the washer in the sprinkler if required.
3.	Clear the area around the sprinkler of any foliage or weeds to ensure good distribution.
4.	Check sprinklers across the shift at the top, middle and end of the laterals.
5.	Check sprinklers in shifts across all sub-mains to ensure uniformity.
6.	Check the cost of refurbishment of the sprinkler to its replacement cost. It is sometimes cheaper to buy a new one.
7.	If replacing a sprinkler in a system with a different brand or type, ensure that the specifications of the new sprinkler are similar to the old one. They should have similar discharges and wetted diameters, as well as operate at the same pressure. Check with your designer before putting in a different make or model.

(Source: Swan Hill Irrigation Managment Course, Book 1, Chapter 3)