Irrigation system maintenance: Timely care can cut down-time later

Bill Kranz
University of Nebraska

Wear and tear on irrigation pumps and motors can contribute
to a gradual decline in water application efficiency that may not always be
easily identifiable. Regularly recording the static and pumping water levels,
output pressure, flow rate and energy use provides an excellent reference for
evaluating pump performance. Without records, you may not be aware of how
system performance has changed over time.

Each irrigation system should be equipped with a recently
calibrated water meter, pressure gauge, and a means of monitoring the water
level in the well (air line or a hole for an electric resistance probe). Gauges
to monitor such variables as motor water temperature, oil pressure, revolutions
per minute, and hours of operation should be maintained to provide a means for
monitoring the system as well as shutting it down if it is not working at the
appropriate level.

Other motor records should include hours of operation, oil
and fuel use rates and engine operating temperature. Engine overhauls and part
replacements are easier to plan for if hours of operation are recorded.

In the spring, check control boxes, pipelines, the engine
compartments, and exterior oil cooling coils for rodents. Also check all wire
coverings which rodents may have damaged, creating the potential for electrical
shorts. Corrosion also can contribute to wiring problems. A pre-startup check
of all electrical connections will reduce the chance of electrical failure or
personal injury.

Before the first irrigation next spring, check your owners
manual and perform routine maintenance, including:

1. Change the engine oil and filter,
2. Check drive belts (if any),
3. Grease all drive shafts on pump, and motor,
4. Replace fuel filters,
5. Check the operation of the chemical injection pumps,
6. Check and clean the battery power cables,
7. Drain, flush and refill the cooling system,for 30-60 minutes.
8. Drain and replace the lubricating oil in pump gear drive,
9. Refill the reservoir for lubrication of the pump drive shaft,
10. Check the gear drive to be sure it is free moving and clean the non-reverse
    pins with a wire brush, and lubricate each pin,
11. Start the motor and allow it to run at 1000 rpm

Some pump installations may not require all of these
maintenance checks or they may require different or additional repairs. Check
your owner's manual for what best suits your system.

The water distribution system, especially the drive tower
tires, gear boxes and alignment panels, also need routine maintenance. Oil
lubrication of the gear boxes is essential; bearings and seals should be
checked regularly. Lubricating oil containing water, or steel filings can
drastically increase the wear and tear. Drain any water out of the bottom of
the gear box prior to each irrigation season. Refill gear box oil annually and
replaced it after the first irrigation season and every 3000-4000 hours of
operation thereafter.

With hydraulically driven systems, check for oil leaks. Oil
distribution hoses degrade over time and should be closely inspected for
severely worn or degraded areas. Ruptured hoses are costly in terms of oil
spillage and present a safety hazard to operators. Rather than chance a
breakdown, replace hoses that appear to be a hazard.

Most self-propelled systems have numerous moving parts that
require lubrication. Begin each season with every grease receptacle and oil
reservoir filled to the recommended level. All electric components should be
sealed to prevent bugs, dust or rodents from damaging components, which could
lead to system failure or personal injury.

Irrigation systems are equipped with safety switches
designed to shut the system down under specific conditions. These switches
normally include a low pressure shutoff, system alignment and over-watering
safety, end gun control and automatic shutoff at the end of a revolution. Your
system may include other switches. Test your system by running it and creating
situations which should prompt the safety switches to shut the system down. For
example, to test alignment control, start and stop the system several times
while moving both forward and in reverse to determine if the system realigns
itself. If not, determine why not.

Finally, many systems utilize on/off control of the end gun.
This feature is used to accommodate roadways, farmsteads or other areas where
irrigation is unwanted. The switch activates a solenoid valve to cutoff flow to
the end gun. Pressurize the system and determine if the switch is functioning
properly and check for a leaky solenoid valve.

Sprinkler nozzle wear depends on the quality of the water
and the system operating pressure. Sprinklers will need to be replaced more
often on systems operating at high pressure than those operating at low
pressure. A walk by inspection of the system can identify sprinklers that are
plugged, badly worn or not operating properly. Generally, plan to replace
sprinklers after about eight to 10 years of use. Systems with extremely low
water will experience problems sooner.

Walk-by inspections can indicate sprinkler maintenance
needs, such as pressure regulator failure or non-operational sprinklers. Often
these problems can go unnoticed during the irrigation season. Some problems can
be seen from a distance while others will require more scrutiny to identify.
For water to be applied uniformly, all nozzles or sprinklers must be
functioning properly.