2 August 2002

A CLEAN IRRIGATOR FOR DIRTY

WATER

Dirty water irrigation systems provide an efficient means of disposing waste liquid on

pasture. But for a hassle-free life they must be kept running smoothly. Mervyn Bailey reports

A DIRTY water irrigator is one of the simplest and least demanding pieces of kit on the dairy farm. But like anything mechanical, it does need looking after to minimise wear, keep it working effectively and provide a long service life.

As Giles Russell, irrigation service manager at Midland Slurry Systems, points out, there is one rule to remember – what goes in must come out. And if this includes stones or other abrasive materials, then the working life of such equipment can be considerably shortened.

It is, therefore, good practice to keep the pump intake pipe in the cleanest water, near the dirty water lagoons surface and use a filter where necessary.

"Filters are a nuisance when they become blocked. But if silage or stones get into the system they will soon cause a blockage further down the line where it can be more difficult to clear."

The pump itself is a specialist item which should be left to a specialist, Mr Russell suggests, so maintenance at the intake end is largely confined to checking for pipe wear and leaks.

Reeler units are simpler devices with little to go wrong, as long as chains and bearings are greased monthly when in use.

They are driven by the water being pumped, which rotates the boom, and in turn reels in the hose. But bear in mind that water being pumped through a partially wound hose adds significantly to the dry weight of the machine, so it is worth using the recommended tyre pressure to minimise rolling resistance.

The Midland Slurry Systems Aquareel comes in two sizes – the Mini and the Midi – and, like others of its type, uses small rubber nozzles at the outlets to give a good distribution pattern. But blocking can be a problem when water filtration is not sufficient.

"Blockages can often be cured by sticking your finger in and pulling the obstruction out," advises Mr Russell.

The NC Pulse Jetter, which MSS sells south of the M62, is an altogether different design, which accumulates the liquid in a pressure vessel, then blasts it through a large bore irrigation gun. Apart from being less prone to blockages, the Pulse Jetter covers a large area from one position.

The latest version uses the same principle as the original, but differs slightly in the way it works. Dirty water is pumped into an upright metal cylinder where it traps and pressurises a pocket of air.

At 7.5 bar pressure a poppet valve is triggered, allowing water to be released through two discharge pipes – one large bore, which provides the main coverage, and a smaller bore tube that ensures ground within a 15m radius of the machine also receives a decent coating.

"The previous model filled a rubber bag inside the main chamber until there was sufficient pressure to trip the release valve," explains Mr Russell. "A change in legislation called for the new design. Replacement bags for the older type, which tend to perish after a few years, are no longer available, but a modification is being developed."

Maintenance requirements are limited to applying a monthly dose of light grade oil to the poppet valve actuator shaft, which moves back and forth each time the Jetter discharges. This is not necessary on older models as these rely on water to keep the shaft lubricated.

"While the oil can is out, it is worth giving the drawbar jack a drop or two," suggests Mr Russell. "Because the machine is shaken every time the water is dispensed, the jack takes a lot of grief and can become stuck."

The springs that hold the poppet valve closed against the rising pressure within the main vessel can be lubricated with oil through holes in the spring cover, which is within the main guard.

Otherwise, draining any condensation from the booster tank – which ensures there is always the correct amount of air in the main vessel before it is filled – is all that needs to be done on a regular basis. Once a month should do, taking care not to lose too much air from the system.

On both new and old Pulse Jetters, it is important to check the thrust plate distance on the upright part of the main outlet tube. This should be between 0.5mm and 1mm; otherwise the pipe will lift when the system fires, allowing water to leak out instead of being discharged through the nozzle. &#42

Giles Russell points out the oil lubrication point for the Pulse Jetters poppet valve actuator shaft. His right hand is above the rubber bellows that push the valve open and the stroke adjusters which alter system pressure and discharge distance.

Maintenance needs of hose reel irrigators, like this Aquareel, are limited to monthly greasing of chains and bearings and maintaining correct tyre pressures.

&#8226 Avoid stones in intake.

&#8226 Grease reeler monthly.

&#8226 Check jetters.