There are two categories irrigators fall into, high application rate and low application rates. However choosing the right irrigator is really a case of deciding the risks associated with the application rate and depth.
Choosing the method of irrigating is the most important part of the decision-making process. Remember that the value of the nutrients is measured by the amount that is utilised. If you over apply then there is a wasted amount that becomes valueless. A good system design will try to utilise as much of the nutrients as possible. The objective in this process is to minimise that amount of fertilisers brought onto the farm. This cost saving will be the repayment method and reason for irrigating effluent onto land in the first instance.
The soil type will determine the rate and depth that suits. What this means is each soil type will have a maximum application rate or how fast the liquid should be applied. This is measured by mm per hour. The soils also have a maximum application depth. This is measured by the total volume that it receives in a pumping session.
The implications of getting it right are the nutrients are staying in the root zone and the plant can uptake those nutrients. Any nutrients that pass the root zone are lost. They can make their way into underground water which becomes an environmental issue.
Applying at a higher rate will also cause ponding and runoff. Both are an undesirable result.
When designing a system you should set parameters around volume pumped, uniformity and labour. You should be able to pump one days' waste in one hour or spend no more than 3 hours a fortnight in total labour. The uniformity should be consistent over the application area (equal amounts applied to the irrigated area).
The majority of effluent pumps are designed to pump solids up to 10% and normally have an open impellor. They come in different sizes depending on the required volume and head. They start at 5 to 35 horsepower or as high a head as required. The open impellor pump is primarily used to run such applicators as the Larall Smart Hydrant, Rain guns, Spitfire Irrigator and Traveling irrigators or pretty much anything with a larger nozzle that say 10mm.
The open impellor pumps are also used as transfer pumps for effluent containing solids. This includes feeding mechanical separators, transferring from sump to ponds and vise versa. Transfer pumps are usually high volume, low pressure.
With the introduction of Low Application Rate systems where solids have to be removed such as Irri-Pod, K-Line and Larall, the closed impellor pressure pump can be used. These pumps are usually used to pump water. The closed impellor pump will produce a greater volume per hour that the equivalent size closed impellor making them more efficient.
There are four different types of effluent pumps.
1. Long Shaft (open impellor)
2. Short Shaft (open impellor)
3. Submersible (open impellor)
4. Shore Mounted (open impellor and closed impellor)
The main open impellor effluent pump brands are Doda, Gillies, Numedic and Reid & Harrison. There are many closed impellor pumps. Some brands are Davies, Gillies, Grunfos and Lowara.