murray

Murray Matters - Is your diesel powered pump costing you money?

By Adrian Smith, Senior Land Services Officer (Mixed Farming Systems)

In a series of tests of irrigation pumps across NSW, it was found that many were not performing as they should, costing irrigators money and resulting in potentially lost production. With the summer irrigation season fast approaching, river and bore pumpers still have time to evaluate their existing pump station setups to see if they are performing correctly.

Poor pump performance can be the result of a number of things – wear and tear, incorrectly matched pump and motor, pumping outside the pump/motor design, incorrect impeller size and the like.

How well your pump setup converts diesel fuel to water moved is a measure of the pump efficiency. For diesel setups, pump efficiencies in the 70-85 per cent range are acceptable and easily achievable. Your pump needs to be performing as efficiently as possible in order to minimise pumping costs.

Testing your pump performance

It is relatively easy to measure the performance of your pump. There are two steps:

1.      Determine how much fuel is used per unit (eg. megalitre) of water pumped, and

2.      Determine the pump efficiency.

1.      What is pumping costing?

Things you need to know (or work out) are:

·         Measure the fuel used and the volume of water pumped.

·         Calculate the pumping cost (divide the fuel used in litres/hour, by the volume pumped, in ML/hour), and then multiply this number by the cost of diesel. This will give you a cost per ML pumped.

2.      How efficiently is your pump performing?

Things you need to know (or work out) are:

·         Fuel used per unit volume of water pumped

·         The specific fuel consumption for your particular engine

·         The total dynamic head of your system.

The most difficult thing to measure is the total dynamic head, which is comprised of a number of individual components, including the static head (distance between the water level and the outlet), and friction losses in the pipe work and fittings, pressure head (operating pressure) and velocity head (energy lost due to motion).

That said, in most surface (non-pressurised) irrigation systems, a simple measure of the distance from the water level to the height of the discharge pipe (or height of the water if the discharge is submerged), is all you need to work out the total head.

[Image result for batescrew pumps and valves]

Caption: Ensuring your diesel powered pumps (river pumps or bores) are operating efficiently will pay dividends in the long term.

Other things to consider?

In order to calculate pump efficiency correctly, energy losses due to the motor, transmission, climatic conditions, etc. are accounted for through a process called derating.

Things to consider as part of this ‘derating’ are:

·         Altitude (as altitude increases, power produced decreases, but for most pumpers along the river systems in the Murray region, this is not something to really worry about)

·         Temperature (as ambient temperature increase, internal combustion engine efficiency decreases)

·         Transmission losses (if the pump is not direct-coupled to your engine, there will be a loss of energy in transmission – with V belts being less efficient than gear drives).

Apart from these, you need to know the actual pump speed, and the rpm of the motor. Remember that pump performance charts are usually specific to a certain pump speed and impeller size. And an individual impeller has a specific ‘duty’, so changing the impeller (and wear has the same effect), will affect the performance of your pump.

One underlying assumption with all this is that the diesel engine itself is running efficiently. If it is not, the results will suggest the pump is running less efficiently than it actually is. This can also be accounted for when assessing the performance of the pump, using a measurement called specific fuel consumption.

Overall

While it may seem complicated to determine your pump’s efficiency, it really is not. Keep track of things that are easily measurable, so that you can quickly realise when there is a problem (or that a problem might be just ‘round the corner’!). In a year like this when you may be pumping large volumes of water, simple measures to save a few dollars per megalitre pumped can amount to a significant overall saving.

For further information or assistance, please contact Adrian Smith at Murray Local Land Services in Deniliquin, and take a look at the NSW DPI Primefact publication ‘Is your diesel pump costing you money?’ by clicking on the following link - http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0004/165217/is-your-diesel-pump-costing-you-money.pdf

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