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February 2017
MANAWATU FARMING LIFESTYLES
DAIRY Pond crust gone for 10th the cost?
Yep!
Irrigation Matters with Clem Powell The mystery of pumps In most water reticulation or irrigation systems, you are going to need a pump, unless the water is from a pressurised scheme at farm gate or as some lucky farmers I visited recently in Middlemarch Otago have, gravity fed from surrounding hills — a whole 160psi of it! Could this be why some couplings had leaking O-rings?
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Wear a helmet. A helmet is a must while riding a quad bike around the farm.
I often get asked about gravity for irrigation but there are a lot of considerations, enough for another blurb perhaps? Pumps work via energy transferred from the shaft to the water in the pump body. So what? Well the critical thing here is that energy costs money, pumping usually occurs over a considerable period and the wrong pump can, consequently, be a very expensive purchase! Just as Mum’s shopping basket’s engine has a different power curve to the farm ute, which is also different to a truck engine, so pumps are also massively different in performance and efficiency at the particular performance you require. Yes, you may get away with towing the boat with Mum’s shopping basket — for a short duration, but the fuel bill is going to be the highest ever and it can’t last.
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It’s the same with pumps. I often see pumps from clearance sales which have run a low pressure system, being applied to a medium or high pressure system. After all ‘it’s a big pump isn’t it? The guy before was running way more gear than me’. Yup, but now your diesel motor is valve bouncing trying to produce the pressure required, and also the pump is not running in its ‘happy spot’. You could also be pressurising a lot of water, which is going nowhere due to different irrigation flow. Energy cost again! Actually the chance of buying the right pump from a clearance sale are about the same as a winning lottery ticket! One in a million. The best efficiency is usually somewhere around two-thirds full flow on most pumps. This is not maximum pressure, so beware of advertising stuff from certain companies saying ‘Max flow… Max pressure’. This does not mean you can get both at once. Even then some of the claims are at best, ‘optimistic’, as observed by our technicians. Buying a pump Using a reputable irrigation professional should avoid these pitfalls. 1. Ask for proof that the pump you are considering is the correct one! Pump curves are not so difficult to read and you can always ask regional council field staff or other professionals to help impartially. Irri-Max Ltd and others have an open policy about what the client is getting. Don’t allow ‘secret squirrel’ stuff. Look for the best efficiency point — is this the same as your intended flow? Does the pump have the ability
to produce the required pressure at reasonable input speed? Ask about the pumps Nett Positive Suction Head (NPSH). You might not understand it but a simple calculation is this — start with value of nine then subtract your suction height (pump above water), then see if the balance is larger than the NPSH value at your intended flow. Say your pump is 4m above water (not the best installation), then the NPSH can not be more than five, in fact even this would be a call to get some proper hydraulic engineering done to avoid disappointment. Probably pump techs will laugh at my equation above as there are more factors to it than this, but my intention is merely to give the layman some warning signs of what may work or not. NPSH available varies massively from pump to pump! 2. Have you the right of return if it doesn’t meet specs? What is the cost of this ‘experiment’? eg you may have to change mounting points, flanges, engineering, etc. if it doesn’t work and you need to fit another model. Don’t buy a pig in a poke! 3. Pressure gauges: Insist the pump has a pressure gauge so you can verify the promised performance on your system. 4. Is the suction system large enough? Avoid the ‘thick shake with small straw effect’. 5. Irri-Max Ltd have been importing and supplying irrigation and effluent pumps for more than 20 years. Please contact Clement (Clem) Powell on 0800 426 296 for more information.
PUMPING PROBLEM? NO PROBLEM FOR US!
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0800 426 296 Contact our friendly team today on: 0508 872 466 www.landbasedtraining.co.nz
Ferbo Diesel Pumps for reliable and economic operation from 10hp to 240hp as standard
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