24 Irrigation
Selecting booster pumps for irrigation The sizing of pumping systems for irrigation needs careful consideration to achieve optimum performance, efficiency and long-term reliability. Based on the application and environment, T-T Pumps looks at the primary factors and requirements to consider when choosing booster pumps for irrigation.
H
ead and flow are the main requirements for any irrigation system; however, a lot of information is required to get the best efficiency and reliability. Head is seen as the highest point of discharge from the pumps, but we need to understand the total amount of static head and other head losses in the system to define the total head. Pipework costs may push installers towards using less costly small-bore mains to the discharge points, only to undermine the long-term energy cost and system performance. Unfortunately, the friction loss within a small-bore irrigation system will demand more energy, escalating the running costs where energy is concerned. With this in mind, the greater the flow, the larger the bore pipework needs to be, especially for the main distribution pipework. Other losses are found in any pipework system and should be accounted for when calculating the total head. Sprinklers, irrigators, fittings and valves will have an identified head loss value, and by careful selection and design, some of these losses can be reduced. Once the total head and flow have been determined, the process of selecting the pumping system can begin. Most facilities, such as golf clubs, sports grounds, parks and large gardens, will require a system using two or more pumps with a ‘jockey’ pump to cope with small fluctuations in pressure demands. PUMP CONTROL SYSTEMS The control of these pumps is via an electrical control system which will monitor the pressure with the
Quarter 3 2021
discharge water main and start the pumps as demand increases. One pump may be required initially, but an additional pump will be deployed to maintain pressure as demand increases.
A reliable and efficient control system will have a myriad of additional built-in protection features. In some cases, the control systems may be as simple as using mechanical pressure switches to activate the motors via crude ‘direct online’ starting methods, but more commonly, variable speed drives are being used to match performance with demand, giving better overall performance and economy. A reliable and efficient control system will have a myriad of additional built-in protection features, supplementary to the
expected motor overload protection; dry running protection is essential to avoid damaging the pumps due to lack of incoming water. Equally, under pressure protection may be provided to shut the system down if there is a delivery main bursts or an unplanned discharge beyond normal planned flows occurs. POWER SUPPLY The power supply is a very important consideration when specifying an irrigation system. It is important to ensure that there is sufficient supply to meet the demand of a new system. In addition, the location of a system is important. A system needs to be positioned to optimise the irrigation obligations. However, greater distances from the power source need larger power cabling to avoid voltage drop, which will otherwise undermine the system, and this can have a significant cost implication. Recent examples of booster pump installations for irrigation www.bpma.org.uk
