The purchase price is just a portion of the total costs of the pump in the long term.
Start by comparing performance first – when you go on your investigations take a metric conversion table or calculator with you and a pencil and paper. The most efficient level of performance as indicated on a typical pump performance table is around halfway on the performance curve if it is mapped out on a graph, or between 40% and 80% of the full flow with no restriction.
Once you have two pumps or more comparable on performance, say with the same performance at pumping to 1 metre, they might have distinctly different power consumption levels, which might make a significant difference in costs over the life of the pump if it is running all the time.
Running cost of a garden water pump
Running costs = (Watts x Hrs/1000) x KWH rate.
In my experience I have had two pumps of very similar performance, but one was rated at 80watts and the other (a very modern one) at 15Watts. Over the period of a year with a KWH unit rate of 9p, the 80Watt motor would have cost £26.28p to run and the 15Watt would have cost £4.92p. So add this into an equation for the real costs of your pump by simply multiplying by the length of the guarantee and adding it on to purchase price of the pump.
Now, guarantees are another factor of the price.
One year long guarantees are a thing of the dim and distant past. The average punter nowadays is coming to expect 3 or even 5 year guarantees. To mean anything at all this must be ‘continuously rated’ i.e. if it is a 5 year guarantee the pump must still be guaranteed to run for 5years continuously non-stop.
So taking this into account, if guarantees are any indication of life expectancy, they must surely be added to the equation in cost estimates. These two pumps I had in mind before, the 80watt pump had a three year guarantee and the 15watt had a 5year guarantee. It was then quite possibly going to last another two thirds longer than the first one, so in fairness two thirds of the cost of the first needs to be added to its original cost to be a comparison.
At this rate they ought to have been giving the first one away in order to make it a viable comparable economic choice.
Over the coming months I am going to be testing a number of popular makes of pump against each other that purport to have similar performance figures and putting them through their paces for the various tasks they seem most suited. The conditions, unfortunately for the manufacturers (and for myself who will be carrying out the tests) are that they wont be carried out in sterile pristine tanks.
It will be the muck and mire of an ordinary garden pool at Blagdon Water Gardens – the original home of the pump that changed the playing field. Here will be all the detritus and grime to block them up as in the real world and I will undoubtedly have the cold numb fingers that will struggle to dismantle them for maintenance. To start with we will try out small pumps moving from 1000 to 1500 litres per hour that give a good fountain or perhaps provide the flow for a small waterfall.