Diaphragm and spray pumps
Diaphragm and spray pumps
Almost the whole range runs on twelve volts, and the weakest model gives barely four litres a minute at forty PSI while the strongest gives nineteen litres at seventy PSI. Inside works a flexible diaphragm driven by the motor, so the pump draws the water itself and does not need it for cooling. Alongside the three-chamber models there is also a pump with a filter on the suction side rated at two hundred and sixteen watts, plus a separate digital pressure switch for mains voltage. The spraying side is covered by a sixty-litre quad sprayer with a boom and a hose of over six metres, and by a high-pressure sprayer pump at a hundred and thirty PSI.
The fastest way to get lost in the range is to compare PSI with megapascals. One megapascal equals a hundred and forty-five PSI and at the same time ten bar, so the agricultural pump quoted at nine tenths of a megapascal actually delivers a hundred and thirty PSI. Exactly as much as the model quoted straight away at a hundred and thirty PSI, only written in a different unit. Convert every figure into one unit before you start comparing prices.
Some of the pumps have a built-in pressure switch, and that changes how you work with them. Open the nozzle and the pump starts, close it and the pump stops, so you need not watch it at the switch. The switch answers to the pressure in the hose rather than to your command, which is why a leaking joint will set it going over and over. The separate digital switch in the range does the same for mains pumps up to one and a half kilowatts and adds IP65 protection.
A submersible pump burns out without water in moments, while with a diaphragm pump it is the other way round, because running dry does it no harm. The diaphragm separates the liquid from the drive, and the drive lubricates itself, so the pump needs no water flowing through it to keep cool. Four models in the range state this outright, on the rest the description makes no such promise, and that is the whole difference. When you are drawing from a drum that runs empty, it is exactly that property that makes the description worth reading.
The last figure people forget is the current, because two hundred and sixteen watts comes to eighteen amps at twelve volts. A cigarette lighter socket is usually fused at ten to fifteen amps, that is a hundred and twenty to a hundred and eighty watts, so the strongest pump in the range does not belong in it. The weaker seventy-watt models draw six amps and give no trouble, but wire the powerful pump straight to the battery through a fuse of its own.