Dirty water and drainage pumps
Dirty water and drainage pumps
The range starts at the three-hundred-and-twenty-watt submersible with six thousand litres an hour and ends at the two-thousand-two-hundred-watt model, which gives a thousand litres a minute and pushes them to eighteen metres. In between sit a five-hundred-and-fifty-watt model, an eleven-hundred-watt one and a thirteen-hundred-watt one, all with a float switch. Beside them the range holds a twelve-volt drainage pump with seventy litres a minute and five metres of head, running off a battery. The wattage is not the main thing, though, because the job is decided by what has to pass through the outlet.
The first question is how big the dirt in the water is, and the bore of the outlet answers it. A drainage pump is built for clean water and passes grit of about five millimetres, a dirty water pump copes with thirty and more. The range shows it plainly, because the drainage model has a twenty-five-millimetre outlet and the strongest dirty water pump one of seven and a half centimetres. A dirty water pump therefore runs an open impeller with wide passages, which shows up as less head per watt.
The second question is how much water may stay behind, and this is where the two groups part company most. A drainage pump with flat suction takes the level down to a single millimetre, after which only a floor to mop is left. A dirty water pump leaves a few centimetres, because if it sat right on the bottom, sand and silt would clog it. Both suit a flooded cellar, only after the dirty water pump you will go round again with the mop.
A float switch cuts in and out on the water level, only the float must have room to swing out. A freely hanging float wants a chamber about thirty-five centimetres across, and in a narrower one it catches on the wall. If you are lowering the pump down a narrow pipe, look for a model with a vertical float, which manages on twenty-five centimetres. A shorter float cable means a smaller gap between switching on and off, so the pump starts more often and leaves less water.
The last thing is how you get the pump into the sump, because it goes down on a rope and not by the cable. Pulling on the cable damages the gland where the cable enters the motor, and water works its way in there over time. Tie the rope to the handle, leave the cable hanging slack, and the pump will last considerably longer.
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