The main types of small 12V pump and what each is for

Pump names can feel like a maze. Underneath, there are only a few ways to move water, and each one suits certain jobs.

The first split is how the pump pushes. Some squeeze a fixed amount of water along. Others spin a wheel and fling it.

Squeezers: diaphragm and piston pumps

A diaphragm pump flexes a sheet of rubber, plastic or Teflon back and forth, and valves on each side keep the water moving one way. Wikipedia calls it a positive displacement pump, which just means it traps a set amount of water and pushes it out¹. Piston and plunger pumps sit in the same family, called reciprocating pumps².

Here's what the diaphragm design is said to offer. It's described as self priming, with good suction lift¹. "Priming" means getting water into the pump so it can start pulling. "Suction lift" is how high the pump can pull water up to itself.

The same page says these pumps can be built to cope with a fair amount of grit, and that they have good dry running characteristics¹. Treat that as a general description of the design. Your own pump's manual decides whether running it dry is allowed.

Piston pumps are a different story. A reciprocating pump is often used where only a small amount of liquid is moved and the delivery pressure is quite large². So they point to pressure jobs, not bulk filling.

Spinners: centrifugal pumps

A centrifugal pump has a wheel called an impeller that spins the water outward. It needs water inside to work. Wikipedia describes priming as filling the pump with liquid, and says most centrifugal pumps sit below the level of the water they draw from³.

That's the mistake beginners make. They put a plain centrifugal pump above the water, switch it on, and wonder why nothing happens. The pump is full of air, and a spinning wheel can't pull air up a hose. If that sounds familiar, the checks in priming problems and how to fix them will help.

Some centrifugal pumps are built to clear the air from the suction line themselves. Wikipedia notes this design is used for small pumps, such as garden pumps³. It also warns that other pump types may suit high pressure better, and that large solids or debris may clog the pump³.

Pumps that live in the water

A submersible pump has a sealed motor joined to the pump body, and the whole thing sits under the water⁴. It pushes water to the surface rather than pulling it⁴. That's why it suits a deep tank or a rain barrel: there's no suction lift to worry about.

Matching the pump to the job

The tap row is a prompt to check, not a pick. A tank-to-tap setup shows how a pressure switch and the other parts fit together.

A note on solar

If you plan to run a pump from panels, the type matters even more. A university guide says surface pumps designed for solar power typically lift between 10 and 20 feet⁵. That's roughly 3 to 6 metres. Check any pump's rated lift before you buy, and read what the flow and lift numbers mean so the label makes sense.