A dishwasher spray arm is a hollow tube that spins above the dishes and fires water at them. Use the buttons to look inside it and follow the water from the feed pipe out through the nozzles.
A spray arm is the rotating tube that sits under or above the dish racks. It is fed with water under pressure and throws that water at the dishes through a row of small holes, so the load is rinsed from several directions as the arm turns.
The part you cannot see from outside is the internal manifold: the sealed hollow channel that runs the whole length of the arm and feeds every nozzle.
From outside it is just a plastic arm with holes. Cutting it open shows how one small feed pipe at the centre can supply a whole row of nozzles, and why the holes are cut at a slant rather than pointing straight up.
Two ideas matter most: water only needs one entry point at the hub to reach the whole arm, and the arm itself has no motor — the slanted jets spin it.
The wash pump drives hot, soapy water through the machine. One branch of that flow rises up the feed pipe and enters the spray arm at its centre, at the hub.
The water spreads into the manifold, the sealed hollow channel that runs inside the arm. Because the channel is one continuous space, water reaches it from a single entry point yet fills the whole length.
From the central hub the channel forks and runs out along the left and right halves of the arm. Each half carries water past its own row of nozzles, so pressure stays even along the length.
At each nozzle the water is squeezed through a small hole and leaves as a fast, narrow jet. The holes are cut at a slant, so every jet is aimed up at the dishes from an angle rather than straight on.
A slanted jet pushes sideways as it leaves. The arm is free to turn on its centre bearing, so those sideways pushes add up and drive the arm round, sweeping the jets across the whole load.
The wash pump pushes water up a feed pipe that enters the arm at its centre. From there the water flows into the hollow channel inside the arm and out to every nozzle.
It is the sealed hollow channel inside the spray arm. It carries water from the centre hub out along both halves of the arm so that every nozzle receives water at the same pressure.
The slant matters twice. It aims the jets at the dishes from an angle, and it makes each jet push sideways, so the reaction spins the arm around.
No motor turns it. The arm is mounted on a bearing and the sideways push from its own slanted jets drives it round, like a small water-powered turbine.
No. It is a passive part. The same wash pump that circulates the water supplies the arm, and the heater that warms the wash water sits elsewhere in the machine.
The jets only reach surfaces they can see. Dishes stacked so they shade one another, or a nozzle blocked by food, leave spots the water never reaches.