There's a statement up the page that is just plain WRONG.

Liquid flowing in a tube is NOT absolutely limited by the smallest hole it has to go through.

Pressure at one end of a system is converted into flow according to Bernoulli's equation. Flow restriction in the pipe is due to friction between pipe wall and the liquid. This friction decreases the fluid's available energy as it goes along the pipe.

When the fluid goes through a restriction some of the energy that is in the form of pressure turns into kinetic energy to speed up the liquid as it flows past the restriction. In the restriction, where the fluid is speeded up, the fluid will have less pressure. This is also called the Venturi effect or Bernoulli effect. This is what "pulls" gasoline into the carb airstream through the boosters and jets.

As the liquid passes the restriction it slows down and the kinetic energy turns into pressure energy again.

The downside to this speeding up and slowing down is that some energy is lost turning the pressure into velocity and then back again. So there is less available energy to push the fluid through the line. The restriction slows flow because it wastes the fluid's energy. It is NOT because it is an absolute limiter of flow.

R.