How does a water tap adjust the rate of flow ?

Question

When I try to obstruct water flow with my finger,the flow doesn't decrease,instead,water velocity increases according to continuity equation,so how can a tap do it?

Answer 1

It obstructs the flow. velocity may increase for a bit, but volume goes down, and the flow levels out in a few inches.

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Answer 2

The reason you fail to reduce the disharge is because your finger is acting as a venturi. In other words the static head (p/density *g)is being converted is being converted to a velocity head (v squared/2g). To stop this from happening you need to introduce a sharp o*****e or opening such as in a tap (Globe valve). The sharp o*****e creates "eddies" or turbulence at the opening and energy is converted to heat by the fluid friction. Also the static pressure increases as the o*****e diameter reduces. Our fingers do not offer this sharp edge. Try blocking the pipe with a plate and small hole. There will be a reducing of pressure. Also the flow reduction is not linear as it depends on many other variables