[reformedliberal]

How does the pressure give them the velocity?

Sorry, I am a math dunce.

[Pikachu_Dad]

cause pressure drop is the driving force for determining the flow rate.

W = K * (dp)^.5

Using this formula, the flow rate is determined by a constant (K) and the square root of the pressure drop.

A more general formula is:

W = 1891 * d^2 * (dp * rho / K ) ^.5
where K is f * L / D

In this formula,

the little d is the diameter of the pipe in inches.

rho is the density of the fluid

K is the resistance of the piping. It is calculated from the friction factor (f); the length of the pipe in feet (L) and the diameter of the pipe in feed (D).

since all of these terms (except the pressure drop) are constants, once they are calculated, they can be used to reduce the equation to the first, more simple term.

[mad_as_he$$]

If you know the size of the pipe(which I am not sure they do exactly) then you can tell the velocity using the pressure. However, things like friction etc will also have a bearing on the actual velocity.