Calculation of pressure from flow rate of water Anybody kindly help me to find how to calculate pressure in bar from flow rate. I have a pipe and from that I am transferring water at a constant flow rate of 5ml/min. At this flow rate, with a 0.5 cm diameter pipe, what will be the pressure generated by water?
 A: If the flow is laminar, i.e. not turbulent, then the relationship between flow rate and pressure is given by the Hagen–Poiseuille equation:
$$\text{Flow rate} = \frac{\pi r^4 (P - P_0)}{8 \eta l}$$
where $r$ is the radius of the pipe or tube, $P_0$ is the fluid 
pressure at one end of the pipe, $P$ is the fluid pressure at the other end of 
the pipe, $\eta$ is the fluid's viscosity, and $l$ is the length of the pipe or 
tube.
For turbulent flow there is no simple analytic treatment, but there is an empirical equation called the Darcy–Weisbach equation:
$$ P - P_0 = f_D \frac{l}{2r} \frac{\rho V^2}{2} $$
where $V$ is the flow velocity and $f_D$ is an empirically measured constant called the Darcy friction factor.
There is an online calculator for the Darcy-Weisback equation here.
A: The flow rate is proportional to the pipe section and flow velocity, and the relationship between the three is
$$Q = 3600 \left(\frac{\pi D^2}{4}\right)v$$
where $Q$ is the flow rate ($\text{m}^3 \text{/h}$), $D$ is the pipe inner diameter ($\text{m}$) and $v$ is the average velocity of the fluid ($\text{m/s}$).
