$120$

$4.$ Two elevated tanks supply water to a demand node with a valve at its outlet $($Figure $4).$ The elevated tanks are cylindrical and have diameters of $5m.$ The initial water level in Tank $1$ is $96m$ and the initial water level in Tank $2$ is $89m.$ The valve is half open and has a discharge coefficient of $0\mathrm{.}15\frac{m^{\frac{5}{2}}}{s}.$ The initial steady$-$state flow through the valve is $350\frac{L}{s}.$ The valve discharges to the atmosphere. Both pipes have a Hazen$-$Williams $\text{'}C\text{'}$ factor of $100,$ an internal diameter of $250mm,$ and a length of $300m.$ Assuming quasi$-$steady conditions in the system, determine the pressure head at the demand node and the flow in the pipes in the first three time steps of the simulation. Use a time step of $15$ seconds to carry out the quasi$-$steady state simulation.