Valve¶
The discharge across a valve is given by equation the discharge through a valve proportional to valve area and pressure head
\[
Q = A \sqrt{\frac{2g \Delta H}{k}}
\]
Equation: Discharge through a valve proportional to valve area and pressure head difference.
where
- g — the gravity constant
- k — the flow factor which depends on the opening of the valve.
- A — full open flow area of the valve
- DH — the energy drop over the valve. An assumption for this equation is that the valve is located in a pipe which is running under pressure. However, should the system run under non-pressurised flow conditions the flow area A in equation the discharge through a valve proportional to valve area and pressure head of the valve is reduced by a linear reduction for non-pressurised flow conditions:
\[
A\left(d\right) = A\left(\frac{d}{d_{f}}\right)
\]
Equation: Valve flow area as function of opening depth normalized by full valve opening depth.
where
- d — the depth of the flow depth
- df — the pressurised flow depth This means that the velocity head upstream and downstream of the valve is equal and equation the discharge through a valve proportional to valve area and pressure head can be rewritten to
\[
Q~=~A\sqrt[N]{\frac{2g h}{k}}
\]
Equation: Valve discharge equation relating flow to pressure drop and hydraulic geometry.
where
h = the drop in pressure over the valve.