# Hydrodynamic calculation Needle valve closing flow against the direction of movement of the piston

## Values for calculation

## Calculation

### Velocity in valve

$$v_{max}=\cfrac{4\cdot 10^6\cdot Q_{max}}{π\cdot D^2}$$### Theoretical pressure in the valve at full opening

$$Δ_h=\cfrac{v_{max}^2}{2\cdot g}\cdot \left(ζ+1\right)$$### Pressure parameter

$$p=\cfrac{Δ_h}{H}$$$$0 < p \le 1$$### Effective closing time factor

$$c_{ef}=0$$### Under-pressure behind the valve

$$P_{u}=\max\left(-\cfrac{L\cdot v_{max}}{g\cdot t\cdot c_{ef}}, -10\right)$$