## Maximum allowable pressure $PS$ of a valves

Maximum allowable pressure $PS$ must be based on the most stringent conditions, which act on the valve. According to the maximum allowable pressure, the $PN$valve must be selected. $PS\le PN$

$PS$ | maximum allowable pressure | $\mathrm{MPa}$ |

$H_{v=0}$ | static pressure before valve in closed position at zero flow | $\mathrm{MPa}$ |

$∆P$ | increasing pressure on water hammer | $\mathrm{MPa}$ |

$P_{atm}$ | under-pressure behind the valves (atmospheric pressure) | $\mathrm{MPa}$ |

**Example:**

We have to determine maximum allowable pressure $PS$ of a valves (Butterfly valve $DN2000$ the valve is controlled by a gearbox with a drive) with the following parameters:

Static pressure before valve in closed position at zero flow $H_{v=0}=1.2\ \mathrm{MPa}$; the length of the pipeline before the valve $L=1000\ \mathrm{m}$; steel pipe $D=2000\ \mathrm{mm}$; thickness of the pipe wall $e=30\ \mathrm{mm}$; max. flow $Q=30\ \mathrm{m^3/s}$; density water $\rho=998.8\ \mathrm{kg/m^3}$; medium compressibility factor $\beta=477.1\cdot10^3$; closing time $45\ \mathrm{s}$; local loss factor for an open valve $\xi=0.106$; the space behind the valve is non-perfect aerated $P_{atm}=0.1\ \mathrm{MPa}$.

was calculated by

Effective closing time factor

Water Hammer

**maximum allowable pressure:**

**Literature:**

- ČSN EN 13445-3: Netopené tlakové nádoby – část 3: Konstrukce a výpočet.