**Maximum allowable pressure ***PS* of a valves

*PS*of a valves

**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.

$PS\ge {H}_{v=0}+\Delta P+{P}_{atm}$

*PS* - maximum allowable pressure - [MPa]

*H _{v=0}* - static pressure before valve in closed position at zero flow - [MPa]

*ΔP* - increasing pressure on water hammer - [MPa]

*P _{atm}* - under-pressure behind the valves (atmospheric pressure) - [MPa]

**Under-pressure behind the valves:**

For non-perfect aerated space behind the valve

${P}_{atm}=\mathrm{0,1}MPa$For perfect aerated space behind the valve

${P}_{atm}=0MPa$**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} = 1,2MPa*; the length of the pipeline before the valve

*L = 1000m*; steel pipe

*D = 2000mm*; thickness of the pipe wall

*e = 30mm*; max. flow

*Q = 30 m*; density water

^{3}/s*ρ = 998,8Kg/m*; medium compressibility factor

^{3}*β = 477,1*10*; closing time

^{-12}*45s*; local loss factor for an open valve

*ξ = 0,106*; the space behind the valve is non-perfect aerated

*P*

_{atm}= 0,1MPaIncreasing pressure on water hammer:

$\mathrm{\Delta}P=\mathrm{0,39}MPa$was calculated by

was calculated by

$PS\ge {H}_{v=0}+\Delta P+{P}_{atm}$ $=\mathrm{1,2}+\mathrm{0,39}+\mathrm{0,1}$ $=\mathrm{1,69}MPa$$PS\le PN\to PN25$

**Literature:**

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

MET-Calc: Effective closing time factor

**Download PDF:**

**Social media:**