Maximum allowable pressure 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.

PSPN
PSHv=0+ΔP+Patm

PS - maximum allowable pressure - [MPa]

Hv=0 - static pressure before valve in closed position at zero flow - [MPa]

ΔP - increasing pressure on water hammer - [MPa]

Patm - under-pressure behind the valves (atmospheric pressure) - [MPa]


Under-pressure behind the valves:

For non-perfect aerated space behind the valve

Patm=0,1MPa

For perfect aerated space behind the valve

Patm=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 Hv=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 m3/s; density water ρ = 998,8Kg/m3; medium compressibility factor β = 477,1*10-12; closing time 45s; local loss factor for an open valve ξ = 0,106; the space behind the valve is non-perfect aerated Patm = 0,1MPa

Increasing pressure on water hammer:

ΔP=0,39MPa

was calculated by

Effective closing time factor

Water hammer

was calculated by

PSHv=0+ΔP+Patm =1,2+0,39+0,1 =1,69MPa

PSPNPN25


Literature:

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

MET-Calc: Effective closing time factor

MET-Calc: Water hammer


Download PDF:

Maximum allowable pressure PS of a valves.pdf


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