Relief valve (PSV) simulation

1 inlet -> process (passthrough) + relief (to flare)

Governing equations

The exact equations the solver works for a relief valve (psv) — the same math shown in the app's "Theory" panel, not a black box.

$A$

required effective orifice area [m^2] (rounded up to an API 526 letter)

$W$

relief mass rate [kg/s]

$P_1$

relieving pressure [Pa, absolute]

$P_{set}$

set pressure [Pa, gauge] — the equipment design pressure

$\alpha$

allowable overpressure/accumulation fraction (0.10 typical)

$K_d$

effective discharge coefficient

$K_b$

back-pressure correction

$K_c$

rupture-disc combination factor

$K_w$

liquid back-pressure correction

$k$

ratio of specific heats c_p/c_v

$Z$

compressibility

$M$

molar mass [kg/mol]

$Q$

fire heat absorption [W]

$C$

API 521 constant (43200 with drainage, else 70900)

$F$

environment factor (1.0 bare, 0.3 insulated)

$A_{wet}$

wetted surface area [m^2]

$\lambda$

latent heat of the relieving vapour [J/kg]

Parameters

set_pressure [Pa, gauge — the protected equipment's MAWP, required]; scenario [blocked_outlet|fire|specified, default blocked_outlet]; overpressure_fraction [default 0.10]; for scenario=fire: wetted_area [m^2], environment_factor [1.0 bare, 0.3 insulated], adequate_drainage [bool]; for scenario=specified: relief_rate [mol/s]. Optional superimposed_back_pressure / built_up_back_pressure [Pa, gauge], valve_type [conventional|balanced_bellows|pilot_operated], rupture_disc [bool], discharge_coefficient, kb, kw [API 520 Figures 30/31]. relieving [bool, default False] models the valve LIFTED so the relief leg carries the load to a flare; left off, the valve is shut (process passes through unchanged) and only the sizing is reported.

Example flowsheets that use it