What is a safety valve?

A safety valve (or pressure relief valve) is a device that automatically releases fluid when pressure exceeds a predetermined set point. It protects equipment from overpressure per ASME Section VIII, ISO 4126, or PED requirements.

How is orifice area calculated for gas service?

For gas/vapor service per API 520: A = W / (C × Kd × P₁ × Kb × √(M/TZ)), where W is required capacity, C is gas constant factor, Kd is discharge coefficient, P₁ is relieving pressure, Kb is back pressure correction, M is molecular weight, T is temperature, and Z is compressibility factor.

What are standard API orifice designations?

API 526 defines standard orifice sizes designated by letters: D (0.110 in²), E (0.196 in²), F (0.307 in²), G (0.503 in²), H (0.785 in²), J (1.287 in²), K (1.838 in²), L (2.853 in²), M (3.60 in²), N (4.34 in²), P (6.38 in²), Q (11.05 in²), R (16.0 in²), T (26.0 in²).

What is the difference between set pressure and relieving pressure?

Set pressure is the pressure at which the valve begins to open. Relieving pressure is the set pressure plus allowable overpressure (typically 10% for single valves per ASME VIII). The sizing calculation uses relieving pressure (absolute) as P₁.

Do I need to account for back pressure?

Yes. Constant back pressure reduces the effective differential across the valve. For conventional valves, the back pressure correction factor Kb adjusts the capacity. Balanced bellows or pilot-operated valves are less affected by back pressure.

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Calculadora de dimensionamiento de válvulas de seguridad

Dimensione válvulas de seguridad de presión según ISO 4126 / API 520. Calcule el área del orificio requerida y seleccione la letra del orificio estándar para servicio de gas, vapor o líquido.

ISO 4126API 520/526Gas / Vapor / Líquido

Tipo de fluido

Capacidad requerida (kg/h)

Presión de apertura (bar g)

Presión de retorno (bar g, 0 si es atm)

Temperatura de alivio (°C)

Peso molecular (para gas, p. ej. 29 para aire)

Relación de calores específicos k (Cp/Cv)

Compresibilidad Z

Preajustes rápidos

Resultados

Área del orificio requerida

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Letra del orificio estándar

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Área del orificio estándar

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Presión de alivio (abs)

—

Kd (Coef. de descarga)

—

Sección transversal de la válvula

Dimensionamiento de gas / vapor (API 520)

Designaciones estándar de orificios API (API 526)

Letra	Área (mm²)	Área (in²)	Entrada × Salida típica
D	71.0	0.110	1″ × 2″
E	126.5	0.196	1″ × 2″
F	198.1	0.307	1½” × 2½”
G	324.5	0.503	1½” × 3″
H	506.5	0.785	2″ × 3″
J	830.3	1.287	3″ × 4″
K	1186	1.838	3″ × 6″
L	1841	2.853	4″ × 6″
M	2323	3.600	4″ × 6″
N	2800	4.340	4″ × 6″
P	4116	6.380	6″ × 8″
Q	7129	11.05	6″ × 10″
R	10323	16.00	8″ × 10″
T	16774	26.00	8″ × 12″

⚠️ Nota: Esta calculadora proporciona un dimensionamiento preliminar. La selección final de la válvula debe ser verificada por el fabricante de la válvula y cumplir con los códigos aplicables (ASME VIII, PED, etc.).