Pressure relief valve sizing calculator will carry out sizing calculations based on equations used in API virus scan520 “7th Edition” and API 521 “4th Edition”.

Main Features:

Support SI and US Units of measurements,

Below are input variables that are currently available in the unit of measurements below;

Make input in different measurement units for Volumetric flow rate, Mass Flow rate, Temperature, Viscosity and Pressure.

Mass flow rate Volumetric flow rate Pressure Temperature
kg/h, kg/s, kg/min, kg/d Nm3/min, Nm3/s, Nm3/h kPaa, kPag, Paa ‘K, ‘C, ‘F, ‘R
t/d, t/h Nm3/d, scfm , scfd, scfs MPaa, atm, Pag,
lb/h, lb/s, lb/d Mmscfd, L/m, USGPM bara, barg, psia, psig
Viscosity Density Specific heat capacity Latent heat
cP, Pa.s, kg/m s kg/m3 (1) J/gmol ‘K (1) kJ/kg (1)
Kg/m h, lb/ft s, lb/ft h lb/ft3  (2) Btu/lb ‘F (2) Btu/lb (2)
Diameter Length Depth Elevation
m (1) m (1) m (1) m (1)
ft (2) ft (2) ft (2) ft (2)

(1) SI Units Mode only (2) US Units Mode only

  • Size conventional and pilot operated relief valves for gas or vapour relief.
  • Size conventional and pilot operated relief valves for liquid relief.
  • Size conventional and pilot operated relief valves for saturated and superheated steam relief.
  • Size conventional and pilot operated relief valves for vaporizing liquids (wetted vessels)
  • Evaluate multiple cases in one go.
  • Save and load your input.
  • Copy results and paste it anywhere in any document
  • Generate a summary report which can be printed or saved in different formats “Excel, Word and PDF”
  • Calculated variables are based on input and service, mainly the following variables are calculated for all services; Relieving Pressure, Required effective discharge area, Actual discharge area, Equivalent Orifice diameter of device, Installed Relief rate and Designation. More calculated variables are displayed depending on selected service and input parameters.
  • For vessel fire case (Vaporizing liquids – wetted vessels) the software will also calculate the rate of vaporization, the total heat absorption and the total wetted area. Calculations support both vertical, horizontal and spherical vessel orientation.


Click here to download the demo version of the product. Please also note that the demo version of this software will only operate with set examples which are restricted in our demo version.  The full version of this product does not have any restrictions.

We don’t offer a fully working demo version.

This software is available for purchase from BUY NOW page. The software also comes as a calculator included with Process Engineering Calculator

Screen Shots

To view more screen shots please follow the links available in our screen shots page

Video demonstration clip is also available to view – please click here

Video is also available on YouTube Channel, Click here

Relief valve calculator

System Requirements

This software needs the following system requirements to run:

Microsoft Windows operating system (Windows 7, Windows 8.1, Windows 10 & Windows 11)
64MB RAM Minimum, 30MB free disk space, Microsoft .Net 4.8 installed