Actual Orifice Areas For Different Relief Valve Manufacturers Based On Api 526 Orifice Designations

There is also something called a "redbook" that lists actual areas as required by ASME. If you look at the design requirements for API and ASME, you will note the requirements are a bit different.

Bobby

See http://www.nationalb...s/NB18/NB18.pdf

Having read your post, I need to make some clarifications;

1. API-526 Lists Effective orifice areas as listed also in API-520 (sizing).

Effective orifice areas should only be selected when using API-520 Effective coefficient of discharge (eg.0.975 for vapour).

The purpose of this, is to bring all manufacturers on a level playing field at enquiry stage. Ie., they all calculate the same area. This why API-RP-520 is a Recommended Practice and a user standard.

2. Actual orifice areas, are exactly that, as measured. They vary between manufacturers (as you have stated) since each valve design has a differing Actual coefficient of discharge derived from type test. The average actual coefficient of discharge is then derated by a 0.9 factor to give Kdr. Hence in sizing for actual area and capacity only ACTUAL area and Kdr can be used together. Never mix API effective with ASME actual figures.

The ASME calculation method is the same as the API-520 method except API only states effective areas and coefficients.

Effective areas are only approx 10% less that actual (not uniform due to varying test coefficients. A larger actual area is compensating for a low coefficient).

The excel sheet in the main specifies actual areas (in my opinion, should also list corresponding actual coefficient from "red book NB-18" against the state of fluid (liq/vap). Heading should be corrected. Note also for Anderson Greenwood Crosby "J series" could cover various valve styles all with varying coefficients same caution applies to other makers styles). Best to always refer to manufacturers catalogue and/or NB-18.

Hope that clarifies.