# Calculate pressure drop across Orifice plate? **URL:** \ **Category:** Flow Measurement\ **Tags:** pressure\ **Created:** [September 4, 2016, 6:07am UTC](https://forumautomation.com/t/calculate-pressure-drop-across-orifice-plate/1322 "2016-09-04T06:07:59Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![automate](https://forumautomation.com/letter_avatar_proxy/v4/letter/a/51bf81/32.png) [@automate](https://forumautomation.com/u/automate)\ **Post date:** [September 4, 2016, 6:07am UTC](https://forumautomation.com/t/calculate-pressure-drop-across-orifice-plate/1322/1 "2016-09-04T06:07:59Z")
How to calculate pressure drop across orifice plate (liquid/steam application)? How to calculate LRV and URV? ---
**Author:** ![denizen](https://forumautomation.com/letter_avatar_proxy/v4/letter/d/848f3c/32.png) [@denizen](https://forumautomation.com/u/denizen)\ **Post date:** [September 4, 2016, 6:15am UTC](https://forumautomation.com/t/calculate-pressure-drop-across-orifice-plate/1322/2 "2016-09-04T06:15:13Z")
While calculating an orifice there are three variables of which two can be selected: flow, bore diameter en pressure drop. If you need to know the pressure drop, you must not only have selected a required (maximum) flow, but also the bore diameter in respect to the line size. Typically the ratio d(bore) / Di (line) would be 0,65 - 0,75. Rule of thumb is that the calculated dP at max flow is 70 to 80 % of (URV - LRV). Usually LRV is taken as 0 and URV is a multiple of 500 mbar ISO standard for measurement of fluid flow - ISO 5167 > **[ISO 5167-1:2003](https://www.iso.org/standard/28064.html)** > > Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full — Part 1: General principles and requirements Tool to calculate flow rate through an orifice > **[Calculator: Water Flow Rate through an Orifice | TLV - A Steam Specialist...](https://www.tlv.com/global/TI/calculator/water-flow-rate-through-orifice.html)** > > Online calculator to quickly determine Water Flow Rate through an Orifice. Includes 53 different calculations. Equations displayed for easy reference.