{"id":19445,"date":"2026-11-05T23:32:45","date_gmt":"2026-11-05T20:32:45","guid":{"rendered":"https:\/\/azeidkgroup.com\/sa\/media-center\/"},"modified":"2026-11-10T16:32:50","modified_gmt":"2026-11-10T13:32:50","slug":"fire-hydrant-flow-test","status":"publish","type":"post","link":"https:\/\/azeidkgroup.com\/en\/sa\/media-center\/fire-hydrant-flow-test\/","title":{"rendered":"Fire Hydrant Flow Testing: Method and How to Read the Results"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"19445\" class=\"elementor elementor-19445 elementor-19444 elementor-bc-flex-widget\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-1bb6f49 e-con-full az-el-article e-flex e-con e-parent\" data-id=\"1bb6f49\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-c678187 elementor-widget elementor-widget-text-editor\" data-id=\"c678187\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p class=\"az-intro\">Before a sprinkler system is designed or a fire pump selected, the designer needs one reliable figure: how much water can the supply deliver, and at what pressure? A <strong>hydrant flow test<\/strong> is the field method for getting that figure, and also a way to check the condition of a network after years in service.<\/p>\n<p>This article explains what the test measures, the equipment and steps, how flow is calculated and converted to available flow at a reference pressure, and how to read the results. <a href=\"\/en\/sa\/services\/testing-commissioning-handover\/\">AZEIDK&#8217;s testing, commissioning and handover service<\/a> covers testing of fire pumps and fire networks and recording results in the handover file, and water supply data is one of the inputs reviewed at that stage.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-498bf54 elementor-widget elementor-widget-text-editor\" data-id=\"498bf54\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<div class=\"az-keybox\"><h2>Key takeaways<\/h2><ul><li>The test measures three values: static pressure, residual pressure during flow, and the flow rate from one or more hydrants.<\/li><li>The technical reference is NFPA 291, a recommended practice that creates no requirements by itself. Its latest edition is 2025.<\/li><li>Flow is calculated from the pitot reading, outlet diameter and discharge coefficient, then converted to available flow at 20 psi (about 1.4 bar).<\/li><li>The 2022 edition of NFPA 291 recommends a residual pressure drop of at least 10% from static so the result can be extrapolated reliably.<\/li><li>The result is an input to hydraulic calculations and is compared with the system demand, with a safety margin set by the designer.<\/li><\/ul><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f002dcf elementor-widget elementor-widget-text-editor\" data-id=\"f002dcf\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>What does a hydrant flow test measure?<\/h2>\n<p>The test uses at least two hydrants. The first is the &#8220;test&#8221; or residual hydrant, fitted with a cap and pressure gauge. The second is the &#8220;flow&#8221; hydrant, which is opened so its discharge can be measured.<\/p>\n<ul><li><strong>Static pressure:<\/strong> network pressure with all hydrants closed.<\/li><li><strong>Residual pressure:<\/strong> pressure at the test hydrant while the flow hydrant is open.<\/li><li><strong>Flow:<\/strong> the discharge from the flow hydrant, calculated from pitot pressure.<\/li><\/ul>\n<p>The 2022 edition of NFPA 291 separates two purposes: a test that determines the supply available in the main, and a test that evaluates the flow available from an individual hydrant using a single hydrant. Each purpose uses a different hydrant arrangement.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7628888 elementor-widget elementor-widget-text-editor\" data-id=\"7628888\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>When do you need the test?<\/h2>\n<ul><li><strong>Before design:<\/strong> to establish the water supply data for sprinkler and standpipe hydraulic calculations, and to see whether the network needs a fire pump.<\/li><li><strong>Before drawing approval:<\/strong> many authorities and consultants ask for recent test data, because network conditions change.<\/li><li><strong>In service:<\/strong> NFPA 25 calls for a flow test of underground and exposed piping at five-year intervals to assess its internal condition. This is separate from the annual hydrant operation, which confirms the hydrant works but does not measure its capacity. The full framework is in our <a href=\"\/en\/sa\/media-center\/nfpa-25-itm-water-based-systems-guide\/\">guide to inspection, testing and maintenance of water-based systems<\/a>.<\/li><li><strong>After a major change:<\/strong> such as new buildings on the same network or a noticed drop in pressure.<\/li><\/ul>\n<p>Public mains and private site networks differ. On a public network the test is coordinated with the network operator; the private hydrant network and its underground mains are the owner&#8217;s responsibility. Hydrant types are covered in our <a href=\"\/en\/sa\/media-center\/fire-hydrants-landing-valves-guide\/\">fire hydrants and landing valves guide<\/a>.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-22e48a9 elementor-widget elementor-widget-text-editor\" data-id=\"22e48a9\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>Equipment<\/h2>\n<ul><li>An outlet cap with a calibrated pressure gauge for the test hydrant.<\/li><li>A pitot tube with a calibrated gauge, or a flow diffuser with a built-in gauge, for the flow hydrant.<\/li><li>The correct hydrant operating wrench for the operating nut.<\/li><li>Tools to measure the actual inside diameter of the outlet, and a recording form.<\/li><li>Arrangements to discharge water safely away from pedestrians, vehicles and foundations.<\/li><\/ul>\n<p>NFPA 291 recommends avoiding pitot readings below 10 psi where possible, and the 2016 edition also advised avoiding readings above 30 psi, because accuracy falls at both ends. If the reading falls outside a suitable range, change the number or size of open outlets.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0373bba elementor-widget elementor-widget-text-editor\" data-id=\"0373bba\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>Test steps<\/h2>\n<ol><li>Select the test and flow hydrants on the same main, with the flow hydrant normally downstream of the test hydrant.<\/li><li>Fit the gauge cap to the test hydrant, open it slowly and record static pressure once the needle settles.<\/li><li>Open the flow hydrant slowly, one hydrant at a time where several are used, to avoid pressure surges in the network.<\/li><li>Let water run until debris has cleared and flow has stabilised.<\/li><li>Read pitot pressure and residual pressure at the same moment.<\/li><li>Close the flow hydrant slowly, then confirm static pressure returns.<\/li><li>Record date, time, outlet diameter and type, flow duration and all readings.<\/li><\/ol>\n<p>The 2022 edition of NFPA 291 recommends testing during peak demand, because a test at low demand can give a better picture than reality.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-aff0b93 elementor-widget elementor-widget-text-editor\" data-id=\"aff0b93\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>The calculation: from pitot reading to available flow<\/h2>\n<h3>Measured flow<\/h3>\n<p>Flow in gpm is calculated as Q = 29.83 \u00d7 c \u00d7 d\u00b2 \u00d7 \u221aP, where d is the inside outlet diameter in inches, P is pitot pressure in psi and c is the discharge coefficient, which depends on outlet shape, with values from the NFPA 291 reference figure: about 0.90 for a smooth, well-rounded outlet, 0.80 for a square, sharp-edged outlet and 0.70 for an outlet projecting into the barrel.<\/p>\n<h3>Available flow at the reference pressure<\/h3>\n<p>Flow at the measured residual pressure is not enough. What matters is the flow the network can deliver at a reference pressure, which is 20 psi in NFPA 291. It is extrapolated as QR = QF \u00d7 ((S \u2212 20) \u00f7 (S \u2212 R))^0.54, where S is static pressure, R is residual pressure and QF is measured flow.<\/p>\n<h3>Hypothetical example<\/h3>\n<div class=\"az-table-wrap\"><table><thead><tr><th>Item<\/th><th>Value<\/th><\/tr><\/thead><tbody><tr><td>Static pressure S<\/td><td>70 psi (about 4.8 bar)<\/td><\/tr><tr><td>Residual pressure R<\/td><td>55 psi (about 3.8 bar), a 21% drop<\/td><\/tr><tr><td>Outlet diameter and coefficient<\/td><td>2.5 in, c = 0.90<\/td><\/tr><tr><td>Pitot pressure P<\/td><td>15 psi<\/td><\/tr><tr><td>Measured flow QF<\/td><td>about 650 gpm (about 2,460 L\/min)<\/td><\/tr><tr><td>Available flow at 20 psi<\/td><td>650 \u00d7 (50 \u00f7 15)^0.54 \u2248 1,245 gpm (about 4,710 L\/min)<\/td><\/tr><\/tbody><\/table><\/div>\n<p>These figures are for illustration and do not represent a real network. The drop here is 21%, above the 10% recommended in the 2022 edition, so the extrapolation is acceptable. If the drop is very small, open another outlet or hydrant, because extrapolating from a slight drop magnifies the error.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-9a2836c elementor-widget elementor-widget-text-editor\" data-id=\"9a2836c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>Reading the results and using them in design<\/h2>\n<p>Results are normally plotted on graph paper with flow raised to the 1.85 power, so the supply curve appears as a straight line from static pressure through the test point. The system demand from the hydraulic calculations, including hose allowance, is then plotted on the same sheet. If the demand sits below the supply curve with an adequate margin, the network is sufficient. If not, the answer is a fire pump, a tank or a design change.<\/p>\n<p>How system demand is built and reviewed is explained in our article on <a href=\"\/en\/sa\/media-center\/sprinkler-hydraulic-calculations-explained\/\">sprinkler hydraulic calculations<\/a>, and our <a href=\"\/en\/sa\/services\/engineering-design-calculations\/\">engineering design and calculations<\/a> service links test data to the design.<\/p>\n<h3>Hydrant colour coding<\/h3>\n<p>NFPA 291 recommends classifying public hydrants by rated flow at 20 psi and colouring the bonnet and caps to match, with a reflective chrome yellow barrel unless another local colour has been adopted. The 2025 edition added recommendations for colour-coding private hydrants.<\/p>\n<div class=\"az-table-wrap\"><table><thead><tr><th>Class<\/th><th>Rated flow at 20 psi<\/th><th>Bonnet and cap colour<\/th><\/tr><\/thead><tbody><tr><td>AA<\/td><td>1,500 gpm or more<\/td><td>Light blue<\/td><\/tr><tr><td>A<\/td><td>1,000 to 1,499 gpm<\/td><td>Green<\/td><\/tr><tr><td>B<\/td><td>500 to 999 gpm<\/td><td>Orange<\/td><\/tr><tr><td>C<\/td><td>Below 500 gpm<\/td><td>Red<\/td><\/tr><\/tbody><\/table><\/div>\n<p>The hydrant in the hypothetical example above would be Class A. In Saudi Arabia AZEIDK supplies American Fire Control hydrants, the F-7700 and F-8700 dry barrel and the FW-9000 wet barrel; the brand is introduced in our <a href=\"\/en\/sa\/media-center\/american-fire-control-afc-brand-saudi-arabia\/\">American Fire Control in Saudi Arabia<\/a> article. Check each model&#8217;s outlet sizes on its datasheet before testing.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5ad2da2 elementor-widget elementor-widget-text-editor\" data-id=\"5ad2da2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>Common mistakes in flow testing<\/h2>\n<ul><li>Opening or closing the hydrant quickly, causing pressure surges that can damage the network.<\/li><li>A very small residual drop, which makes the extrapolation unreliable.<\/li><li>Using the nominal outlet size instead of the measured inside diameter, or a discharge coefficient that does not match the outlet shape.<\/li><li>Gauges that are not calibrated or have no current calibration certificate.<\/li><li>Testing at low demand and then basing the design on an optimistic result.<\/li><li>Confusing the annual hydrant operation with a test that determines network capacity.<\/li><\/ul>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7def9e5 elementor-widget elementor-widget-text-editor\" data-id=\"7def9e5\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>Frequently asked questions<\/h2><div class=\"az-faq\"><details class=\"az-faq__item\"><summary><h3>Is NFPA 291 mandatory?<\/h3><\/summary><p>It is a recommended practice that creates no requirements by itself, but many authorities and consultants adopt its test and classification method.<\/p><\/details><details class=\"az-faq__item\"><summary><h3>What is the difference between annual hydrant operation and a flow test?<\/h3><\/summary><p>The NFPA 25 annual operation confirms the hydrant opens and flows for at least a minute, without measuring capacity. A flow test measures pressures and flow to determine the available supply.<\/p><\/details><details class=\"az-faq__item\"><summary><h3>Why is 20 psi used as the reference?<\/h3><\/summary><p>Because NFPA 291 uses it as the residual pressure that keeps firefighting effective and protects the network from negative pressure and backflow.<\/p><\/details><details class=\"az-faq__item\"><summary><h3>How long does water flow during the test?<\/h3><\/summary><p>Until debris has cleared, flow is stable and readings are taken at the same moment. The reference sets no fixed duration.<\/p><\/details><details class=\"az-faq__item\"><summary><h3>Can an old test be used for a new design?<\/h3><\/summary><p>A recent test is preferred, because the network changes as users are added or pipes deteriorate. Many authorities ask for recent data when drawings are submitted.<\/p><\/details><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2a5a1bf elementor-widget elementor-widget-text-editor\" data-id=\"2a5a1bf\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h2>Conclusion<\/h2>\n<p>A hydrant flow test is simple in equipment but exact in detail: two hydrants, calibrated gauges, slow opening and closing, an adequate pressure drop, and a correct discharge coefficient and extrapolation. Its result decides whether the network is enough for the design or needs a pump or a tank, so it deserves careful execution and documentation.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a9bea24 elementor-widget elementor-widget-text-editor\" data-id=\"a9bea24\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p class=\"az-cta\"><strong>Need water supply data for your project, or an assessment of an existing network?<\/strong> The AZEIDK team carries out hydrant flow tests on site and hands over the results and water supply data before design or handover. <a href=\"\/en\/sa\/contact\/\">Talk to the AZEIDK team<\/a><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5874712 elementor-widget elementor-widget-text-editor\" data-id=\"5874712\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<div class=\"az-source\"><strong>References:<\/strong> <a href=\"https:\/\/www.fire-police-ems.com\/NFPA291-2025.shtml\" rel=\"noopener\" target=\"_blank\">NFPA 291, Recommended Practice for Water Flow Testing and Marking of Hydrants, 2025 ed.<\/a> (edition listing, Fire-Police-EMS), <a href=\"https:\/\/webstore.ansi.org\/standards\/nfpa\/nfpa2912025\" rel=\"noopener\" target=\"_blank\">NFPA 291-2025 (most recent edition)<\/a> (ANSI Webstore), <a href=\"https:\/\/blog.qrfs.com\/370-nfpa-guidance-on-fire-hydrant-testing\" rel=\"noopener\" target=\"_blank\">NFPA Guidance on Fire Hydrant Testing<\/a> (QRFS), <a href=\"https:\/\/nfsa.org\/2021\/02\/12\/why-arent-all-fire-hydrants-red\/\" rel=\"noopener\" target=\"_blank\">Why Aren&#8217;t All Fire Hydrants Red?<\/a> (NFSA), <a href=\"https:\/\/nfsa.org\/?p=17420\" rel=\"noopener\" target=\"_blank\">Hydrant Flow Testing<\/a> (NFSA), <a href=\"https:\/\/www.mwua.org\/nfpa-291-hydrant-flow-testing\/\" rel=\"noopener\" target=\"_blank\">NFPA 291 Hydrant Flow Testing<\/a> (MWUA), <a href=\"https:\/\/open-exam-prep.com\/study-guides\/nicet-itwbs\/water-supply-systems-private-mains\/flow-testing-pitot-calculations\" rel=\"noopener\" target=\"_blank\">Water Supply Flow Testing and Pitot Tube Calculations<\/a> (Open Exam Prep)<\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Hydrant flow testing per NFPA 291: static and residual pressure, pitot readings, available flow at 20 psi, hydrant colour classes and common site mistakes.<\/p>\n","protected":false},"author":0,"featured_media":22295,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[221],"tags":[],"azeidk_region":[223],"class_list":["post-19445","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-azeidk-articles"],"acf":[],"_links":{"self":[{"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/posts\/19445","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/comments?post=19445"}],"version-history":[{"count":2,"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/posts\/19445\/revisions"}],"predecessor-version":[{"id":19479,"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/posts\/19445\/revisions\/19479"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/media\/22295"}],"wp:attachment":[{"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/media?parent=19445"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/categories?post=19445"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/tags?post=19445"},{"taxonomy":"azeidk_region","embeddable":true,"href":"https:\/\/azeidkgroup.com\/en\/wp-json\/wp\/v2\/azeidk_region?post=19445"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}