{"id":100217,"date":"2026-02-15T20:27:54","date_gmt":"2026-02-15T20:27:54","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100217"},"modified":"2026-02-15T20:27:54","modified_gmt":"2026-02-15T20:27:54","slug":"safety-valve-sizing","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/nb\/calculators\/safety-valve-sizing\/","title":{"rendered":"Kalkulator for st\u00f8rrelsesvalg av sikkerhetsventil | ISO 4126 | Overtrykksventil"},"content":{"rendered":"\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Safety Valve Sizing Calculator\",\"alternateName\":[\"PSV Sizing Tool\",\"API 520 Calculator\",\"Relief Valve Calculator\"],\"description\":\"Free safety valve sizing calculator per ISO 4126 and API 520. Calculate required orifice area for gas, steam, and liquid service.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/safety-valve-sizing\/\",\"applicationCategory\":\"Engineering Calculator\",\"operatingSystem\":\"Any (Web Browser)\",\"offers\":{\"@type\":\"Offer\",\"price\":\"0\",\"priceCurrency\":\"EUR\"},\"creator\":{\"@type\":\"Organization\",\"name\":\"Vibromera\",\"url\":\"https:\/\/vibromera.eu\/\"},\"datePublished\":\"2024-01-01\",\"dateModified\":\"2025-02-14\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true}\n<\/script>\n\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[\n{\"@type\":\"Question\",\"name\":\"What is a safety valve?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"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.\"}},\n{\"@type\":\"Question\",\"name\":\"How is orifice area calculated for gas service?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"For gas\/vapor service per API 520: A = W \/ (C \u00d7 Kd \u00d7 P\u2081 \u00d7 Kb \u00d7 \u221a(M\/TZ)), where W is required capacity, C is gas constant factor, Kd is discharge coefficient, P\u2081 is relieving pressure, Kb is back pressure correction, M is molecular weight, T is temperature, and Z is compressibility factor.\"}},\n{\"@type\":\"Question\",\"name\":\"What are standard API orifice designations?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"API 526 defines standard orifice sizes designated by letters: D (0.110 in\u00b2), E (0.196 in\u00b2), F (0.307 in\u00b2), G (0.503 in\u00b2), H (0.785 in\u00b2), J (1.287 in\u00b2), K (1.838 in\u00b2), L (2.853 in\u00b2), M (3.60 in\u00b2), N (4.34 in\u00b2), P (6.38 in\u00b2), Q (11.05 in\u00b2), R (16.0 in\u00b2), T (26.0 in\u00b2).\"}},\n{\"@type\":\"Question\",\"name\":\"What is the difference between set pressure and relieving pressure?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"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 P\u2081.\"}},\n{\"@type\":\"Question\",\"name\":\"Do I need to account for back pressure?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"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.\"}}\n]}\n<\/script>\n\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"BreadcrumbList\",\"itemListElement\":[\n{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/vibromera.eu\/\"},\n{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Calculators\",\"item\":\"https:\/\/vibromera.eu\/calculators\/\"},\n{\"@type\":\"ListItem\",\"position\":3,\"name\":\"Safety Valve Sizing\",\"item\":\"https:\/\/vibromera.eu\/calculators\/safety-valve-sizing\/\"}\n]}\n<\/script>\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin>\n\n<link 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svg{width:100%;height:auto;display:block}.vc-viz-title{font-family:var(--vc-mono);font-size:11px;font-weight:500;letter-spacing:0.1em;text-transform:uppercase;color:var(--vc-ink-muted);margin-bottom:12px}\n<\/style>\n\n<div class=\"vc-calculator\" id=\"vc-safety-valve\">\n\n<header class=\"vc-header\">\n    <p class=\"vc-header-eyebrow\">Free Engineering Tool<\/p>\n    <h1 class=\"vc-header-title\">Safety Valve Sizing Calculator<\/h1>\n    <p class=\"vc-header-subtitle\">Size pressure safety valves per ISO 4126 \/ API 520. Calculate required orifice area and select standard orifice letter for gas, steam, or liquid service.<\/p>\n    <div class=\"vc-badges\"><span class=\"vc-badge\">ISO 4126<\/span><span class=\"vc-badge\">API 520\/526<\/span><span class=\"vc-badge\">Gas \/ Steam \/ Liquid<\/span><\/div>\n<\/header>\n\n<div class=\"vc-card\">\n    <form class=\"vc-form\" id=\"vc-form\" autocomplete=\"off\">\n        <div class=\"vc-form-grid\">\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-fluid\">Fluid Type<\/label>\n                <select class=\"vc-select\" id=\"vc-fluid\">\n                    <option value=\"gas\" selected>Gas \/ Vapor<\/option>\n                    <option value=\"steam\">Steam<\/option>\n                    <option value=\"liquid\">Liquid<\/option>\n                <\/select>\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-capacity\">Required Capacity <span class=\"vc-label-hint\" id=\"vc-cap-unit\">(kg\/h)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-capacity\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 5000\" value=\"5000\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-setpress\">Set Pressure <span class=\"vc-label-hint\">(bar g)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-setpress\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 10\" value=\"10\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-backpress\">Back Pressure <span class=\"vc-label-hint\">(bar g, 0 if atm)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-backpress\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 0\" value=\"0\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-temp\">Relieving Temperature <span class=\"vc-label-hint\">(\u00b0C)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-temp\" inputmode=\"decimal\" step=\"any\" placeholder=\"e.g. 200\" value=\"200\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-mw\">Molecular Weight <span class=\"vc-label-hint\">(for gas, e.g. 29 for air)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-mw\" inputmode=\"decimal\" step=\"any\" min=\"1\" placeholder=\"e.g. 29\" value=\"29\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-k\">Ratio of Specific Heats k <span class=\"vc-label-hint\">(Cp\/Cv)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-k\" inputmode=\"decimal\" step=\"any\" min=\"1\" max=\"2\" placeholder=\"e.g. 1.4\" value=\"1.4\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-z\">Compressibility Z<\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-z\" inputmode=\"decimal\" step=\"any\" min=\"0.1\" max=\"2\" placeholder=\"1.0\" value=\"1.0\">\n            <\/div>\n        <\/div>\n        <div class=\"vc-presets\">\n            <div class=\"vc-presets-label\">Quick presets<\/div>\n            <button type=\"button\" class=\"vc-preset-btn\" data-fl=\"gas\" data-w=\"5000\" data-sp=\"10\" data-t=\"200\" data-mw=\"29\" data-kk=\"1.4\">Air 5t\/h @ 10 bar<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-fl=\"steam\" data-w=\"10000\" data-sp=\"25\" data-t=\"250\" data-mw=\"18\" data-kk=\"1.3\">Steam 10t\/h @ 25 bar<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-fl=\"liquid\" data-w=\"20000\" data-sp=\"15\" data-t=\"50\" data-mw=\"18\" data-kk=\"1.0\">Water 20t\/h @ 15 bar<\/button>\n        <\/div>\n    <\/form>\n\n    <div class=\"vc-results\" id=\"vc-results\">\n        <div class=\"vc-results-head\"><h2 class=\"vc-results-title\">Results<\/h2>\n            <button type=\"button\" class=\"vc-copy-btn\" id=\"vc-copy-btn\"><svg width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><rect x=\"9\" y=\"9\" width=\"13\" height=\"13\" rx=\"2\"\/><path d=\"M5 15H4a2 2 0 01-2-2V4a2 2 0 012-2h9a2 2 0 012 2v1\"\/><\/svg> Copy<\/button>\n        <\/div>\n        <div class=\"vc-result-grid\">\n            <div class=\"vc-rcard vc-rcard-primary\"><div class=\"vc-rcard-label\">Required Orifice Area<\/div><div class=\"vc-rcard-value\" id=\"vc-r-area\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Standard Orifice Letter<\/div><div class=\"vc-rcard-value\" id=\"vc-r-letter\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Standard Orifice Area<\/div><div class=\"vc-rcard-value\" id=\"vc-r-stdarea\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Relieving Pressure (abs)<\/div><div class=\"vc-rcard-value\" id=\"vc-r-p1\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Kd (Discharge Coeff)<\/div><div class=\"vc-rcard-value\" id=\"vc-r-kd\">\u2014<\/div><\/div>\n        <\/div>\n        <div class=\"vc-viz\" id=\"vc-viz\"><div class=\"vc-viz-title\">Valve Cross-Section<\/div><div id=\"vc-viz-svg\"><\/div><\/div>\n    <\/div>\n<\/div>\n\n<div class=\"vc-section vc-open\" id=\"vc-sec-theory\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"true\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udcd8<\/span><span class=\"vc-section-title\">Theory &amp; Formulas<\/span><\/span><svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner vc-theory\">\n        <h3>Gas \/ Vapor Sizing (API 520)<\/h3>\n        <div class=\"vc-formula-box\" id=\"vc-katex-1\"><\/div>\n        <h3>Standard API Orifice Designations (API 526)<\/h3>\n        <table class=\"vc-table\">\n            <thead><tr><th>Letter<\/th><th>Area (mm\u00b2)<\/th><th>Area (in\u00b2)<\/th><th>Typical Inlet \u00d7 Outlet<\/th><\/tr><\/thead>\n            <tbody>\n                <tr><td>D<\/td><td>71.0<\/td><td>0.110<\/td><td>1&#8243; \u00d7 2&#8243;<\/td><\/tr>\n                <tr><td>E<\/td><td>126.5<\/td><td>0.196<\/td><td>1&#8243; \u00d7 2&#8243;<\/td><\/tr>\n                <tr><td>F<\/td><td>198.1<\/td><td>0.307<\/td><td>1\u00bd&#8221; \u00d7 2\u00bd&#8221;<\/td><\/tr>\n                <tr><td>G<\/td><td>324.5<\/td><td>0.503<\/td><td>1\u00bd&#8221; \u00d7 3&#8243;<\/td><\/tr>\n                <tr><td>H<\/td><td>506.5<\/td><td>0.785<\/td><td>2&#8243; \u00d7 3&#8243;<\/td><\/tr>\n                <tr><td>J<\/td><td>830.3<\/td><td>1.287<\/td><td>3&#8243; \u00d7 4&#8243;<\/td><\/tr>\n                <tr><td>K<\/td><td>1186<\/td><td>1.838<\/td><td>3&#8243; \u00d7 6&#8243;<\/td><\/tr>\n                <tr><td>L<\/td><td>1841<\/td><td>2.853<\/td><td>4&#8243; \u00d7 6&#8243;<\/td><\/tr>\n                <tr><td>M<\/td><td>2323<\/td><td>3.600<\/td><td>4&#8243; \u00d7 6&#8243;<\/td><\/tr>\n                <tr><td>N<\/td><td>2800<\/td><td>4.340<\/td><td>4&#8243; \u00d7 6&#8243;<\/td><\/tr>\n                <tr><td>P<\/td><td>4116<\/td><td>6.380<\/td><td>6&#8243; \u00d7 8&#8243;<\/td><\/tr>\n                <tr><td>Q<\/td><td>7129<\/td><td>11.05<\/td><td>6&#8243; \u00d7 10&#8243;<\/td><\/tr>\n                <tr><td>R<\/td><td>10323<\/td><td>16.00<\/td><td>8&#8243; \u00d7 10&#8243;<\/td><\/tr>\n                <tr><td>T<\/td><td>16774<\/td><td>26.00<\/td><td>8&#8243; \u00d7 12&#8243;<\/td><\/tr>\n            <\/tbody>\n        <\/table>\n        <div class=\"vc-warning-box\"><p style=\"margin:0;font-size:14px;color:var(--vc-ink-secondary);\"><strong>\u26a0\ufe0f Note:<\/strong> This calculator provides preliminary sizing. Final valve selection must be verified by the valve manufacturer and comply with applicable codes (ASME VIII, PED, etc.).<\/p><\/div>\n    <\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-related\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udd17<\/span><span class=\"vc-section-title\">Related Calculators<\/span><\/span><svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-related\">\n        <a class=\"vc-related-link\" href=\"\/calculators\/flange-rating-calculator\/\">Flange P-T Rating<\/a>\n        <a class=\"vc-related-link\" href=\"\/calculators\/risk-assessment-matrix\/\">Risk Assessment Matrix<\/a>\n    <\/div><\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-faq\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\u2753<\/span><span class=\"vc-section-title\">Frequently Asked Questions<\/span><\/span><svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-faq-list\" id=\"vc-faq-list\"><\/div><\/div><\/div>\n<\/div>\n\n<div class=\"vc-promo\"><div class=\"vc-promo-text\"><strong>Vibromera \u2014 Portable Balancing &amp; Vibration Analysis<\/strong><br>Professional vibration and process monitoring instruments for industrial maintenance.<\/div><a class=\"vc-promo-link\" href=\"https:\/\/vibromera.eu\/\" target=\"_blank\" rel=\"noopener\">Learn More<\/a><\/div>\n<footer class=\"vc-footer\"><p>&copy; 2024\u20132025 <a href=\"https:\/\/vibromera.eu\/\">Vibromera<\/a> \u2014 Engineering Calculators<\/p><p style=\"font-size:12px;margin-top:4px;\">Based on ISO 4126, API 520\/526. Last updated: February 2025<\/p><div class=\"vc-footer-links\"><a href=\"\/calculators\/engineering-calculators\/\">All Calculators<\/a><a href=\"https:\/\/vibromera.eu\/contacts\/\">Contact<\/a><\/div><\/footer>\n<\/div>\n\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/katex@0.16.11\/dist\/katex.min.js\"><\/script>\n<script>\n(function(){\n'use strict';\nvar SLUG='safety-valve-sizing';\nfunction $(id){return document.getElementById(id)}\nfunction fmt(n,d){if(isNaN(n))return'\u2014';return n.toFixed(d===undefined?2:d).replace(\/(\\.\\d*?)0+$\/,'$1').replace(\/\\.$\/,'')}\n\nvar ORIFICES=[{letter:'D',area:71.0},{letter:'E',area:126.5},{letter:'F',area:198.1},{letter:'G',area:324.5},{letter:'H',area:506.5},{letter:'J',area:830.3},{letter:'K',area:1186},{letter:'L',area:1841},{letter:'M',area:2323},{letter:'N',area:2800},{letter:'P',area:4116},{letter:'Q',area:7129},{letter:'R',area:10323},{letter:'T',area:16774}];\n\nfunction selectOrifice(reqArea){\n    for(var i=0;i<ORIFICES.length;i++){if(ORIFICES[i].area>=reqArea)return ORIFICES[i]}\n    return ORIFICES[ORIFICES.length-1];\n}\n\nfunction calculate(){\n    var fluid=$('vc-fluid').value;\n    var W=parseFloat($('vc-capacity').value);\n    var Pset=parseFloat($('vc-setpress').value);\n    var Pb=parseFloat($('vc-backpress').value)||0;\n    var T=parseFloat($('vc-temp').value);\n    var M=parseFloat($('vc-mw').value);\n    var k=parseFloat($('vc-k').value);\n    var Z=parseFloat($('vc-z').value)||1.0;\n    if(!W||W<=0||isNaN(Pset)||Pset<=0||isNaN(T)){$('vc-results').classList.remove('vc-visible');return}\n\n    var overpressureFrac=0.10;\n    var P1abs=(Pset*(1+overpressureFrac)+1.01325)*0.1; \/\/ MPa abs\n    var P1bar=Pset*(1+overpressureFrac)+1.01325;\n    var Kb=1.0;\n    if(Pb>0){var r=(Pb+1.01325)\/P1bar;Kb=Math.max(0.1,1-r)}\n    var Kd,A;\n\n    if(fluid==='gas'||fluid==='steam'){\n        Kd=0.975;\n        var C_coeff=0.03948*Math.sqrt(k*Math.pow(2\/(k+1),(k+1)\/(k-1)));\n        \/\/ API 520 simplified: A = W \/ (C \u00d7 Kd \u00d7 P1 \u00d7 Kb \u00d7 sqrt(T_K*Z\/M)) \u2014 areas in mm\u00b2\n        var TK=T+273.15;\n        A=(W\/3600)\/(C_coeff*Kd*(P1abs*1000)*Kb)*Math.sqrt(TK*Z\/M)*1e6; \/\/ mm\u00b2\n        if(fluid==='steam'){\n            \/\/ Steam: simplified Napier formula for saturated\/superheated\n            \/\/ W(kg\/h)=51.5\u00d7Kd\u00d7A(mm\u00b2)\u00d7P1(MPa)\u00d7Ksh (Ksh\u22481 for saturated)\n            A=W\/(51.5*Kd*P1abs*Kb); \/\/ mm\u00b2\n        }\n    } else {\n        \/\/ Liquid: A = Q \/ (Kd \u00d7 Kw \u00d7 sqrt(2\u00d7\u0394P\u00d7\u03c1))\n        Kd=0.65;\n        var rho=1000; \/\/ water assumed\n        var dP=(Pset*overpressureFrac)*1e5; \/\/ Pa overpressure\n        if(dP<=0)dP=Pset*0.1*1e5;\n        var Qm3s=W\/3600\/rho;\n        A=Qm3s\/(Kd*Kb*Math.sqrt(2*dP\/rho))*1e6; \/\/ mm\u00b2\n    }\n\n    if(isNaN(A)||A<=0||!isFinite(A)){$('vc-results').classList.remove('vc-visible');return}\n\n    var sel=selectOrifice(A);\n    $('vc-r-area').innerHTML=fmt(A,1)+' <span class=\"vc-rcard-unit\">mm\u00b2<\/span> <span class=\"vc-rcard-unit\">('+fmt(A\/645.16,3)+' in\u00b2)<\/span>';\n    $('vc-r-letter').textContent=sel.letter;\n    $('vc-r-stdarea').innerHTML=fmt(sel.area,0)+' <span class=\"vc-rcard-unit\">mm\u00b2<\/span> <span class=\"vc-rcard-unit\">('+fmt(sel.area\/645.16,3)+' in\u00b2)<\/span>';\n    $('vc-r-p1').innerHTML=fmt(P1bar,2)+' <span class=\"vc-rcard-unit\">bar abs<\/span>';\n    $('vc-r-kd').textContent=Kd;\n    $('vc-results').classList.add('vc-visible');\n    drawValveViz(A, sel, Pset, fluid);\n    saveHistory({fluid:fluid,W:W,Pset:Pset,area:fmt(A,1),letter:sel.letter,_summary:fluid+' '+W+'kg\/h @ '+Pset+'bar \u2192 '+sel.letter+' ('+fmt(A,1)+' mm\u00b2)'});\n}\n\nfunction drawValveViz(reqArea, sel, Pset, fluid) {\n    var el = $('vc-viz-svg'); if (!el) return;\n    var W = 400, H = 280, cx = W \/ 2, cy = H \/ 2;\n    var s = '<svg viewBox=\"0 0 ' + W + ' ' + H + '\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\">';\n    s += '<rect width=\"' + W + '\" height=\"' + H + '\" fill=\"var(--vc-surface)\" rx=\"4\"\/>';\n    \/\/ Valve body (simplified cross-section)\n    \/\/ Inlet pipe (bottom)\n    s += '<rect x=\"' + (cx - 20) + '\" y=\"' + (cy + 50) + '\" width=\"40\" height=\"60\" fill=\"rgba(42,92,140,0.08)\" stroke=\"var(--vc-blue)\" stroke-width=\"2\" rx=\"2\"\/>';\n    \/\/ Valve seat area\n    s += '<rect x=\"' + (cx - 35) + '\" y=\"' + (cy + 10) + '\" width=\"70\" height=\"40\" fill=\"rgba(42,92,140,0.08)\" stroke=\"var(--vc-blue)\" stroke-width=\"2\" rx=\"4\"\/>';\n    \/\/ Orifice (highlighted)\n    var orifW = Math.min(Math.max(Math.sqrt(sel.area) * 0.4, 12), 40);\n    s += '<rect x=\"' + (cx - orifW \/ 2).toFixed(1) + '\" y=\"' + (cy + 28) + '\" width=\"' + orifW.toFixed(1) + '\" height=\"8\" fill=\"var(--vc-accent)\" opacity=\"0.7\" rx=\"2\"\/>';\n    s += '<text x=\"' + cx + '\" y=\"' + (cy + 60) + '\" text-anchor=\"middle\" font-size=\"9\" font-family=\"var(--vc-mono)\" fill=\"var(--vc-accent)\" font-weight=\"600\">' + sel.letter + ' (' + fmt(sel.area, 0) + ' mm\u00b2)<\/text>';\n    \/\/ Spring housing (top)\n    s += '<rect x=\"' + (cx - 25) + '\" y=\"' + (cy - 60) + '\" width=\"50\" height=\"70\" fill=\"rgba(100,100,100,0.06)\" stroke=\"var(--vc-ink-muted)\" stroke-width=\"1.5\" rx=\"4\"\/>';\n    \/\/ Spring coils\n    for (var i = 0; i < 5; i++) {\n        var sy = cy - 50 + i * 12;\n        s += '<path d=\"M' + (cx - 15) + ',' + sy + ' Q' + cx + ',' + (sy - 5) + ' ' + (cx + 15) + ',' + sy + '\" fill=\"none\" stroke=\"var(--vc-ink-muted)\" stroke-width=\"2\"\/>';\n    }\n    \/\/ Disc\n    s += '<rect x=\"' + (cx - 22) + '\" y=\"' + (cy + 6) + '\" width=\"44\" height=\"6\" fill=\"var(--vc-ink)\" rx=\"2\"\/>';\n    \/\/ Outlet pipe (side)\n    s += '<rect x=\"' + (cx + 35) + '\" y=\"' + (cy + 12) + '\" width=\"55\" height=\"30\" fill=\"rgba(42,122,75,0.08)\" stroke=\"var(--vc-green)\" stroke-width=\"1.5\" rx=\"2\"\/>';\n    \/\/ Flow arrows (inlet)\n    s += '<polygon points=\"' + cx + ',' + (cy + 100) + ' ' + (cx - 6) + ',' + (cy + 112) + ' ' + (cx + 6) + ',' + (cy + 112) + '\" fill=\"var(--vc-blue)\"\/>';\n    s += '<polygon points=\"' + cx + ',' + (cy + 82) + ' ' + (cx - 5) + ',' + (cy + 90) + ' ' + (cx + 5) + ',' + (cy + 90) + '\" fill=\"var(--vc-blue)\" opacity=\"0.5\"\/>';\n    \/\/ Flow arrow (outlet)\n    s += '<polygon points=\"' + (cx + 80) + ',' + (cy + 27) + ' ' + (cx + 72) + ',' + (cy + 22) + ' ' + (cx + 72) + ',' + (cy + 32) + '\" fill=\"var(--vc-green)\"\/>';\n    \/\/ Labels\n    s += '<text x=\"' + cx + '\" y=\"' + (cy + 128) + '\" text-anchor=\"middle\" font-size=\"9\" font-family=\"var(--vc-mono)\" fill=\"var(--vc-blue)\">Inlet ' + Pset + ' bar<\/text>';\n    s += '<text x=\"' + (cx + 62) + '\" y=\"' + (cy + 52) + '\" text-anchor=\"middle\" font-size=\"8\" font-family=\"var(--vc-mono)\" fill=\"var(--vc-green)\">Outlet<\/text>';\n    s += '<text x=\"' + cx + '\" y=\"' + (cy - 66) + '\" text-anchor=\"middle\" font-size=\"8\" font-family=\"var(--vc-mono)\" fill=\"var(--vc-ink-muted)\">Spring<\/text>';\n    s += '<text x=\"' + cx + '\" y=\"22\" text-anchor=\"middle\" font-size=\"10\" font-family=\"var(--vc-mono)\" fill=\"var(--vc-ink-secondary)\" font-weight=\"600\">' + fluid.toUpperCase() + ' Service<\/text>';\n    s += '<\/svg>';\n    el.innerHTML = s;\n}\n\n$('vc-form').addEventListener('input',calculate);\n$('vc-form').addEventListener('change',calculate);\n\ndocument.querySelectorAll('.vc-preset-btn').forEach(function(btn){btn.addEventListener('click',function(e){e.preventDefault();$('vc-fluid').value=this.getAttribute('data-fl');$('vc-capacity').value=this.getAttribute('data-w');$('vc-setpress').value=this.getAttribute('data-sp');$('vc-temp').value=this.getAttribute('data-t');$('vc-mw').value=this.getAttribute('data-mw');$('vc-k').value=this.getAttribute('data-kk');calculate()})});\n\n$('vc-copy-btn').addEventListener('click',function(){var text='Safety Valve Sizing\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nFluid: '+$('vc-fluid').value+'\\nCapacity: '+$('vc-capacity').value+' kg\/h\\nSet Pressure: '+$('vc-setpress').value+' bar g\\nRequired Area: '+$('vc-r-area').textContent+'\\nOrifice: '+$('vc-r-letter').textContent+' ('+$('vc-r-stdarea').textContent+')\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nvibromera.eu\/calculators\/safety-valve-sizing\/';if(navigator.clipboard){navigator.clipboard.writeText(text).then(function(){var b=$('vc-copy-btn');b.classList.add('vc-copied');b.innerHTML='<svg width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><polyline points=\"20 6 9 17 4 12\"\/><\/svg> Copied!';setTimeout(function(){b.classList.remove('vc-copied');b.innerHTML='<svg width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><rect x=\"9\" y=\"9\" width=\"13\" height=\"13\" rx=\"2\"\/><path d=\"M5 15H4a2 2 0 01-2-2V4a2 2 0 012-2h9a2 2 0 012 2v1\"\/><\/svg> Copy'},2000)})}});\n\ndocument.querySelectorAll('.vc-section-toggle').forEach(function(btn){btn.addEventListener('click',function(){var s=this.closest('.vc-section');s.classList.toggle('vc-open');this.setAttribute('aria-expanded',s.classList.contains('vc-open'))})});\n\nvar faqData=[\n    {q:'What is a safety valve?',a:'<p>A safety valve (or pressure relief valve, PSV) automatically releases fluid when pressure exceeds a set point, protecting equipment from <strong>overpressure<\/strong>. Required by ASME Section VIII, PED, and ISO 4126.<\/p>'},\n    {q:'How is orifice area calculated for gas service?',a:'<p>Per API 520: A = W \/ (C \u00d7 Kd \u00d7 P\u2081 \u00d7 Kb \u00d7 \u221a(M\/(T\u00d7Z))), where W = mass flow, C = gas constant factor dependent on k, Kd = discharge coefficient (~0.975), P\u2081 = relieving pressure absolute, Kb = back pressure factor, M = molecular weight, T = temperature (K), Z = compressibility.<\/p>'},\n    {q:'What are standard API orifice letters?',a:'<p>API 526 defines standard orifice sizes: <strong>D<\/strong> (71 mm\u00b2) through <strong>T<\/strong> (16,774 mm\u00b2). Each letter corresponds to a fixed orifice area and standardized valve body sizes.<\/p>'},\n    {q:'What is the difference between set pressure and relieving pressure?',a:'<p><strong>Set pressure<\/strong> = pressure at which valve begins to open. <strong>Relieving pressure<\/strong> = set pressure + allowable overpressure (typically 10%). Sizing uses relieving pressure (absolute) as P\u2081.<\/p>'},\n    {q:'Do I need to account for back pressure?',a:'<p>Yes. Constant back pressure reduces effective differential. The correction factor Kb adjusts capacity. <strong>Balanced bellows<\/strong> or <strong>pilot-operated<\/strong> valves are less affected by back pressure than conventional valves.<\/p>'}\n];\nvar fl=$('vc-faq-list');faqData.forEach(function(f){fl.innerHTML+='<div class=\"vc-faq-item\"><button type=\"button\" class=\"vc-faq-q\"><span>'+f.q+'<\/span><svg class=\"vc-faq-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button><div class=\"vc-faq-a\"><div class=\"vc-faq-a-inner\">'+f.a+'<\/div><\/div><\/div>'});\nfl.addEventListener('click',function(e){var b=e.target.closest('.vc-faq-q');if(b)b.closest('.vc-faq-item').classList.toggle('vc-open')});\n\nfunction saveHistory(entry){var key='vc_history_'+SLUG;var arr=[];try{arr=JSON.parse(localStorage.getItem(key))||[]}catch(e){}entry._ts=new Date().toISOString();arr.unshift(entry);if(arr.length>10)arr=arr.slice(0,10);try{localStorage.setItem(key,JSON.stringify(arr))}catch(e){}}\n\nfunction init(){\n    try{katex.render('A = \\\\frac{W}{C \\\\cdot K_d \\\\cdot P_1 \\\\cdot K_b} \\\\cdot \\\\sqrt{\\\\frac{T \\\\cdot Z}{M}} \\\\quad [\\\\text{mm}^2]',$('vc-katex-1'),{displayMode:true,throwOnError:false})}catch(e){}\n    calculate();\n}\nif(document.readyState==='loading')document.addEventListener('DOMContentLoaded',init);else init();\n})();\n<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Gratis kalkulator for st\u00f8rrelser p\u00e5 sikkerhetsventiler i henhold til ISO 4126 \/ API 520. Beregn n\u00f8dvendig dyseareal, standard dysebokstav og minimum ventilst\u00f8rrelse for gass-, damp- og v\u00e6skebruk.<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-100217","calculator","type-calculator","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100217","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator"}],"about":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/types\/calculator"}],"version-history":[{"count":1,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100217\/revisions"}],"predecessor-version":[{"id":100532,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100217\/revisions\/100532"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/media?parent=100217"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/categories?post=100217"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/tags?post=100217"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}