{"id":100172,"date":"2026-02-15T20:22:18","date_gmt":"2026-02-15T20:22:18","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100172"},"modified":"2026-07-13T00:16:29","modified_gmt":"2026-07-13T00:16:29","slug":"npsh-calculator","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/he\/calculators\/npsh-calculator\/","title":{"rendered":"NPSHA Determination Worksheet"},"content":{"rendered":"\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"NPSHA Determination Worksheet\",\"description\":\"Engineering worksheet for net positive suction head available using either a supply-reservoir energy balance or a pump-suction pressure measurement. NPSHR and margin acceptance are not assessed.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/npsh-calculator\/\",\"applicationCategory\":\"EngineeringApplication\",\"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\":\"2026-07-13\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true,\"featureList\":[\"Supply-reservoir NPSHA route\",\"Pump-suction measurement route\",\"Absolute or gauge pressure basis\",\"Strict SI input\",\"Decimal point or comma\"],\"keywords\":\"NPSHA, net positive suction head available, pump suction, cavitation, ANSI HI 9.6.1\"}\n<\/script>\n\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"What does this worksheet calculate?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"It calculates NPSH available at a defined pump datum for one documented steady operating point. It does not calculate the pump's NPSH required or decide an acceptable margin.\"}},{\"@type\":\"Question\",\"name\":\"Can suction pressure, static elevation and suction losses be entered together?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Not in one route. A pressure measured at the pump suction already reflects the upstream elevation and losses. The worksheet separates a pump-suction measurement route from a supply-reservoir energy-balance route to prevent double counting.\"}},{\"@type\":\"Question\",\"name\":\"Does NPSHA above NPSH3 guarantee no cavitation?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. NPSH3 is associated with a 3 percent first-stage head drop, and cavitation-related effects can occur with margin above it. Select margin using the pump, liquid, service and current application standard.\"}},{\"@type\":\"Question\",\"name\":\"What NPSH margin should be used?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"There is no universal 0.5 metre or 1.3 multiplier rule. ANSI\/HI 9.6.1-2024 provides application-specific guidance; a licensed source and the pump manufacturer's data are required for a project decision.\"}}]}\n<\/script>\n\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"BreadcrumbList\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/vibromera.eu\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Calculators\",\"item\":\"https:\/\/vibromera.eu\/calculators\/\"},{\"@type\":\"ListItem\",\"position\":3,\"name\":\"NPSHA Determination Worksheet\",\"item\":\"https:\/\/vibromera.eu\/calculators\/npsh-calculator\/\"}]}\n<\/script>\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n<link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin>\n<link 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8px}\n@media(max-width:600px){.vc-form-grid,.vc-result-grid{grid-template-columns:1fr}.vc-field-full,.vc-rcard-primary,.vc-result-status{grid-column:1}.vc-promo{flex-direction:column;align-items:flex-start}.vc-header{padding-left:8px;padding-right:8px}}@media print{.vc-section-body,.vc-faq-a,.vc-results{max-height:none!important}.vc-results{padding:24px!important}.vc-copy-btn,.vc-section-chevron,.vc-promo{display:none!important}}\n<\/style>\n\n<div class=\"vc-calculator\" id=\"vc-npsha\">\n<header class=\"vc-header\">\n  <p class=\"vc-header-eyebrow\">Engineering determination worksheet<\/p>\n  <h1 class=\"vc-header-title\">NPSH Available (NPSHA)<\/h1>\n  <p class=\"vc-header-subtitle\">Determine NPSHA for one documented steady operating point without double-counting suction pressure, elevation or losses. This worksheet does not calculate NPSHR or approve a cavitation margin.<\/p>\n  <div class=\"vc-badges\"><span class=\"vc-badge\">Two exclusive routes<\/span><span class=\"vc-badge\">SI units<\/span><span class=\"vc-badge\">ANSI\/HI boundary<\/span><\/div>\n<\/header>\n\n<div class=\"vc-card\">\n  <form class=\"vc-form\" id=\"vc-form\" autocomplete=\"off\" novalidate>\n    <div class=\"vc-form-grid\">\n      <div class=\"vc-field vc-field-full\">\n        <label class=\"vc-label\" for=\"vc-route\">Determination route<\/label>\n        <select class=\"vc-select\" id=\"vc-route\">\n          <option value=\"\">\u2014 Select one route \u2014<\/option>\n          <option value=\"reservoir\">Supply reservoir \/ vessel energy balance<\/option>\n          <option value=\"measurement\">Pressure measured at pump suction<\/option>\n        <\/select>\n      <\/div>\n\n      <div class=\"vc-route vc-field vc-field-full\" id=\"vc-reservoir-intro\" data-route=\"reservoir\" hidden>\n        <div class=\"vc-info-box\"><p>Use pressure at the supply liquid surface, signed elevation from that surface to the pump NPSH datum, and all suction-line losses. The supply-surface velocity is assumed negligible.<\/p><\/div>\n      <\/div>\n      <div class=\"vc-route vc-field\" data-route=\"reservoir\" hidden><label class=\"vc-label\" for=\"vc-surface-abs\">Surface pressure <span class=\"vc-label-hint\">(kPa absolute)<\/span><\/label><input class=\"vc-input\" id=\"vc-surface-abs\" inputmode=\"decimal\" placeholder=\"absolute, not gauge\"><\/div>\n      <div class=\"vc-route vc-field\" data-route=\"reservoir\" hidden><label class=\"vc-label\" for=\"vc-static-z\">Surface elevation minus pump datum <span class=\"vc-label-hint\">(m; signed)<\/span><\/label><input class=\"vc-input\" id=\"vc-static-z\" inputmode=\"decimal\" placeholder=\"positive when surface is above datum\"><\/div>\n      <div class=\"vc-route vc-field\" data-route=\"reservoir\" hidden><label class=\"vc-label\" for=\"vc-loss\">All suction losses <span class=\"vc-label-hint\">(m of pumped liquid; \u2265 0)<\/span><\/label><input class=\"vc-input\" id=\"vc-loss\" inputmode=\"decimal\" placeholder=\"entrance, pipe, valves, fittings, strainer\"><\/div>\n\n      <div class=\"vc-route vc-field vc-field-full\" data-route=\"measurement\" hidden>\n        <div class=\"vc-warning-box\"><p>Use a pressure plane at the pump suction. Do not add upstream static elevation or suction friction again; their effect is already present in the measured pressure.<\/p><\/div>\n      <\/div>\n      <div class=\"vc-route vc-field\" data-route=\"measurement\" hidden><label class=\"vc-label\" for=\"vc-pressure-basis\">Suction pressure basis<\/label><select class=\"vc-select\" id=\"vc-pressure-basis\"><option value=\"\">\u2014 Select pressure basis \u2014<\/option><option value=\"absolute\">Direct absolute suction pressure<\/option><option value=\"gauge\">Gauge pressure plus local ambient absolute pressure<\/option><\/select><\/div>\n      <div class=\"vc-route vc-pressure-mode vc-field\" data-route=\"measurement\" data-pressure=\"absolute\" hidden><label class=\"vc-label\" for=\"vc-suction-abs\">Suction pressure <span class=\"vc-label-hint\">(kPa absolute)<\/span><\/label><input class=\"vc-input\" id=\"vc-suction-abs\" inputmode=\"decimal\"><\/div>\n      <div class=\"vc-route vc-pressure-mode vc-field\" data-route=\"measurement\" data-pressure=\"gauge\" hidden><label class=\"vc-label\" for=\"vc-suction-gauge\">Suction gauge pressure <span class=\"vc-label-hint\">(kPa gauge; signed)<\/span><\/label><input class=\"vc-input\" id=\"vc-suction-gauge\" inputmode=\"decimal\"><\/div>\n      <div class=\"vc-route vc-pressure-mode vc-field\" data-route=\"measurement\" data-pressure=\"gauge\" hidden><label class=\"vc-label\" for=\"vc-ambient-abs\">Local ambient pressure <span class=\"vc-label-hint\">(kPa absolute)<\/span><\/label><input class=\"vc-input\" id=\"vc-ambient-abs\" inputmode=\"decimal\"><\/div>\n      <div class=\"vc-route vc-field\" data-route=\"measurement\" hidden><label class=\"vc-label\" for=\"vc-velocity\">Mean velocity at suction plane <span class=\"vc-label-hint\">(m\/s; \u2265 0)<\/span><\/label><input class=\"vc-input\" id=\"vc-velocity\" inputmode=\"decimal\"><\/div>\n      <div class=\"vc-route vc-field\" data-route=\"measurement\" hidden><label class=\"vc-label\" for=\"vc-gauge-z\">Gauge-plane elevation minus NPSH datum <span class=\"vc-label-hint\">(m; signed)<\/span><\/label><input class=\"vc-input\" id=\"vc-gauge-z\" inputmode=\"decimal\" placeholder=\"positive when gauge is above datum\"><\/div>\n\n      <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-vapor-abs\">Liquid vapor pressure <span class=\"vc-label-hint\">(kPa absolute at operating temperature; \u2265 0)<\/span><\/label><input class=\"vc-input\" id=\"vc-vapor-abs\" inputmode=\"decimal\"><\/div>\n      <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-density\">Liquid density <span class=\"vc-label-hint\">(kg\/m\u00b3 at operating condition; &gt; 0)<\/span><\/label><input class=\"vc-input\" id=\"vc-density\" inputmode=\"decimal\"><\/div>\n      <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-gravity\">Acceleration used for head conversion <span class=\"vc-label-hint\">(m\/s\u00b2; &gt; 0)<\/span><\/label><input class=\"vc-input\" id=\"vc-gravity\" inputmode=\"decimal\" placeholder=\"for example standard gravity 9.80665\"><\/div>\n      <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-record\">Operating-point \/ source record<\/label><input class=\"vc-input\" id=\"vc-record\" type=\"text\" placeholder=\"flow, speed, liquid temperature, pressure source, datum\"><\/div>\n      <div class=\"vc-field vc-field-full\"><label class=\"vc-check\" for=\"vc-gate\"><input id=\"vc-gate\" type=\"checkbox\"><span>I documented one steady operating point, pressure reference (absolute or gauge), liquid temperature\/density\/vapor pressure, measurement or reservoir plane, NPSH datum and all inputs used. I am not applying this steady rotodynamic-pump worksheet to pulsating\/reciprocating flow, flashing mixtures or an unverified instrument reading.<\/span><\/label><\/div>\n    <\/div>\n    <div class=\"vc-validation\" id=\"vc-validation\" role=\"status\" aria-live=\"polite\"><\/div>\n  <\/form>\n\n  <div class=\"vc-results\" id=\"vc-results\">\n    <div class=\"vc-results-head\"><h2 class=\"vc-results-title\">Calculated NPSHA<\/h2><button type=\"button\" class=\"vc-copy-btn\" id=\"vc-copy-btn\">Copy<\/button><\/div>\n    <div class=\"vc-result-grid\">\n      <div class=\"vc-rcard vc-rcard-primary\"><div class=\"vc-rcard-label\">NPSH available at stated datum<\/div><div class=\"vc-rcard-value\" id=\"vc-r-npsha\">\u2014<\/div><\/div>\n      <div class=\"vc-rcard\"><div class=\"vc-rcard-label\" id=\"vc-r-ref-label\">Reference absolute pressure<\/div><div class=\"vc-rcard-value\" id=\"vc-r-ref\">\u2014<\/div><\/div>\n      <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Pressure-above-vapor head<\/div><div class=\"vc-rcard-value\" id=\"vc-r-pressure-head\">\u2014<\/div><\/div>\n      <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Velocity-head term<\/div><div class=\"vc-rcard-value\" id=\"vc-r-velocity-head\">\u2014<\/div><\/div>\n      <div class=\"vc-rcard\"><div class=\"vc-rcard-label\" id=\"vc-r-route-label\">Elevation \/ loss term<\/div><div class=\"vc-rcard-value\" id=\"vc-r-route-term\">\u2014<\/div><\/div>\n      <div class=\"vc-result-status\" id=\"vc-r-status\">NPSHR, NPSH3, margin adequacy, cavitation damage and fitness for service are not assessed.<\/div>\n    <\/div>\n  <\/div>\n<\/div>\n\n<div class=\"vc-section vc-open\">\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\">Equations, datum and scope<\/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>Route 1 \u2014 supply reservoir or vessel<\/h3>\n    <div class=\"vc-formula-box\">NPSHA = (p_surface,abs \u2212 p_v)\/(\u03c1g) + (z_surface \u2212 z_datum) \u2212 h_loss<\/div>\n    <p>This steady energy-balance route uses the absolute pressure acting on the supply liquid surface. The surface velocity is assumed negligible; <em>h<\/em><sub>loss<\/sub> must include entrance, pipe, fitting, valve, strainer and other suction losses at the documented flow.<\/p>\n    <h3>Route 2 \u2014 measurement at pump suction<\/h3>\n    <div class=\"vc-formula-box\">NPSHA = (p_s,abs \u2212 p_v)\/(\u03c1g) + v_s\u00b2\/(2g) + (z_gauge \u2212 z_datum)<\/div>\n    <p>For a gauge-pressure instrument, <span style=\"font-family:var(--vc-mono)\">p_s,abs = p_ambient,abs + p_s,gauge<\/span>. The upstream static elevation and friction are not added because their effect is already contained in the measured suction pressure.<\/p>\n    <h3>What the result means<\/h3>\n    <p>NPSHA is the total suction head absolute above the vapor-pressure head, expressed as metres of the pumped liquid at the stated condition and datum. Pressure, density and vapor pressure must describe the same operating state.<\/p>\n    <div class=\"vc-warning-box\"><p><strong>No universal margin:<\/strong> the removed rules \u201cNPSHA \u2265 NPSHR + 0.5 m\u201d and \u201cNPSHA \u2265 1.3 \u00d7 NPSHR\u201d are not general acceptance criteria. NPSH3 is associated with a 3% first-stage head drop; cavitation effects can occur even with margin above it. Use current ANSI\/HI 9.6.1, the manufacturer&#8217;s curve at the same flow\/speed\/liquid, and the controlling project specification.<\/p><\/div>\n    <h3>Excluded cases<\/h3>\n    <ul><li>Transient, pulsating or reciprocating-pump acceleration head.<\/li><li>Flashing or two-phase mixtures, gas entrainment, uncertain vapor pressure or incompatible density data.<\/li><li>Instrument elevation\/velocity corrections or suction losses that have not been established.<\/li><li>NPSHR\/NPSH3 derivation, margin selection, cavitation-free guarantee, erosion\/life prediction or pump acceptance testing.<\/li><\/ul>\n  <\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\">\n  <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udcda<\/span><span class=\"vc-section-title\">Standards and source boundary<\/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 vc-source-list\">\n    <h3>Publicly verified sources<\/h3>\n    <ul><li><a href=\"https:\/\/datatool.pumps.org\/pump-fundamentals\/pump-principles\/\" target=\"_blank\" rel=\"noopener\">Hydraulic Institute Data Tool \u2014 Pump Principles<\/a>: public NPSHA definition; updated 19 July 2024.<\/li><li><a href=\"https:\/\/www.pumps.org\/resources\/pump-faqs\/\" target=\"_blank\" rel=\"noopener\">Hydraulic Institute Pump FAQs<\/a>: system inputs, suction losses and NPSH3 limitation.<\/li><li><a href=\"https:\/\/www.pumps.org\/wp-content\/uploads\/2025\/02\/PSC-Exam-Formula-Reference-Sheet.pdf\" target=\"_blank\" rel=\"noopener\">Hydraulic Institute Pump System Certification formula sheet<\/a>: pump-suction measurement equation and velocity\/elevation terms.<\/li><li><a href=\"https:\/\/www.iso.org\/standard\/55821.html\" target=\"_blank\" rel=\"noopener\">ISO 17769-1:2012<\/a>: current pump vocabulary, symbols and units standard; confirmed 2023.<\/li><li><a href=\"https:\/\/www.iso.org\/standard\/41202.html\" target=\"_blank\" rel=\"noopener\">ISO 9906:2012<\/a>: current rotodynamic-pump hydraulic acceptance-test scope. This worksheet is not an ISO 9906 acceptance test.<\/li><\/ul>\n    <div class=\"vc-info-box\"><p><strong>Licensed-source boundary:<\/strong> ANSI\/HI 9.6.1-2024 is the current NPSH-margin guideline. Its public table of contents confirms an informative NPSHA appendix and application-specific margin sections; exact closed recommendations are <strong>NEEDS_LICENSED_SOURCE<\/strong> and are not reproduced or guessed here.<\/p><\/div>\n  <\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\">\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\"><a class=\"vc-related-link\" href=\"\/calculators\/pump-head-power\/\">Pump Head and Power<\/a><a class=\"vc-related-link\" href=\"\/calculators\/pipe-pressure-drop\/\">Pipe Pressure Drop<\/a><a class=\"vc-related-link\" href=\"\/calculators\/specific-speed-calculator\/\">Specific Speed<\/a><\/div><\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\">\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 field balancing instruments and software.<\/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&ndash;2026 <a href=\"https:\/\/vibromera.eu\/\">Vibromera<\/a> &mdash; Engineering Calculators<\/p><p style=\"font-size:12px;margin-top:4px\">NPSHA worksheet reviewed 13 July 2026. Calculation is informational and does not replace pump\/system engineering review.<\/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>\n(function(){\n  'use strict';\n  function $(id){return document.getElementById(id)}\n  function strictNumber(raw){\n    var text=String(raw||'').trim();\n    if(!text||(text.indexOf(',')!==-1&&text.indexOf('.')!==-1))return null;\n    text=text.replace(',','.');\n    if(!\/^[+-]?(?:\\d+(?:\\.\\d*)?|\\.\\d+)$\/.test(text))return null;\n    var value=Number(text);\n    return Number.isFinite(value)?value:null;\n  }\n  function read(id,test){var value=strictNumber($(id).value);return value!==null&&test(value)?value:null}\n  function positive(value){return value>0}\n  function nonnegative(value){return value>=0}\n  function anyFinite(){return true}\n  function fmt(value){return value.toFixed(4).replace(\/(\\.\\d*?)0+$\/,'$1').replace(\/\\.$\/,'')}\n  function setText(id,text){$(id).textContent=text}\n  function hideResult(message){$('vc-results').classList.remove('vc-visible');$('vc-validation').textContent=message||''}\n  function showRoute(){\n    var route=$('vc-route').value;\n    document.querySelectorAll('.vc-route').forEach(function(node){node.hidden=node.getAttribute('data-route')!==route});\n    showPressureMode();\n    hideResult('');\n  }\n  function showPressureMode(){\n    var route=$('vc-route').value,basis=$('vc-pressure-basis').value;\n    document.querySelectorAll('.vc-pressure-mode').forEach(function(node){node.hidden=route!=='measurement'||node.getAttribute('data-pressure')!==basis});\n  }\n  function calculate(){\n    var route=$('vc-route').value;\n    if(!route)return hideResult('Select one determination route.');\n    if(!$('vc-gate').checked)return hideResult('Confirm the operating-point, pressure-reference and scope record.');\n    if(!$('vc-record').value.trim())return hideResult('Enter the operating-point and source record.');\n    var pv=read('vc-vapor-abs',nonnegative),rho=read('vc-density',positive),g=read('vc-gravity',positive);\n    if(pv===null||rho===null||g===null)return hideResult('Enter complete valid vapor pressure, density and acceleration values.');\n    var refPressure,pressureHead,velocityHead,routeTerm,npsha;\n    if(route==='reservoir'){\n      var surface=read('vc-surface-abs',positive),z=read('vc-static-z',anyFinite),loss=read('vc-loss',nonnegative);\n      if(surface===null||z===null||loss===null)return hideResult('Complete the reservoir route: absolute surface pressure, signed elevation and nonnegative total suction loss.');\n      refPressure=surface;\n      pressureHead=(surface-pv)*1000\/(rho*g);\n      velocityHead=0;\n      routeTerm=z-loss;\n      npsha=pressureHead+routeTerm;\n      setText('vc-r-ref-label','Supply-surface absolute pressure');\n      setText('vc-r-route-label','Signed elevation minus suction loss');\n    }else{\n      var basis=$('vc-pressure-basis').value;\n      if(!basis)return hideResult('Select the suction pressure basis.');\n      if(basis==='absolute'){\n        refPressure=read('vc-suction-abs',positive);\n        if(refPressure===null)return hideResult('Enter a positive absolute suction pressure.');\n      }else{\n        var gauge=read('vc-suction-gauge',anyFinite),ambient=read('vc-ambient-abs',positive);\n        if(gauge===null||ambient===null)return hideResult('Enter signed gauge pressure and positive local ambient absolute pressure.');\n        refPressure=ambient+gauge;\n        if(!(refPressure>0))return hideResult('Ambient plus gauge pressure must give a positive absolute suction pressure.');\n      }\n      var velocity=read('vc-velocity',nonnegative),gaugeZ=read('vc-gauge-z',anyFinite);\n      if(velocity===null||gaugeZ===null)return hideResult('Enter nonnegative suction velocity and the signed gauge-to-datum elevation.');\n      pressureHead=(refPressure-pv)*1000\/(rho*g);\n      velocityHead=velocity*velocity\/(2*g);\n      routeTerm=gaugeZ;\n      npsha=pressureHead+velocityHead+routeTerm;\n      setText('vc-r-ref-label','Calculated suction absolute pressure');\n      setText('vc-r-route-label','Gauge-plane elevation correction');\n    }\n    if(!Number.isFinite(npsha))return hideResult('The entered values did not produce a finite result.');\n    setText('vc-r-npsha',fmt(npsha)+' m');\n    setText('vc-r-ref',fmt(refPressure)+' kPa abs');\n    setText('vc-r-pressure-head',fmt(pressureHead)+' m');\n    setText('vc-r-velocity-head',fmt(velocityHead)+' m');\n    setText('vc-r-route-term',fmt(routeTerm)+' m');\n    setText('vc-r-status',(npsha<=0?'Calculated NPSHA is non-positive. ':'')+'NPSHR, NPSH3, margin adequacy, cavitation damage and fitness for service are not assessed.');\n    $('vc-validation').textContent='';\n    $('vc-results').classList.add('vc-visible');\n  }\n  $('vc-route').addEventListener('change',showRoute);\n  $('vc-pressure-basis').addEventListener('change',function(){showPressureMode();calculate()});\n  $('vc-form').addEventListener('input',calculate);\n  $('vc-form').addEventListener('change',calculate);\n  $('vc-copy-btn').addEventListener('click',function(){\n    var text='NPSHA determination\\n'+$('vc-r-npsha').textContent+'\\n'+$('vc-r-ref-label').textContent+': '+$('vc-r-ref').textContent+'\\nPressure-above-vapor head: '+$('vc-r-pressure-head').textContent+'\\nVelocity head: '+$('vc-r-velocity-head').textContent+'\\n'+$('vc-r-route-label').textContent+': '+$('vc-r-route-term').textContent+'\\n'+$('vc-r-status').textContent+'\\nRecord: '+$('vc-record').value.trim()+'\\nvibromera.eu\/calculators\/npsh-calculator\/';\n    if(navigator.clipboard)navigator.clipboard.writeText(text).then(function(){var button=$('vc-copy-btn');button.classList.add('vc-copied');button.textContent='Copied!';setTimeout(function(){button.classList.remove('vc-copied');button.textContent='Copy'},2000)})\n  });\n  document.querySelectorAll('.vc-section-toggle').forEach(function(button){button.addEventListener('click',function(){var section=this.closest('.vc-section');section.classList.toggle('vc-open');this.setAttribute('aria-expanded',String(section.classList.contains('vc-open')))})});\n  var faqData=[\n    ['What does this worksheet calculate?','NPSH available at a defined pump datum for one documented steady operating point. NPSHR, NPSH3 and margin adequacy are not calculated.'],\n    ['Why are there two exclusive routes?','A pressure measured at pump suction already contains the upstream elevation and loss effects. Adding reservoir elevation and friction to that measurement would count them twice.'],\n    ['Does NPSHA above NPSH3 guarantee no cavitation?','No. NPSH3 corresponds to a 3% first-stage head drop, and cavitation-related effects can occur with margin above it.'],\n    ['What margin should I use?','Use the pump manufacturer data at the same operating point and the current application-specific guidance in ANSI\/HI 9.6.1-2024 or the controlling project specification. No universal margin is assigned here.']\n  ];\n  var faqList=$('vc-faq-list');\n  faqData.forEach(function(item){var wrapper=document.createElement('div');wrapper.className='vc-faq-item';var button=document.createElement('button');button.type='button';button.className='vc-faq-q';button.textContent=item[0];var answer=document.createElement('div');answer.className='vc-faq-a';var inner=document.createElement('div');inner.className='vc-faq-a-inner';var paragraph=document.createElement('p');paragraph.textContent=item[1];inner.appendChild(paragraph);answer.appendChild(inner);wrapper.appendChild(button);wrapper.appendChild(answer);faqList.appendChild(wrapper)});\n  faqList.addEventListener('click',function(event){var button=event.target.closest('.vc-faq-q');if(button)button.closest('.vc-faq-item').classList.toggle('vc-open')});\n  showRoute();\n})();\n<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Determine NPSH available using one of two exclusive routes: a supply-reservoir energy balance or a pump-suction pressure measurement. NPSHR and margin acceptance are not assessed.<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-100172","calculator","type-calculator","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/calculator\/100172","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/calculator"}],"about":[{"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/types\/calculator"}],"version-history":[{"count":3,"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/calculator\/100172\/revisions"}],"predecessor-version":[{"id":102509,"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/calculator\/100172\/revisions\/102509"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/media?parent=100172"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/categories?post=100172"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/he\/wp-json\/wp\/v2\/tags?post=100172"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}