{"id":100201,"date":"2026-02-15T20:26:27","date_gmt":"2026-02-15T20:26:27","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100201"},"modified":"2026-07-13T06:13:06","modified_gmt":"2026-07-13T06:13:06","slug":"pump-cavitation-frequency","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/nb\/calculators\/pump-cavitation-frequency\/","title":{"rendered":"Pump Vane-Passing Frequency &#038; NPSH Record Worksheet"},"content":{"rendered":"\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Pump Vane-Passing Frequency and NPSH Record Worksheet\",\"description\":\"Calculate shaft and vane-passing kinematic frequencies and optionally compare two controlled NPSHA\/NPSHR record values without predicting a universal cavitation band or risk category.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/pump-cavitation-frequency\/\",\"applicationCategory\":\"EngineeringApplication\",\"operatingSystem\":\"Any\",\"offers\":{\"@type\":\"Offer\",\"price\":\"0\"},\"creator\":{\"@type\":\"Organization\",\"name\":\"Vibromera\",\"url\":\"https:\/\/vibromera.eu\/\"},\"dateModified\":\"2026-07-13\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true}<\/script>\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"Is vane-passing frequency the cavitation frequency?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. Vane-passing frequency is the kinematic rate at which rotating vanes pass a stationary location. Cavitation can change broadband or discrete vibration and acoustic features, but the sensitive band and trend depend on the pump, operating point, sensor, mounting and transfer path.\"}},{\"@type\":\"Question\",\"name\":\"Does a positive NPSHA minus NPSHR value prove that cavitation cannot occur?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. The worksheet reports raw difference and ratio only. The applicable margin must come from the current controlled pump, system and application specification; NPSHR is pump- and operating-point-specific and NPSHA is system-specific.\"}},{\"@type\":\"Question\",\"name\":\"Why were the 1.3 and 2.0 NPSH risk thresholds removed?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"They were presented as universal risk boundaries without a controlled application basis. ANSI\/HI 9.6.1:2024 provides application-specific margin guidance, so this open worksheet does not invent or reproduce a universal table.\"}},{\"@type\":\"Question\",\"name\":\"Can a BPF harmonic alone diagnose cavitation?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. The worksheet lists harmonic coordinates but predicts no amplitude or fault. Diagnosis needs a controlled baseline, operating point, sensor and bandwidth, hydraulic performance data and corroborating evidence.\"}}]}<\/script>\n<script type=\"application\/ld+json\">{\"@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\":\"Pump vane-passing frequency and NPSH record\",\"item\":\"https:\/\/vibromera.eu\/calculators\/pump-cavitation-frequency\/\"}]}<\/script>\n<style>\n:root{--vc-surface:#fff;--vc-alt:#f8f6f2;--vc-ink:#1a1a1a;--vc-secondary:#5a5650;--vc-muted:#807b73;--vc-accent:#b84f22;--vc-accent-light:#fdf0ea;--vc-yellow:#825f00;--vc-yellow-light:#fff8dc;--vc-red:#9d2b24;--vc-red-light:#fff0ee;--vc-border:#d9d4cc;--vc-border-light:#e8e4dd;--vc-shadow:0 1px 3px 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1fr}.vc-result-grid{grid-template-columns:1fr 1fr}}@media(max-width:560px){.vc-grid,.vc-result-grid{grid-template-columns:1fr}.vc-form,.vc-results{padding:18px}.vc-results-head{align-items:flex-start;flex-direction:column}}@media print{.vc-section-body,.vc-results{display:block!important}.vc-copy,.vc-chevron,.vc-actions{display:none}}\n<\/style>\n<div class=\"vc-calculator\">\n<header class=\"vc-header\"><p class=\"vc-eyebrow\">Pump kinematics plus raw record comparison<\/p><h1 class=\"vc-title\">Pump Vane-Passing Frequency &amp; NPSH Record Worksheet<\/h1><p class=\"vc-subtitle\">Calculate shaft and vane-passing coordinates from documented speed and vane count. Optionally compare controlled NPSHA and NPSHR values at the same operating point\u2014without inventing a cavitation frequency band or risk category.<\/p><div class=\"vc-badges\"><span class=\"vc-badge\">VPF = Z \u00d7 n \/ 60<\/span><span class=\"vc-badge\">No universal 1\u2013100 kHz band<\/span><span class=\"vc-badge\">No NPSH risk score<\/span><\/div><\/header>\n<div class=\"vc-card\"><form class=\"vc-form\" id=\"vc-form\" novalidate><div class=\"vc-grid\">\n<div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-speed-units\">Speed unit<\/label><select class=\"vc-select\" id=\"vc-speed-units\"><option value=\"rpm\">r\/min (RPM)<\/option><option value=\"hz\">Hz (rev\/s)<\/option><\/select><\/div>\n<div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-speed\">Documented shaft speed n <span class=\"vc-hint\" id=\"vc-speed-hint\">(r\/min)<\/span><\/label><input class=\"vc-input\" id=\"vc-speed\" inputmode=\"decimal\" autocomplete=\"off\"><\/div>\n<div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-vanes\">Equally spaced rotating vanes Z <span class=\"vc-hint\">(positive integer)<\/span><\/label><input class=\"vc-input\" id=\"vc-vanes\" inputmode=\"numeric\" autocomplete=\"off\"><\/div>\n<div class=\"vc-field vc-wide\"><label class=\"vc-label\" for=\"vc-frequency-source\">Speed\/vane source and stationary observation location<\/label><input class=\"vc-input\" id=\"vc-frequency-source\" autocomplete=\"off\" placeholder=\"Asset, impeller revision, tachometer\/record, operating point and observer (e.g. cutwater or diffuser)\"><\/div>\n<div class=\"vc-subhead vc-wide\">Optional NPSH record comparison<\/div>\n<div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-head-units\">Head unit<\/label><select class=\"vc-select\" id=\"vc-head-units\"><option value=\"m\">metre (m)<\/option><option value=\"ft\">foot (ft)<\/option><\/select><\/div>\n<div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-npsha\">Controlled NPSHA <span class=\"vc-hint vc-head-unit\">(m)<\/span><\/label><input class=\"vc-input\" id=\"vc-npsha\" inputmode=\"decimal\" autocomplete=\"off\" placeholder=\"Leave both NPSH fields blank to skip\"><\/div>\n<div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-npshr\">Manufacturer\/project NPSHR <span class=\"vc-hint vc-head-unit\">(m)<\/span><\/label><input class=\"vc-input\" id=\"vc-npshr\" inputmode=\"decimal\" autocomplete=\"off\" placeholder=\"Same operating point\"><\/div>\n<div class=\"vc-field vc-wide\"><label class=\"vc-label\" for=\"vc-npsh-source\">NPSH source, revisions and common operating conditions<\/label><input class=\"vc-input\" id=\"vc-npsh-source\" autocomplete=\"off\" placeholder=\"System calculation and pump curve\/data sheet; flow, speed, liquid, temperature, datum and revision\"><\/div>\n<label class=\"vc-check vc-wide\" for=\"vc-confirm\"><input id=\"vc-confirm\" type=\"checkbox\"><span>I confirm that speed and vane count describe the same rotor and observation context; any NPSHA\/NPSHR pair uses the same head basis, datum and operating point; and I will not treat VPF\/harmonics or raw NPSH arithmetic as proof of cavitation, absence of cavitation, fault amplitude, compliance, alarm setting or required margin.<\/span><\/label>\n<div class=\"vc-actions vc-wide\"><button class=\"vc-calc-btn\" type=\"submit\">Calculate documented coordinates<\/button><\/div>\n<\/div><\/form><div class=\"vc-error\" id=\"vc-error\" role=\"alert\"><\/div>\n<div class=\"vc-results\" id=\"vc-results\" aria-live=\"polite\"><div class=\"vc-results-head\"><div><h2 class=\"vc-results-title\">Kinematic frequency record<\/h2><div class=\"vc-results-basis\" id=\"vc-results-basis\">\u2014<\/div><\/div><button type=\"button\" class=\"vc-copy\" id=\"vc-copy\">Copy record<\/button><\/div><div class=\"vc-result-grid\">\n<div class=\"vc-result vc-primary\"><div class=\"vc-result-label\">Vane-passing frequency (1\u00d7 VPF)<\/div><div class=\"vc-result-value\" id=\"vc-vpf\">\u2014<\/div><\/div>\n<div class=\"vc-result\"><div class=\"vc-result-label\">Shaft rotational frequency (1\u00d7)<\/div><div class=\"vc-result-value\" id=\"vc-shaft\">\u2014<\/div><\/div>\n<div class=\"vc-result\"><div class=\"vc-result-label\">2\u00d7 VPF coordinate<\/div><div class=\"vc-result-value\" id=\"vc-vpf2\">\u2014<\/div><\/div>\n<div class=\"vc-result\"><div class=\"vc-result-label\">4\u00d7 VPF coordinate<\/div><div class=\"vc-result-value\" id=\"vc-vpf4\">\u2014<\/div><\/div>\n<\/div><div class=\"vc-npsh-output\" id=\"vc-npsh-output\"><h3>Raw NPSH record comparison\u2014not a risk verdict<\/h3><div class=\"vc-npsh-line\" id=\"vc-npsh-line\">\u2014<\/div><div class=\"vc-npsh-line\" id=\"vc-npsh-basis\">\u2014<\/div><\/div><div class=\"vc-warning\"><strong>Coordinates do not diagnose:<\/strong> a spectral line at VPF or its harmonics may reflect rotor\u2013stator hydraulic interaction, but this worksheet predicts no amplitude or cause. Cavitation assessment needs controlled hydraulic performance, operating state, baseline\/trend, sensor and bandwidth\/transfer-path evidence.<\/div><\/div><\/div>\n\n<section class=\"vc-section vc-open\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"true\"><span class=\"vc-section-title\">Equations, units and physical boundary<\/span><span class=\"vc-chevron\">\u2304<\/span><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\">\n<h3>Rotational and vane-passing coordinates<\/h3><div class=\"vc-formula\">f<sub>shaft<\/sub> = n \/ 60<br>f<sub>VPF<\/sub> = Z f<sub>shaft<\/sub> = Zn \/ 60<br>f<sub>k<\/sub> = k f<sub>VPF<\/sub>, &nbsp;k = 2, 3, 4<\/div>\n<p>n is shaft speed in r\/min, Z is the positive integer count of equally spaced rotating vanes, and frequencies are in hertz. If speed is entered in rev\/s (Hz), f<sub>shaft<\/sub> equals that input. Counts per minute are frequency in hertz multiplied by 60.<\/p>\n<p>This is kinematics for a stationary observer such as a cutwater or diffuser location. It neither predicts that a spectral component will be present nor assigns its amplitude or cause. Different impeller\/stator geometry, unequal spacing, variable speed, slip, multiple stages and measurement transfer paths require the actual design and signal record.<\/p>\n<h3>Optional raw NPSH arithmetic<\/h3><div class=\"vc-formula\">\u0394NPSH = NPSHA \u2212 NPSHR<br>R = NPSHA \/ NPSHR<br>1 ft = 0.3048 m exactly<\/div>\n<p>NPSHA is system-specific and NPSHR is pump\/manufacturer-specific. Difference and ratio are shown only for two values entered from controlled sources at the same flow, speed, liquid, temperature, reference datum and head definition. A positive difference is not an assurance of zero cavitation or adequate reliability margin.<\/p>\n<\/div><\/div><\/section>\n<section class=\"vc-section\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-title\">Confirmed defects removed from the former estimator<\/span><span class=\"vc-chevron\">\u2304<\/span><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\">\n<div class=\"vc-table-wrap\"><table class=\"vc-table\"><thead><tr><th>Former output or claim<\/th><th>Confirmed problem and correction<\/th><\/tr><\/thead><tbody>\n<tr><td>\u201cExpected cavitation frequency 1\u2013100 kHz\u201d<\/td><td>Cavitation is not one universal frequency interval. Sensitive bands\/trends depend on pump geometry, operating point, fluid, sensor, mounting, acquisition bandwidth and structural\/acoustic transfer path. The invented range output was removed.<\/td><\/tr>\n<tr><td>Elevated 3\u00d7 BPF labelled a cavitation indicator<\/td><td>VPF harmonics are coordinates, not unique diagnoses. Hydraulic interaction, recirculation and other sources can affect them, while cavitation response can appear in different broadband or discrete bands. Harmonics are now unlabeled arithmetic only.<\/td><\/tr>\n<tr><td>NPSHA\/NPSHR ratios &gt;2, 1.3\u20132, 1\u20131.3 and &lt;1 as universal low\/moderate\/high\/critical risk<\/td><td>Current Hydraulic Institute guidance is application-specific. The closed margin rules were not implemented; only raw difference and ratio remain.<\/td><\/tr>\n<tr><td>\u201cPositive margin prevents cavitation\u201d and \u201cbelow NPSHR means cavitation certain\u201d<\/td><td>Those categorical statements ignore the definition and operating-point basis of the manufacturer value, uncertainty, margin requirement and cavitation mechanisms. No prognosis is emitted.<\/td><\/tr>\n<tr><td>Defaults, presets, auto-calculation, partial numeric parsing, URL\/history persistence<\/td><td>They produced authoritative-looking results from example or stale inputs. The replacement starts blank, requires provenance and confirmation, validates strict complete numbers and calculates only on submit.<\/td><\/tr>\n<tr><td>ISO 10816 \/ ISO 1940 implication<\/td><td>Rotor-balance and pump vibration-evaluation standards do not turn Zn\/60 into a cavitation-frequency diagnosis. The worksheet calls the equation general kinematics and states each standards boundary.<\/td><\/tr>\n<\/tbody><\/table><\/div>\n<\/div><\/div><\/section>\n<section class=\"vc-section\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-title\">Standards lifecycle and published checks<\/span><span class=\"vc-chevron\">\u2304<\/span><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\">\n<h3>Published vane-passing example<\/h3><p>NASA contractor report <a href=\"https:\/\/ntrs.nasa.gov\/api\/citations\/19730017750\/downloads\/19730017750.pdf?attachment=true\" target=\"_blank\" rel=\"noopener\"><em>Fan and Pump Noise Control<\/em>, SVHSER 6183 (May 1973)<\/a> publishes the same kinematic equation and a pump example with four vanes at 5,500 r\/min, reporting a vane-passage frequency of 367 Hz. The exact arithmetic is 4 \u00d7 5,500 \/ 60 = 366.666\u2026 Hz, which rounds to the published value.<\/p>\n<h3>No universal cavitation band<\/h3><p>The peer-reviewed experimental study by <a href=\"https:\/\/doi.org\/10.1016\/j.euromechflu.2018.10.015\" target=\"_blank\" rel=\"noopener\">Mousmoulis et al., <em>European Journal of Mechanics B\/Fluids<\/em> 75 (2019), 300\u2013311<\/a> used flow visualization, acoustic emission and vibration on different impellers. It reports geometry-dependent behavior and cites markedly different useful vibration features (for example, around 1,600 Hz for one pump and 148 Hz for another). That evidence contradicts a universal 1\u2013100 kHz diagnostic output.<\/p>\n<h3>NPSH guidance is application-specific<\/h3><p>The Hydraulic Institute\u2019s official current product information for <a href=\"https:\/\/www.pumps.org\/product\/ansi-hi-9-6-1-rotodynamic-pumps-guideline-for-npsh-margin\/\" target=\"_blank\" rel=\"noopener\">ANSI\/HI 9.6.1:2024, <em>Rotodynamic Pumps Guideline for NPSH Margin<\/em><\/a> states that NPSHA is system-specific, NPSHR is pump\/manufacturer-specific, and the appropriate margin is application-dependent. The 2024 edition supersedes 2017. Its licensed recommendations are not copied or replaced with generic ratios here.<\/p>\n<h3>ISO scope<\/h3><p><a href=\"https:\/\/www.iso.org\/standard\/41202.html\" target=\"_blank\" rel=\"noopener\">ISO 9906:2012<\/a>, Edition 2, remains published and is at close-of-review stage. Its official abstract covers hydraulic performance acceptance tests for rotodynamic pumps; closed procedures and acceptance details remain <strong>NEEDS_LICENSED_SOURCE<\/strong>. It is not used as a cavitation-frequency formula.<\/p>\n<p><a href=\"https:\/\/www.iso.org\/standard\/41726.html\" target=\"_blank\" rel=\"noopener\">ISO 10816-7:2009<\/a> remains published, was confirmed in 2020 and is marked to be revised; ISO\/AWI 20816-7 is under development. Its official scope is evaluation of vibration on industrial rotodynamic pumps above 1 kW, including bearing-housing measurement requirements. No universal cavitation band or NPSH ratio is inferred from that scope.<\/p>\n<p>Sources and lifecycle checked 13 July 2026. Detailed ANSI\/HI and ISO rules must come from the authorized current documents and the controlled project\/OEM specification.<\/p>\n<\/div><\/div><\/section>\n<section class=\"vc-section\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-title\">Frequently asked questions<\/span><span class=\"vc-chevron\">\u2304<\/span><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\">\n<div class=\"vc-faq\"><button type=\"button\">Is VPF the same as blade-pass frequency?<\/button><div>In this worksheet VPF\/BPF means the rate at which Z equally spaced rotating vanes pass a stationary observation location: Z times shaft rotational frequency. Document the terminology used by the pump\/OEM record.<\/div><\/div>\n<div class=\"vc-faq\"><button type=\"button\">Why are harmonics listed if they do not diagnose a fault?<\/button><div>They are search coordinates for a spectrum or order map. Their presence, amplitude and trend must be interpreted against operating state, baseline, sensor path and hydraulic\/mechanical evidence.<\/div><\/div>\n<div class=\"vc-faq\"><button type=\"button\">Can I enter one NPSH value only?<\/button><div>No. The optional comparison requires both values and their common operating-point provenance. Leave both blank if no controlled pair is available.<\/div><\/div>\n<div class=\"vc-faq\"><button type=\"button\">Does a ratio above 2 mean low risk?<\/button><div>This worksheet deliberately makes no such classification. Use the current applicable ANSI\/HI\/OEM\/project margin requirement for the specific pump and service.<\/div><\/div>\n<\/div><\/div><\/section>\n<section class=\"vc-section\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-title\">Related engineering pages<\/span><span class=\"vc-chevron\">\u2304<\/span><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-related\"><a href=\"\/calculators\/vibration-unit-converter\/\">Vibration unit conversion<\/a><a href=\"\/calculators\/pump-power-calculator\/\">Pump hydraulic power<\/a><a href=\"\/calculators\/fft-frequency-resolution\/\">FFT grid and record resolution<\/a><\/div><\/div><\/div><\/section>\n<footer class=\"vc-footer\">Kinematic coordinates and raw document-controlled NPSH arithmetic only; no cavitation diagnosis or margin approval. \u00b7 <a href=\"\/calculators\/engineering-calculators\/\">All calculators<\/a><\/footer>\n<\/div>\n<script>\n(function(){\n\"use strict\";\nvar FT_TO_M=0.3048;\nfunction byId(id){return document.getElementById(id)}\nfunction parseNumber(text){var s=String(text).trim();if(!s||s.indexOf('.')>=0&&s.indexOf(',')>=0||!\/^[-+]?(?:\\d+(?:[.,]\\d*)?|[.,]\\d+)(?:[eE][-+]?\\d+)?$\/.test(s))return null;var n=Number(s.replace(',','.'));return Number.isFinite(n)?n:null}\nfunction pumpFrequencyModel(x){if(!x||!Number.isFinite(x.speed)||!Number.isFinite(x.vanes))throw new Error('Speed and vane count must be finite.');if(x.speed<=0)throw new Error('Shaft speed must be greater than zero.');if(!Number.isInteger(x.vanes)||x.vanes<=0)throw new Error('Vane count must be a positive integer.');var shaftHz;if(x.speedUnits==='rpm')shaftHz=x.speed\/60;else if(x.speedUnits==='hz')shaftHz=x.speed;else throw new Error('Choose a supported speed unit.');var rpm=shaftHz*60,vpfHz=shaftHz*x.vanes,vpfCpm=vpfHz*60,harmonics=[2*vpfHz,3*vpfHz,4*vpfHz];if(![shaftHz,rpm,vpfHz,vpfCpm].concat(harmonics).every(Number.isFinite))throw new Error('A frequency result is outside the finite numeric range.');return{rpm:rpm,shaftHz:shaftHz,vpfHz:vpfHz,vpfCpm:vpfCpm,harmonicsHz:harmonics}}\nfunction toMetres(value,units){if(!Number.isFinite(value))throw new Error('Head must be finite.');if(units==='m')return value;if(units==='ft')return value*FT_TO_M;throw new Error('Choose a supported head unit.')}\nfunction fromMetres(value,units){if(!Number.isFinite(value))throw new Error('Head must be finite.');if(units==='m')return value;if(units==='ft')return value\/FT_TO_M;throw new Error('Choose a supported head unit.')}\nfunction npshComparisonModel(x){if(!x||!Number.isFinite(x.npshaM)||!Number.isFinite(x.npshrM))throw new Error('Both NPSH values must be finite.');if(x.npshaM<0)throw new Error('NPSHA must be zero or greater.');if(x.npshrM<=0)throw new Error('NPSHR must be greater than zero.');var marginM=x.npshaM-x.npshrM,ratio=x.npshaM\/x.npshrM;if(!Number.isFinite(marginM)||!Number.isFinite(ratio))throw new Error('An NPSH result is outside the finite numeric range.');return{npshaM:x.npshaM,npshrM:x.npshrM,marginM:marginM,ratio:ratio}}\nwindow.vbmPumpFrequencyModel=pumpFrequencyModel;window.vbmNpshComparisonModel=npshComparisonModel;window.vbmPumpParse=parseNumber;window.vbmPumpToMetres=toMetres;window.vbmPumpFromMetres=fromMetres;window.vbmPumpConstants={FT_TO_M:FT_TO_M};\nfunction fmt(n){if(n===0||Object.is(n,-0))return'0';var a=Math.abs(n),s;if(a>=1e9||a<1e-7)s=n.toExponential(9);else s=n.toPrecision(10);return s.replace(\/(\\.\\d*?[1-9])0+(e|$)\/,'$1$2').replace(\/\\.0+(e|$)\/,'$1').replace('e+','e')}\nfunction fail(message){byId('vc-error').textContent=message;byId('vc-error').classList.add('vc-show');byId('vc-results').classList.remove('vc-visible')}\nfunction hideOutput(){byId('vc-error').classList.remove('vc-show');byId('vc-results').classList.remove('vc-visible');byId('vc-npsh-output').classList.remove('vc-visible')}\nfunction updateUnits(){byId('vc-speed-hint').textContent=byId('vc-speed-units').value==='rpm'?'(r\/min)':'(Hz)';var h=byId('vc-head-units').value==='m'?'(m)':'(ft)';document.querySelectorAll('.vc-head-unit').forEach(function(node){node.textContent=h})}\nfunction clearRelevant(kind){if(kind==='speed')byId('vc-speed').value='';else{byId('vc-npsha').value='';byId('vc-npshr').value=''}byId('vc-confirm').checked=false;hideOutput()}\nfunction calculate(){var speed=parseNumber(byId('vc-speed').value),vanes=parseNumber(byId('vc-vanes').value),speedUnits=byId('vc-speed-units').value,frequencySource=byId('vc-frequency-source').value.trim(),aText=byId('vc-npsha').value.trim(),rText=byId('vc-npshr').value.trim(),npshSource=byId('vc-npsh-source').value.trim(),headUnits=byId('vc-head-units').value;if(speed===null||vanes===null)return fail('Enter complete finite speed and vane-count values. A comma may replace the decimal point; do not use thousands separators or unit suffixes.');if(!frequencySource)return fail('Enter the controlled speed\/vane source and stationary observation location.');if(!byId('vc-confirm').checked)return fail('Confirm the kinematic, common-operating-point and non-diagnostic conditions before calculation.');var frequencies;try{frequencies=pumpFrequencyModel({speed:speed,vanes:vanes,speedUnits:speedUnits})}catch(error){return fail(error.message)}var compareNpsh=aText!==''||rText!=='';var npsh=null,a,r;if(compareNpsh){a=parseNumber(aText);r=parseNumber(rText);if(a===null||r===null)return fail('Enter both finite NPSHA and NPSHR values, or leave both blank.');if(!npshSource)return fail('Enter the source and common operating conditions for the NPSH pair.');try{npsh=npshComparisonModel({npshaM:toMetres(a,headUnits),npshrM:toMetres(r,headUnits)})}catch(error){return fail(error.message)}}byId('vc-error').classList.remove('vc-show');byId('vc-vpf').textContent=fmt(frequencies.vpfHz)+' Hz \u00b7 '+fmt(frequencies.vpfCpm)+' CPM';byId('vc-shaft').textContent=fmt(frequencies.shaftHz)+' Hz \u00b7 '+fmt(frequencies.rpm)+' r\/min';byId('vc-vpf2').textContent=fmt(frequencies.harmonicsHz[0])+' Hz';byId('vc-vpf4').textContent=fmt(frequencies.harmonicsHz[2])+' Hz';byId('vc-results-basis').textContent='Frequency source: '+frequencySource+' \u00b7 Z='+vanes+' \u00b7 n='+fmt(frequencies.rpm)+' r\/min';if(npsh){var unit=headUnits==='m'?'m':'ft',margin=fromMetres(npsh.marginM,headUnits);byId('vc-npsh-line').textContent='NPSHA '+fmt(a)+' '+unit+' \u2212 NPSHR '+fmt(r)+' '+unit+' = '+fmt(margin)+' '+unit+'; raw ratio = '+fmt(npsh.ratio)+'.';byId('vc-npsh-basis').textContent='Source\/conditions: '+npshSource;byId('vc-npsh-output').classList.add('vc-visible')}else byId('vc-npsh-output').classList.remove('vc-visible');byId('vc-results').classList.add('vc-visible')}\nbyId('vc-form').addEventListener('submit',function(e){e.preventDefault();calculate()});byId('vc-form').addEventListener('input',hideOutput);byId('vc-form').addEventListener('change',hideOutput);byId('vc-speed-units').addEventListener('change',function(){clearRelevant('speed');updateUnits()});byId('vc-head-units').addEventListener('change',function(){clearRelevant('head');updateUnits()});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',section.classList.contains('vc-open')?'true':'false')})});document.querySelectorAll('.vc-faq button').forEach(function(button){button.addEventListener('click',function(){this.parentNode.classList.toggle('vc-open')})});byId('vc-copy').addEventListener('click',function(){if(!byId('vc-results').classList.contains('vc-visible')||!navigator.clipboard)return;var lines=[byId('vc-results-basis').textContent,'1x VPF: '+byId('vc-vpf').textContent,'1x shaft: '+byId('vc-shaft').textContent,'2x VPF: '+byId('vc-vpf2').textContent,'4x VPF: '+byId('vc-vpf4').textContent];if(byId('vc-npsh-output').classList.contains('vc-visible'))lines.push(byId('vc-npsh-line').textContent,byId('vc-npsh-basis').textContent);lines.push('Kinematic coordinates\/raw comparison only; no cavitation diagnosis or margin verdict.');navigator.clipboard.writeText(lines.join('\\n'))});updateUnits();\n})();\n<\/script>\n\n","protected":false},"excerpt":{"rendered":"<p>Calculate shaft and vane-passing kinematic frequencies and optionally compare controlled NPSHA\/NPSHR values without inventing a cavitation band or risk category.<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-100201","calculator","type-calculator","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100201","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":2,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100201\/revisions"}],"predecessor-version":[{"id":102542,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100201\/revisions\/102542"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/media?parent=100201"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/categories?post=100201"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/tags?post=100201"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}