{"id":100065,"date":"2026-02-15T20:14:37","date_gmt":"2026-02-15T20:14:37","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100065"},"modified":"2026-02-15T20:14:37","modified_gmt":"2026-02-15T20:14:37","slug":"cooling-tower-fan-vibration","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/nb\/calculators\/cooling-tower-fan-vibration\/","title":{"rendered":"Kalkulator for vibrasjon av kj\u00f8let\u00e5rnviften"},"content":{"rendered":"\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Cooling Tower Fan Vibration Calculator\",\"description\":\"Calculate BPF, tip speed, centrifugal force, and permissible unbalance for cooling tower fans.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/cooling-tower-fan-vibration\/\",\"applicationCategory\":\"Engineering 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.vc-faq-chevron{transform:rotate(180deg)}\n.vc-faq-a{max-height:0;overflow:hidden;transition:max-height 0.3s ease}\n.vc-faq-item.vc-open .vc-faq-a{max-height:2000px}\n.vc-faq-a-inner{padding:0 16px 14px;font-size:14px;color:var(--vc-ink-secondary);line-height:1.65}\n.vc-faq-a-inner p{margin:0 0 8px}\n@media print{.vc-section-body{max-height:none!important}.vc-results{max-height:none!important;padding:24px!important}.vc-promo{display:none!important}}\n<\/style>\n\n<div class=\"vc-calculator\" id=\"vc-ct-fan\">\n\n<header class=\"vc-header\">\n    <p class=\"vc-header-eyebrow\">Free Engineering Tool<\/p>\n    <h1 class=\"vc-header-title\">Cooling Tower Fan Vibration Calculator<\/h1>\n    <p class=\"vc-header-subtitle\">Calculate blade pass frequency, tip speed, centrifugal force from unbalance, permissible unbalance per ISO 21940, and assess tower structure resonance risk for cooling tower fans.<\/p>\n    <div class=\"vc-badges\"><span class=\"vc-badge\">ISO 21940<\/span><span class=\"vc-badge\">BPF<\/span><span class=\"vc-badge\">Tip Speed<\/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-diam\">Fan Diameter <span class=\"vc-label-hint\">(m)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-diam\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 8\" value=\"8\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-blades\">Number of Blades<\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-blades\" inputmode=\"numeric\" step=\"1\" min=\"1\" placeholder=\"e.g. 6\" value=\"6\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-rpm\">Fan RPM <span class=\"vc-label-hint\">(typically 100\u2013300)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-rpm\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 180\" value=\"180\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-bmass\">Total Blade Assembly Mass <span class=\"vc-label-hint\">(kg)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-bmass\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 500\" value=\"500\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-tip\">Tip Clearance <span class=\"vc-label-hint\">(mm)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-tip\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 25\" value=\"25\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-grade\">Balance Grade<\/label>\n                <select class=\"vc-select\" id=\"vc-grade\">\n                    <option value=\"6.3\" selected>G6.3 \u2014 Standard for fans<\/option>\n                    <option value=\"2.5\">G2.5 \u2014 Precision balance<\/option>\n                    <option value=\"16\">G16 \u2014 Rough service<\/option>\n                <\/select>\n            <\/div>\n        <\/div>\n    <\/form>\n\n    <div class=\"vc-results vc-visible\" id=\"vc-results\">\n        <div class=\"vc-results-head\">\n            <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\">\n                <div class=\"vc-rcard-label\">Blade Pass Frequency (BPF)<\/div>\n                <div class=\"vc-rcard-value\" id=\"vc-r-bpf\">\u2014<\/div>\n            <\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Tip Speed<\/div><div class=\"vc-rcard-value\" id=\"vc-r-tip\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">1\u00d7 Frequency<\/div><div class=\"vc-rcard-value\" id=\"vc-r-1x\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Permissible Unbalance (Total)<\/div><div class=\"vc-rcard-value\" id=\"vc-r-ubal\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Centrifugal Force at Tolerance<\/div><div class=\"vc-rcard-value\" id=\"vc-r-force\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Tip Speed Assessment<\/div><div class=\"vc-rcard-value\" id=\"vc-r-tipassess\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\" style=\"grid-column:1\/-1;\"><div class=\"vc-rcard-label\">Tower Structure Resonance Concern<\/div><div class=\"vc-rcard-value\" id=\"vc-r-resonance\">\u2014<\/div><\/div>\n        <\/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\">\n        <span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udcd8<\/span><span class=\"vc-section-title\">Theory &#038; Guidelines<\/span><\/span>\n        <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>\n    <\/button>\n    <div class=\"vc-section-body\">\n        <div class=\"vc-section-inner vc-theory\">\n            <h3>Key Formulas<\/h3>\n            <div class=\"vc-formula-box\">BPF = Number of Blades \u00d7 RPM \/ 60 [Hz]<\/div>\n            <div class=\"vc-formula-box\">Tip Speed = \u03c0 \u00d7 D \u00d7 RPM \/ 60 [m\/s]<\/div>\n            <h3>Tip Speed Guidelines<\/h3>\n            <ul>\n                <li><strong>&lt; 55 m\/s<\/strong> \u2014 Normal for FRP blades<\/li>\n                <li><strong>55\u201365 m\/s<\/strong> \u2014 Acceptable, check blade stress<\/li>\n                <li><strong>&gt; 65 m\/s<\/strong> \u2014 High stress, risk of blade fatigue<\/li>\n            <\/ul>\n            <h3>Tower Structure Resonance<\/h3>\n            <p>Cooling tower structures typically have natural frequencies of 1\u20135 Hz. If the fan 1\u00d7 frequency or BPF falls near a tower natural frequency, severe vibration amplification can occur. Maintain at least 20% separation margin.<\/p>\n            <h3>Vibration Limits for Cooling Tower Fans<\/h3>\n            <p>Due to the flexible structure, cooling tower fans have stricter vibration limits than most rotating equipment:<\/p>\n            <ul>\n                <li><strong>Normal:<\/strong> &lt; 3 mm\/s velocity RMS on fan bridge structure<\/li>\n                <li><strong>Alert:<\/strong> 3\u20135 mm\/s \u2014 investigate at next opportunity<\/li>\n                <li><strong>Alarm:<\/strong> 5\u20138 mm\/s \u2014 schedule maintenance soon<\/li>\n                <li><strong>Trip:<\/strong> &gt; 8 mm\/s \u2014 shut down to prevent structural damage<\/li>\n            <\/ul>\n\n            <h3>Common Causes of Cooling Tower Fan Vibration<\/h3>\n            <ul>\n                <li><strong>Blade pitch mismatch:<\/strong> All blades must have the same pitch angle (\u00b10.5\u00b0)<\/li>\n                <li><strong>Blade mass difference:<\/strong> Weigh all blades \u2014 match within 1% or add balance weights<\/li>\n                <li><strong>Hub unbalance:<\/strong> After blade replacement, check rotor balance<\/li>\n                <li><strong>Gearbox problems:<\/strong> Gear mesh frequency and bearing defect frequencies<\/li>\n                <li><strong>Tower structure resonance:<\/strong> fn of structure too close to 1\u00d7 or BPF<\/li>\n                <li><strong>Ice\/debris buildup:<\/strong> Uneven deposits change balance<\/li>\n                <li><strong>Loose blade bolts:<\/strong> Creates impulsive vibration and harmonics<\/li>\n                <li><strong>Motor\/drive issues:<\/strong> VFD-driven fans can excite resonances at certain speeds<\/li>\n            <\/ul>\n\n            <h3>Tip Clearance Guidelines<\/h3>\n            <p>Tip clearance is the gap between the blade tip and the fan stack (venturi). It directly affects\n            both aerodynamic efficiency and vibration behavior. Proper tip clearance ensures uniform\n            airflow distribution and minimizes recirculation losses:<\/p>\n            <ul>\n                <li><strong>Too small (&lt;0.5% of diameter):<\/strong> Risk of blade-to-stack contact, especially with thermal expansion<\/li>\n                <li><strong>Optimal (0.5\u20131.5% of diameter):<\/strong> Best efficiency with adequate safety margin<\/li>\n                <li><strong>Too large (&gt;2% of diameter):<\/strong> Airflow recirculation reduces efficiency by 5\u201315%<\/li>\n            <\/ul>\n\n            <h3>Permissible Unbalance per ISO 21940<\/h3>\n            <p>The permissible specific unbalance (eccentricity) is determined by the balance grade and rotational speed:<\/p>\n            <div class=\"vc-formula-box\">e_per = G \u00d7 1000 \/ \u03c9 [\u03bcm]<\/div>\n            <div class=\"vc-formula-box\">U_per = e_per \u00d7 M [g\u00b7mm]<\/div>\n            <p>Where G is the balance grade (mm\/s), \u03c9 is the angular velocity (rad\/s), and M is the total rotating mass (kg). For cooling tower fans, the total blade assembly mass (including hub) should be used.<\/p>\n\n            <h3>Centrifugal Force from Unbalance<\/h3>\n            <p>The centrifugal force generated at the permissible unbalance limit:<\/p>\n            <div class=\"vc-formula-box\">F = M \u00d7 e_per \u00d7 \u03c9\u00b2 \/ 10\u2076 [N]<\/div>\n            <p>This force rotates at shaft speed and is transmitted through the gearbox to the fan bridge structure. For cooling towers with flexible structures, even modest forces can cause significant structural vibration.<\/p>\n\n            <h3>Blade Pass Frequency Explained<\/h3>\n            <p>BPF is the frequency at which blades pass a fixed point. It generates an aerodynamic pulsation that excites the fan stack and structure. In the vibration spectrum, BPF appears as a distinct peak with possible harmonics (2\u00d7BPF, 3\u00d7BPF). High BPF amplitude indicates:<\/p>\n            <ul>\n                <li>Blade pitch angle differences between blades<\/li>\n                <li>Uneven blade spacing (manufacturing or installation error)<\/li>\n                <li>Obstruction near the blade path (structural member, debris)<\/li>\n                <li>Blade tip running too close to the fan stack on one side<\/li>\n            <\/ul>\n\n            <h3>Gearbox Considerations<\/h3>\n            <ul>\n                <li><strong>Gear mesh frequency:<\/strong> Number of teeth \u00d7 input shaft RPM \u2014 monitor for gear defects<\/li>\n                <li><strong>Oil analysis:<\/strong> Regular oil sampling helps detect gear wear before vibration increases<\/li>\n                <li><strong>Gearbox mount bolts:<\/strong> Check torque regularly \u2014 looseness causes sub-synchronous vibration<\/li>\n                <li><strong>Alignment:<\/strong> Motor-to-gearbox coupling alignment is critical for preventing premature failure<\/li>\n            <\/ul>\n\n            <div class=\"vc-info-box\">\n                <p style=\"margin:0;font-size:14px;color:var(--vc-ink-secondary)\"><strong>Monitoring tip:<\/strong> Trending vibration at 1\u00d7 RPM over time is the most effective way to detect developing unbalance in cooling tower fans. Set up automated alerts using permanently mounted accelerometers or scheduled route-based measurements.<\/p>\n            <\/div>\n\n            <div class=\"vc-warning-box\">\n                <p style=\"margin:0;font-size:14px;color:var(--vc-ink-secondary)\"><strong>\u26a0\ufe0f Important:<\/strong> Cooling tower fan vibration limits are typically stricter than general rotating machinery due to the flexible support structure. Many operators use 5 mm\/s velocity as an alarm level and 8 mm\/s as a trip level. Always verify tip clearance after any maintenance that may have shifted the fan assembly.<\/p>\n            <\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<!-- FAQ -->\n<div class=\"vc-section\" id=\"vc-sec-faq\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\">\n        <span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\u2753<\/span><span class=\"vc-section-title\">Frequently Asked Questions<\/span><\/span>\n        <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>\n    <\/button>\n    <div class=\"vc-section-body\">\n        <div class=\"vc-section-inner\">\n            <div class=\"vc-faq-list\" id=\"vc-faq-list\"><\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-related\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\">\n        <span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udd17<\/span><span class=\"vc-section-title\">Related Calculators<\/span><\/span>\n        <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>\n    <\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-related\">\n        <a class=\"vc-related-link\" href=\"\/calculators\/residual-unbalance-iso1940\/\">General Residual Unbalance<\/a>\n        <a class=\"vc-related-link\" href=\"\/calculators\/paper-machine-roll-balance\/\">Paper Machine Roll Balance<\/a>\n        <a class=\"vc-related-link\" href=\"\/calculators\/crusher-rotor-balance\/\">Crusher Rotor Balance<\/a>\n    <\/div><\/div><\/div>\n<\/div>\n\n<div class=\"vc-promo\"><div class=\"vc-promo-text\"><strong>Vibromera \u2014 Portable Balancing &#038; Vibration Analysis<\/strong><br>Professional field balancing instruments and software. Used in 50+ countries.<\/div><a class=\"vc-promo-link\" href=\"https:\/\/vibromera.eu\/\" target=\"_blank\" rel=\"noopener\">Learn More<\/a><\/div>\n<footer class=\"vc-footer\"><p>\u00a9 2024\u20132025 <a href=\"https:\/\/vibromera.eu\/\">Vibromera<\/a> \u2014 Engineering Calculators<\/p><p style=\"font-size:12px;margin-top:4px;\">Based on ISO 21940. 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\n<\/div>\n\n<script>\n(function(){\n    'use strict';\n    function $(id){return document.getElementById(id)}\n    function fmt(n,d){if(isNaN(n)||!isFinite(n))return'\u2014';return n.toFixed(d===undefined?2:d).replace(\/(\\.\\d*?)0+$\/,'$1').replace(\/\\.$\/,'')}\n\n    function calculate(){\n        var diam=parseFloat($('vc-diam').value);\n        var blades=parseInt($('vc-blades').value);\n        var rpm=parseFloat($('vc-rpm').value);\n        var bmass=parseFloat($('vc-bmass').value);\n        var tip=parseFloat($('vc-tip').value);\n        var grade=parseFloat($('vc-grade').value);\n\n        if(!diam||diam<=0||!blades||!rpm||rpm<=0||!bmass||bmass<=0){return}\n\n        var omega=2*Math.PI*rpm\/60;\n        var f1x=rpm\/60;\n        var bpf=blades*rpm\/60;\n        var tipSpeed=Math.PI*diam*rpm\/60;\n        var eper=grade*1000\/omega;\n        var uper=eper*bmass;\n        var force=bmass*(eper\/1e6)*omega*omega;\n\n        $('vc-r-bpf').innerHTML=fmt(bpf,2)+' <span class=\"vc-rcard-unit\">Hz ('+fmt(bpf*60,0)+' CPM)<\/span>';\n        $('vc-r-tip').innerHTML=fmt(tipSpeed,1)+' <span class=\"vc-rcard-unit\">m\/s<\/span>';\n        $('vc-r-1x').innerHTML=fmt(f1x,3)+' <span class=\"vc-rcard-unit\">Hz ('+fmt(rpm,0)+' CPM)<\/span>';\n        $('vc-r-ubal').innerHTML=(uper>=1000?fmt(uper,0):fmt(uper,1))+' <span class=\"vc-rcard-unit\">g\u00b7mm (G'+grade+')<\/span>';\n        $('vc-r-force').innerHTML=fmt(force,1)+' <span class=\"vc-rcard-unit\">N<\/span>';\n\n        \/\/ Tip speed assessment\n        if(tipSpeed<55){$('vc-r-tipassess').innerHTML='<span class=\"vc-status-pass\">Normal<\/span> <span class=\"vc-rcard-unit\">(&lt;55 m\/s)<\/span>'}\n        else if(tipSpeed<65){$('vc-r-tipassess').innerHTML='<span class=\"vc-status-warn\">Elevated<\/span> <span class=\"vc-rcard-unit\">(55\u201365 m\/s)<\/span>'}\n        else{$('vc-r-tipassess').innerHTML='<span class=\"vc-status-fail\">High \u2014 check blade stress<\/span> <span class=\"vc-rcard-unit\">(&gt;65 m\/s)<\/span>'}\n\n        \/\/ Tower resonance concern\n        var resonanceRisk='';\n        if(f1x>=1&&f1x<=5){resonanceRisk='<span class=\"vc-status-fail\">WARNING: 1\u00d7 frequency ('+fmt(f1x,2)+' Hz) is within typical tower natural frequency range (1\u20135 Hz). Verify tower fn and ensure >20% separation.<\/span>'}\n        else if(bpf>=1&&bpf<=5){resonanceRisk='<span class=\"vc-status-warn\">CAUTION: BPF ('+fmt(bpf,2)+' Hz) is within typical tower natural frequency range.<\/span>'}\n        else{resonanceRisk='<span class=\"vc-status-pass\">Low risk<\/span> \u2014 1\u00d7 ('+fmt(f1x,2)+' Hz) and BPF ('+fmt(bpf,2)+' Hz) are outside typical tower fn range (1\u20135 Hz).'}\n        $('vc-r-resonance').innerHTML=resonanceRisk;\n\n        $('vc-results').classList.add('vc-visible');\n    }\n\n    $('vc-form').addEventListener('input',calculate);\n    $('vc-form').addEventListener('change',calculate);\n    $('vc-copy-btn').addEventListener('click',function(){var t='Cooling Tower Fan Calculation\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nDiameter: '+$('vc-diam').value+' m, '+$('vc-blades').value+' blades\\nRPM: '+$('vc-rpm').value+'\\nBPF: '+$('vc-r-bpf').textContent+'\\nTip Speed: '+$('vc-r-tip').textContent+'\\nUnbalance: '+$('vc-r-ubal').textContent+'\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nvibromera.eu';if(navigator.clipboard){navigator.clipboard.writeText(t).then(function(){var b=$('vc-copy-btn');b.classList.add('vc-copied');b.textContent='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    document.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\n    \/\/ FAQ\n    var faqData=[\n        {q:'What balance grade should I use for a cooling tower fan?',a:'<p>G6.3 is standard for most cooling tower fans. For fans on particularly flexible structures or fans with persistent vibration problems, consider G2.5. G16 may be acceptable for small, low-speed fans with rigid supports.<\/p>'},\n        {q:'How do I check for tower structure resonance?',a:'<p>Perform a bump test (impact test) on the fan bridge\/deck structure with the fan stopped. Compare the measured natural frequencies to the fan 1\u00d7, BPF, and their harmonics. Maintain at least 20% frequency separation. If resonance exists, consider adding structural stiffening or changing fan speed.<\/p>'},\n        {q:'Why does vibration change with temperature?',a:'<p>Thermal expansion affects tip clearance and blade pitch. The fan stack and blades expand at different rates. Additionally, air density changes with temperature affect aerodynamic loading. It is normal to see some vibration variation between summer and winter operation.<\/p>'},\n        {q:'Can I balance a cooling tower fan in place?',a:'<p>Yes, field balancing is the standard practice for cooling tower fans because the rotors are too large to remove economically. Single-plane balancing is usually sufficient. A portable balancer with a vibration sensor on the fan bridge\/gearbox is the typical setup.<\/p>'},\n        {q:'What about VFD-driven cooling tower fans?',a:'<p>Variable frequency drives allow speed adjustment but can excite structural resonances at certain speeds. Program the VFD to skip (lock out) speed ranges near structural natural frequencies. Also, VFDs can introduce electrical noise that appears as vibration \u2014 use proper grounding and shielded cables.<\/p>'},\n        {q:'How do I measure tip clearance?',a:'<p>Tip clearance should be measured with the fan stopped and locked out. Use a feeler gauge or tape measure at multiple blade positions (minimum 3\u20134 points around the circumference). The variation in tip clearance between blades indicates potential tracking issues. Typical acceptable range is 0.5\u20131.5% of fan diameter.<\/p>'},\n        {q:'What causes one blade to vibrate more than others?',a:'<p>Individual blade vibration differences can be caused by: blade pitch angle variation, blade mass differences, blade damage or delamination (FRP blades), ice or debris buildup on one blade, loose blade bolts, or blade root cracking. Inspect all blades visually and check pitch angles with an inclinometer.<\/p>'},\n        {q:'What is the typical maintenance interval for cooling tower fans?',a:'<p>Annual inspection is standard. Check: blade condition (cracks, erosion, delamination), blade bolt torque, tip clearance, gearbox oil level and condition, vibration levels, hub and blade root for cracks, and fan stack for corrosion. In corrosive environments (coastal, chemical plants), increase frequency to semi-annual.<\/p>'}\n    ];\n    var faqList=$('vc-faq-list');\n    faqData.forEach(function(faq){faqList.innerHTML+='<div class=\"vc-faq-item\"><button type=\"button\" class=\"vc-faq-q\"><span>'+faq.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\">'+faq.a+'<\/div><\/div><\/div>'});\n    faqList.addEventListener('click',function(e){var btn=e.target.closest('.vc-faq-q');if(!btn)return;btn.closest('.vc-faq-item').classList.toggle('vc-open')});\n\n    calculate();\n})();\n<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Gratis online vibrasjonskalkulator for kj\u00f8let\u00e5rnvifter. Beregn BPF, vippehastighet, sentrifugalkraft, tillatt ubalanse og bekymringer om strukturell resonans i t\u00e5rnet for kj\u00f8let\u00e5rnvifter.<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-100065","calculator","type-calculator","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100065","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\/100065\/revisions"}],"predecessor-version":[{"id":100380,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/calculator\/100065\/revisions\/100380"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/media?parent=100065"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/categories?post=100065"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/tags?post=100065"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}