Is vane-passing frequency the cavitation frequency?

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.

Does a positive NPSHA minus NPSHR value prove that cavitation cannot occur?

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.

Why were the 1.3 and 2.0 NPSH risk thresholds removed?

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.

Can a BPF harmonic alone diagnose cavitation?

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.

Pump kinematics plus raw record comparison

Pump Vane-Passing Frequency & NPSH Record Worksheet

Calculate shaft and vane-passing coordinates from documented speed and vane count. Optionally compare controlled NPSHA and NPSHR values at the same operating point—without inventing a cavitation frequency band or risk category.

VPF = Z × n / 60No universal 1–100 kHz bandNo NPSH risk score

Kinematic frequency record

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Vane-passing frequency (1× VPF)

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Shaft rotational frequency (1×)

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2× VPF coordinate

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4× VPF coordinate

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Raw NPSH record comparison—not a risk verdict

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Coordinates do not diagnose: a spectral line at VPF or its harmonics may reflect rotor–stator 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.

Rotational and vane-passing coordinates

f_velenas = n / 60
f_VPF = Z f_velenas = Zn / 60
f_k = k f_VPF, k = 2, 3, 4

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_velenas equals that input. Counts per minute are frequency in hertz multiplied by 60.

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.

Optional raw NPSH arithmetic

ΔNPSH = NPSHA − NPSHR
R = NPSHA / NPSHR
1 pėda = tiksliai 0,3048 m

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.

Former output or claim	Confirmed problem and correction
“Expected cavitation frequency 1–100 kHz”	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.
Elevated 3× BPF labelled a cavitation indicator	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.
NPSHA/NPSHR ratios >2, 1.3–2, 1–1.3 and <1 as universal low/moderate/high/critical risk	Current Hydraulic Institute guidance is application-specific. The closed margin rules were not implemented; only raw difference and ratio remain.
“Positive margin prevents cavitation” and “below NPSHR means cavitation certain”	Those categorical statements ignore the definition and operating-point basis of the manufacturer value, uncertainty, margin requirement and cavitation mechanisms. No prognosis is emitted.
Defaults, presets, auto-calculation, partial numeric parsing, URL/history persistence	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.
ISO 10816 / ISO 1940 implication	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.

Published vane-passing example

NASA contractor report Fan and Pump Noise Control, SVHSER 6183 (May 1973) 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 × 5,500 / 60 = 366.666… Hz, which rounds to the published value.

No universal cavitation band

The peer-reviewed experimental study by Mousmoulis et al., European Journal of Mechanics B/Fluids 75 (2019), 300–311 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 1–100 kHz diagnostic output.

NPSH guidance is application-specific

The Hydraulic Institute’s official current product information for ANSI/HI 9.6.1:2024, Rotodynamic Pumps Guideline for NPSH Margin 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.

ISO taikymo sritis

ISO 9906:2012, 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 NEEDS_LICENSED_SOURCE. It is not used as a cavitation-frequency formula.

ISO 10816-7:2009 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.

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.

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.

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.

No. The optional comparison requires both values and their common operating-point provenance. Leave both blank if no controlled pair is available.

This worksheet deliberately makes no such classification. Use the current applicable ANSI/HI/OEM/project margin requirement for the specific pump and service.