Interactive tool. Allowable residual unbalance for single-plane rotors under API 4W/N or ISO 21940-11 G-grades, with the allowable unbalance mass at your radius and the rotating force at speed. US and SI units.
This calculator returns the allowable residual unbalance for a single-plane rotor under the API 4W/N criterion or an ISO 21940-11 balance quality grade. Enter the rotor weight, the maximum continuous speed, and the correction radius, and select the criterion; it returns the allowable residual unbalance, the allowable unbalance mass at your radius, the specific unbalance, and the rotating force at speed, in US or SI units, with a printable record. Companion tool to Single-Plane Balancing: The Fundamentals. Part of the balancing series.
The calculator's results have been compared with those of a separately written program in 6,000 randomized cases, and every displayed value agreed with it within the precision of the ISO equation's constant. Further tests confirmed that the results scale with rotor weight, speed, and correction radius as the equations require, and that the API criterion corresponds to grade G 0.665 at any weight and speed. The calculator also reproduced the results of multiple worked examples from reference documents.
Sample output
The calculator's output for the worked example in Single-Plane Balancing: The Fundamentals: a 50 lb single-stage impeller with a maximum continuous speed of 3,560 RPM and a 7 in correction radius, on the API 4W/N criterion.
Result
API 4W/N
Allowable residual unbalance (oz·in | g·in)
0.0562 | 1.59
Allowable unbalance mass at r(oz | g)
0.00803 | 0.228
Specific unbalance (g·mm/kg = e in µm)
1.78
Rotating force at N(lbf)
1.26
Force as share of rotor weight (%)
2.5
The printed record of the same example. Click the image to enlarge it.
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