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Balancing grades ISO 1940 vs API 610

Balancing grades ISO 1940 vs API 610

Balancing grades ISO 1940 vs API 610

(OP)
please explain the relationship between ISO balance grades and grades specified in API 610 (such as 4W/N,4W/N etc W - mass of rotor, N- RPM).

In API 610 it mentioned as a note that 4W/N is equivalent to ISO 1940 Gr 1.0. Also that the grades mentioned in API  are mid values of the range of the equivalent ISO grade.

Please clarify How should one interpret the above?  

RE: Balancing grades ISO 1940 vs API 610

4W/N is in traditional American units (with a conversion factor) - oz.-in. of unbalance.

ISO permisable imbalance for balance grade G would be:

Uper = G M/Omega - M mass of rotor Omega - rad/sec (rad/time)

Uper = M e_per Omega/Omega - e_per = unbalance eccentricitgy

Uper_oz-in in oz-in = W lb 16 oz/lb 1 in/25.4 mm 60 sec/min/(N rpm 2 pi rad/rev) === or

U_oz-in = 6.0153 W/N  - W in lbs N in rpm

API = 4W/N  or equivalently

G_API = 4/6.0153 = 0.665

So, a balance grade G=1 does not quite meet API.  

Regards,

Bill

RE: Balancing grades ISO 1940 vs API 610

The following equation had a G left out

U_oz-in = 6.0153 W/N  - W in lbs N in rpm
 SHOULD BE

Uper_oz-in = 6.0153 G W/N  - W in lbs N in rpm

With G being the ISO balance grade.

Regards,

Bill

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