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The American Petroleum Association (API) has issued Standard 671, which refers to special couplings for refinery applications.The limits established by API relate to dynamic unbalances; three limits are given, and couplings must be balanced so that the residual unbalance does not exceed the larger of the three:
- Ud <= ( K1 . W) /rpm
- Ud <= K2 . W
- Ud = K3.
The constants K are established as a function of the method of balancing.
API Standard 671 Balancing Limit Constants |
|
| Method of Balancing |
K1 |
K2 |
K3 |
| Component Balance only |
4 |
0.0008 |
0.001 |
| Component Balance and Assembly Check Balance |
40 |
0.008 |
0.100 |
| Component Balance and Assembly Balance |
4 |
0.0008 |
0.010 |
API standard relates to the maximum potential unbalance allowable.Potential unbalance is the maximum unbalance recorded after couplings are repeatedly disassembled and subsequently reassembled. The potential unbalance shall not exceed the larger of the following limits:
- Ud <= 40 W / rpm
- Ud <= 0.008 . W
- Ud <= 0.1
The units for Ud are ounce . inches; API also provides limits in SI units.
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