Balancing Disc not allowed as per API 610, 11th and 12th Editon 1

[CuriousMecEng]

API 610 12th Edition :
6.7 Wear Rings and Running Clearances
Radial running clearances shall be used to limit internal leakage and, where necessary, balance axialthrust. "Impeller pump-out vanes or close axial clearances shall not be used to balance axial thrust".

1. Does this means that balancing disc is not allowed as per API 610? (Confusion since the statement is added in wear ring section)
2. Also, what is the quantitative measurement of "close axial clearances"?

Thanks in advance.

 

[SB1976]

Hi CuriousMecEng,

1. No, it does not. Your interpretation is rather not correct. In diffuser design / mixed flow pumps, impeller vanes direct fluid away from the shaft and creates a hydraulic thrust in opposite direction (similar to reaction turbine blades) which do not balance the overall pump thrust. Such a means of axial thrust mitigation is not reliable and hence cannot be counted upon.

Axial clearances minimize fluid leakage thereby limiting axial thrust due to return line. But the problem is, during off-design operating conditions, this clearance will open wide leading to more thrust eventually.

2. Figures for axial clearances have not be given in API 610. However, same shall be such that seal chamber face runout (TIR) as specified to be 0.5 microm/mm is not exceeded.

Hope the above helps.

 

[CuriousMecEng]

@S.Barman: Thank you for the reply.