API 610 BB4 pump - balancing disc.

[adula29]

Hello,

The api standard does not allow the use of axial clearances to balance axial thrust. Is it possible to use a balancing disc (axial clearances) to balance the axial thrust or not?
Unless it is only possible for the application feed water pumps.

 

[adula29]

Any help ? ;(

 

[SB1976]

Hi Abdula29,

The reason API 610 does not recommend axial clearances for axial thrust balance purposes is to avoid high internal rubbing across the two surfaces (balance disc and impeller shroud / backplate). This is particularly true for Boiler Feed Water Pumps as you said you are dealing with now, wherein any choke in the balance line for multistage pump will cause this axial clearance to close thereby promoting heavy rubbing. Regardless of the balance line choke, in case of BFW Pumps, boiler load is not known definitely during start-up and hence pump flow is rather reduced from rated duty. This reduction in flow leads to high radial and axial thrust thereby leading to reduced axial clearances and promoting high wear across the surfaces.

Trust the explanation helps.