There are two different design configurations for incorporating the Little Split Flow feature into horizontal or vertical inline API Standard 610 overhung pumps, i.e.,

1. The auxiliary impeller hub is back-to-back with the primary impeller hub, reference prototype BW/IP sectional drawing.
2. The auxiliary impeller has the same orientation on the shaft as the primary impeller, reference CPC sectional drawing.

To facilitate comparison, liquid flowing thru the pumps is color-coded, i.e.

• Inlet liquid - green
• Primary discharge - red
• Secondary discharge (from auxiliary impeller) - blue

The Flowserve and Sulzer designs use external feed lines from the primary impeller discharge to the auxiliary impeller inlet. They also use back (hub) wear rings on the primary impeller. This configuration has running clearances at four locations. The auxiliary impeller hub ring clearance breaks down approx. 100% of the total differential head (TDH); the other three running clearances each break down approx. 50% of the TDH.

• The CPC design provides for internal feed from the primary impeller discharge to the auxiliary impeller inlet by deleting back (hub) wear rings from the primary impeller, and unbalancing the auxiliary impeller to off-set the primary impeller axial dynamic unbalance. This configuration has running clearances at three locations. Each running clearance breaks down approx. 50% of the TDH. This configuration also minimizes the shaft cantilever, compared with the Flowserve/Sulzer designs, which in turn, results in lower dynamic rotor deflections at the running clearances.
• Both designs provide axial hydraulic balance of the rotors and shaft seals operate at the primary impeller discharge head.

WEM 5/13/02