(SSL Module Only) When centrifugal pumps are pumping slurries the solids in the slurry can cause decreased pump performance. This is known as de-rating, as the process involves reducing the pump head curves provided by manufacturers which are based on clear water.

The SSL module offers three methods to estimate pump de-rating. The first is based on a standard published by the Hydraulic Institute in 2016. In AFT Fathom it is called the “ANSI/HI Standard 12.1-12.6-2016ANSI/HI Standard 12.1-12.6-2016, Rotodynamic (Centrifugal) Slurry Pumps, 2016,  published by Hydraulic Institute, 6 Campus Drive, Parsippany, New Jersey, USA ” method. The second is based on the Warman method.  The third allows the user to define a CH, CQ and CE rather than having them calculated.

When the SSL module is used, a new tab appears on the Pump Properties Window called Slurry De-Rating (Figure 1). Here the user can choose the de-rating method. The de-rating factors are shown in the Output window Pump Summary as CH (for head correction) and CE (for efficiency correction). Figure 2 shows the Pump Summary with correction factors displayed. If you do not see them in your Output you can add them to the Pump Summary in the Output Control window opened from the Tools menu.

Theory of Pump De-Rating

The head reduction for slurry pumps is based on ANSI/HI Standard 12.1-12.6-2016, page 52, Figure 12.3.2.7 (not shown here). Correction factors for solids density, solids concentration and percent of fine particles are applied per the standard. This figure and methodology is the same as found in Wilson, et al. 2006 on page 243.

The Warman Method is in use in industry but is not widely available. The method used in AFT Fathom is based on a white paper by Walker, C. I.,Walker, C. I., The effect of settling slurries on pump performance, undated, Warman International. Undated, page 2, and uses a correction factor for impeller size.