AFT Application Topics

When priming (filling) an empty pipe system, pumps will be dealing with a different system than when the system is liquid full. When the physical system is already liquid full, then a siphoning effect occurs. That means that any pipe elevation increases from the pump discharge do not impact the pump head requirement. All that matters is the elevation of the system discharge point(s).

However, when the system is not liquid full, such as during a filling operation, the siphon effect cannot be counted on. That means the pump must overcome the high point elevations in the pipes.

AFT Fathom always assumes the system is liquid full. A pump must be sized of course to handle the liquid full operation. But a special case should also be considered for priming the system. This could lead to a higher head requirement than during liquid full operation. Note that the flow requirement during priming is not the same as normal liquid full operation. In fact, the flow requirement is essentially zero as all the pump needs to do is push a small amount of fluid over the elevation highpoints at near zero (dead head) flow. AFT Fathom’s Scenario Manager is very useful for this situation.

Resources

Product tip – Overcoming New Heights – Systems Priming Before Siphon Effect Can Help