Heavy Duty Flap Pumps or HDF (SA) Pumps are recommended for abrasive slurries, suspended and non-suspended solids and line size solids requirements. HDF feature:All HDF pumps are configured in bottom discharge porting arrangements. Thick wall constructed of Sand Casted Aluminum, Cast Iron and Stainless Steel welastomer. TPE (thermal plastic elastomers) and PTFE options in diaphragms and check valves.