very early BDs,(~before 1956?)had a turbine pump,then a cast aluminum centrifugal dual section pump was used-a small auxillary pump to provide lint filter circulation-the drain impeller having 4 curved blades.~1965,pump body changed to corrosion proof polypropylene plastic,drain impeller now 15 blades and pumps with and without aux.filter pump used.The BD pumps,except perhaps the earliest,have a built in valve operated by by the "wig wag"mechanism-diagram of a very early ~1943 patent drawing of a BD showed a solenoid actuated clutch on the pump.DDs have a turbine pump with rubber impeller directly mounted to the washer motor-no major changes to these pumps during DD production AFAIK.VMW uses permanent magnet,sealess,"magnetic"centrifugal pump of the type used by about every washer for the last 12-15 years-the pumps turn at 3600 rpm on 60 HZ power.