Neptune Chemical Pump Co. designed its 500-D Series Hydraulic Diaphragm Metering Pumps for use in a wide array of industries and applications.Neptune 500-D Series (duplex) pumps are designed with features that set the standard in the industry. Its EZE-CLEAN valve cartridges can be removed from the pump heads without having to disturb the pump’s piping. Neptune’s Variable Oil By-pass stroke adjustment provides better valve performance than variable-linkage designs.